(1999; 168 pages) [Spanish]
4. Chemical and physical methods used in evaluating chemical reference substances
It is important to establish by individual testing that a substance proposed for use as a chemical reference is suitable.
The methods used to establish the suitability of such a substance fall into two broad groups: those intended primarily to identify the substance and those used to establish its purity. With most methods, the percentage purity of a chemical reference substance cannot be expressed as an absolute value if the impurities have not been identified. The quoted purity is then an estimate based upon the data obtained by the various analytical methods.