3] Internal standards for amino acid analysis

Abstract

The general purpose of internal standards is to monitor physical and chemical losses and variations during the analysis of amino acids by ion exchange and gas-liquid chromatography. The standard must not interfere with the analysis (e.g., by coeluting with any of the amino acids in the sample), but it can monitor the analysis only to the degree that its characteristics match those of the sample. Other properties of the internal standard requiring special attention are stability and the means of detection. These are more critical in gas liquid chromatography of amino acids, where greater use has been made of precolumn derivatization, high column temperatures, and non-amino acid internal standards. Column parameters, such as length, temperature, and pH, can be quite important in regard to the selection and use of an internal standard in ion-exchange analysis of amino acids. Almost without exception, internal standards appropriate for the long column (150 cm), used for the analysis of neutral and acidic amino acids, will not be of value on the short columns (5 to 50 cm) used for basic amino acids. Thus, for each internal standard, the particular column and conditions reported must be noted.