Internal standardisation for arsenic and its species determination using inductively coupled plasma mass spectrometry

Analysis of urine by MIP-OES: challenges and strategies to correct matrix effects

This work investigated the potential of microwave-induced plasma optical emission spectrometry (MIP-OES) for urine analysis using a complex matrix containing carbon and high concentrations of easily ionizable elements (EIEs). The goals were to study interferences originating from the urine matrix for 14 analytes with total energies varying from 1.85 to 12.07 eV, along with strategies to correct matrix effects and compare the results with those reported in the literature using inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that the urine matrix caused suppression of the signals for some elements and increased them for others. Therefore, an internal standardization calibration method and three levels of dilution, i.e., 2-, 20-, and 200-fold, were applied as strategies to correct non-spectral interferences. Also, Ga, Ge, Pd, Rh, Sc and Y and four molecular species present in the nitrogen plasma (i.e., CN, N₂, N₂⁺, and OH) were investigated as potential internal standards (ISs). The accuracy and precision were evaluated by addition and recovery experiments and best results were obtained using ISs Ge, Rh and Sc for 20-fold dilution and N₂⁺ for 200-fold dilution. The LODs ranged from 0.33 to 329 μg L^-1 and deviations were lower than 11%. The combined use of these strategies led to successful urine analysis for a spiked sample by MIP-OES.

Evaluation of internal standards for inductively coupled plasma-mass spectrometric analysis of arsenic in soils

Arsenic (As) is a common contaminant in soils, and analysis of soils by inductively coupled plasma-mass spectrometry (ICP-MS) is often used to detect As in soil extracts. Internal standards (ISs) are part of ICP-MS analyses to enhance precision and accuracy by compensating for instrument variability; however, an improper choice of IS can result in negative analytical bias. The goal of this study was to develop a protocol for evaluating ISs commonly used in ICP-MS. Three soils of varying clay content and total As were extracted with a dilute electrolyte [0.005 mol L^-1 Mg(NO₃ )₂ ] and an acid digest. Arsenic concentrations were quantified by ICP-MS using typical ISs: ⁶ Li, ⁴⁵ Sc, ⁶⁹ Ga, ⁸⁹ Y, ¹⁰³ Rh, ¹¹⁵ In, ¹⁵⁹  Tb, and ²⁰⁹ Bi. Standard addition was used as a benchmark for As quantification. The most consistent IS was ¹¹⁵ In. Elevated, naturally occurring concentrations were detected for several of the ISs, particularly in the total digests, emphasizing the necessity for screening soils prior to analysis.

Non-spectral interferences in single-particle ICP-MS analysis: An underestimated phenomenon

This work demonstrates the effect of NaCl and carbon-related interferences on the analysis of arsenic and silver nanoparticles (NPs) by single-particle inductively coupled plasma mass spectrometry. Spectral interference caused by ArCl⁺ ions disturbing arsenic NPs analysis was eliminated using ammonia as reaction gas in a dynamic reaction cell of inductively coupled plasma mass spectrometer. In comparison to aqueous dispersions, non-spectral interferences caused by sodium lead to under-evaluation of arsenic and silver NPs diameter by about 7% and 15% at NaCl concentration of 450 mg L^-1 and about 28% and 41% at NaCl concentration of 4500 mg L^-1, respectively. As a consequence of lower transport efficiency, sodium non-spectral interferences also lead to about a 9% lower number of detected NPs for dispersions of both arsenic and silver NPs in 4500 mg L^-1 NaCl. On the contrary, measurement of NPs in matrices containing methanol gives results where Ag and As NPs diameter is over-evaluated by about 3% and 15% at a methanol content of 1% (v/v) and about 6% and 20% at a methanol content of 2% (v/v), respectively, in comparison to aqueous dispersions. In addition, the organic carbon species behave as surfactants and increase the transport efficiency; this leads to an increase in the determined number concentration of NPs. In comparison to aqueous dispersions, this is over-evaluated by about 17% for Ag NPs and about 10% for As NPs at a methanol content of 5% (v/v).