Minerals and Trace Elements in Milk, Milk Products, Infant Formula, and Adult/Pediatric Nutritional Formula, ICP-MS Method: Collaborative Study, AOAC Final Action 2015.06, ISO/DIS 21424, IDF 243.

AOAC Final Action Official MethodSM 2015.06 "Minerals and Trace Elements in Milk, Milk Products, Infant Formula and Adult/Pediatric Nutritional Formula, ICP-MS Method" was collaboratively studied. Note that "milk, milk products" has now been added to the title of the Final Action method because whole milk and several dairy ingredients were successfully incorporated into the collaborative study for the purpose of developing an International Organization for Standardization/International Dairy Federation standard (ISO/DIS 21424; in progress). The method determines sodium, magnesium, phosphorus, potassium, calcium, iron, manganese, zinc, copper, chromium, molybdenum, and selenium by inductively coupled plasma (ICP)-MS after microwave digestion. Ten laboratories participated in the study, and data from five different model ICP-MS units were represented. Thirteen products, five placebo products, and six dairy samples were tested as blind duplicates in this study, along with a standard reference material, for a total 50 samples. The overall repeatability and reproducibility for all samples met Standard Method Performance Requirements put forth by the AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals, with a few exceptions. Comparisons are made to ICP-atomic emission data from a collaborative study of AOAC Official Method 2011.14 carried out concurrently on these same samples.

Characterization of Final Action Official MethodSM 2011.19 and First Action Official Method 2015.06 Performance at Analyte Levels Corresponding to CODEX STAN 72 (1981) Minimum Levels.

A limited single-laboratory validation (SLV) was conducted in the authors' laboratory to investigate the performance of AOAC Official MethodsSM 2011.19 Determination of Chromium (Cr), Selenium (Se), and Molybdenum (Mo) in Infant Formula and Adult Nutritional Products by Inductively Coupled Plasma/Mass Spectrometry and 2015.06 Determination of Minerals and Trace Elements in Infant Formula and Adult/Pediatric Nutritional Formula by Inductively Coupled Plasma/Mass Spectrometry at analyte levels below the practical LOQs (PLOQs) already published for these Final Action Official Methods. This work was needed to verify that the actual LOQs were below the minimum requirements for minerals in infant formula as given in CODEX STAN 72 (1981). Linearity studies at low levels were conducted as well as the analysis of blanks over multiple days to establish the LOQs (as opposed to PLOQs) for these nutrients. Several placebo matrixes from the AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) program were tested over multiple days at two different sample sizes to quantitate the effect of doubling the sample size given in the original publications. The SLV results indicate that both methods can meet the Codex minimum requirements as-is, without modification of the methods, albeit with a relaxation of the stringent precision criteria originally established for these methods by SPIFAN. Precision can be improved by doubling the sample size, but this step is not necessary to use the method for its intended purpose. A concurrent collaborative study of Method 2015.06 showed that the RSDR obtained across eight laboratories for several infant formula placebos containing mineral concentrations between the PLOQ and LOQ were indeed worse than SPIFAN expectations, but reasonable Horwitz ratios (HorRat) were nonetheless obtained for these analytes.

Determination of Chromium, Selenium, and Molybdenum in Infant Formula and Adult Nutritional Products by Inductively Coupled Plasma/Mass Spectrometry: Collaborative Study, Final Action 2011.19.

AOAC First Action Method 2011.19: Chromium, Selenium, and Molybdenum in Infant Formula and Adult Nutritional Products, was collaboratively studied. This method uses microwave digestion of samples with nitric acid, hydrogen peroxide, and internal standard followed by simultaneous detection of the elements by an inductively coupled plasma (ICP)/MS instrument equipped with a collision/reaction cell. During this collaborative study, nine laboratories from four different countries, using seven different models of ICP/MS instruments, analyzed blind duplicates of seven infant, pediatric, and adult nutritional formulas. One laboratory's set of data was rejected in its entirety. The method demonstrated acceptable repeatability and reproducibility and met the AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) Standard Method Performance Requirements (SMPRs®) for almost all of the matrixes analyzed. The Cr, Mo, and Se SPIFAN requirement for repeatability was ≤5% RSD. The SMPR called for a reproducibility of ≤15% RSD for products with ultratrace element concentrations above the targeted LOQ of 20 µg/kg Cr/Mo and 10 µg/kg Se (as ready-to-feed). During this collaborative study, RSDr ranged from 1.0 to 7.0% and RSDR ranged from 2.5 to 13.4% across all three ultratrace elements.

Application of inductively coupled plasma/mass spectrometry for the measurement of chromium, selenium, and molybdenum in infant formula and adult nutritional products: First Action 2011.19.

An inductively coupled plasma/MS method was developed for the simultaneous determination of Cr, Se, and Mo in infant formula and other nutritional products. All samples were digested using a closed vessel microwave oven system, together with Ni and Te internal standards. The practical quantitation limits for Cr, Se, and Mo were 0.4, 0.2, and 0.4 ng/mL, respectively; dilution factors were 250 for powders and 50 for liquids. The Cr, Se, and Mo concentrations in 10 nutritional products were within specification limits; within-day and day-to-day (6 independent days) precision values were <5% RSD. For two control samples, the observed precision was < or = 2% RSD over 10 independent days. Cr, Se, and Mo results were within the certified limits in three National Institute of Standards and Technology standard reference materials. The average sample spike recoveries for 10 nutritional products ranged from 93 to 107%. Robustness studies showed a minimal effect from concomitant easily ionized element concentrations. However, the choice of internal standard and matrix-matching carbon content were critical to obtaining accurate Se results. All indications are that this method would be a suitable candidate as a global reference method for the determination of these trace elements in infant formula, adult nutritionals, and other nutritional

Simultaneous determination of chromium, selenium, and molybdenum in nutritional products by inductively coupled plasma/mass spectrometry: single-laboratory validation.

An inductively coupled plasma/MS method was developed for the simultaneous determination of Cr, Se, and Mo in infant formulas and other nutritional products. All samples were digested using a closed vessel microwave oven system, together with Ni and Te internal standards. The practical quantitation limits for Cr, Se, and Mo were 0.4, 0.2, and 0.4 ng/mL, respectively; dilution factors were 250 for powders and 50 for liquids. The Cr, Se, and Mo concentrations in 10 nutritional products were within specification limits, and within-day and day-to-day (6 independent days) precision values were <5% RSD. For two control samples, the observed precision was < or = 2% RSD over 10 independent days. In three National Institute of Standards and Technology standard reference materials, Cr, Se, and Mo results were within the certified limits. The average sample spike recoveries for 10 nutritional products ranged from 93 to 107%. Robustness studies showed a minimal effect from concomitant easily ionized element concentrations. However, the choice of internal standard and matrix matching carbon content were critical to obtaining accurate Se results. All indications are that this method would be a suitable candidate as a global reference method for the determination of these trace elements in nutritional products.