Evaluation of the long-term stability of arsenic species in certified reference materials: certification of arsenobetaine, As(V), and dimethylarsinic acid in NMIJ CRMs 7901-a, 7912-a, and 7913-a.

The long-term stabilities of arsenobetaine (AsB), arsenate (As(V)), and dimethylarsinic acid (DMA), which are arsenic (As) compounds in certified reference materials (CRMs), namely, NMIJ CRMs 7901-a, 7912-a, and 7913-a, were monitored. The CRMs were developed and certified by the National Metrology Institute of Japan (NMIJ) and the National Institute of Advanced Industrial Science and Technology (AIST) in 2009 to prepare a calibrant for the speciation analysis of As species. The CRMs were prepared from high-purity reagent powders as raw materials, and each reagent was dissolved in water or diluted acid. The certification of the CRMs for AsB, As(V), and DMA was conducted by NMIJ. The concentration of total As was determined by more than three independent analytical techniques. Then, the obtained As concentrations were converted into the concentration of each chemical species, and the mass fractions of each certified value were certificated. The long-term stability of As species in the CRMs under storage was performed by liquid chromatography-inductively coupled plasma-mass spectrometry, and this report presents data on long-term stability that occurred approximately 13 years. The obtained monitoring results were evaluated using both measurement results with uncertainty and a statistical parameter method, complying with ISO Guide 35. According to the results, the long-term stability of all mass fractions was confirmed.