SPSFAM Heavy Metals ERP Book

1080 K ubachka et al .: J ournal of AOAC I nternational V ol . 100, N o . 4, 2017 filter (discarding approximately the first 1 mL to waste) into a 15 mL polypropylene centrifuge tube. Fill an autosampler vial approximately half full before analysis. Store the unused portion up to 48 h at 4°C in the event the sample needs to be reanalyzed.

MMA standards; these laboratories reprocessed their data and resubmitted. Data were omitted from one laboratory for failure to properly determine and verify concentrations of DMA and MMA stock standards as required in the method. In addition, the AOAC INTERNATIONAL Interlaboratory Study Workbook for Blind (Unpaired) Replicates was used to estimate repeatability and reproducibility of the method (18). Before analyzing validation samples, laboratories were instructed to estimate their analytical solution detection limit (ASDL), analytical solution quantitation limit (ASQL), and corresponding method LOD and LOQ for As(III), As(V), DMA, and MMA in RTD juice and juice concentrate samples. These results are tabulated in Table 2. Laboratories determined the concentration SDs (σ) for each arsenic species by analyzing 10 replicates of a low-level mixed standard containing between 0.04 and 0.4 ng/g each of As(III), As(V), DMA, and MMA. Per the FDAEAM 3.2, the ASDL and ASQL values for each arsenic species were calculated using approximately 3.8σ and 30σ, respectively (19). The use of 30σ to calculate ASQL, rather than the 10σ commonly used, accounts for uncertainty in the signal measurement used to determine ASDL, as well as additional sources of uncertainty. ASDL and ASQL results obtained for DMA and MMA by one laboratory were significantly higher compared to the other seven participants and were rejected as outliers using both the Dixon and Grubbs tests. The higher limits obtained by this laboratory were concluded to be related to a known issue with the verification of the DMA and MMA standard concentrations. As expected, the average ASDLs obtained for each of the species based on arsenic concentrations were very similar, with averages ranging from 0.043 µg/kg for As(III) to 0.047 µg/kg for As(V). The respective method LODs and LOQs for As(III), DMA, MMA, and As(V) were calculated using a dilution factor of 5× for RTD juice samples and 30× for juice concentrate samples and are shown in Table 2. Because this method does not provide effective control over potential oxidation/reduction of iAs species during sample preparation, iAs results are provided as a sum of theAs(III) andAs(V) detected. This makes interpretation of the iAs method LOD more difficult. The method LOD for iAs was conservatively estimated as the highest method LOD Analytical Limits

(b)  FAPs for juice concentrates .—For this validation, duplicates of three levels were prepared for sample AJC1 by the following method: Prepare an analytical portion fortified with As(III), DMA, MMA, and As(V) at levels of 35, 100, and 200 μg/kg each by combining approximately 1 g concentrate and appropriate amounts of the 1000 ng/g multianalyte spiking solution in a 15 mL polypropylene centrifuge tube. Dilute to 6 g total with DIW and mix thoroughly. Next, transfer a 2 g portion of this solution to another 15 mL polypropylene centrifuge tube and dilute to 10 g total with DIW and mix thoroughly (the spiking levels are 1.2, 3.3, and 6.7 ng/g each in these solutions, respectively). Draw an approximately 4 mL aliquot of the analytical solution into a syringe and dispense through a 0.45 μm nylon or PTFE syringe filter (discarding the first approximately 1 mL to waste) into a 15 mL polypropylene centrifuge tube. Fill an autosampler vial approximately half full before analysis. Store the unused portion up to 48 h at 4°C in the event the sample needs to be reanalyzed. (c)  Method blank .—Take 2 g DIW through the sample preparation procedures described above for RTD juices and juice concentrates.

HPLC-ICP-MS Analysis, Quantification, and Identification

Details regarding the analysis of the samples and the quantification and identification of arsenic species can be found in First Action Official Method 2016.04 (17).

Results and Discussion

Data Reporting and Statistical Analysis

Laboratories reported their data by populating the reporting template with the proper data. The central laboratory compiled the data into one spreadsheet and examined it for validity. Upon examining the data, two laboratories had incorrectly calculated the concentrations of their DMA and

Table 2. Summary of ASDL, ASQL, and respective method LOD and LOQ for iAs, DMA, and MMA ( n = 7 laboratories) Analytical limit Sample Parameter As(III), µg/kg As(V), µg/kg iAs, µg/kg a DMA, n/g MMA, ng/g ASDL n 8 8 7 7 x̅ 0.043 0.047 0.046 0.045 σ 0.011 0.005 0.016 0.014 RSD 26% 11% 35% 31% ASQL x̅ 0.32 0.36 0.36 0.34 LOD RTD juice x̅ 0.22 0.24 0.24 0.23 0.23 LOQ RTD juice x̅ 1.6 1.8 1.8 1.8 1.7 LOD Juice concentrate x̅ 1.3 1.4 1.4 1.4 1.4 LOQ Juice concentrate x̅ 9.7 11 11 11 10 a  The method LOD and LOQ for iAs assumes that at a minimum, either As(III) or As(V) must be detected at a level ≥LOD.