Effect of methanol and sodium dodecylsulfate on radial profiles of ion abundance in inductively coupled plasma mass spectrometry

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• 作者：Shulan Liu and Diane Beauchemin
• 关键词：Radial profiling ; Matrix effect ; Organic solvent ; Surfactant ; ICP-MS
• 刊名：Spectrochimica Acta Part B: Atomic Spectroscopy
• 出版年：2006
• 出版时间：March 2006
• 年：2006
• 卷：61
• 期：3
• 页码：319-325
• 全文大小：205 K

文摘

The radial profiles of some background ions and analytes spanning the mass range and with a wide range of first ionization potentials were investigated using inductively coupled plasma time-of-flight mass spectrometry. In particular, three different matrices were considered to assess the effect of organic modifiers: 1) 1 % HNO₃, 2) 1 % HNO₃ with 2 % v/v methanol, 3) 1 % HNO₃ with 0.2 % m/v sodium dodecylsulfate (SDS). Although these concentrations of methanol and SDS induced the same sample transport increase (37 % ), as measured with a silica gel trap at the exit of the spray chamber, neither of them resulted in a 37 % increase in signal across the mass range. In fact, the change in analyte signal as a function of m/z followed opposite trends in these two matrices. With 0.2 % m/v SDS, suppression was observed at high m/z with an increasing enhancement as m/z decreased, which was ascribed to electrostatic effects in solution. In contrast, little change or enhancement was seen at high m/z while suppression was evident at lower m/z (with the notable exception of As) with 2 % v/v methanol, as a result of a widening of the radial profile, which was inversely dependent on m/z. Although, the total carbon concentration was quite different in these two matrices, i.e. 0.8 M with 2 % methanol and 0.08 M with 0.2 % SDS, it cannot account for the completely different radial profiles that they produced. Indeed, the same bell-shaped distributions of analyte ions were observed with 0.2 % SDS as in 1 % HNO₃ alone. However, a bimodal distribution, with maxima on either side of the central axis, resulted in presence of 2 % MeOH. This distribution was found to be similar to that of several background ions (C⁺, CO⁺ and ArC⁺), which further substantiates the suggestion that ionization then predominantly occurs through charge transfer with carbon-containing ions. This bimodal distribution also suggests that a volatile organic solvent such as methanol quickly spreads into the surrounding area of the central channel upon sample introduction in the plasma.