AOAC OMA# 2011.14 (Final Action Review)-OMB

2011.14 (MTE-01) MLT FOR ERP USE ONLY DO NOT DISTRIBUTE

178  P oitevin : J ournal of AOAC I nternational V ol . 95, N o . 1, 2012

Robustness study .—Analysis of spiking elements in eight food-grade salts with and without ion buffer, and through repeatability and reproducibility tests on six reference materials with different ICP-OES equipments (axial and radial grating configurations), and with open- and closed-vessel microwave- based digestions. Ring trial .—With nine independent and experienced food industry laboratories on five in-house and certified reference materials using this method. Statistic results of performed SLV tests show that the method developed for the determination of nine nutritional minerals by ICP-OES is fit-for-purpose in terms of specificity, sensitivity, linearity, trueness, and precision according to ISO 17025.AOAC acceptability criteria (recovery, precision, and HorRat values) are also fulfilled for all food matrixes covering the nine sectors of the AOAC food triangle. Improvements to AOAC Method 984.27 (e.g., microwave digestion, internal standardization, ion buffering, and extension to all food matrixes) provide global satisfactory ruggedness results for all matrixes tested. Robustness and efficiency of the method was proved through a successful ring trial. This full validation, using well-characterized reference materials, demonstrated that the method is a cost-efficient (multielemental), time-saving (high-throughput sample digestion), accurate, and fit-for-purpose analytical method for all laboratories in the food industry, and is well established and harmonized within 25 Nestlé laboratories. AOAC Official Method 2011.14 Calcium, Copper, Iron, Magnesium, Manganese, Potassium, Phosphorus, Sodium, and Zinc in Fortified Food Products Microwave Digestion and Inductively Coupled Plasma-Optical Emission Spectrometry First Action 2011 (Applicable to analysis of calcium, copper, iron, potassium, magnesium, manganese, phosphorus, sodium, and zinc in fortified food products.) Upper limits (mg/kg): Ca (24000); Cu (210); Fe (850); K (32000); Mg (7500); Mn (20); Na (16 000); P (16 000); and Zn (320). LOQ (mg/kg): Ca (150); Cu (2); Fe (10); K (200); Mg (50); Mn (0.05); Na (100); P (100); and Zn (5). See Tables 2011.14A — I for results of the interlaboratory study supporting acceptance of the method. These results are slightly different from those shown previously in J. AOAC Int. (1) due to the application of classical rather than robust statistics.

laboratory use at 200 ± 20°C, up to 600 psi and controlled temperature or pressure ramping capability. It is recommended that vessel design be selected that will withstand the maximum possible pressure (600 psi), since organic residues of rich-fat or rich-carbohydrate samples, if not given sufficient time to predigest, will generate significant pressure during digestion.

C. Reagents

O (18MΩ) .—For slurry preparation

( a )  High-grade water , H 2

and/or dilution.

( b )  Nitric acid (HNO 3

), 65% (w/v) .—Trace metal grade

throughout. ( c )  Hydrochloric acid (HCl), 37% ( w / v) .—Trace metal grade throughout. ( d )  Hydrogen peroxide (H 2 O 2 ), 97% (w/v) .—Trace metal grade throughout.

D. Determination

Caution : Before using chemicals, refer to the supplier guide for chemical safety and/or other adequate manuals or safety data sheets approved by local authorities. Use fume hood, and wear full personal laboratory protective clothing, gloves, and appropriate eye protection (safety glasses) when using glassware and preparing standards or test portions with acid solutions. ( a )  Sample preparation .—( 1 ) Test sample preparation .— Homogenize a representative sample by grinding as finely as possible and/or by preparing a slurry with H 2 O. For infant cereals and fortified milk powders, preheat water at 50°C. Prepare slurry by weighing 10.0 ± 0.1 g test sample, and place into a 100 mL Erlenmeyer flask; add 90.0 ± 0.1 g H 2 O. Mix well with stopper. ( 2 )  Test portion preparation .—Accurately weigh 0.50 ± 0.01 g test portion or sample mass on a dry weight basis in the prepared slurry to MDC vessel (1.00 ± 0.01 g into a 100 mL volumetric flask for MDO). Note : An optimal analytical test portion mass of 0.5 g (1.0 g for MDO) is based on an empirical maximum energy release by the food of 3 kcal and 90–110% recovery. Line the MDC vessel walls or Pasteur pipet with weighing paper during sample transfer to keep sample from adhering to sides of vessel, or use a Pasteur pipet to transfer liquid samples. Weigh fluid samples or test portion from slurry test sample directly after mixing. Note: Remove weighing paper from sample prior to placing MDC vessels in oven. Carefully add 5.0 ± 0.1 mL HNO 3 into MDC/MDO vessel, then 5 mL H 2 O 2 only into MDO vessel. Loosely cap MDC vessel without sealing. Predigest for at least 10 min at room temperature or until vigorous foaming subsides. Close MDC vessels and distribute onto microwave carousel to ensure uniform microwave power application on all samples. ( 3 )  Food-grade salt sample preparation .—Weigh 0.20 ± 0.01 g food-grade salt (a minimum dilution factor of 500 is recommended) into a 100 mL volumetric flask. Add deionized water and 10 mL HNO 3 . Dissolve salt and dilute to volume with deionized water. ( b )  Test portion digestion .— Caution : Application of MDS involves hot pressurized acid solutions and concentrated acids. Use fume hood and wear full personal laboratory protective clothing, gloves, and appropriate eye protection (safety glasses)

Digestion

A. Principle

Test portion is heated at 200°C either with nitric acid in a closed-vessel microwave digestion system (MDC) or with a combination of hydrogen peroxide, nitric acid, and hydrochloric acid in an open-vessel microwave digestion system (MDO).

B. Apparatus

Microwave .—Commercial MDC or MDO designed for