Halogenated mobile phase additives for improved detection performance in liquid chromatography—negative chemical ionization mass spectrometry

Abstract

The addition of 0.1–1% of chloroacetonitrile to an acetonitrile—water eluent can significantly improve the detection performance in column liquid chromatography—negative chemical ionization mass spectrometry (LC—NCI MS) using a direct liquid introduction interface. The addition of the chlorine-containing modifier does not change the retention times of the chlorophenols used as test compounds. However, the sensitivity for the lower chlorinated phenols is enhanced up to 30-fold. In addition, fragmentation is suppressed and the mass spectra are often characterized by only one main cluster over the whole 170–330°C temperature range studied. With most test compounds, so-called chloride attachment also occurs to some extent, especially at relatively low ion source temperatures. However, for phenol and mono- and dichlorophenol fairly intense [M + Cl] − clusters are even observed at source temperatures of 300°C. For a further evaluation two phenoxyacetic acids, lindane, l-leucine and l-ascorbic acid were studied, and the utilization of other chlorine-, bromine- and fluorine-containing additives was explored.