6. AOACSPIFANMethods-2018Awards

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Collaborative Study Results and Discussion

Conclusions

The key precision performance metrics of the multilaboratory study per sample matrix are summarized in Table 6. The RSD r derived from analysis of the blinded duplicates was roughly the same as for the known duplicates (raw data not shown from the participating laboratories, but the RSD r obtained is consistent with the intermediate precision data from the SLV shown in Table 3). For instance, none of the seven matrixes produced an RSD r higher than the method’s 10% RSD duplicate criterion for Cr, 7% for Se, or 5% for Mo. Note, however, that repeatability of Se for three of the seven matrixes was between 5 and 7%, further justification for the change of this QC criterion to 7%. In terms of the repeatability SMPR, two matrixes had RSD r of >5% for Cr, as did three matrixes for Se. The highest RSD r observed for the blinded duplicates was 7.0%, and in this case, as well as the other four cases, the corresponding reproducibility was only slightly higher. The RSD R of method 2011.19 for each matrix was, on the average, about half of the SMPR of 15%. HorRat were similarly low, averaging 0.46 for Cr, 0.27 for Mo, and 0.32 for Se. The authors’ opinion is that the RSD R expected from this study is a function of how far above the instrument quantification limit we are at the determination stage, not of the absolute level of the analyte. Methods with good sensitivity, good linearity over the calibration range, and adequate required system suitability should be able to produce comparable reproducibility at the low ppb level, and this appears to be supported by other SPIFANMLT studies (publications in progress). The individual sample results submitted by each laboratory are given in Tables 7–9. Each value given is the mean of known duplicates, prepared per the method. Then, the blinded duplicate results are shown for each participating laboratory, for each matrix. The footnotes indicate which samples were rejected, either by the method’s QC criteria, or by the AOAC-supplied statistical package (5). The laboratories could have analyzed new samples and obtained data to replace the rejected results, but there was not enough time to do so, or perhaps they did not realize this was an option. Although there were five cases in which both blind duplicate samples were rejected (thus Table 6 records the number of laboratories as seven for that matrix), the footnotes indicate that retaining the data would keep the RSD R under 15% in all but one case. The data in Tables 7–9 also indicate why Laboratory 1 data were totally excluded from the study; except for a few Mo results, its data were significantly lower than that of any other laboratory across the board. Also, Laboratory 1 stood out as having the most problems with sensitivity and linearity (Table 1), and perhaps contamination was an issue due to the number of (known) duplicate failures for Cr (Table 2). It may be a coincidence, but that laboratory was using the oldest ICP/MS instrument, a PerkinElmer ELAN DRC-e, which may not have had the capability to do the required collisional/reaction chemistry to eliminate low-mass interferences. Comments about the performance of the method were requested. One laboratory pointed out that the 10% powder reconstitution in the method was different than the 11.1% reconstitution recommended by SPIFAN and proceeded to use the latter (it made no discernible difference). Another comment was that the ICP/MS instrument model DRC-e could not use ammonia gas for Se determination, which may be the reason for Laboratory 1’s exclusion from this study.

AOAC Method 2011.19 was successfully studied in collaboration by eight laboratories using multiple ICP/MS instrument models and testing a variety of infant, pediatric, and adult nutritional matrixes. The method demonstrated acceptable repeatability and reproducibility and met the SPIFAN SMPRs for reproducibility for all seven matrixes analyzed. The multilaboratory collaborative study data were summarized and presented to the AOAC ERP in September 2014. After reviewing the data, the AOAC ERP voted to move AOAC 2011.19 to Final Action status, and the method was approved by the AOAC Official Methods Board as a Final Action method (6). The authors would like to thank the following collaborators and their associates: Yue Fenpeng, Chinese Academy of Inspection and Quarantine (CAIQ), Beijing, China Fan Xiang, Entry-Exit Inspection and Quarantine, Shanghai, China Yue Zhang and Shuqi Zhang, Zhejiang Test Academy, Hangzhou City, China Sudhakar Yadlapalli, First Source Laboratory Solutions, Hyderabad, India Isabelle Malaviole, Laboratory Aquanal, Pessac, France Ashutosh Mittal, Syngene International Ltd, Bangalore, India Michael Gray, Mead Johnson, Evansville, IN Marissa Feller, Covance Laboratories, Madison, WI Diana Mould and Michael Farrow, U.S. Food and Drug Administration, Atlanta, GA. (1) Cubadda, F., Raggi, A., Testoni, A., & Zanasi, F. (2002) J. AOAC Int. 85 , 113–121 (2) Sharpless, K.E., Thomas, J.B., Christopher, S.J., Greenberg, R.R., Sander, L.C., Shantz, M.M., Welch, M.J., & Wise, S.A. (2007) Anal. Bioanal. Chem. 389 , 171–178. http://dx.doi.org/10.1007/s00216-007-1315-y (3) Pacquette, L., Szabo, A., & Thompson, J. (2011) J. AOAC Int . 94 , 1240–1252 (4) AOAC SMPR 2011.009 (2012) J. AOAC Int . 95 , 297. http:// dx.doi.org10.5740/jaoac.int.11-0441 (5) AOAC Interlaboratory Study Workbook for Blind (Unpaired) Replicates (2013) Version 2.1, AOAC INTERNATIONAL, Rockville, MD (6) Official Methods of Analysis (2012) 19th Ed., AOAC INTERNATIONAL, Rockville, MD. www.eoma.aoac.org, Method 2011.19 Recommendation Acknowledgments References