The stability of the arsenic compound standard solutions currently supplied by the National Metrology Institute of Japan (NMIJ) (CRM 7901-a arsenobetaine (AsB), 7912-a As(V), and 7913-a dimethylarsinic acid (DMA) solutions) was studied for the past 13 years or more since they were certified.
Arsenic exist in nature in a high number of different compounds having different toxicity. Because of such structure dependent toxicity, it is not the total element content that is informative for a risk assessment but the distribution of species. In general, the inorganic As species (iAs), including arsenite (AsIII) and arsenate (AsV), are usually regarded as the most toxic forms, while some organic species such as arsenobetaine and arsenocholine are considered to be non-toxic or much less toxic. Moreover, arsenobetaine (AsB) and dimethylarsinic acid (DMA) are organoarsenics that are among the most widely distributed As species in natural environments, such as hydrosphere, lithosphere, and biosphere.
The concentration of elements in agriculture products are related to certain extend to the levels in the environment, where they were grown. Therefore, it is critical to know the As species in agriculture products and foods to facilitate accurate risk evaluation related to food safety. In order to support such speciation analysis, the National Metrology Institute of Japan (NMIJ) has developed and supplied many compositional certified reference materials (CRMs) for the analysis of As compounds in marine products and grains and has also developed and distributed SI traceable As compound standard solutions. Key characteristics of such CRMs are their stability and homogeneity, since these have a major impact on the validity of certified values and their uncertainties.
The new study:
In this study, the stability of the As compound standard solutions currently supplied by the NMIJ (NMIJ CRM 7901-a AsB, 7912-a As(V), and 7913-a DMA solutions) in the past 13 years or more was evaluated. Already as a part of the certification, the purity of the standard solutions was investigated. Using liquid chromatography coupled with ICP-MS (LC-ICP-MS) the arsenic species other than the analyte were determined. The Arsenobetaine standard solution was found to contain 0.3% of trimethylarsine oxide and the dimethylarsinic acid was contaminated with 0.002% of As(V) and 0.003 % of monomethylarsonic acid. Anyhow, these impurities were very low and their amounts are within the uncertainty range.
Using again LC-ICP-MS for speciation analysis, the concentration of the arsenic species were determined and compared with the certified values. Using the results of 13 years (with the exception of the year 2016, where results could not be obtained), no significant stability problem could be found. The stability monitoring results in approximately 13 years were similar to the expanded uncertainties of the certified values, and the results overlapped within the expanded uncertainties.
The original publication
Tomohiro Narukawa, 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
, Anal. Sci., (2023). DOI: 10.1007/s44211-023-00312-w
Related studies (newest first):
Thomas P.J. Linsinger, Guy Auclair, Barbara Raffaelli, Andrée Lamberty, Bernd M. Gawlik, Conclusions from 13 years of stability testing of CRMs for determination of metal species,
Trends Anal. Chem., 30/6 (2011) 875-886. DOI: 10.1016/j.trac.2011.01.015
T. Narukawa, T. Kuroiwa, I. Narushima, Y. Jimbo, T. Suzuki, K. Chiba, Preparation and certification of arsenate [As(V)] reference material, NMIJ CRM 7912-a,
Anal. Bioanal. Chem. 397 (2010) 493–499. DOI: 10.1007/s00216-010-3564-4
T. Narukawa, K. Chiba, T. Kuroiwa, T. Yarita, A. Takatsu, Preparation and certification of arsenobetaine reference material NMIJ CRM 7901-a,
Anal. Bioanal. Chem., 389 (2007) 661–666 (2007). DOI: 10.1007/s00216-007-1445-2