Argentometric titration for the determination of liquid chromatographic injection reproducibility

The reproducibility of autosamplers for high-performance liquid chromatogra phy can be checked by the injection of a sodium chloride solution without a n installed column. The dispensed chloride plug is analyzed quantitatively by argentometric titration, If the titration can be performed with high eno ugh precision, the autosampler performance is investigated without addition al effects. Experiments with a 20-muL loop were performed, We found the fol lowing repeatabilities (relative standard deviations): titration, 0.07%; 10 -muL "pull loop" injection (partial filling of the loop), 0.6%; and 20-muL "full loop" injection, 0.1%, In contrast to these data, the relative standa rd deviations obtained from chromatographic peaks include the steps of inje ction, separation, detection, and integration without any knowledge of the individual contributions. Such values are higher; we found for chromatograp hic peak areas of parabens 2% under pull loop conditions and 0.17% by full loop. The titration approach allows the determination of the contribution o f the injection to the uncertainty budget of a liquid chromatographic analy sis.