Suitable interface for coupling liquid chromatography to inductively coupled plasma-mass spectrometry for the analysis of organic matrices. 2 Comparison of Sample Introduction Systems

Abstract

Liquid chromatography (LC) coupled with a specific detection such as inductively coupled plasma-mass spectrometry (ICP-MS/MS) is a technique of choice for elementary speciation analysis for complex matrices. The analysis of organic matrices requires the introduction of volatile solvents into the plasma which is an analytical challenge for this coupling technique. Detection sensitivity can be significantly affected by instrumental limitations. Among those, we were interested in the solute dispersion into the interface located between LC and ICP-MS/MS. This interface consists in both a Sample Introduction System (SIS) and a possible flow splitter. This study, divided into two parts, investigated the analytical performance (in terms of sensitivity and efficiency) generated by the coupling of LC and ICP-MS in the specific case of organic matrices. In Part I [1], we previously discussed the impact of extra column dispersion on the performance of LC-ICP-MS, first from a theoretical point of view and next, by assessing extra-column dispersion in 55 published studies on LC-ICP-MS. It was shown that SIS was rarely optimized with respect to its contribution to extra-column band broadening. The critical impact of flow splitting on extra-column dispersion was also pointed out. The present Part II is dedicated to the experimental comparison of commercially available SIS by assessing extra-column band broadening and hence the contribution of SIS to the loss in both efficiency and sensitivity. It is shown that the peak variance, due to SIS, can vary from 10 to 8000 μL² depending on the combination of both nebulizer and spray chamber. Whereas the highest values (i.e. > 2000 μL²) are much too high in high performance liquid chromatography (HPLC), even the lowest values (i.e. < 100 μL²) can be inappropriate in ultra-high pressure liquid chromatography (UHPLC) as highlighted in this study. In light of these results, it appears that nebulizer and spray chamber have to be chosen together with respect to the chromatographic technique (HPLC or UHPLC) and that both peak dispersion and peak intensity depend on key parameters including SIS device geometry, flow rate entering the interface or spray chamber temperature.

Keywords: Extra-column dispersion; Inductively coupled plasma; LC-ICP-MS; Sample introduction system; Speciation; Ultra high performance liquid chromatography.