INTERNAL STANDARDIZATION AND ITS VALUE IN THE ASSESSMENT OF THE SUITABILITY OF THE COLUMN FOR QUANTITATIVE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The requirement that the best precision be obtained for a pharmaceutical raw material assay using automated high-performance liquid chromatography, with valve injection, over long runs, suggested that the inclusion of an internal standard would be beneficial in allowing an additional method for the calculation of results. The accurate volume injection of the valve and loop system thus permitted standard calibration and subsequent sample evaluation by the peak-height ratio method as well as from absolute peak heights alone. After a number of experiments, column deterioration rendered the assays invalid, and retrospective analysis of the data demonstrated the merits of internal standard related parameters in showing the decline in performance of the column. The major benefits derived from the approach adopted were criteria for judging the acceptability of the assay results, without excessive replication for a particular sample, and prior warning of the need to re-pack the column.