The volumetric material from a clinical laboratory It comprises a set of glass utensils (mostly) that have the function of measuring volumes, for this they have a printed measurement scale. Each measuring instrument has a specific utility within the laboratory.
Some make grotesque measurements without much accuracy, while others are special for measuring more exact volumes. The choice of volumetric material for the execution of a procedure or the preparation of solutions will depend on what the professional needs to do..
There are laboratory procedures that do not require that the volumes be exact, but in others the accuracy is essential. Therefore, there are them in various forms, details and capacities..
The measurement scale of the different volumetric instruments is expressed in ml or cm3, however they may vary in their appreciation. The appreciation of an instrument refers to the distance between two measurements, which allows defining the minimum measurable quantity when using that scale.
That is, some allow volumes to be measured taking microliters (µl) into account, such as 1.3 ml. This means that the instrument is capable of measuring 1 ml with 3 µl, therefore its appreciation is good and the minimum measurable quantity is 0.1 ml or what is equal to 1 µl..
On the other hand, there are others in which their measurement scale can only measure specific volumes, that is, the measurement jumps from 1 ml to another without intermediate divisions. For example 1 ml, 2 ml, 3 ml, 4 ml etc. In this case the appreciation is not so good and the minimum measurable quantity is 1 ml..
Another important parameter is the capacity or range of a volumetric instrument. This refers to the maximum volume that can be measured. Eg 0.1 ml, 0.2 ml, 1 ml, 5 ml, 10 ml pipettes, or 100 ml, 250 ml, 500 ml, 1000 ml volumetric flasks.
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Measurement materials are classified into two groups: those that offer an approximate measurement volume and those that offer a measurement volume with greater precision..
- Material with approximate measurement volume: graduated cylinder or cylinder, flasks or Erlenmeyer flasks and beakers, graduated conical beakers, Pasteur pipettes and droppers.
- Higher precision volumetric material: single-gauge or terminal serological pipettes, double-gauge or sub-terminal serological pipettes, single-gauge volumetric pipettes, double-gauge volumetric pipettes, burettes, volumetric flasks, automated micropipettes.
The higher precision materials in turn are classified in class A and class B. The A are of better quality and have a higher cost, and the B of a lower quality but are cheaper..
It is the process by which the difference between the value that the volumetric instrument claims to measure with which it actually measures is analyzed. This difference is the uncertainty value of the instrument and should be considered in your measurements..
In this process, it must be taken into account that volume measurements vary with changes in temperature, since heat expands the liquid and cold contracts it. Therefore, a measurement correction table is used according to the measurement temperature..
The procedure consists of weighing the empty instrument, then weighing the instrument filled with water to its maximum capacity for which it was designed. Then you have to measure the mass of water by subtracting the weight of the full instrument minus the vacuum..
The value obtained is multiplied by the correction factor according to the temperature (the correction table is used).
Then the uncorrected measured value is subtracted from the corrected one. That difference represents the uncertainty value. Subsequently, this procedure is repeated several times to obtain various uncertainty measures. The standard deviation is taken from the total uncertainty. This represents the absolute uncertainty.
In order to perform this procedure, it is necessary to confirm that the instruments are clean and physically intact..
The verification step complements the calibration step, because once the absolute uncertainty value has been obtained, the relative uncertainty is also searched and it is verified if the percentage (%) of measurement error is within the permissible ranges established by ISO standards. for each instrument or if it goes out of them.
If it goes outside the permitted value, the material must be discontinued.
As its name indicates, its body is a thin cylinder, it has a base that gives it stability and a spout at the top to help the transfer of liquids. On the body is the scale printed in ml.
The graduated cylinder is used to measure volumes when precision is not very important, they also serve to transfer liquids. There are plastic and glass. Various capacities are available on the market, for example: 25 ml, 50 ml, 100 ml, 200 ml, 500 ml and 1000 ml.
1000 ml cylinders are commonly used to measure 24 hour urine.
The beaker is cylinder-shaped but wider than the test tube, it has a spout in the mouth that facilitates the transfer of liquids.
Its uses are very diverse. With them you can weigh substances, mix and heat solutions. Available capacities range from 50 ml to 5000 ml.
Regarding quality, they are type C. Therefore, their measurements are not precise at all, and therefore they are not recommended for preparing solutions..
There are several types or designs: Griffin glass, Berzelius glass and flat glass..
They are glasses with a wide mouth, flat base, straight body, and not very tall. They have a peak on the edge. They are the most frequently used. They feature a small scale printed.
This glass has a wide mouth, flat base, and a straight body, but its height is higher than that of the Griffin glass..
Wide-mouthed glass, has a spout to aid the transfer of substances and is low in height. It does not have a printed measurement scale. It is commonly used for the crystallization of substances and for incubating solutions in water baths..
The Erlenmeyer flask was designed by Richard August Emil Erlenmeyer, hence its name.
It has a wide base and a narrow neck at the top. In this way it is ideal for mixing solutions, especially for liquids that tend to evaporate, since it can be easily covered with parafilm paper or with a stopper made of gauze or cotton..
Between the base and the neck it has a printed graduated scale, but its measurement is not precise.
It can also be used to heat solutions. It is frequently used to prepare and sterilize culture media or to preserve non-photosensitive solutions, both at room temperature and in the refrigerator.
It is useful in substance titration or titration procedures and as a receiving container in distillation or filtration equipment.
There are several capacities, for example: 50 ml, 125 ml, 225 ml, 500 ml, 1000 ml, and even 6000 ml.
As the name suggests, they are shaped like an inverted cone. They have a measuring scale and a support base. They are not very precise instruments, therefore they should not be used to prepare solutions that require accuracy..
There are two types: serological and volumetric..
Serological pipettes are thin cylinders that are used to accurately measure volumes. There are two types, terminals and sub-terminals.
The terminals have only one capacity, which is at the top where the measurement scale begins. The measured liquid is released until the last drop comes out.
The sub-terminals have a more precise measurement because they have double gauging, one at the beginning or upper part of the pipette and another before the end of the pipette. Therefore, the operator must take care of the leveling in the two gauges.
There are 0.1 ml, 0.2 ml, 1 ml, 2 ml, 5 ml, 10 ml and 25 ml. The quality of a pipette is evaluated based on the precision of its measurements. In this sense, the market offers pipettes type A (better quality) and type B (lower quality).
The maximum quantity that can be measured is stated on the top of the pipette. For example, 10 ml. The volume between two measurement lines is described below. For example, 1/10 ml. This means that the volume that you measure from one line to another is 0.1 ml. This is called instrument appreciation..
These pipettes are a cylinder like the previous ones, but in the upper part they have a safety bulb, especially to prevent accidents in case of dangerous liquids. In the center they have a more pronounced dilation. After dilation the thin cylinder continues.
Like serological pipettes, there are terminals and sub-terminals, class A and class B. Volumetric pipettes are more accurate than serological pipettes.
The volumetric flask or volumetric flask consists of two parts, the lower part is balloon-shaped and the upper part has a moderately long, narrow, cylindrical neck. In the part of the neck it has a mark called capacity.
It does not have a measurement scale, it only has the maximum capacity that is achieved when the liquid reaches the capacity (level).
To make this instrument flush, it must be taken into account that the liquid level will generally be observed in a convex way, so the lower part of the curve must be above the gauging line..
With some liquids that have an adhesion force greater than the cohesion force, the liquid-air interface takes the concave shape. In this case, the upper part of the meniscus should be touching the gauging line.
For this, it is necessary that the observer's view is perpendicular to the line of the gauging. It will not be flush properly if the observer is looking from above or below. These tightening recommendations are also valid for the rest of the volumetric measuring utensils that have capacity..
The volumetric flask is a high precision instrument, used when it is necessary to prepare solutions with an exact concentration. It is ideal for preparing stock solutions, standard solutions, dilutions, etc..
The existing capacities are 25 ml, 50 ml, 200 ml, 250 ml, 500 ml, 1000 ml and 2000 ml. Usually the flask expresses its capacity and the temperature at which the liquids should be measured.
They are graduated glass tubes similar to pipettes, but they have a kind of key or valve (spigot and tap) at the bottom that opens and closes, managing to control the output of the liquid. They are ideal for the solution titration process. There are 10 ml, 20 ml, 25 ml and 50 ml.
This small instrument is a finer graduated cylinder towards the lower end. It usually provides 20 drops for each ml of liquid, that is, one drop is equal to 0.05 ml. To measure the necessary drops, take care that the cylinder does not contain air bubbles. Sucks with a pacifier.
It is very important that the laboratory equipment is washed properly. It is recommended that it be cleaned as quickly as possible after use to avoid deterioration of the material..
After washing, one way to verify if it was clean is to observe if the wet material has drops of water stuck on its surface. If that happens, the glass is greasy and not very clean. In optimal conditions the surface should be left with a smooth film of water.
First of all, it should be washed with tap water and soap. Brushes or sponges can sometimes be used to aid cleaning. Subsequently, rinse very well and then pass several times through distilled or deionized water.
Special soaps for cleaning laboratory glassware are available on the market. These soaps come in two forms, as a powder and as a soap solution..
This type of soap is highly recommended, since it guarantees a more effective cleaning, does not leave any type of residue and does not require scrubbing, that is, it is enough to immerse the material in a tray with soap and water and then rinse well with water tap and then deionized.
Sometimes the material can be immersed in 10% nitric acid for a reasonable time and subsequently immersed in deionized water several times..
This type of washing is not done routinely. It is usually indicated when the glassware is very stained or greasy. This mixture is highly corrosive, so it must be handled with care, and its frequent use damages glassware..
The chromic mixture is prepared by weighing 100 g of potassium dichromate (KtwoCrtwoORtwo) and dissolve in 1000 ml of water, then to this mixture is added little by little 100 ml of concentrated sulfuric acid (HtwoSW4). In that order.
The glassware is dipped in this solution and left overnight. The next day the chromic mixture is collected and saved to be used on another occasion. This mixture is reusable, as many times as possible, and will only be discarded when it turns green..
The material will require several rinses with plenty of water, as the mixture leaves residue adhering to the glass.
The material can be allowed to air dry on an absorbent surface, preferably upside down, in the case of instruments that allow it. Another option is oven drying, but this has the drawback that only approximate volume measurement materials can be dried in this way..
High precision measuring materials should never be dried in an oven, as the heat causes them to lose their calibration.
In this case, if it is necessary to dry them more quickly, a little ethanol or acetone is placed inside the instrument and passed over the entire internal surface, and then cleaned. As these substances are volatile, the remainder will evaporate quickly, leaving the instrument completely dry..
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