AOAC Methods for Review in Codex STAN 234_11-2018

AOAC Official Methods Listed in CXS 234 for Milk and Milk Products

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985.35 Minerals in Infant Formula, Enteral Products, and Pet Foods, Atomic Absorption Spectrophotometric Method

mixing, these composites were apportioned into screw-top plastic jars for shipment to collaborators. For the replicate por- tion to be spiked, 6 g of either soy powder or whey powder was weighed into a screw-top plastic jar. The material was to be added to the ashing vessel with the spiking solution. The mini- mum weight specified for use for powders was 1.5 g. Collaborators analyzed 4 liquid formulae: 8 fl. oz. cans and bottles of the same lot, with labels removed, representing 2 of the RTF soy products and the single enteral formula, and a 32 fl. oz. can with the label printed on the can representing the third RTF soy formula. No attempt was made to eliminate can-to-can variation within lots because of the instability of the product once opened. Collaborators analyzing a spiked liquid were given directions to weigh a 30 g portion of the 32 fl. oz. RTF soy formula or the enteral formula into the ashing vessel and to add the accompanying spiking solution. The only formula iden- tified for the collaborators was the 32 fl. oz. can with the label printed directly on the can. A spiking solution containing all 9 minerals in a plastic screw-top vial was included. Collaborators were directed to add this solution to the designated formula to be spiked and then to rinse the vial 3 times, collecting the rinses in the ashing vessel. Because Pwas included in the same spiking solution and only one portion was to be spiked, collaborators were required to use the same preparation step for P and the other minerals. An in-house study was conducted to investigate whether re- sults for phosphorus would be compromised by this procedure. No differences were found between results obtained fromusing the extracts from the atomic absorption method for minerals and the results of the official phosphorus method in the in- house study. The results are summarized in Table 12. Liquids Spiking Solution

Final Action 1985 Final Action 1988 Revised First Action 1997

(Applicable to Ca, Mg, Fe, Zn, Cu, Mn, Na, and K.) Caution: See Appendix B: safety notes on safe handling of acids. Dispose of waste solvents in an appropriatemanner com- patible with applicable environmental rules and regulations. Method Performance: See Table 985.35A for method performance data. A. Principle Organicmatrix is destroyed by dry ashing inmuffle furnace. Remaining ash is dissolved in diluted acid and analyte is deter- mined by atomic absorption spectrophotometry (AAS). B. Apparatus ( a ) Glassware .—Thoroughly clean all glassware by soak- ing overnight in 20 % HNO 3 . Rinse all glassware 3 × with dis- tilled-deionized or 18 M Ω resistance H 2 O. ( b ) Evaporation dish .—100 mL unetched Vycor (or Pt), flat-bottom, with pour spout; capable of withstanding tempera- tures up to 600°C. ( c ) Atomic absorption spectrophotometer .—Equipment should be well maintained with good response per unit concen- tration, for example, 0.200 abs or above 4 mg/L Cu. ( d ) Furnace .—With pyrometer to control temperature range of 250°–600° ± 10°C. C. Reagents ( a ) Water .—Distilled, deionized, or 18 M Ω resistance for preparation of standard or sample solutions. ( b ) Standard stock solutions .—Commercially prepared, certified AA standards, or prepared in laboratory by Method 969.23A ( c ) ( see 35.1.21) for Na, 969.23A(d ) ( see 2.6.01) for K, 965.09B(a) ( see 2.6.01) for Ca, 965.09B(b) ( see 2.6.01) for Cu, 965.09B(c) ( see 2.6.01) for Fe, 965.09B(e) ( see 2.6.01) for Mg, 965.09B(f) ( see 2.6.01) for Mn, and 965.09B(g) ( see 2.6.01) for Zn. ( c ) Nitric acid .—Unless specified otherwise, use redistilled or ultrapure. ( d ) Lanthanum oxide .—La 2 O 3 , 99.99 % ; AAS quality. ( e ) Lanthanum chloride solution .—LaCl 3 , 1 % (w/v). Weigh 11.7 g ( ± 100 mg) La 2 O 3 and transfer to 1 L volumetric flask. Add enough H 2 O to wet powder and then slowly add 50 mL concentrated HCl ( Caution : exothermic reaction). Let powder dissolve and then dilute to volume with H 2 O and mix. Lanthanum chloride solution is stable up to 6 months when stored at room temperature. ( f ) Cesium chloride solution .—CsCl, 10 % (w/v). Weigh 12.7 g (± 100 mg) CsCl and transfer to 100 mL volumetric flask. Dilute to volume with H 2 O and mix. Make fresh every 6 months. ( g ) Filter pulp .—Analyzed ash-free.

Within-Laboratory Variability

Liquid RTF soy formulae and soy powders with nearly iden- tical concentrations of particular elements were used to esti- mate within-laboratory variability by mechanical application of the Youden “closely matched pair” approach.

Blank Determination

To identify problems due to contamination, collaborators were asked to run 2 blanks through each method.

Concentration Ranges

Estimates of concentration ranges for all minerals in the products were supplied to each collaborator. However, actual concentrations found for some elements were outside these ranges. As a consequence, one collaborator reported 2 determi- nations for elements found to be outside the ranges supplied. The first reported values were used in this report.

10/9/2018