Study on carbon-induced signal enhancement in inductively coupled plasma mass spectrometry: an approach from the spatial distribution of analyte signal intensities

Abstract

To obtain further insight into the mechanism of carbon-induced signal enhancement, accurate quantification of carbon-induced signal enhancement in inductively coupled plasma mass spectrometry (ICP-MS) has been examined. Spatial intensity distributions and axial intensity profiles of the analyte ion (M⁺) in ICP were obtained by measuring elemental solutions with and without carbon (i.e., 5% (v/v) 2-propanol, IPA). Addition of 5% (v/v) IPA significantly spread and shifted the M⁺ intensity zone, particularly in the axial direction, toward the sampling cone. The result indicated that the carbon-induced zone-shift in the axial direction should be considered for accurate quantification. As an index for quantifying carbon-induced signal enhancement, an enhancement factor (EF_sum), was defined based on the axial intensity profiles by dividing the sum of analyte signal intensities for axial sampling positions from 4 to 15 mm, obtained with 5% (v/v) IPA, by the sum of those obtained without 5% (v/v) IPA. The EF_sum values were estimated for 26 elements with a wide range of first ionization energies (IEs) and analyte oxide bond dissociation energies (BDEs). There was no clear relationship between EF_sum values and IEs or BDEs of elements, even though the existing hypotheses about the mechanism of carbon-induced signal enhancement have suggested that IE or BDE was a major factor that determines carbon-induced signal enhancement. Large EF_sum values were estimated for P, As, Se, and I. Chemical forms of these elements in elemental solutions are oxoacids in common. The results might imply that a mechanism that depends on the chemical forms of elements is also involved in carbon-induced signal enhancement.