A Study of the Sources of Error in Quantitative Gas Chromatography: Reproducibility of The Response of a Catharometer

Abstract

From a theoretical study of the response of the catharometer it results that this response depends on the carrier gas mass flow-rate, the carrier gas pressure in the measuring cell, the bridge current, the detector temperature and the sample mass. Both peak height and peak area depend on these factors but peak height depends in addition on the column temperature and the injection function. We have built a special equipment in which most of these factors (gas flow-rate, gas pressure, temperatures, bridge current, sample mass) are controlled within a few parts per 104 in one day and the injection function is very reproducible. This allows the standard deviation for the nitrogen peak in an air analysis is 5 ×10−4 for peak height and area. From these results the analysis of air can be made with an error of less than 10−3 at the 95% confidence level. By slightly changing the set values of the various experimental parameters, it is possible to determine their influence on the quantitative results. For such small changes there is a linear relationship between the relative variation of the response and the relative fluctuations of the parameters. The corresponding proportionality coefficients have been determined. From these values, it is possible to derive the extent of control which it is necessary to achieve in order to obtain an accuracy between 10−2 and 10−4 at the only condition that the resolution of the peaks is good, the peaks themselves are symmetrical and no loss of compound occurs during the injection or the analysis of the mixture.