Definition - What does aliquot mean?
In chemistry and other branches of science, an aliquot is a fraction of a specimen. This portion is often used for testing of the specimen.
SureHire explains aliquot
When a drug or alcohol test is performed, a specimen such as blood, saliva, or urine is taken from the test subject. An aliquot, or measured portion of that specimen, is then used to perform the actual testing. The aliquot portion serves as a representative sample of the specimen as a whole.