6. AOACSPIFANMethods-2018Awards

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1406  Jing et al. : J ournal of AOAC I nternational Vol. 98, No. 5, 2015

difficult to put into practice for LC/MS/MS methods. The flags raised can disrupt laboratory operations, and the subsequent investigation/retest is often ambiguous as to whether the result is more accurate, or even statistically different from the flagged result. Given the excellent performance of AOAC 2014.04 and good agreement among different methods on a variety of matrixes, we conclude that confirmatory ion transitions are not necessary for this method. An SLV of AOAC 2014.04 has been performed, and the method has met all the requirements for precision, accuracy, linearity, LOQ, and specificity as outlined in SMPR 2012.010 for carnitine. The method simultaneously determines choline, and the data show that it has also met the requirements of SMPR 2012.013 for that analyte. (1) Starkey, D.E., Denison, J.E., Seipelt, C.T., & Jacobs, W.A. (2008) J. AOAC Int . 91 , 130–142 (2) Andrieux, P., Kilinc, T., Perrin, C., & Campos-Giménez, E., (2008) J. AOAC Int . 91 , 777–785 (3) Fu, S., Tao, B., Lai, S., Zhang, J., & Yiping, R. (2012) J. AOAC Int . 95 , 157–162 (4) Phillips, M.P., & Sander L.C. (2012) J. AOAC Int . 95 , 1479–1486 (5) Oates, K., Chen, L., DeBorba, B., Rohrer, J., Mohindra, D., Thermo Fisher Scientific Application Note 193. www.dionex. com/en-us/webdocs/115182-AU193-IC-Choline-InfantFormula- AdultNutritional-AU70918_E.pdf (accessed August 9, 2015) Conclusions References

at the primary transition varied on a given day and a given instrument. Table 12 shows the results. Daily ratios for carnitine were, overall, more consistent than those for choline, especially for data collected on the TQS instrument. For 4 of the 12 days of TQS choline data, the transition ratio was approximately twice that observed on the remaining days. There is no obvious explanation for this shift. Within-day uniformity was generally good on those days (within an acceptable range), although on 3 of those 4 days the ratio RSDs were modestly larger. Despite the large shift in the ion ratio on those days, however, there was no other indication that data quality was compromised. Overall, within-day RSD ranges were carnitine/TQD: 1.3–2.7%, carnitine/ TQS: 0.6–3.6%, choline/TQD: 0.7–1.5%, and choline/TQS: 1.1–5.4%. These are consistent with expectations, generally, for LC/MS/MS methods. Because of the differences between instrument platforms as well as day-to-day shifts, it is not possible to assign meaningful ranges appropriate for all instruments on all days. A better alternative is to base the expected ratio in the samples to that determined for the current daily calibration standards, and to use some multiple of the SD of the ratio determined for the three standards to set a limit for the ratio expected in the samples. Thus, if a particular sample’s ratio was 2–3 SD away (the exact setting is arbitrary) from the typical ratio in the daily calibration standards, that would be flagged as a possibly invalid result (caused by a coeluting molecule that happened to have exactly the same parent and primary daughter ion mass) and investigated (e.g., diluted and reanalyzed). The AOAC ERP has previously suggested this type of approach for MS/MS platforms to deliver the most highly specific methods to the analytical community. As reasonable as this approach sounds, we have found it very