Electrospray Nebulisation Interface for Micro-High Performance Liquid Chromatography–Inductively Coupled Plasma Mass Spectrometry

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Abstract
An electrospray nebulisation interface has been developed and evaluated for combining micro-high performance liquid chromatography with inductively coupled plasma mass spectrometry. Using a 15 cm×220 µm id packed capillary column with an eluent (methanol) flow rate of 2 µl min –1 , it was possible to introduce the entire column effluent into the plasma. Within the electrospray interface, the solvent was nebulised into nitrogen flowing at 140 ml min –1 by applying +3.1 kV to the gold-coated outlet taper relative to a grounded counter electrode. The spray was subsequently mixed with the nebuliser gas (argon containing 2% oxygen). The influence of adding 20% nitrogen, 2% oxygen and 2 µl min –1 methanol to the nebuliser argon on the background mass spectrum, nebuliser flow rate and rf incident power, respectively, was evaluated. The addition of nitrogen reduced the 40 Ar 16 O + and 40 Ar 012 C + interference ions and lowered the overall background response. The influence of the interface on chromatographic peak broadening was studied using two closely eluting analytes: ferrocene and triphenylarsine. The interface caused a 15.7% decrease in resolution. With a series of organometallic compounds, log–log plots of peak area versus mass injected were linear over three orders of magnitude with correlation coefficients greater than 0.9944. The reproducibility of sample injections, based on manual injection, was better than 6.5% RSD. The system showed detection limits in the low picogram range (1.2 pg for ferrocene, 35 pg for triphenylarsine and 55 pg for tetrabutyltin).