The Effect of Plasma Density on the Degree of Suppression of Analyte Signals in ICP-MS
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The Effect of Plasma Density on the Degree of Suppression of Analyte Signals in ICP-MS T. K. Nurubeyli Institute of Physics, Azerbaijan National Academy of Sciences, Baku, Az-1143, Azerbaijan e-mail: [email protected] Received February 7, 2020; revised March 3, 2020; accepted June 16, 2020
Abstract—Possible effects of ionization phenomena on the analytical signal in inductively coupled plasma mass spectrometry with a high-temperature ion source are considered. The dependences of the degree of suppression of ion signals on the electron density are calculated and experimentally determined for ions of matrix and impurity elements. It is shown that the degree of signal suppression depends rather strongly on the electron density in the analytical zone in the presence of matrix elements with different first ionization potentials. The effects of the inductive plasma power and sputtering argon rate on the sensitivity of the mass spectrometer are studied by the example of an ICP-MS mass spectrometer (Agilent Technologies). The experimental results showed that the origin of the suppression of the analyte signals at the output is apparently associated with the ion–electron recombination of ions (both matrix and impurity ones) in the plasma region. DOI: 10.1134/S1063784220120166
INTRODUCTION The method of mass spectrometry with inductively coupled plasma (ICP-MS) is currently one of the main multielement methods for the analysis of various substances. A few years after the introduction of ICPMS into analytical practice, it was found that the method has limitations associated with spectral and nonspectral matrix effects [1], which reduce the number of determined elements and increase their detection limit. Spectral interference is understood as the overlap in the mass spectrum of signals from different ions with approximately the same ratio of the mass to the charge (m/q). Over the years of development of ICP-MS, significant progress has been made in eliminating spectral overlaps [2]. The situation is much worse with the elimination of the nonspectral matrix effect, which is understood as a group of phenomena leading to the suppression (enhancement) of the analyte signal in the presence of a matrix element (solvent elements or internal standard). The origin of the manifestation of the matrix effect has already been rather well studied; a number of ways to take it into account and reduce it have been proposed [3]. However, it should be noted that, despite the 30 years of development of ICP-MS, the method still has limitations on the content of the matrix in the analyzed solution at the level of 0.05–0.2 mass %, depending on the nature of the matrix element. The known reasons for such phenomena are strong ionization of many elements of the periodic system, as well as a change in the effi-
ciency of transport of analyte ions due to strong fields of space charge in the ion beam [4]. Most of the experimental data on matrix ionization phenomena in ICP-MS found in the literature are most often fragmentary information on the de
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