AOAC Final Action Methods in 2018

Table 2011.14J. Interlaboratory study results for infant formula and adult nutrition products and placebos SMPR 2014.004 SPIFAN product samples

SPIFAN placebo samples

Element

Range, mg/100 g RSD r , % RSD R , % Range, mg/100 g RSD r , % RSD R , % Range, mg/100 g RSD r , % RSD R , %

Ca Cu

20–1280

5 5 5 5 5 5 5 5 5 5 5

10 16 10 10 10 10 16 10 10 10 10

35–99 a

3.9 NA 3.9 3.6 2.3 2.2 NA 3.3 2.8 2.6 3.0

8.7 NA 9.3 9.5 6.0 7.4 NA 7.7 7.5 7.6

7.4–63

2.3

7.9

0.001–0.005

NA b

0.0036–0.0039 0.0065–0.011

29.4 12.2

82.8 38.8

0.005–1.2 0.01–20 10–2000

0.029–0.239

Fe

0.54–2.4 44–222

0.018–0.49

8.6 2.9 1.8 9.0 5.4 2.7 1.9 8.8

18

K

7.6–177 1.7–5.1

6.5

Mg Mn

3–110

4.3–39

10.3 32.6 13.2

0.001–0.005

NA

0.0008–0.0037 0.0064–0.0083

0.005–1.0

0.0059–0.42

12.2

Na

10–850 15–800 0.1–18

15–140 23–95 0.34–2.6

5.0–138

7.9 5.4

P

24–71

Zn

0.0065–0.46

18.5

a  Adult RTF High Fat excluded for Ca due to presence of insoluble tricalcium phosphate. b  NA = Not applicable.

or without appropriate in-line addition system (e.g., T connector) linked between the peristaltic pump and nebulizer to avoid manual addition of ionization buffer and internal standards to each sample solution. A thermostated cyclonic spray chamber equipped with a micro-concentric nebulizer or other components designed to optimize aerosol and maximize precision are recommended. Follow manufacturer’s recommendations. Select peristaltic pump rotation speed, sample, and internal standard pump tubes of similar size to maximize mixing accuracy while maintaining the required detection levels. ( l )  Sampler tubes .—For autosampler. C. Reagents ( a )  High-grade water (18 MΩ) .—ISO 3696 Grade 2, 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. ( e ) 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.) ( f )  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 10000 mg/kg (e.g., for calcium, magnesium, phosphorus, potassium, and sodium) commercial stock standard solutions. However, it is also acceptable to use

commercially prepared, custom-blended stock standard mixtures containing all of the nine elements at appropriate concentrations. A number of companies provide this stock standard service. ( g )  Intermediate stock solution .—(Suggested composition of the intermediate stock standard solution, in mg/kg: Ca = 1500; Cu = 10; Fe = 50; K = 2000; Mg = 500; Mn = 0.25; Na = 1000; P = 1000; Zn = 20.) Add into a 500 mL volumetric flask, 75 mL calcium 10000 mg/kg, 5 mL copper 1000 mg/kg, 25 mL iron 1000 mg/kg, 100 mL potassium, 25 mL magnesium 10000 mg/kg, 0.125 mL manganese 1000 mg/kg, 50 mL sodium 10 000 mg/kg, 50 mL phosphorus 10000 mg/kg, and 10 mL zinc 1000 mg/kg. Add 10 mL HNO 3 and dilute to volume with H 2 O. Store in a high- density polyethylene bottle. ( h )  Working standard solutions .—Standards prepared from intermediate stock standard solution are designed to have the same acid concentration as digested test solutions (i.e., 10%, v/v, HNO 3 ) for MDC or 15% (v/v) for MDO using combined acids (HNO 3 , H 2 O 2 , and HCl). See Table 2011.14K for suggested concentrations of the six working standards. ( 1 )  Std6 .—Pipet 15.0 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. Table 2011.14K. Suggested concentrations of the six standard solutions, mg/L Element Std0 Std1 Std2 Std3 Std4 Std5 Std6 Ca 0 7.5 15 30 75 150 225 Cu 0 0.05 0.1 0.2 0.5 1.0 1.5 Fe 0 0.25 0.5 1.0 2.5 5 7.5 K 0 10 20 40 100 200 300 Mg 0 2.5 5 10 25 50 75 Mn 0 0.00125 0.0025 0.005 0.0125 0.025 0.0375 Na 0 5 10 20 50 100 150 P 0 5 10 20 50 100 150 Zn 0 0.1 0.2 0.4 1.0 2.0 3.0

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