Portable electrospray ionization mass spectrometry (ESI-MS) for analysis of contaminants in the field

Abstract

Hitherto analysis of chemicals in the field using mass spectrometry (MS) has been limited to analysis of non-polar and thermally stabile organic compounds using either a direct gas leak or a membrane inlet as MS interface. Recently, Professor R. Graham Cooks’ group demonstrated that miniature mass spectrometers operating at elevated pressures (>0.13 Pa (1 · 10−3 Torr)) can be combined with electrospray ionization (ESI) for analysis of polar as well as thermally labile organic compounds. We present a simple miniaturized ESI unit for analysis of small liquid samples using miniature mass spectrometry. The ESI unit operates without pumps and supplementary sheath gases, which makes it very simple to handle in the field. 20–30 µL of sample solution is simply dropped into a small cavity in the ESI unit, where after the spray is initiated by applying high voltage to it. The miniaturized ESI unit was tested in combination with a miniature mass spectrometer (the Mini 10 developed by Professor R. Graham Cooks, Purdue University, IN) and we found that common herbicides (Atrazine, Prometryne, Terbutryne and Triadimefone) could be detected with detection limits around 1 mg L−1 and with a quantitative reproducibility of +/−30%. These characteristics, although high for environmental samples, are comparable to detection limits obtained with other ESI units used with miniature mass spectrometers and represent an early step forward towards a future field instrument. A major advantage of the capillary spray cell is its direct compatibility with micro extraction techniques for sample pre-concentration.