6. AOACSPIFANMethods-2018Awards

71

1712 Thompson et al.: J ournal of AOAC I nternational V ol. 98, N o. 6, 2015

Specificity and linearity studies were conducted with pure analyte (no matrix). For the specificity studies, individual standards of each analyte were prepared at 50 mg/L. For linearity, standards were prepared at nine concentrations of each analyte, spanning a range from 50% of the lowest calibration standard to 50% above the highest calibration standard. For precision studies, the 11 SPIFAN matrixes (infant powder, milk; infant powder, soy; infant powder, milk partially hydrolyzed; infant powder, soy partially hydrolyzed; adult powder, low fat; adult powder, milk; pediatric formula powder; infant elemental powder; infant RTF, milk; adult RTF, high protein; and adult RTF, high fat) were tested for all 12 elements on 8 days in duplicate each day, by two analysts using two Agilent ICP/MS units. For accuracy/recovery studies, each SPIFAN matrix was spiked with various concentrations of each analyte and analyzed by the method in triplicate over 3 days. Finally, Standard Reference Material (SRM) 1849a [National Institute of Standards and Technologies (NIST), Gaitherburg, MD] was used to verify accuracy. The SRM is a milk-based hybrid infant/ adult nutritional powder with certified values for Ca, Cu, Cr, Fe, Mg, Mn, Mo, P, K, Se, Na, and Zn and was included as a QC sample (QCS) in each run of the method. AOAC Official Method 2015.06 Minerals and Trace Elements in Infant Formula and Adult/Pediatric Nutritional Formula ICP/MS Method First Action 2015 (Applicable for determination of Na, Mg, P, K, Ca, Cr, Mn, Fe, Cu, Zn, Se, and Mo in infant formula and adult/pediatric nutritional formula.) Caution: Chemicals employed are common-use solvents and

Analytical range a , b 0.001–1.0 0.001–1.2 0.01–20 0.1–18 3–110 15–800 10–850 20–1280 10–2000 20–1600 20–1000 10–500 LOD a , b NA c NA NA NA NA NA NA NA NA 7 7 4 LOQ a , b 0.001 0.001 0.01 0.1 3 15 10 20 10 20 20 10 Repeatability ≤5% at >0.005 b ≤8% at <0.005 b ≤5%

SMPR 2014.004 SMPR 2011.009 Parameter Mn Cu Fe Zn Mg P Na Ca K Cr Mo Se

≤10% ≤10% ≤10% ≤10% ≤10% ≤8% ≤8% ≤8% ≤8% ≤15% ≤15% ≤15%

90–110% of mean spiked recovery over the range of the assay

reagents, harmful if inhaled, swallowed, or absorbed through the skin. Refer to adequate manuals or Materials Safety Data Sheets (MSDSs) to ensure that the safety guidelines are applied before using chemicals. Microwave operation involves hot pressurized acid solution. Use appropriate personal protective equipment such as a laboratory coat, safety glasses, rubber gloves, and a fume hood. Dispose of all materials according to federal, state, and local regulations.

A. Principle This method is an extension of AOAC Final Action Method 2011.19 to determine nine additional elements. Nitric acid, ISTD, and hydrogen peroxide are added to the sample in microwave vessels, and the samples are digested using preprogrammed temperature control. The addition of hydrogen peroxide helps reduce carbon and nitrous oxide levels in the digestate. The presence of carbon in the samples causes signal enhancement of Se. Therefore, to matrix match the samples, carbon in the form of methanol is added to both the standard solutions and the digestate before analysis. Ge (for 11 elements) and Te (just for Se) are used as ISTDs. Analysis is performed by ICP/MS. Polyatomic interferences with the lowmass elements are reduced or eliminated by analyzing in the He collision mode using kinetic energy discrimination (KED). For Se measurements, the H 2 gas mode is preferred for increased sensitivity. Quantitation of 12 elements

Recovery 90–110% at >0.005 b

80–115% at <0.005 b

a  Concentrations apply to a) RTF liquids “as-is”; b) reconstituted powders (25 g into 200 g of water); and c) liquid concentrated diluted 1:1 by weight. b  mg/100 g reconstituted final product for Mn, Cu, Fe, Zn, Mg, P, Na, Ca, and K; µg/100 g for Cr, Mo, Se. c  NA = Not applicable.

Table 1. Summary of SLV acceptance criteria from SMPR 2011.009 and SMPR 2014.004 Reproducibility (over the analytical range)