Estimation of arsenobetaine in the NIES candidate certified reference material no. 18 human urine by HPLC-ICP-MS using different chromatographic conditions

HPLC-ICP-MS, employing a silica-based LC-SCX cation-exchange column, styrene-divinylbenzene copolymer-based PRP-X100 anion exchange column, an ODS reversed-phase and gel-permeation (polyvinyl alcohol-based resin) GS-220 columns, has been used for the separation, identification, and quantification of arsenic compounds, particularly arsenobetaine (AB), present in NIES candidate certified reference material (CRM) no. 18 human urine. AB is the predominant arsenic species, followed by dimethylarsinic acid, methylarsonic acid and arsenic acid. The peak of each arsenic compound has been validated by spiking of the authentic standard solution to the urine sample and by using the above chromatographic systems. The high concentration of chloride that co-elutes with the arsenic acid from the LC-SCX and with the AB from the GS-220 columns has interfered with the ion signals of arsenic acid and AB, by forming the molecular ions 40 Ar 35 Cl and 38 Ar 37 Cl + in the plasma. Thus, the concentration of AB has been carefully estimated on the GS-220 after extracting the chloride interference ( 37 Cl: 35 Cl = 1:3.1271) by measuring the 40 Ar 37 Cl + . The peak of AB overlapped with the peak of arsenous acid and hindered the estimation of AB on the ODS and PRP-X100 columns. But AB has been baseline separated from the other arsenic compounds and also from the chloride with 20 mM pyridine at pH 2.60 on the LC-SCX. So, the LC-SCX column has been proven and used for the determination of AB in NIES candidate CRM no. 18 human urine. The concentrations of AB, estimated by the standard addition method and found using the LC-SCX and GS-220 columns, are 70.5 ± 5.5 (n = 20) and 71.5 ± 4 μgl -1 (n = 9). The concentration of AB thus found has been applied as the baseline value for the collaborative study to certify the AB in the NIES candidate CRM no. 18 human urine.