Electrospray as Interface in the Coupling of Micro High-performance Liquid Chromatography to Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

An electrospray nebulizer with a miniaturized spray chamber is described which is suitable for coupling micro-HPLC with ICP-AES for speciation of organometallic compounds in microlitre samples. The sensitivity and selectivity, the main characteristics of an interface in such a hyphenated technique, were established. For optimizing these features, experiments were carried out without the use of a chromatographic column. Signal-to-background ratios and detection limits were determined by continuously feeding a test solution of metal–acetylacetonates, in methanol–water (8+2, v/v), directly to the nebulizer, at a flow rate of 10 µl min ^-1 . The peak dispersion caused by the interface was measured by injecting various volumes of a test solution into a carrier stream of methanol, at the same flow rate. At this low liquid flow rate, the mass detection limits were, even measured by a radially viewed ICP, of the order of 10–100 pg. The time standard deviation of the peak dispersion caused by the interface was 1.25–2 s, equivalent to a volume standard deviation of 0.2–0.3 µl, respectively, depending on the applied nebulizer gas flow rate. It was found that these times were equal to the residence times of the analytes in the gas transfer line, consisting of the spray chamber and connecting tubing to the ICP torch. These small dispersions allow the combination of high-performance micro-capillary LC with ICP-AES detection.