Stochastic Utility of Internal Standard Method in Liquid Chromatography

Abstract

A probability theory is presented to judge the utility of the internal standard method in high-performance liquid chromatography (HPLC). The relative standard deviation (RSD) of experimental results in the internal standard method is theoretically predicted based on the recently proposed uncertainty theory for sample dilution and HPLC measurement. The experiments comprise the taking of sample solution, addition of internal standard, dilution, measurement on HPLC and signal processing. Two kinds of correlation between concentrations of analyte and internal standard are formulated distinctively in the sample preparation process and in the HPLC measurement. The RSD values for the total experimental process are calculated from the volume error of pipette, signal shape of analytes and some probabilistic properties of baseline drift in chromatograms and are shown to be in good agreement with the observed ones over a wide range of dilution degree. The external calibration is also examined.