Determination of arsenic compounds by high-performance liquid chromatography-ultrasonic nebulizer-high power nitrogen-microwave-induced plasma mass spectrometry: an accepted coupling.

Abstract

To establish a sensitive, accurate, and precise determination of arsenic compounds, a high power nitrogen microwave-induced plasma (1.3 kW) mass spectrometer (N2-MIP-MS) has been successfully coupled with an ultrasonic nebulizer (HPLC-USN) that is attached to a high-performance liquid chromatograph. It is examined as an element-specific detector for its applicability to the optimization and determination of seven arsenic compounds [arsenic acid, methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), arsenocholine (AC), trimethylarsine oxide (TMAO), and tetramethylarsonium ion (CMI)]. This HPLC-USN-MIP-MS coupling is an encouraging combination as an alternative method for mass spectroscopy for elemental speciation analysis. Interchanging of the MIP-MS fabricated nebulizer (concentric) with an ultrasonic nebulizer, increases 3-6 times the ion signals for the anionic and 6-12 times those for the cationic arsenic compounds as compared to traditional methods. The HPLC-USN-MIP-MS combination used is excellent, amplifying the ion signals about 1.5-2 times for cationic and 1.3-2.8 times for the anionic arsenic compounds as compared to the HPLC-ICPMS coupling. The detection limits for As(V), MA, DMA, AB, TMAO, AC, and TMI (in Milli-Q-water) obtained with the optimized HPLC-USN-N2-MIP-MS system are 0.46, 0.36, 0.73, 0.21, 3.64, 0.39, and 0.32 microg L(-1), respectively, about 13-50 times lower than the HPLC-MIP-MS and about 3-11 times lower than the HPLC-ICPMS. The detection limits of As(V), MA, DMA, AB, TMAO, AC, and TMI, which spike in the urine, are deteriorated by 1.7-4.2 times compared with the detection limits of the seven different As compounds, which are prepared in the Milli-Q-water. The repeatability (RSD for three successive analyses) and reproducibility (RSD for three successive analyses performed on three different days), considering peak area and peak height, achieved for seven different arsenic compounds are 0.5-7 and 0.7-8%, comparable with the HPLC-ICPMS (0.3-8.5%; 4-12%) and HPLC-MIP-MS (0.4-9%; 5-12%) systems. The combined HPLC-USN-N2-MIP-MS has been adequately applied to the determination of AB in NIES Candidate Human Urine CRM. The results agree with the HPLC-ICPMS values. Chloride interference as 40Ar35Cl+ is not found in the urine and with the high chloride matrix (10000 mg L(-1)).