AOAC OMA# 2011.14 (Final Action Review)-OMB

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 (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 (16000); Zn (320). Limit of quantitation (LOQ; mg/kg): Ca (150); Cu (2); Fe (10); K (200); Mg (50); Mn (0.05); Na (100); P (100); Zn (5). See Tables 2011.14A – I for the results of the interlaboratory study supporting acceptance of the method. [ Note : Results shown in Tables 2011.14A – I are slightly different from those shown in J. AOAC Int . 92 , 1484(2009) due to classical statistics applied instead of robust statistics applied in the tables included in J. AOAC Int . 95 , 177(2012).] 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 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. First Action 2011 Final Action 2013

C. Reagents ( a ) High-grade water, (18 MΩ) .—For slurry preparation 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 example : Infant cereals and fortified milk powders, preheat water at 50°C. Prepare the 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 next step.) Carefully add 5.0 ± 0.1 mL HNO 3 into MDC/MDO vessel (and then 5 mL H 2 O 2 only into MDO vessel). Loosely cap MDC vessel without sealing.

Table 2011.14A. Interlaboratory study results for calcium Matrix Mean, mg/kg Rec., % S r a

RSD r

b , % S

R c , ng/g RSD R

d , % HorRat

No. of labs e Outlier labs f

Chocolate milk powder Dietetic milk powder 2

9732.17 5678.58 5983.54

99 152.10 1.56

264.03 184.11 251.67

2.71 3.24 4.21 6.88

0.68 0.74 0.97 1.06

9 9 9 9

NS g

98

75.93

1.34

NS NS NS

Infant cereal

100 210.58 3.52

Peanut butter NIST SRM 2387 409.90 (411) h

100 13.37

3.26

28.20

Wheat gluten NIST RM 8418

367.56 (369) h

100

3.51

0.95

12.90

3.51

0.53

7

2, 4C

a S r = Standard deviation for repeatability (within laboratory). b RSD r = Relative standard deviation for repeatability. c S R = Standard deviation for reproducibility (among laboratories). d RSD R = Relative standard deviation for reproducibility. e Reporting laboratories minus outliers. f C = Cochran outlier; SG = Single Grubbs outlier; DG = Double Grubbs outlier. g NS = Not significant. h Value in parentheses = Certified or reference values.

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