branches of medicine: Hematology; Laboratory diagnostics; Nephrology; Oncology; Rheumatology
Clinics in St. Petersburg where this test is performed for adults (249)
Clinics in St. Petersburg where this test is performed for children (129)
Description
Uric acid is formed during the metabolism of purines, during the breakdown of nucleic acids. When the metabolism of purine bases is disrupted, the level of uric acid in the body increases, its concentration in the blood and other biological fluids increases, and deposition in the tissues occurs in the form of salts - urates. Serum uric acid levels are used to diagnose gout, evaluate kidney function, diagnose urolithiasis, .
Material for research
The patient's blood is taken from a vein. Blood plasma is used for analysis.
Readiness of results
Within 1 business day. Urgent execution 2-3 hours.
Interpretation of the data obtained
Units of measurement: µmol/l, mg/dl.
Conversion factor: mg/dL x 59.5 = µmol/L.
Normal values: children under 14 years old 120 - 320 µmol/l, women over 14 years old 150 - 350 µmol/l, men over 14 years old 210 - 420 µmol/l.
Increased uric acid levels:
gout, Lesch-Nyhan syndrome (genetically determined deficiency of the enzyme hypoxanthine-guanine phosphoribosyl transferase - GGPT), leukemia, myeloma, lymphoma, renal failure, toxicosis of pregnant women, prolonged fasting, alcohol consumption, taking salicylates, diuretics, cytostatics, increased physical activity, diet rich in purine bases, idiopathic familial hypouricemia, increased protein catabolism with oncological diseases, pernicious (B12 - deficiency) anemia.
Reducing uric acid levels:
Konovalov-Wilson disease (hepatocerebral dystrophy), Fanconi syndrome, taking allopurinol, radiocontrast agents, glucocorticoids, azathioprine, xanthinuria, Hodgkin's disease.
Preparing for the study
The study is carried out in the morning strictly on an empty stomach, i.e. between last appointment food must pass at least 12 hours, 1-2 days before blood donation it is necessary to limit intake fatty foods, alcohol, adhere to a low-purine diet. Immediately before donating blood, you must refrain from smoking for 1-2 hours, do not drink juice, tea, coffee (especially with sugar), you can drink clean still water. Eliminate physical stress.
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1 microgram per liter [µg/l] = 1000 nanograms per liter [ng/l]
Initial value
Converted value
kilogram per cubic meter kilogram per cubic centimeter gram per cubic meter gram per cubic centimeter gram per cubic millimeter milligram per cubic meter milligram per cubic centimeter milligram per cubic millimeter exagram per liter petagram per liter teragram per liter gigagram per liter megagram per liter kilogram per liter hectogram per liter decagram per liter grams per liter decigrams per liter centigrams per liter milligrams per liter micrograms per liter nanograms per liter picograms per liter femtograms per liter attograms per liter pound per cubic inch pound per cubic foot pound per cubic yard pound per gallon (US) pound per gallon (UK) ounce per cubic inch ounce per cubic foot ounce per gallon (US) ounce per gallon (UK) grain per gallon (US) grain per gallon (UK) grain per cubic foot short ton per cubic yard long ton per cubic yard slug per cubic foot average density of the Earth slug per cubic inch slug per cubic yard Planck density
More about density
General information
Density is a property that determines how much of a substance by mass is per unit volume. In the SI system, density is measured in kg/m³, but other units are also used, such as g/cm³, kg/l and others. In everyday life, two equivalent quantities are most often used: g/cm³ and kg/ml.
Factors affecting the density of a substance
The density of the same substance depends on temperature and pressure. Typically, the higher the pressure, the more tightly the molecules are compacted, increasing density. In most cases, an increase in temperature, on the contrary, increases the distance between molecules and reduces density. In some cases, this relationship is reversed. The density of ice, for example, is less than the density of water, despite the fact that ice colder than water. This can be explained by the molecular structure of ice. Many substances transition from liquid to solid state of aggregation change the molecular structure so that the distance between molecules decreases and the density, accordingly, increases. During the formation of ice, the molecules line up in a crystalline structure and the distance between them, on the contrary, increases. At the same time, the attraction between the molecules also changes, the density decreases, and the volume increases. In winter, you must not forget about this property of ice - if the water in the water pipes freezes, they can break.
Density of water
If the density of the material from which the object is made is greater than the density of water, then it is completely immersed in water. Materials with a density lower than that of water, on the contrary, float to the surface. A good example is ice, which is less dense than water, floating in a glass on the surface of water and other drinks that are mostly water. We often use this property of substances in Everyday life. For example, when constructing ship hulls, materials with a density higher than the density of water are used. Since materials with a density higher than the density of water sink, air-filled cavities are always created in the ship's hull, since the density of air is much lower than the density of water. On the other hand, sometimes it is necessary for an object to sink in water - for this purpose, materials with a higher density than water are chosen. For example, in order to sink light bait to a sufficient depth while fishing, anglers tie a sinker made of high-density materials, such as lead, to the fishing line.
Oil, grease and petroleum remain on the surface of the water because their density is lower than that of water. Thanks to this property, oil spilled in the ocean is much easier to clean up. If it mixed with water or sank to the seabed, it would cause even more damage to the marine ecosystem. This property is also used in cooking, but not of oil, of course, but of fat. For example, it is very easy to remove excess fat from the soup as it floats to the surface. If you cool the soup in the refrigerator, the fat hardens, and it is even easier to remove it from the surface with a spoon, slotted spoon, or even a fork. In the same way it is removed from jellied meat and aspic. This reduces the calorie content and cholesterol content of the product.
Information about the density of liquids is also used during the preparation of drinks. Multilayer cocktails are made from liquids of different densities. Typically, lower-density liquids are carefully poured onto higher-density liquids. You can also use a glass cocktail stick or bar spoon and slowly pour the liquid over it. If you take your time and do everything carefully, you will get a beautiful multi-layered drink. This method can also be used with jellies or jellied dishes, although if time permits, it is easier to chill each layer separately, pouring a new layer only after the bottom layer has set.
In some cases, the lower density of fat, on the contrary, interferes. Products with a high fat content often do not mix well with water and form a separate layer, thereby deteriorating not only the appearance, but also the taste of the product. For example, in cold desserts and smoothies, high-fat dairy products are sometimes separated from low-fat dairy products such as water, ice and fruit.
Density of salt water
The density of water depends on the content of impurities in it. Rarely found in nature and in everyday life pure water H 2 O without impurities - most often it contains salts. Good example - sea water. Its density is higher than that of fresh water, so fresh water usually “floats” on the surface of salt water. Of course, it is difficult to see this phenomenon under normal conditions, but if fresh water is enclosed in a shell, for example in a rubber ball, then this is clearly visible, since this ball floats to the surface. Our body is also a kind of shell filled fresh water. We are made up of 45% to 75% water - this percentage decreases with age and with increasing weight and amount of body fat. Fat content of at least 5% of body weight. U healthy people up to 10% body fat if they exercise a lot, up to 20% if they are of normal weight, and 25% or higher if they are obese.
If we try not to swim, but simply float on the surface of the water, we will notice that it is easier to do this in salt water, since its density is higher than the density of fresh water and the fat contained in our body. The Dead Sea's salt concentration is 7 times the average salt concentration in the world's oceans, and it is famous around the world for allowing people to easily float on the surface of the water without drowning. Although, it is a mistake to think that it is impossible to die in this sea. In fact, people die in this sea every year. The high salt content makes the water dangerous if it gets into your mouth, nose, or eyes. If you swallow such water, you can get a chemical burn - in severe cases such unlucky swimmers are hospitalized.
Air density
Just as in the case of water, bodies with a density lower than the density of air have positive buoyancy, that is, they take off. A good example of such a substance is helium. Its density is 0.000178 g/cm³, while the density of air is approximately 0.001293 g/cm³. You can see helium soar in the air if you fill a balloon with it.
The density of air decreases as its temperature increases. This property of hot air is used in balloons. The balloon in the photograph at the ancient Mayan city of Teotihuocan in Mexico is filled with hot air that is less dense than the surrounding cold morning air. That is why the ball flies at a fairly high altitude. While the ball flies over the pyramids, the air in it cools down and is heated again using a gas burner.
Density calculation
Often the density of substances is indicated for standard conditions, that is, for a temperature of 0 °C and a pressure of 100 kPa. In educational and reference books you can usually find such densities for substances that are often found in nature. Some examples are shown in the table below. In some cases, the table is not enough and the density must be calculated manually. In this case, the mass is divided by the volume of the body. The mass can be easily found using a scale. To find out the volume of a body of a standard geometric shape, you can use formulas to calculate volume. The volume of liquids and solids can be found by filling a measuring cup with the substance. For more complex calculations, the liquid displacement method is used.
Liquid displacement method
To calculate the volume in this way, first pour a certain amount of water into a measuring vessel and place the body whose volume needs to be calculated until it is completely immersed. The volume of a body is equal to the difference in the volume of water without the body and with it. It is believed that this rule was derived by Archimedes. Volume can be measured in this way only if the body does not absorb water and does not deteriorate from water. For example, we will not measure the volume of a camera or fabric product using the liquid displacement method.
It is unknown to what extent this legend reflects actual events, but it is believed that King Hiero II gave Archimedes the task of determining whether his crown was made of pure gold. The king suspected that his jeweler had stolen some of the gold allocated for the crown and instead made the crown from a cheaper alloy. Archimedes could easily determine this volume by melting the crown, but the king ordered him to find a way to do this without damaging the crown. It is believed that Archimedes found the solution to this problem while taking a bath. Having immersed himself in water, he noticed that his body had displaced a certain amount of water, and realized that the volume of displaced water was equal to the volume of the body in the water.
Hollow bodies
Some natural and man-made materials are composed of particles that are hollow, or particles so small that they behave like liquids. In the second case, an empty space remains between the particles, filled with air, liquid, or other substance. Sometimes this place remains empty, that is, it is filled with a vacuum. Examples of such substances are sand, salt, grain, snow and gravel. The volume of such materials can be determined by measuring the total volume and subtracting from it the volume of voids determined by geometric calculations. This method is convenient if the shape of the particles is more or less uniform.
For some materials, the amount of empty space depends on how tightly the particles are packed. This complicates calculations because it is not always easy to determine how much empty space there is between particles.
Table of densities of substances commonly found in nature
| Substance | Density, g/cm³ |
|---|---|
| Liquids | |
| Water at 20°C | 0,998 |
| Water at 4°C | 1,000 |
| Petrol | 0,700 |
| Milk | 1,03 |
| Mercury | 13,6 |
| Solids | |
| Ice at 0°C | 0,917 |
| Magnesium | 1,738 |
| Aluminum | 2,7 |
| Iron | 7,874 |
| Copper | 8,96 |
| Lead | 11,34 |
| Uranus | 19,10 |
| Gold | 19,30 |
| Platinum | 21,45 |
| Osmium | 22,59 |
| Gases at normal temperature and pressure | |
| Hydrogen | 0,00009 |
| Helium | 0,00018 |
| Carbon monoxide | 0,00125 |
| Nitrogen | 0,001251 |
| Air | 0,001293 |
| Carbon dioxide | 0,001977 |
Density and mass
Some industries, such as aviation, require materials that are as light as possible. Since low-density materials also have low mass, in such situations they try to use materials with the lowest density. For example, the density of aluminum is only 2.7 g/cm³, while the density of steel is from 7.75 to 8.05 g/cm³. It is due to the low density that 80% of aircraft bodies use aluminum and its alloys. Of course, you should not forget about strength - today few people make airplanes from wood, leather, and other lightweight but low-strength materials.
Black holes
On the other hand, the higher the mass of a substance per given volume, the higher the density. Black holes - an example physical bodies with a very small volume and enormous mass, and, accordingly, enormous density. Such an astronomical body absorbs light and other bodies that are close enough to it. The largest black holes are called supermassive.
Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question in TCTerms and within a few minutes you will receive an answer.
Creatinine is the anhydride of creatine (methylguanidinacetic acid) and is an elimination form produced in muscle tissue. Creatine is synthesized in the liver, and after release, 98% of it enters muscle tissue, where phosphorylation occurs, and in this form plays an important role in storing muscle energy. When this muscle energy is needed to carry out metabolic processes, phosphocreatine is broken down into creatinine. The amount of creatine converted into creatinine is maintained at a constant level, which is directly related to the body's muscle mass. In men, 1.5% of creatine reserves are converted to creatinine daily. Creatine obtained from food (especially meat) increases creatine and creatinine stores. Decreasing protein intake lowers creatinine levels in the absence of the amino acids arginine and glycine, precursors to creatine. Creatinine is a stable nitrogenous constituent of the blood, unaffected by most foods, exercise, circadian rhythms or other biological constants, and is associated with muscle metabolism. Impaired renal function reduces creatinine excretion, causing an increase in serum creatinine levels. Thus, creatinine concentrations approximately characterize the level of glomerular filtration. The main value of determining serum creatinine is the diagnosis of renal failure. Serum creatinine is a more specific and sensitive indicator of renal function than urea. However, in chronic kidney disease, it is used to determine both serum creatinine and urea, in combination with blood urea nitrogen (BUN).
Material: deoxygenated blood.
Test tube: vacutainer with/without anticoagulant with/without gel phase.
Processing conditions and sample stability: serum remains stable for 7 days at
2-8 °C. Archived serum can be stored at -20°C for 1 month. Must be avoided
defrosting and re-freezing twice!
Method: kinetic.
Analyzer: Cobas 6000 (with 501 modules).
Test systems: Roche Diagnostics (Switzerland).
Reference values in the SYNEVO Ukraine laboratory, µmol/l:
Children:
Newborns: 21.0-75.0.
2-12 months: 15.0-37.0.
1-3 years: 21.0-36.0.
3-5 years: 27.0-42.0.
5-7 years: 28.0-52.0.
7-9 years: 35.0-53.0.
9-11 years: 34.0-65.0.
11-13 years: 46.0-70.0.
13-15 years: 50.0-77.0.
Women: 44.0-80.0.
Men: 62.0-106.0.
Conversion factor:
µmol/l x 0.0113 = mg/dl.
µmol/l x 0.001 = mmol/l.
Main indications for the purpose of the analysis: serum creatinine is determined at the first examination in patients without or with symptoms, in patients with symptoms of urinary tract diseases, in patients with arterial hypertension, with acute and chronic renal diseases, non-renal diseases, diarrhea, vomiting, profuse sweating, with acute illnesses, after surgery or in patients in need of intensive care, for sepsis, shock, multiple injuries, hemodialysis, for metabolic disorders (diabetes mellitus, hyperuricemia), during pregnancy, diseases with increased protein metabolism (multiple myeloma, acromegaly), during treatment with nephrotoxic medications.
Interpretation of results
Increased level:
Acute or chronic kidney disease.
Obstruction urinary tract(postrenal azotemia).
Reduced renal perfusion (prerenal azotemia).
Congestive heart failure.
Shock states.
Dehydration.
Muscle diseases (myasthenia gravis, muscular dystrophy, polio).
Rhabdomyolysis.
Hyperthyroidism.
Acromegaly.
Reduced level:
Pregnancy.
Decreased muscle mass.
Lack of protein in the diet.
Severe liver diseases.
Interfering factors:
Higher levels are recorded in men and in individuals with large muscle mass; the same creatinine concentrations in young and elderly people do not mean the same level of glomerular filtration (in old age, creatinine clearance decreases and creatinine formation decreases). In conditions of decreased renal perfusion, increases in serum creatinine occur more slowly than increases in urea levels. Since there is a forced decline in kidney function by 50% with an increase in creatinine values, creatinine cannot be considered as a sensitive indicator for mild or moderate kidney damage.
Serum creatinine levels can be used to estimate glomerular filtration rate only under conditions of balance, when the rate of creatinine synthesis is equal to the rate of its elimination. To check for this condition, two determinations are required 24 hours apart; Differences of more than 10% may indicate the absence of such balance. In renal impairment, glomerular filtration rate may be overestimated by serum creatinine because creatinine elimination is independent of glomerular filtration and tubular secretion, and creatinine is also eliminated through the intestinal mucosa, presumably metabolized by bacterial creatine kinases.
Medicines
Raise:
Acebutolol, ascorbic acid, nalidixic acid, acyclovir, alkaline antacids, amiodarone, amphotericin B, asparaginase, aspirin, azithromycin, barbiturates, captopril, carbamazepine, cefazolin, cefixime, cefotetan, cefoxitin, ceftriaxone, cefuroxime, cimetidine, ciprofloc sacin, clarithromycin, diclofenac, diuretics, enalapril, ethambutol, gentamicin, streptokinase, streptomycin, triamterene, triazolam, trimethoprim, vasopressin.
Reduce: glucocorticoids
Chapter 2. Principles of laboratory research.
Laboratory testing of the patient can be divided into three phases:
- preliminary, which includes the collection and transportation of biological material to the laboratory;
- analytical phase in the laboratory;
- the final phase, which includes the communication of results and their interpretation (the so-called post-analytical phase).
This chapter discusses some general principles relevant to the first, preliminary, phase. The following discusses general provisions regarding the third phase. These are units of measurement, boundaries of normality and pathology, and critical values of indicators.
PRELIMINARY PROCEDURES
It's hard to overestimate the importance correct execution preliminary procedures for laboratory tests. The high quality, accuracy, and suitability of laboratory results for use in clinical settings largely depend on both the correct delivery of samples to the laboratory and the quality of procedures performed during the analysis process. Let's consider the following main aspects of the preliminary phase of laboratory research:
- referral for analysis;
- sample collection time;
- sampling technique;
- sample volume;
- packaging and labeling of samples;
- safety precautions when collecting and transporting biological samples.
This chapter covers only the basic principles. Preliminary procedures are described in more detail in the relevant chapters. However, you need to understand that in practice they may differ in detail between different laboratories. Therefore, these rules should not be formally transferred to the practice of your laboratory. (editor's comment: For use in laboratories in Russia, a manual “Quality control systems for medical laboratories: recommendations for implementation and monitoring.” / Ed. V. L. Emanuel and A. Kalner. - WHO, 2000 - 88 p.)
Referral for analysis
Each biological sample must be accompanied by a completed special form for analysis, signed medical worker, issuing it, or noted by nurses in several instances where the answer should be received. Errors in referral may result in the patient receiving a late notification of a “bad” test or in the test not being included in the patient’s medical record at all. Attention to detail in accompanying documents especially (vitally) important when referring patients for blood transfusions. Most cases of failed blood transfusions are the result of an error in the accompanying documentation. All referrals for testing must include the following information:
- patient information, including first name, last name, patronymic, date of birth and medical history number;
- department (therapeutic, surgical), ward number, outpatient clinic;
- biological material (venous blood, urine, biopsy, etc.);
- date and time of analysis collection;
- name of the test (blood sugar, complete blood cell count, etc.);
- clinical details (this information should explain why a particular test is needed; usually this is a preliminary diagnosis or symptoms);
- a description of therapy if medications taken by the patient may distort test results or their interpretation;
- if required, a note indicating the need for urgent analysis;
- a note about the cost and payment of the procedure.
Sample collection time
Whenever possible, transportation of biological samples to the laboratory should be organized in such a way that analysis is carried out without undue delay. It is bad if samples are left for several hours or overnight before being sent to the laboratory - in many cases they become unsuitable for analysis. Some biochemical tests (for example, to determine blood hormone levels) require samples to be taken at a specific time of day, while for others (for example, to determine blood glucose levels), it is very important to know the time of sample collection. Sometimes (particularly when analyzing blood gases) the test needs to be performed immediately after sample collection, so it is necessary to have the laboratory fully prepared. It is best to obtain samples for microbiological testing before administering antibiotic therapy, which inhibits the growth of microorganisms in culture.
Sampling technique
Taking blood from a vein
Most biochemical tests require venous blood, which is obtained using a technique called venipuncture. Venipuncture is performed using a syringe with a needle or a special syringe tube (Fig. 2.1).
- The patient may be afraid of the venipuncture procedure itself. Therefore, it is important to calmly and confidentially, in simple words, explain to him how blood is taken and that discomfort and painful sensations usually disappear after inserting a needle into a vein.
- If the patient has ever previously felt ill during a blood draw, it is best to encourage them to lie down during the procedure
- If the patient has previously received intravenous solutions, blood should not be taken for analysis from the same arm. This prevents the risk of contaminating the blood sample with the drug administered intravenously.
- Hemolysis (damage to red blood cells during blood collection) may render the sample unusable for analysis. Hemolysis can occur by rapid evacuation of blood through a thin needle or by vigorous shaking of the tube. When using a regular syringe, the needle is removed before the sample is placed in the container.
- Applying a tourniquet to long time may distort the analysis results. This should be avoided and blood should not be collected if the tourniquet is used for more than 1 minute. Try to draw blood from a vein in your other arm.
- Although v. cephalica And v. basilica most convenient for drawing blood; if they are not available, veins can be used back side arms or legs.
Rice. 2.1. Venous blood collection using the Vacutainer system
Vacutainer system: Required additional equipment: |
|
Take the needle in the area of the dyed area and tear the white paper wrapping. Remove it along with the white plastic protective cap. The system CANNOT BE USED if the paper packaging is broken. |
|
| Insert the needle into the needle holder and remove the colored protective film from the needle. | |
Apply a tourniquet 10 cm above the elbow so that the vein becomes visible and it is convenient to choose a place for puncture. Wipe the puncture site with a swab dipped in alcohol: let it dry. |
|
| Remove the protective cap from the needle. Place the patient's arm on the roller and extend it at the elbow. Insert the needle into the vein, cut side up. |
|
| Attach the collection tube to the needle holder. Without moving the needle inside the vein, use a gentle but sharp movement to push the tube to the end of the needle holder. Remove the tourniquet when blood begins to flow into the tube. |
|
Remove the collection tube when it is full of blood. Continue to hold the needle and needle holder in the same position (for further blood collection, attach the next tube in the same way as described above). |
|
| Disconnect the tube from the needle holder. Invert the tube 8-10 times to mix the blood with the stabilizer in the tube. |
|
| Remove the needle holder with the needle from the vein. Place a cotton swab on the puncture site and tell the patient to bend his arm at the elbow for 1-2 minutes. |
|
| Dispose of the needle and needle holder (if disposable) in accordance with the safety instructions. Label the sample according to the rules accepted in the laboratory. |
Capillary blood collection
Capillary blood flows through to the smallest vessels under the skin and can be easily obtained for analysis using a scalpel spear from the finger or (usually in infants) from the heel. The patient himself can master this technique after some training. It is used, for example, by diabetic patients to monitor blood glucose concentrations.
Arterial blood collection
The only test that requires arterial blood is a blood gas test. The arterial blood collection procedure, which is more dangerous and painful than venipuncture, is described in Chapter 6.
Urine collection
There are four commonly used methods for collecting urine:
- mid-micturition (MSU);
- using a catheter (CSU);
- morning portion collection (EMU);
- collection of daily urine, i.e., combining all portions of urine over 24 hours.
The nature of the analysis determines which of these urine collection methods to use. Most non-quantitative methods (eg, urine density or microbiological analysis) use MSU. This is a small portion of urine (10-15 ml), collected during urination at any time of the day. CSU is a urine sample collected from a patient using a urinary catheter. Details of collection of MSU and CSU for microbiological study are described in Chapter 20.
The very first morning urine (EMU) is the most concentrated, so it is convenient to determine substances present in the blood in minimal concentrations. So, it is used to conduct a pregnancy test. This test is based on the determination of human chorionic gonadotropin (HCG), a hormone that is not usually present in urine, but appears in increasing quantities in the first few months of pregnancy. On early stages The concentration of this hormone is so low that if you use non-concentrated urine (not EMU), you can get a false negative result.
Sometimes it is necessary to know exactly how much of a certain substance (such as sodium or potassium) is lost daily in the urine. Quantitative determination can only be made if daily urine is collected. A detailed description of this procedure is given in Chapter 5.
Taking tissue samples for analysis (biopsy)
A very brief description of the biopsy technique required to perform histological examination has already been given in Chapter 1. This procedure is always the responsibility of your doctor, so it is not covered in detail in this guide. However, nurses are involved in collecting cervical cell samples when performing vaginal smear tests (editor's comment: Registration forms for performing cytological studies are standardized by order of the Ministry of Health of the Russian Federation No. 174 dated April 24, 2003).
Sample volume
The volume of blood samples required for testing is determined primarily by the equipment of a particular laboratory. In general, with technological progress, the volume of sample required to conduct a particular analysis decreases significantly. The entry on the referral form “Insufficient material, repeat analysis” is now becoming less and less common. All laboratories have a list of tests, which shows the minimum volumes of blood samples required to perform them. Any employee taking blood for analysis must know these standards. Some blood collection tubes contain trace the amount of chemical preservatives and/or anticoagulants that determine the optimal amount of blood collected in them. In this case, there is a corresponding mark on the wall of the tube to which blood must be drawn. If this is not taken into account, erroneous results may be obtained. Although the amount of MSU and CSU urine is not critical, sample volume in a 24-hour urine collection is very important, so collect all urine portions for a 24-hour period, even if additional capacity is required.
In general, the amount of biological material (sample size) is important for the successful isolation of bacterial isolates. It is more likely to be able to isolate bacteria from a large amount of sputum than from a small amount. Using a syringe and needle to suction out pus is more likely than taking a smear to isolate the causative agent. If the volume of blood added to the culture medium is insufficient, false negative results may be obtained.
Sample packaging
Laboratories follow certain rules regarding the use of bottles and containers. Each type of container serves a specific purpose. For getting reliable results It is necessary that certain containers be used when running certain tests. Sometimes blood collection containers contain some chemical substances(Table 2.1) in the form of liquid or powder. Their addition has two purposes: they protect the blood from clotting and maintain the native structure of blood cells or the concentration of a number of blood components. Therefore, it is important that these chemicals are mixed with the collected blood.
Preservatives may be necessary when collecting 24-hour urine. The need for them is determined by which components of urine are examined.
All containers in which material for microbiological research is collected (urine, sputum, blood, etc.) must be sterile and cannot be used if their insulation is broken. Some bacteria survive outside the human body only if they are preserved in special media for transport.
To preserve biopsy specimens, they must be fixed in formalin. Therefore, containers intended for transporting tissue samples contain this fixative.
All containers containing biological material must be labeled with the patient's full name, date of birth and location (department, clinic or address). Laboratories receive many hundreds of samples every day, which may include two or more samples from patients with the same last name. If a test result needs to be returned to be entered into the medical record, it is very important that the record is accurate and allows the patient to be easily identified.
Incorrectly labeled samples may not be accepted by the laboratory, resulting in the patient having to retake the test, which will require additional time and effort on the part of both the patient and the patient. medical personnel.
Table 2.1. Basic chemical additives used when taking blood for analysis
Ethylenediaminetetraacetate (EDTA) |
An anticoagulant that prevents blood from clotting by binding and effectively removing calcium ions present in the plasma (calcium is necessary for blood clotting). EDTA also protects blood cells from destruction. Added to blood collection tubes for complete blood cell counts and certain other hematology tests |
Heparin (as the sodium or potassium salt of this acid, i.e. heparin sodium or heparin potassium) |
An anticoagulant that prevents blood from clotting by inhibiting the conversion of prothrombin to thrombin. Added to blood collection tubes for the purpose of biochemical studies that require plasma. The anticoagulant properties of heparin are used in therapy |
Citrate (as sodium salt, i.e. sodium citrate) |
An anticoagulant that prevents blood from clotting by binding calcium ions (like EDTA). Added to blood collection tubes to study coagulation processes |
Oxalate (as sodium or ammonium salt, i.e. sodium or ammonium oxalate) |
An anticoagulant that prevents blood from clotting by binding calcium ions (like EDTA). Used with sodium fluoride (see below) to determine blood glucose levels |
Sodium fluoride |
This is an enzymatic poison that stops the metabolization of glucose in the blood after it is collected, i.e., maintains its concentration. Used with ammonium oxalate specifically to determine blood glucose levels |
Safety precautions when collecting and transporting biological samples
All laboratories have their own approved safety procedures for the collection and transport of biological material, based on the assumption that all samples collected are potentially hazardous. Employees involved in these procedures must be aware of safety procedures. Among the many dangers that can be posed by samples of biological material, special mention should be made of human immunodeficiency viruses (HIV) and hepatitis viruses, which can be transmitted through contact with infected blood. Tuberculosis can be contracted through contact with the sputum of a patient, and gastrointestinal infections can be contracted through contact with contaminated feces. Properly organized work should minimize the risk of infection of laboratory personnel and patients. One of the components of good laboratory practice (GLP) is compliance with safety regulations. The following are some general safety precautions that must be observed when collecting and transporting biological material.
- To reduce the risk of infection when taking biological samples, disposable surgical gloves should be used. Open wounds are often gateways to viral and bacterial infections.
- Syringes and needles must be stored securely. It is mainly through them that a laboratory employee comes into contact with potentially infected blood of a patient.
- Large and often serious danger represents a violation of the integrity of sample packaging. This can be prevented by not filling the tubes to the top and using secure caps. Most laboratories have established regulations that, when followed, prevent the leakage of biological material.
- Sample collection must be carried out in accordance with laboratory procedures.
- If it is known that the patient is infected with HIV or hepatitis viruses, additional protective measures (safety glasses, gowns) are used when taking samples. Specimens from such a patient should be clearly labeled in several ways appropriate to the laboratory.
ON THE QUESTION OF INTERPRETING THE RESULTS OF LABORATORY STUDIES
It is known that many laboratories have different methods for assessing laboratory results. Anyone involved in the interpretation of results should be aware that they can be expressed quantitative, semi-quantitative And qualitatively . For example, histological data are qualitative: they are presented in the form of a specialized description of histological preparations prepared from tissue samples and analyzed under a microscope. The histologist gives clinical assessment certain microscopic deviations of a particular sample from the norm. The results of microbiological analysis can be either qualitative or semi-quantitative. The text part of the report reports on the identified pathogenic microorganisms, and their sensitivity to antibiotics is assessed semi-quantitatively. On the contrary, the results of biochemical and hematological studies are quantitative, expressed in specific numbers. Like all other measured indicators (body weight, temperature, pulse), quantitative results laboratory tests expressed in certain units of measurement.
Units of measurement used in clinical laboratories
International System of Units (SI)
Since the 70s of the 20th century, in the UK, all measurement results in scientific and clinical practice have been trying, as far as possible, to be expressed in SI units (the International System of Units was proposed in 1960). In the United States, non-systemic units continue to be used for laboratory test results, which must be taken into account when interpreting data presented in American medical publications for doctors and nursing staff. Of the seven basic SI units (Table 2.2), only three are used in clinical practice:
- meter (m);
- kilogram (kg);
- mole (mole).
Table 2.2. Basic SI units
SI unit |
Unit of measurement |
Reduction |
Kilogram |
mass (weight)* |
|
electric current strength |
||
thermodynamic temperature |
||
amount of substance |
||
luminous powers |
* In this context, these concepts should be considered equivalent.
Everyone is certainly familiar with the meter as a unit of length and the kilogram as a unit of mass or weight. The concept of a mole, in our opinion, requires explanation.
What is a mole?
A mole is an amount of a substance whose mass in grams is equivalent to its molecular (atomic) mass. This is a convenient unit of measurement, since 1 mole of any substance contains the same number of particles - 6.023 x 10 23 (the so-called Avogadro's number).
Examples
Chemuraven 1 mole of sodium (Na)?
Sodium is a monoatomic element with an atomic mass of 23. Therefore, 1 mole of sodium is equal to 23 g of sodium.
What is 1 mole of water (H 2 0)?
A water molecule consists of two hydrogen atoms and one oxygen atom.
Therefore, the molecular weight of water is 2 x 1 + 16 = 18.
Thus, 1 mole of water is equal to 18 g of water.
What is 1 mole of glucose equal to?
The glucose molecule consists of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. The molecular formula of glucose is written as C 6 H 12 O 6.
The atomic mass of carbon is 12.
The atomic mass of hydrogen is 1.
The atomic mass of oxygen is 16.
Therefore, the molecular weight of glucose is 6 x 12 + 12 x 1 + 6 x 16 = 180.
Thus, 1 mole of glucose is equal to 180 g of glucose.
So, 23 g of sodium, 18 g of water and 180 g of glucose each contain 6.023 x 10 23 particles (atoms in the case of sodium or molecules in the case of water and glucose). Knowing the molecular formula of a substance allows you to use the mole as a unit of quantity. For some molecular complexes present in the blood (primarily proteins), the exact molecular mass has not been determined. Accordingly, it is impossible to use a unit of measurement for them such as the mole.
SI decimal multiples and submultiples
If the SI base units are too small or large to measure the exponent, decimal multiples or submultiples are used. In table Table 2.3 presents the most commonly used secondary SI units of length, mass (weight) and quantity of a substance to express the results of laboratory studies.
Volume units
Strictly speaking, SI units of volume should be based on the meter, for example - cubic meter (m 3), cubic centimeter (cm), cubic millimeter (mm 3), etc. However, when the International System of Units was introduced, it was decided to leave the liter in as a unit of measurement for liquids, since this unit was used almost everywhere and it is almost exactly equal to 1000 cm 3. In fact, 1 liter is equal to 1000.028 cm3
The liter (l) is essentially the basic SI unit of volume; in clinical and laboratory practice, the following units of volume derived from the liter are used:
deciliter (dl) - 1/10 (10 -1) liter,
centiliter (cl) - 1/100 (10 -2) liter,
milliliter (ml) - 1/1000 (10 -3) liter
microliter (µl) - 1/1,000,000 (10 -6) liter.
Remember: 1 ml = 1.028 cm 3.
Table 2.3. Secondary SI units of length, mass (weight) and amount of substance used in laboratory practice
The basic unit of length is meter (m)
Secondary units:
Centimeter (cm)- 1/100 (10 -2) meters; 100 cm = 1 m
Millimeter (mm)- 1/1000 (10 -3) meters; 1000 mm = 1 m, 10 mm = 1 cm
Micrometer (µm)- 1/1 000 000 (10 -6) meters; 1,000,000 µm = 1 m, 10,000 µm = 1 cm, 1000 µm = 1 mm
Nanometer (nm)- 1/1 000 000 000 (10 -9) meters; 1,000,000,000 nm = 1 m, 10,000,000 nm = 1 cm, 1,000,000 nm = 1 mm, 1000 nm = 1 µm
The basic unit of mass (weight) is kilogram (kg)
Secondary units:
Gram (g)- 1/1000 (10 -3) kilogram; 1000 g = 1 kg
Milligram (mg)- 1/1000 (10 -3) grams; 1000 mg = 1 g, 1,000,000 mg = 1 kg
Microgram (mcg)- 1/1000 (10 -3) milligram; 1000 mcg = 1 mg, 1,000,000 mcg = 1 g, 1,000,000,000 mcg = 1 kg
Nanogram (ng)- 1/1000 (10 -3) microgram; 1000 ng = 1 mcg, 1,000,000 ng = 1 mg, 1,000,000,000 ng = 1 g, 1,000,000,000,000 ng = 1 kg
Picogram (pg)- 1/1000 (10 -3) nanogram; 1000 pg = 1 ng, 1,000,000 pg = 1 mcg, 1,000,000,000 = 1 mg,
1,000,000,000,000 pg = 1 g
The basic unit of quantity of a substance is the mole (mol)
Secondary units:
Millimol (mmol)- 1/1000 (10 -3) moles; 1000 mmol = 1 mol
Micromoles (µmol)- 1/1000 (10 -3) millimoles; 1000 µmol = 1 mmol, 1,000,000 µmol = 1 mol
Nanomole (nmol)- 1/1000 (10 -3) micromoles; 1000 nmol = 1 µmol, 1,000,000 nmol = 1 mmol,
1,000,000,000 nmol = 1 mol
Picomole (pmol)- 1/1000 (10 -3) nanomoles; 1000 pmol = 1 nmol, 1,000,000 pmol = 1 µmol,
1,000,000,000 pmol = 1 mmol
Units of concentration
Almost all quantitative laboratory tests include determining the concentration of a substance in the blood or urine. Concentration can be expressed as the amount or mass (weight) of a substance contained in a specific volume of liquid. Units of concentration thus consist of two elements - units of mass (weight) and units of volume. For example, if we weighed 20 g of salt and dissolved it in 1 liter (volume) of water, we would obtain a salt solution with a concentration of 20 g per 1 liter (20 g/l). In this case, the unit of mass (weight) is gram, the unit of volume is liter, and the SI unit of concentration is g/l. If the molecular mass of a substance can be accurately measured (for many substances determined in laboratory conditions it is known), then to calculate the concentration, a unit of the amount of the substance (mole) is used.
Here are examples of use different units to express the results of laboratory tests.
What does the phrase mean: “Plasma sodium is 144 mmol/l"?
This means that each liter of plasma contains 144 mmol of sodium.
What does the expression “Plasma albumin is 23 g/l” mean?
This means that every liter of plasma contains 23 g of albumin.
What does the result mean: “Plasma iron is 9 µmol/l”?
This means that every liter of plasma contains 9 micromoles of iron.
What does the entry mean: “Plasma B12 is 300 ng/l”?
This means that every liter of plasma contains 300
ng vitamin B12.
Blood Cell Counting Units
Most hematology tests involve counting the concentration of cells in the blood. IN in this case The unit of quantity is the number of cells, and the unit of volume is again the liter. Normally, a healthy person has from 4,500,000,000,000 (i.e. 4.5 x 10 12) to 6,500,000,000,000 (i.e. 6.5 x 10 12) red blood cells in each liter of blood. Thus, the unit of number of red blood cells in the blood is taken to be 10 12 /l. This allows simplified numbers to be used, so that in practice one might hear a doctor tell a patient that his red blood cell count is 5.3. This, of course, does not mean that there are only 5.3 red blood cells in the blood. In fact, this figure is 5.3 x 10 12 / l. There are significantly fewer leukocytes in the blood than red blood cells, so the unit for counting them is 10 9 /l.
Oscillations normal values
When measurements of any physiological parameters are made (for example, body weight, pulse, etc.), the results are interpreted by comparing them with normal values. This is also true for laboratory results. All quantitative tests have defined normal ranges to help evaluate the patient's test results. Biological diversity does not allow clear boundaries between normal and abnormal values of body weight, height, or any blood or urine parameters. The use of the term “reference values” instead of “normal values” takes this limitation into account. The range of reference values is determined based on the results of measuring a particular indicator in a large population of practically healthy (“normal”) people.
The graph shown in Fig. 2.2 illustrates the results of measurements of the concentration of a hypothetical substance X in the blood in a large population of healthy individuals (reference population) and in patients with a hypothetical disease Y.
Since the level of substance X usually rises in disease Y, it can be used as a hematological indicator to confirm the diagnosis in patients with symptoms of disease Y. The graph shows that the concentration of substance X in healthy people ranges from 1 to 8 mmol/L. The likelihood that a particular patient's value is within normal limits decreases as it moves away from the average value in the reference population. The extremes of the “normal” range may actually be associated with disease Y. To account for this, the normal range is determined by excluding the 2.5% of results in the population that fall on the extreme end of the range. Thus, the reference range is limited by 95% of the results obtained in a population of healthy people. In the case considered, it is 1.9-6.8 mmol/l. Using the range of normal values, we can determine those who are sick with disease Y. It is clear that patients whose concentration of substance X is above 8.0 mmol/l are sick with disease Y, and those with this indicator below 6.0 mmol/l - no. However, values between 6.0 and 8.0 mmol/L, which fall within the shaded area, are less certain.
Lack of certainty of results falling into border regions is a common problem. diagnostic laboratories, which must be taken into account when interpreting them. For example, if the limits of normal values for sodium concentration in the blood in a given laboratory are determined to be from 135 to 145 mmol/l, then there is no doubt that a result of 125 mmol/l indicates the presence of pathology and the need for treatment. On the contrary, although a single result of 134 mmol/L is outside the normal range, this does not mean that the patient is sick. Remember that 5% of people (one in twenty) in the general population are within the reference range.
Rice. 2.2. Demonstration of the normal range of fluctuations in the concentration of a hypothetical substance X and partial coincidence of values in a group of healthy individuals and in a group of individuals suffering from a conditional disease Y (see explanation in the text).
Factors influencing the normal range
There are physiological factors that can influence the normal limits. These include:
- patient's age;
- his gender;
- pregnancy;
- time of day at which the sample was taken.
Thus, blood urea levels increase with age, and hormone concentrations differ between adult men and women. Pregnancy may change the results of thyroid function tests. The amount of glucose in your blood fluctuates throughout the day. Many medicines and alcohol influence one way or another on the results of a blood test. The nature and degree of physiological and medicinal effects are discussed in more detail when considering the relevant tests. Ultimately, the area of normal values of the indicator is influenced by analytical methods, used in a specific laboratory. When interpreting the results of a patient's analysis, one should be guided by the reference range adopted in the laboratory where the analysis was performed. This book provides ranges of normal values of indicators that can be used as reference, but they are comparable to the norms adopted in individual laboratories.
Critical values
If laboratory test results are outside the normal range, the nurse should know at what values the indicator requires immediate health care. Do I need to immediately notify the doctor in such cases? The concept of critical values (sometimes inappropriately called "panic") helps to accept correct solution. Critical values are determined by a pathophysiological condition that is so different from normal that it is life-threatening unless appropriate emergency measures are taken. Not all tests have critical values, but where they do, you can find them in this book along with the normal range. Like normal limits, critical value areas are determined for the conditions of each specific laboratory. How to interpret test results of this patient It is important to use the standards of the particular laboratory in which the study was carried out, and nurses should also be guided by the local protocol adopted regarding the critical values of indicators.
DIFFERENCES BETWEEN SERUM AND PLASMA
Throughout this book, the terms “blood serum” (or just serum) and “blood plasma” (or just plasma) will be used. Therefore, it is important to give precise definitions of these concepts in the introductory chapter. Blood consists of cells (red blood cells, white blood cells and platelets) suspended in a fluid, which is a solution of many different inorganic and organic matter. This is the fluid that is analyzed in most biochemical and some hematological tests. The first step in performing all of these tests is to separate the liquid portion of the blood from the cells. Physiologists call the liquid part of blood plasma. Blood clotting occurs when the fibrinogen protein dissolved in it is converted into insoluble fibrin. The supernatant no longer containing fibrinogen after blood clotting is called serum. The difference between plasma and serum is determined by the type of tube in which the blood is collected. If a regular test tube without any additives is used for this purpose, the blood coagulates and serum is formed. If anticoagulants are added to the test tube, the blood remains liquid (does not clot). The liquid part of the blood that remains after the cells are removed is called plasma. With some important exceptions (most notably coagulation tests), the results of serum and plasma are essentially the same. Therefore, the choice of serum or plasma as a material for analysis is the prerogative of the laboratory.
Case history 1
On the second day after elective surgery, 46-year-old Alan Howard felt unwell. His blood was taken for testing biochemical analysis and general blood test. Among the results obtained were the following:
General blood test is normal. Upon discovering that the patient's potassium and calcium concentrations were significantly different from normal, the nurse immediately reported this to the patient. family doctor, who took the blood for analysis again. After 20 minutes, the laboratory telephoned that the indicators had returned to normal.
Discussion of medical history
Blood taken for counting the formed elements must be protected from clotting. To do this, an anticoagulant called potassium salt EDTA (K+-EDTA). This substance behaves in solution as a chelating agent that effectively binds calcium ions. In addition to protecting blood from clotting, K + -EDTA has two side effects: increased potassium concentration and decreased calcium levels in the blood. A small blood sample intended for automated blood testing contained a sufficiently large amount of anticoagulant to significantly increase potassium levels and decrease calcium concentrations. This case report demonstrates that blood stabilized with K + -EDTA is not suitable for determining potassium and calcium levels. It is an example of how errors during sampling can have a significant impact on the outcome of a laboratory test. In this case, the results obtained were not compatible with life, so the error was quickly identified. If changes in results due to violations of the procedures for taking and transporting samples of biological material are not so great, they may go unnoticed and, therefore, cause greater harm.
Literature cited
1. Emancipator K. (1997) Critical values - ASCP Practice Parameter. Am. J. Clin. Pathol. 108: 247-53.
additional literature
Campbell J. (1995) Making sense of the technique of venepuncture. Nursing Times 91(31): 29-31.
Ravel R. (1995) Various factors affecting laboratory test interpretation. In Clinical Laboratory Medicine, 6th edn, pp. 1-8. Mosby, Missouri
Ruth E., McCall K. & Tankersley C. M. (1998) Phlebotomy Essentials, 2nd edn Lippincott, Philadelphia.
Ensuring the quality of laboratory tests. Preanalytical stage. / Ed. prof. Menshikova V.V. - M.: Labinform, 1999. - 320 p.
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1 millimole per liter [mmol/l] = 0.001 mol per liter [mol/l]
Initial value
Converted value
moles per meter³ moles per liter moles per centimeter³ moles per millimeter³ kilomoles per meter³ kilomoles per liter kilomoles per centimeter³ kilomoles per millimeter³ millimoles per meter³ millimoles per liter millimoles per centimeter³ millimoles per millimeter³ moles per cubic. decimeter molar millimolar micromolar nanomolar Picomolar Femtomolar Attomolar zeptomolar yoctomolar
Mass concentration in solution
More about molar concentration
General information
The concentration of a solution can be measured in different ways, for example as the ratio of the mass of the solute to the total volume of the solution. In this article we will look at molar concentration, which is measured as the ratio between the amount of substance in moles to the total volume of the solution. In our case, the substance is the soluble substance, and we measure the volume for the entire solution, even if other substances are dissolved in it. Quantity of substance is the number of elementary components, such as atoms or molecules of a substance. Since even in small amounts of a substance it is usually big number elementary components, then special units, moles, are used to measure the amount of a substance. One mole equal to the number of atoms in 12 g of carbon-12, that is, approximately 6 x 10²³ atoms.
It is convenient to use moles if we are working with an amount of a substance so small that its amount can easily be measured with home or industrial instruments. Otherwise you would have to work with very large numbers, which is inconvenient, or with very small weight or volume, which is difficult to find without specialized laboratory equipment. The most common particles used when working with moles are atoms, although it is possible to use other particles, such as molecules or electrons. It should be remembered that if non-atoms are used, this must be indicated. Sometimes molar concentration is also called molarity.
Molarity should not be confused with molality. Unlike molarity, molality is the ratio of the amount of solute to the mass of the solvent, rather than to the mass of the entire solution. When the solvent is water and the amount of solute compared to the amount of water is small, then molarity and molality are similar in meaning, but otherwise they are usually different.
Factors affecting molar concentration
Molar concentration depends on temperature, although this dependence is stronger for some solutions and weaker for other solutions, depending on what substances are dissolved in them. Some solvents expand when the temperature increases. In this case, if the substances dissolved in these solvents do not expand with the solvent, then the molar concentration of the entire solution decreases. On the other hand, in some cases, with increasing temperature, the solvent evaporates, but the amount of soluble substance does not change - in this case, the concentration of the solution will increase. Sometimes the opposite happens. Sometimes a change in temperature affects how the solute dissolves. For example, some or all of the solute stops dissolving and the concentration of the solution decreases.
Units
Molar concentration is measured in moles per unit volume, such as moles per liter or moles per cubic meter. Moles per cubic meter is an SI unit. Molarity can also be measured using other units of volume.
How to find molar concentration
To find the molar concentration, you need to know the amount and volume of the substance. The amount of a substance can be calculated using the chemical formula of that substance and information about the total mass of that substance in solution. That is, to find out the amount of solution in moles, we find out from the periodic table the atomic mass of each atom in the solution, and then divide the total mass of the substance by the total atomic mass of the atoms in the molecule. Before adding atomic masses together, we should make sure that we multiply the mass of each atom by the number of atoms in the molecule we are considering.
You can also perform calculations in reverse order. If the molar concentration of the solution and the formula of the soluble substance are known, then you can find out the amount of solvent in the solution, in moles and grams.
Examples
Let's find the molarity of a solution of 20 liters of water and 3 tablespoons of soda. One tablespoon contains approximately 17 grams, and three tablespoons contain 51 grams. Soda is sodium bicarbonate, the formula of which is NaHCO₃. In this example, we will use atoms to calculate molarity, so we will find the atomic mass of the constituents sodium (Na), hydrogen (H), carbon (C), and oxygen (O).
Na: 22.989769
H: 1.00794
C: 12.0107
O: 15.9994
Since oxygen in the formula is O₃, it is necessary to multiply the atomic mass of oxygen by 3. We get 47.9982. Now let's add up the masses of all the atoms and get 84.006609. Atomic mass is indicated in the periodic table in atomic mass units, or a. e.m. Our calculations are also in these units. One a. e.m. is equal to the mass of one mole of a substance in grams. That is, in our example, the mass of one mole of NaHCO₃ is equal to 84.006609 grams. In our problem - 51 grams of soda. We'll find molar mass, dividing 51 grams by the mass of one mole, that is, by 84 grams, and we get 0.6 moles.
It turns out that our solution is 0.6 moles of soda dissolved in 20 liters of water. Let's divide this amount of soda by the total volume of the solution, that is, 0.6 mol / 20 l = 0.03 mol/l. Since a large amount of solvent and a small amount of soluble substance were used in the solution, its concentration is low.
Let's look at another example. Let's find the molar concentration of one piece of sugar in a cup of tea. Table sugar consists of sucrose. First, let's find the weight of one mole of sucrose, the formula of which is C₁₂H₂₂O₁₁. Using the periodic table, we find atomic masses and determine the mass of one mole of sucrose: 12×12 + 22×1 + 11×16 = 342 grams. There are 4 grams of sugar in one cube, which gives us 4/342 = 0.01 moles. There are about 237 milliliters of tea in one cup, which means the sugar concentration in one cup of tea is 0.01 moles / 237 milliliters × 1000 (to convert milliliters to liters) = 0.049 moles per liter.
Application
Molar concentration is widely used in calculations involving chemical reactions. The branch of chemistry in which the relationships between substances in chemical reactions are calculated and often work with moles is called stoichiometry. The molar concentration can be found by the chemical formula of the final product, which then becomes a soluble substance, as in the example with a soda solution, but you can also first find this substance by the formulas of the chemical reaction during which it is formed. To do this, you need to know the formulas of the substances involved in this chemical reaction. Having solved the equation of a chemical reaction, we find out the formula of the molecule of the solute, and then we find the mass of the molecule and the molar concentration using the periodic table, as in the examples above. Of course, you can perform calculations in reverse order, using information about the molar concentration of the substance.
Let's look at a simple example. This time we'll mix baking soda and vinegar to see an interesting chemical reaction. Both vinegar and baking soda are easy to find - you probably have them in your kitchen. As mentioned above, the formula of soda is NaHCO₃. Vinegar is not a pure substance, but a 5% solution of acetic acid in water. The formula of acetic acid is CH₃COOH. The concentration of acetic acid in vinegar may be more or less than 5%, depending on the manufacturer and the country in which it is made, as in different countries The concentration of vinegar varies. In this experiment, you don't have to worry about chemical reactions between water and other substances, since water doesn't react with baking soda. We only care about the volume of water when we later calculate the concentration of the solution.
First, let's solve the equation for the chemical reaction between soda and acetic acid:
NaHCO₃ + CH₃COOH → NaC₂H₃O₂ + H₂CO₃
The reaction product is H₂CO₃, a substance that, due to its low stability, again enters into a chemical reaction.
H₂CO₃ → H₂O + CO₂
As a result of the reaction we obtain water (H₂O), carbon dioxide(CO₂) and sodium acetate (NaC₂H₃O₂). Let's mix the resulting sodium acetate with water and find the molar concentration of this solution, just as before we found the concentration of sugar in tea and the concentration of soda in water. When calculating the volume of water, it is necessary to take into account the water in which acetic acid is dissolved. Sodium acetate is an interesting substance. It is used in chemical warmers, such as hand warmers.
When using stoichiometry to calculate the amount of substances involved in a chemical reaction, or reaction products for which we will later find the molar concentration, it should be noted that only limited quantity substances may react with other substances. This also affects the quantity of the final product. If the molar concentration is known, then, on the contrary, the amount of starting products can be determined by reverse calculation. This method is often used in practice, in calculations related to chemical reactions.
When using recipes, whether in cooking, making medicine, or creating the perfect environment for aquarium fish, you need to know the concentration. In everyday life, it is often more convenient to use grams, but in pharmaceuticals and chemistry molar concentrations are more often used.
In pharmaceuticals
When creating drugs, molar concentration is very important because it determines how the drug affects the body. If the concentration is too high, the drugs can even be fatal. On the other hand, if the concentration is too low, the drug is ineffective. In addition, concentration is important in the exchange of fluids across cell membranes in the body. When determining the concentration of a liquid that must either pass or, conversely, not pass through membranes, either the molar concentration is used or it is used to find osmotic concentration. Osmotic concentration is used more often than molar concentration. If the concentration of a substance, such as a drug, is higher on one side of the membrane compared to the concentration on the other side of the membrane, such as inside the eye, then the more concentrated solution will move across the membrane to where the concentration is lower. This flow of solution through the membrane is often problematic. For example, if fluid moves into a cell, such as into a blood cell, it is possible that the membrane will become damaged and rupture due to this fluid overflow. Leakage of fluid from the cell is also problematic, since this will impair the functioning of the cell. It is desirable to prevent any drug-induced flow of fluid through the membrane out of the cell or into the cell, and to do this, try to make the concentration of the drug similar to the concentration of fluid in the body, for example in the blood.
It is worth noting that in some cases the molar and osmotic concentrations are equal, but this is not always the case. This depends on whether the substance dissolved in water has broken down into ions during the process electrolytic dissociation. When calculating osmotic concentration, particles in general are taken into account, while when calculating molar concentration, only certain particles, such as molecules, are taken into account. Therefore, if, for example, we are working with molecules, but the substance has broken up into ions, then there will be fewer molecules total number particles (including molecules and ions), and therefore the molar concentration will be lower than the osmotic one. To convert molar concentration to osmotic concentration, you need to know the physical properties of the solution.
In the manufacture of medicines, pharmacists also take into account tonicity solution. Tonicity is a property of a solution that depends on concentration. Unlike osmotic concentration, tonicity is the concentration of substances that the membrane does not allow through. The process of osmosis causes solutions of higher concentration to move into solutions of lower concentration, but if the membrane prevents this movement by not allowing the solution to pass through, then pressure occurs on the membrane. This kind of pressure is usually problematic. If a drug is intended to enter the blood or other body fluid, then the tonicity of that drug must be balanced with the tonicity of the body fluid to avoid osmotic pressure on membranes in the body.
To balance the tonicity, medications often dissolved in isotonic solution. An isotonic solution is a solution of table salt (NaCL) in water at a concentration that balances the tonicity of the fluid in the body and the tonicity of the mixture of this solution and the drug. Typically, the isotonic solution is stored in sterile containers and infused intravenously. Sometimes it is used in its pure form, and sometimes as a mixture with medicine.
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