Matrix effects during phosphorus determination with quadrupole inductively coupled plasma mass spectrometry

Abstract

A quadrupole inductively coupled plasma mass spectrometer was evaluated for use in the detection of phosphorus. The influences of nitric acid and methanol (simulating the composition of a sample solution after nitric acid digestion) on phosphorus determination were studied using two different measuring methods at different plasma conditions: detection of phosphorus ions at m/z 31 and detection of phosphorus oxide ions at m/z 47. The existence of polyatomic interferences at m/z 31 and 47 was explored. Nitric acid and methanol are shown to be the sources of polyatomic ions and therefore cause poorer detection limits. Better detection limits were achieved in such matrices when phosphorus was detected as 31P+. The presence of methanol improves the system sensitivity towards phosphorus sevenfold; however, this positive effect is hindered by the high background signal due to carbon-based polyatomic ions. For samples with an organic matrix an appropriate mineralization procedure should be applied (high excess of nitric acid and high temperature) to quantitatively oxidize organic compounds to carbon dioxide, which is easily removed from the sample, in order to achieve correct results.

Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry

“…Be, Se, As, Au, I, P, S,…) were higher than those of elements with about the same mass/charge ratio and low IPs values. Similar results have been reported by other authors [16][17][18][19]. Thus, Allain et al [16] reported a signal enhancement for Hg (600%), As (240%), Au (325%) and Se (250%) when a 36 g L − 1 carbon (as glycerol) solution was introduced into the ICP-MS. To explain these findings, some authors suggested a charge transfer mechanism between the analyte atoms and carbon positively charged ions [20,21].…”

“…For higher carbon concentrations, interferences are more pronounced [16,22]. Similar behavior was obtained using other carbon sources such as acetic acid [23], acetone [15,24], alcohols [18,22], ethylendiamine [25], ammonium carbonate [26] or methane [27].…”

“…In the first step, As and Se, due to their ionization energies close to that of carbon (i.e., 11.26 eV), would suffer from a charge transfer reaction from C ions, thus increasing the As + and Se + populations. It would explain the enhancement in the ion signals observed for these elements in ICP-MS [15,16,18,20,21]. In a second step, these ions would suffer from subsequent ion/electron recombinations thus increasing the population of the excited atoms.…”

Matrix effects of carbon and bromine in inductively coupled plasma optical emission spectrometry

“…Generally speaking, the enhancement factors of As and Se reported in the literature for non-volatile carbon sources (glucose, citric acid, oxalic acid or glycerol) were always lower than for more volatile reagents such as methanol or even for gases (CH 4 ), both in ICP-OES 3,10,11 and in ICP-MS. 1,2,4,6,7,9,[13][14][15]…”

Signal Enhancement of Elements with Different Ionization Potential by Organic Solvent in ICP-MS

“…Rodushkin et al 6 had reported that the analytical performance of ICP-SFMS was significantly improved by addition of methane to the argon gas flow, the signal intensities of As, Te, Se and Sb were enhanced two-to four-fold. Kovacevic et al 7 studied the matrix effect of methanol on ICP-MS signals of phosphorus, a sevenfold increase in the phosphorus signal was observed when water and 2.5 mol L -1 methanol were compared.…”