CRM rapid response approach for the certification of arsenic species

Overview

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Key numbers

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21 the scientific community was lacking suitable certified reference material (CRM) which could be used to
17 in Asia (2, 3) where it is the primary food source. Owing to its high carbohydrate content, palatable and
19 Although it is grown in more than 100 countries and all continents except Antarctica, 90 % of the orld’s
28 produced in the USA, showed that As levels in rice ranged from 5 to 710 μg kg-1 (10). The high
31 of obtained result has to be rigorously validated with suitable certified reference materials (CRMs), which
3 flour NIST 1568b (Table 1).
5 Table 1. Overview of currently available rice based CRMs with certified values for As species and
13 Each participating laboratory (Table 2) was given seven blind samples: five samples of BARI-1 and 2 quality
17 As speciation (Table 3). Each participating laboratory was requested to provide results of five replicate
Table 3. Summary of sample preparation methods for total metal analysis and speciation.
in 7 mL of HNO3 and 0.5 mL Pb, Cd), SA (As) 20 mL of TFA (0.02 M) and 1 %
9 contained eight largely independent analytical methods (Table 3). To evaluate the quality of each data
1 1, dashed red lines represent upper and lower 95 % confidence interval of certified value in BARI-1, and the red line
8 showed no significant difference (t-test at 95 % confidence interval), however, the repeatability of Cd and
9 Hg was above 10 % when analysed by ICP-MS/MS (Lab 1_2, Table 4). It should be noted that at given mass
10 fractions in the samples, analytes were close to the LOQ and therefore, RSDr of around 10 % is acceptable.
15 RSDr above 25 % was reported. Consequently, the RSD of inter-laboratories reproducibility in Pb analysis
16 increased from 5 % to 27 % when results from Lab 3 and 6 were included.
Table 4. Reported mean concentration ± expanded uncertainties of monitored analytes (mg kg-1) in BARI-1. RSDr represents within-laboratory repeatability and
As 0.2401 ± 0.2420 ± 0.2423 ± 0.2796 ± - ND 0.2538 ± 0.2630 ± 0.2660 ± ˂ . 6%
Cd 0.0142 ± 0.0135 ± 0.0117 ± 0.0134 ± - ND 0.0124 ± 0.0128 ± 0.0100 ± ˂ . 11 %
Hg 0.0026 ± 0.0030 ± 0.0026 ± ND - ND ND ˂ . 5 ND ND 6%
Pb 0.0064 ± 0.0061 ± 0.0057 ± 0.0059 ± - ND ND 0.0101 ± ND ND 27 %
iAs - 0.1134 ± 0.1118 ± 0.1147 ± 0.1564 ± 0.1523 ± 0.1071 ± ND ND ND 18 %
Sum of As - 0.2622 ± 0.2373 ± 0.2310 ± - 0.2858 ± 0.2355 ± - - - 8%
3 significant (t-test at 95 % confidence interval). Although HG-ICP-MS is an established technique for iAs
5 Furthermore, iAs recovery in blind SRM 1568b was 58 % above the certified value also indicating that HG-
12 1568b contain significant levels of DMA and, if one considers that 58 % overestimation of iAs is due to
13 contribution from DMA, the corrected value in BARI-1 would be 106 μg kg-1 which corresponds to 94 % of
15 (6 %) and MMA (3 %), whereas RSDR of 18 % was found for iAs. This high value was driven by two labs, Lab
17 Upon exclusion of the results from these two labs, RSDR was reduced to 3 %. In terms of repeatability,
18 RSDr above 10 % was only observed in reported value for MMA by Lab 5. It should be noted, that MMA
19 mass fraction in BARI-1 is only 0.0045 ± 0.0008 mg kg-1 and thus very possibly around the LOD of the
21 participants, this As species was below LOQ of Lab 1 and therefore, only information value was assigned
4 lines represent upper and lower 95 % confidence interval of certified value in BARI-1, and the red line represents
2 quantitative extraction of As species from the rice matrix (Table 4). Quantitative extraction of As species
10 acid whereas the rest of the collaborators used HNO3 of varying concentration (Table 3). The extractions
16 (Table S2). While the uncertainty due to homogeneity in As and As species is reported, it should be noted
26 these elements are stable for an extended period of time as observed in e. g. DORM-4 (54). Therefore, we
6 of the two was taken. Certified values are the best estimate of the mean and uncertainty. For MMA, which
7 fell below LOQ for the employed method at NRC but was measured by three additional laboratories, we
11 values (Table 4) are presented with the corresponding expanded uncertainties estimated in accordance

Methods (brief)

Juris; Gürleyük, Hakan; Wozniak, Ben J.; Feldmann, Joerg; Savage, Laurie;
4 Wozniak2, Joerg Feldmann3, Laurie Savage3, Suladda Deawtong4, Paramee Kumkrong1, 4, Kevin Kubachka5,
25 mg kg-1), lead (0.0064 ± 0.0016 mg kg-1) inorganic As (0.113 ± 0.016 mg kg-1) and dimethylarsinic acid (DMA)
1 retention time close to DMA. Participating laboratories were allowed to use their in-house validated
2 extraction and/or digestion method and detection of total metals was done by ICP-MS whereas HPLC-ICP-
3 MS was used for As speciation. Despite the diversity in sample preparation and quantitation methods
5 generation ICP-MS and HPLC-ICP-MS found iAs overestimation with the former method, possibly due to
6 interference from DMA. The certification was accomplished with a CRM rapid response approach in
11 dilution, HPLC-ICP-MS, quality assurance
27 A study performed in 2008, which evaluated As concentrations in more than two hundreds rice samples
29 concentrations of As in these samples are attributed to soil contamination due to the use of As-containing
2 arsenate) being the dominant fraction in Asian rice, followed by dimethylarsinic acid (DMA) and traces of
3 monomethylarsonic acid (MMA). In rice grown in USA, DMA is found to be dominant (8, 12, 13) and several
12 skin lesions, cardiovascular disease among others (20). On the other hand, MMA and DMA are classified
iAsa As(III)b As(V)c DMA MMA
12 laboratories and complex physical preparation of the sample into a CRM. The costs of such CRM projects
13 Each participating laboratory (Table 2) was given seven blind samples: five samples of BARI-1 and 2 quality
14 control (QC) samples, NRC DORM-4 and NIST 1568b. Some laboratories, included SQID-1 (cuttlefish CRM),

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised