Advantages of reaction cell ICP-MS on doubly charged interferences for arsenic and selenium analysis in foods

Abstract

Recent reports of As concentrations in certain food and drinks have garnered public concern and led to a lowering of the US guideline maximum concentration for inorganic As in apple juice and proposed limits for As in rice products. In contrast Se is an essential micro-nutrient that can be limiting when Se-poor soils yield Se-poor food crops. Rare earth element (REE) doubly charged interferences on As and Se can be significant even when initial ICP-MS tuning minimizes doubly charged formation. We analyzed NIST 1547 (peach leaves) and 1515 (apple leaves), which contain high levels of REEs, by quadrupole ICP-MS with (He) collision mode, H2 reaction mode or triple quadrupole ICP-MS (ICP-QQQ) in mass-shift mode (O2 and O2/H2). Analysis by collision cell ICP-MS significantly over-estimated As and Se concentration due to REE doubly charged formation; mathematical correction increased the accuracy of analysis but is prone to error when analyte concentration and sensitivity is low and interferent is high. For Se, H2 reaction mode was effective in suppressing Gd2+ leading to accurate determination of Se in both SRMs without the need for mathematical correction. ICP-QQQ using mass-shift mode for As+ from m/z 75 to AsO+ at m/z 91 and Se+ from m/z 78 to SeO+ at m/z 94 alleviated doubly charged effects and resulted in accurate determination of As and Se in both SRMs without the need for correction equations. Zr and Mo isobars at 91 and 94 were shown to be effectively rejected by the MS/MS capability of the ICP-QQQ.

Measurement of arsenic species in environmental, biological fluids and food samples by HPLC-ICPMS and HPLC-HG-AFS

“…NIST 1547 Peach leaves and NIST 1515 Apple leaves [218]. For example, Clelutes after As(V) on a PRPX-100 anion exchange column.…”

Kinetic energy discrimination in collision/reaction cell ICP-MS: Theoretical review of principles and limitations

“…Unfortunately doubly charged ion interference cannot be suppressed by the collision cell operating with KED. This section clarifies the reason, which seems to have long been misunderstood [20].…”

Recent Advances in the Measurement of Arsenic, Cadmium, and Mercury in Rice and Other Foods

“…Argon Chloride interference on As at m/z 75 was suppressed by CH 4 or by mass shifting detection to m/z 91 by reaction with O 2 ; detection of AsO at m/z 91 yielded the lowest detection limits and the approach yielded accurate results for seaweed and yellow croaker reference materials, both of which are high in Cl(16). Such reaction cell methods are also particularly suited to avoiding doubly charged interferences of rare earth elements (REEs) on As analysis by mass shifting As to m/z 91(17). …”