Suitable interface for coupling liquid chromatography to inductively coupled plasma-mass spectrometry for the analysis of organic matrices. 1 Theoretical and experimental considerations on solute dispersion.

Liquid chromatography (LC) hyphenated to a specific detection such as inductively coupled plasma-mass spectrometry (ICP-MS) is a technique of choice for elemental speciation analysis. However, various instrumental limitations may considerably reduce the expected sensitivity of the technique. Among those, we were interested by the solute dispersion into the interface located between LC and ICP-MS. The interface consists of a Sample Introduction System (SIS) and a possible flow-splitter prior to SIS. Flow splitting can be required in case of organic matrices to reduce the organic solvent amount entering plasma which may lead to plasma instabilities. Although extra-column dispersion is usually well taken into account with conventional UV detection it has been little studied in the context of LC-ICP-MS and moreover never quantified. Our objective is to assess the loss in column plates and hence in both separation quality and sensitivity which may be generated by the coupling of LC and ICP-MS in the specific case of organic matrices. In this first study, this is done (1) from a theoretical approach; (2) from 55 experimental studies reported in LC-ICP-MS and (3) from our experimental results highlighting the critical impact of the flow splitter on extra-column dispersion depending on both flow-rate and split ratio. It turns out by evaluating the 55 reported studies by means of theoretical calculations, that the loss in plates due to extra-column dispersion was most of the time beyond 50% and even often beyond 90%. Moreover, from our experiments, it has been shown that a very low split ratio (1:50) could generate an additional variance around 200 μL² which induces a loss in theoretical plate of 90% for ultra-high performance LC (UHPLC) column (5 cm × 2.1 mm, 1.7 μm).