ANALYTE ADSORPTION IN LIQUID-CHROMATOGRAPHY VALVE INJECTORS FOR SAMPLES IN NON-ELUTING SOLVENTS

The cause of precision problems arising when using non-eluting solvent s for sample solutions in order to obtain a peak compression effect in low-dispersion liquid chromatography was investigated. Quantitative e vidence was obtained to support the proposition that the problems were caused by adsorption of the analyte in the injection system. This phe nomenon was quite marked when aqueous buffer was used to inject into o rganic-aqueous mobile phases and could still be significant when there was only a few percent difference in the organic content of the mobil e phase and the less eluting injection solvent. While there was eviden ce for adsorption onto the inner walls of the stainless-steel tubing u sed for sample loops, it was clear that, for this case of liquid chrom atography of indomethacin, adsorption onto Vespel rotor seals was the principal contributing factor to the effect.