AOAC Final Action Methods in 2017

50.10.01

A. Principle This method is an extension of 2011.19 ( see 50.1.41) to determine nine additional elements. The method is also extended to support analysis of dairy products (milk, milk powder, whey powder, whey protein concentrate, butter and cheese) for 11 of the 12 elements (Cr is excluded because none of the dairy products contained Cr above the LOQ, and so reproducibility could not be determined). Nitric acid, internal standard (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 inductively coupled plasma-mass spectrometry (ICP-MS). Polyatomic interferences with the low mass elements are reduced or eliminated by analysis in 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 is achieved essentially simultaneously by comparing the analyte–ISTD response ratios in the unknown samples with a standard curve constructed from response ratios of calibration standards. B. Apparatus (a)  ICP mass spectrometer.— With quartz spray chamber, quartz torch, Ni/Pt sample cone, Ni/Pt skimmer cone, autosampler, and

AOAC Official Method 2015.06 Minerals and Trace Elements in Milk, Milk Products, Infant Formula, and Adult/Pediatric Nutritional Formula

ICP-MS Method First Action 2015 Final Action 2017

Codex-Adopted AOAC-ISO Method (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. Also applicable to the determination of Na, Mg, P, K, Ca, Mn, Fe, Cu, Zn, Se and Mo in milk and milk products. See Table  2015.06A for analytical ranges.) Caution: Chemicals used are common-use solvents and reagents that are harmful if inhaled, swallowed, or absorbed through the skin. Refer to adequate manuals or Material 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.

Table 2015.06A. Performance of Method 2015.06 in the SLV and MLT and recommended analytical ranges Parameter Na Mg P K Ca Mn Fe Cu

Zn

Cr

Se

Mo

Low standard, μg/L

500

200

500

1000 1000

5.00

50.0

5.00

20.0

0.800

0.400

0.800

PLOQ, μg/L a

50

20

100

100

100

2.5

5.0

0.50

4.0

0.080

0.20

0.080

PLOQ, mg/100 g b

0.25

0.10

0.50

0.50

0.50

0.012

0.025 0.0025 0.020

0.00040

0.0010

0.00040

PLOQ meets SMPR? c

Yes

Yes

Yes

Yes

Yes

No

No

No

Yes

Yes

Yes

Yes

PLOQ meets Codex? d

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

No

Yes

LOQ, mg/100 g e

0.11 0.0049 0.13

0.56

0.53

0.00050 0.0073 0.00048 0.056

0.00073

0.00031

0.00048

LOQ meets SMPR? c

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

LOQ meets Codex? d

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Avg. repeatability, % f

1.5

1.5

1.9

1.4

1.8

2.1

2.9

2.3

1.6

3.0

3.3

2.1

Avg. reproducibility, % f

3.6

3.5

4.3

3.6

4.1

3.8

6.1

6.3

4.3

4.9

5.0

3.6

Recommended analytical  range, mg/100 g g

2–850 0.7–110 3–800 3–2000 3–1280 0.002–1.0 h

0.04–20 0.002–1.2 0.07–18 0.002–0.16 i

0.0006–0.050 h

0.0002–0.10

a  PLOQ is the lowest level at which the measured 3 day mean of a standard concentration, run as an unknown against the calibration curve, is within 5% of its nominal concentration. This is the preferred lower limit of the method, as it limits the amount of calibration bias in the result. However, sensitivity of ICP-MS typically affords a lower actual LOQ, as measured in the traditional way of measuring blank concentrations over several days. b  PLOQ converted to a product concentration level using the typical dilution factor of 1 g to 50 mL for an RTF. c  Lower limit of the analytical range as set forth in AOAC SMPR 2014.004 [ J. AOAC Int . 98 , 1042(2015) , DOI: 10.5740/jaoac.int.SMPR2014.004]. d  Codex STAN 72-1981 minimum levels for infant formulas and Food for Special Medical Purposes products. e  LOQs derived from measuring several digested and undigested blanks, each run on 5 separate days. Both sets of blanks yielded similar results. f  For 18 samples tested at 10 laboratories in the MLT not counting the Adult High-Fat RTF sample or the samples in which the analyte was at or below the quantitation limit (as opposed to

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