WHAT IS THE ALIQUOT? (WITH EXAMPLES) - CHEMISTRY - 2025

An aliquot is a part or sample of a whole that presents its characteristics and that is separated to facilitate its study. In chemistry, the aliquot can be of a liquid, solid or gaseous material. The technique to extract these “mini” samples will depend on the characteristics of the study; some may be very small, and some may be large.

A typical example of this concept is found in the home: in the preparation of drinks or smoothies. If you want to prepare a pineapple juice with passion fruit, take an aliquot of each of both juices (half the glass, for example), and mix them.

Source: Unknown photographer, via Wikimedia Commons

If you want the pineapple flavor to predominate, then you take an aliquot corresponding to 3/4 of the pineapple juice and not half.

Therefore, the aliquots not only allow to analyze a sample from a small portion of it, but also to prepare other samples with previously calculated characteristics or concentrations.

Examples of aliquots

-Analytic chemistry

The samples are not always liquid, solid ones are also abundant in great proportion. In these cases it is necessary to homogenize it after weighing it, subsequently subjecting it to a digestion process with concentrated strong acids and other compounds.

If necessary, the product of the previous processing must be subjected to an extraction and finally, make a dilution of this preparation.

This action of preparing a dilution to a certain volume and taking a sample from it for analysis is called taking an aliquot; that is to say, one is again at the beginning.

-Medicine

If the doctor deems it necessary, he requests a blood test. To do this, we go to the specialized laboratory where a volume of blood is extracted using an injector. In some cases, just a drop of blood is taken by puncturing the ball of the finger.

Hemoglobin dosage

For the measurement of hemoglobin in the blood, a blood volume of 20 µL will be measured using a pipette with a capacity for this measurement, called a Sahli pipette.

The blood from the pipette is then placed in a test tube with 5 mL of Drabkin's reagent, prepared with potassium cyanide and potassium ferrocyanide.

After shaking the above solution, its optical density is determined in a photometer to obtain the hemoglobin concentration by comparing it with the optical densities of hemoglobin standards.

In this procedure there is a taking of a sample and preparation of a dilution that is inherent to the concept of aliquot.

Urine intake

A sample or aliquot of the urine is collected in a special container and taken to the laboratory for the pertinent determinations. From this sample, the concentration of urea, creatinine, protein, etc. is measured.

Analysis of pathogens

Health organisms constantly take samples or aliquots of various materials such as drinking water, foods such as milk, meat, etc., in order to determine their composition, presence of pathogens or adulterations. In each case, the appropriate procedures are used for the purposes sought.

Aliquots of the different brands of milk are taken to make the different determinations that may reveal, if any, some adulteration of the milk or the presence of pathogens in it.

-Rock samples

To perform the analysis of the presence of an element in a rocky sample (analyte), several steps or stages are required. The first step is to carefully weigh the sample to be analyzed.

Then, the sample is ground and crushed until it is pulverized. Subsequently, the pulverized sample is solubilized prior to its titration.

The usual procedure to solubilize the sample consists of treating it with water and strong acids, followed by the use of fluxes such as sodium carbonate or potassium acid sulfate, depending on the material analyzed.

Once the sample is solubilized, it is placed in a volumetric flask and brought to volume with water. Then an aliquot of the solution is taken into the flask for the corresponding determinations.

- Titration reactions

In a titration reaction, the milliequivalents of the titrant equal the milliequivalent of the analyte.

The titrant being the compound used to determine the presence or mass of the analyte; then, if a quantity of milliequivalents of the titrant is spent in the determination of the analyte, the same quantity of milliequivalents of the analyte will be had.

And where are such equivalents found? Again, in aliquots taken from the sample to be studied volumetrically.

-Samples or aliquots of water

Many times it is necessary to study the level of pollution in a lake or river, either to take measures to remedy or solve the problem, or to verify that the measures that have been taken in this regard are efficient.

For this type of study, it is necessary to take samples or aliquots of water in many places in the river, at points close to and far from drains, and at different depths.

For the collection of water at different depths, bottles with a stopper are used that can be removed when required. Furthermore, the bottles are equipped with a device that allows their closure.

The bottles are located inside metal containers that sink into the water, being able to choose the height of the water in which the aliquots or water samples are to be taken.

-Samples or aliquots of gases

There is a growing interest in improving the quality of the air we breathe and efforts are being made to reduce the emission of polluting gases that can affect the atmosphere and the quality of life of the planet's inhabitants.

The composition of the air is not constant and changes due to various factors such as temperature, rain, wind, etc.

To take an aliquot or sample of the air, the air is passed through filters that can trap the desired material. The collected particles on the filters are weighed and subjected to reactions to analyze their nature.

References

1. Merriam Webster. (2018). Aliquot. Recovered from: merriam-webster.com
2. Reid D. (2018). Using Aliquots in Chemistry: Definition & Function. Study. Recovered from: study.com
3. Wikipedia. (2018). Aliquot. Recovered from: es.wikipedia.org
4. Alors Correderas R. (2008). Determination of hemoglobin in the laboratory.. Recovered from: archivos.csif.es
5. Day, R. A, and Underwood, AL (1986). Quantitative Analytical Chemistry. (Fifth edition). Pearson Prentice Hall.