Difference Between Assay and Purity

Assay vs Purity
 

Substances are hardly found in a pure state. If it is an element, it forms various combinations between them or with other elements in order to exist. Not only elements, molecules and compounds also tend to mix with a large number of other species in nature. Therefore, often all the substances exist as mixtures.

Assay

In chemistry, an assay is an analysis carried out to determine the level of impurities a sample has. It is a quantitative determination. In a sample, after identifying the main material present in it, its concentration is measured in an assay. Assay methods normally incorporate accurate and precise analytical methods. There are various types of assays. Depending on the sample to be analyzed and the other requirements, you can choose the most appropriate assay type. Chemical assays are done using techniques like chromatography, titrations, etc.

Assays are done to determine the purity of metals in an ore. One such method is the wet method where the sample is dissolved in an acid to extract the metal. Sometimes a dry method can also be used where the metal is mixed with a substance to reduce the melting point. Then by fluxing, the impurities are removed while leaving the purified metal as a residue. Bioassays are another type of assays carried out to quantify the effect of samples in biological systems. It includes studies of drugs on micro- organisms, virulence studies on human, bioassay of hormones, etc.

Purity

Pure means absence of contaminants or other materials, which we do not expect to have in a sample. Purity is some kind of a measurement to indicate how pure the sample is. This measurement can be qualitative or quantitative. If the purity is low, that means there are lots of contaminants. If the purity is high, then the contaminants are low. Pure substance cannot be separated into two or more substances by any mechanical or physical method. Pure substance is, therefore, homogenous. It has a uniform composition throughout the sample. Further, the properties of it are also uniform throughout the sample. Elements are pure substances. An element is a chemical substance that consists of only a single type of atoms, hence they are pure. There are about 118 elements given in the periodic table according to their atomic number. For example, the smallest element is the hydrogen, and silver, gold, platinum are some of the commonly known precious elements. Elements can be subjected to chemical changes to form various compounds; however, elements cannot be further broken down by simple chemical methods. Compounds are the other type of pure substances. Compounds are made up by two or more different chemical elements. Although there are two or more elements joined together when forming a compound, these cannot be separated by any physical means. Rather, they can only be decomposed by chemical means. So this makes a compound a pure substance. Purity can be expressed as a fraction or a percentage.