AOAC OMA# 2011.14 (Final Action Review)-OMB

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

P oitevin : J ournal of AOAC I nternational V ol . 95, N o . 1, 2012  183

Table 2011.14I. Interlaboratory study results for zinc Matrix Mean, mg/kg Rec., % S r , mg/kg a RSD r

, % b S R

, mg/kg c RSD R

, % d HorRat No. of labs e Outlier labs f

NA g

Chocolate milk powder Dietetic milk powder 2

18.06 53.65 36.51

0.396 2.19

0.95 2.36 1.27 1.78

5.24 4.40 3.44 6.69

0.51 0.50 0.37 0.69

8 9 9 9

5–SG

NS h

105 1.43 2.66 NA 0.92 2.25 101 1.06 3.96

Infant cereal

NS NS

26.64 (26.3) i

Peanut butter NIST SRM 2387 Wheat gluten NIST RM 8418

49.30 (53.8) i

92

0.96

1.95

3.19

6.46

0.73

9

NS

a  S r

= SD for repeatability (within laboratory).

b  RSD r

= RSD for repeatability.

c  S R

= SD for reproducibility (among laboratories).

d  RSD R = RSD for reproducibility. e  Reporting laboratories minus outliers. f  SG = Single Grubbs outlier.

g  NA = Not available. h  NS = Not significant. i  Certified or reference values.

using only one internal standard line. Following is the list of wavelengths for each element (and its appropriate internal standard), in priority order, that have been found acceptable for main foodstuffs: Wavelength (nm): Ca: 317.933 (In: 303.936); Cu: 324.754 (In: 303.936); Fe: 259.94 (Sr: 338.071); K: 766.491 (Sr: 460.733); Mg: 285.213 (In: 303.936); Mn: 257.610 (Sr: 338.071); Na: 589.592 (Sr: 460.733); P: 213.618 (In: 303.936); and Zn: 213.857 (Sr: 338.071). Other wavelengths that are acceptable for both elements and internal standards could be used as confirmatory analytical lines or alternate wavelengths as certain recommended lines may not be available on some ICP-OES systems: Wavelength (nm): Ca: 317.933 (Y: 371.028); Cu: 324.754 (Y: 371.028), 327.395 (In: 303.936 or Y: 371.028); Fe: 259.94 (Y: 371.028 or Cr: 283.563); Mg: 285.213 (Y: 371.028), 279.028 (In: 303.936); Mn: 257.610 (Sr: 460.733 or Y: 371.028); P: 178.222 (Sr: 460.733 or Y: 371.028); and Zn: 213.857 (Sr: 460.733 or Y: 371.028). Other lines of appropriate sensitivity, free of interferences or corrected for interferences in specific matrixes, may be just as acceptable.

G. Reagents

( a )  Ionization buffer/internal standard solution .—Weigh 1.27 g cesium chloride into a 1000 mL acid-washed volumetric flask. Note : This cesium 0.1% (w/v) solution was tested as the minimal recommended concentration required for element analysis in most food matrixes. Cs solution 1% (w/v) is recommended if an element is present at low concentration in high-salted food raw materials, e.g., culinary products or tastemakers, or if it is analyzed as an impurity in food-grade salts. Add 40 mL indium 1000 mg/kg and 10 mL each of strontium, yttrium, and chromium 1000 mg/kg stock standard solutions as internal standards. Add 10 mL HNO 3 . Dilute to volume with H 2 O, mix, and transfer to an acid-washed polyethylene bottle. Note : Reagent concentrations assume the use of same pump tubing internal diameter for both internal standard/ionization buffer and sample pump tubes using automatic addition. ( b )  Stock standard solution .—Working standards can be prepared from ICP-grade individual element 1000 mg/kg (e.g., for copper, iron, manganese and zinc) and 10 000 mg/kg

Table 2011.14J. Suggested concentration of the six standard solutions, mg/kg Element Std0 Std1 Std2 Std3 Std4

Std5

Std6

Ca Cu Fe Mg Mn Na K

0 0 0 0 0 0 0 0 0

7.5

15

30

75

150 1.0

225 1.5 7.5 300

0.05 0.25

0.1 0.5

0.2 1.0

0.5 2.5 100

5

10

20

40 10

200

2.5

5

25

50

75

0.00125

0.0025

0.005

0.0125

0.025

0.0375

5 5

10 10

20 20

50 50

100 100 2.0

150 150 3.0

P

Zn

0.1

0.2

0.4

1.0