Analytical chemistry pertains to determining the chemical composition of a substance and the quantity of each substance present. From the nanogram to kilogram scale, there is a method for determining what is there and how much. But the important question asked many times is"how do analytical chemists know that they are right?" The answer to this question is chemical standards.

In its simplest terms, a chemical standard is a substance for which the exact composition is known. Or, at least, known as far as possible. Detection limits for most analytical techniques are in the parts per billion (ppb) or parts per trillion level (ppt) and although this may seem a very small amount, it still means a billion molecules of an impurity would not be detected in a drop of water. This is the nature of chemistry. Chemists deal in incredibly large numbers of molecules...