AOAC OMA# 2011.14 (Final Action Review)-OMB
Table 2011.14D. Interlaboratory study results for potassium 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
8996.74 6443.79 6438.19
99 135.82 1.51
208.98 130.04 135.78 187.59
2.32 2.02 2.11 3.03
0.57 0.47 0.49 0.70
9 9 8 9
NS g
100 65.17
1.01
NS
Infant cereal
99 119.83 1.86 102 148.84 2.40
6SG
Peanut butter NIST SRM 2387 6200.24 (6070) h
NS
Wheat gluten NIST RM 8418
411.08 (472) h
87
10.19
2.48
31.31
7.62
1.18
9
NS
Cool vessels to room temperature before venting (MDC vessels). Transfer the MDC digests to 50 mL (100 mL for MDO) volumetric flasks. Dilute to volume withH 2 O andmix. ( Note :Adigestion is judged complete when clear to yellow analytical solutions are produced.) Filter the digested solution using an ashless filter paper for turbid samples containing fat. Discard the first 20 mL filtrate and collect the remaining filtrate for analysis. [ Note : Membrane disc filters (0.45 μm) are not recommended as they are generally not metal-free.] Transfer to polyethylene containers within 2 h. Dilute the samples that are found to be above the standard curve range or have total content of minerals higher than 1000 mg/L with H 2 O. [ Note : Final dilutions require the addition of appropriate amounts of HNO 3 for MDC digests (or appropriate amounts of combined acids for MDO) to maintain the proportion of 10% (v/v) HNO 3 (15%, v/v, combined acids and hydrogen peroxide) in the final solution to be analyzed.] 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.
( 2 ) Digestion vessel decontamination .—Decontaminate the used MDC vessels with 5 mL HNO 3 according to a program close to that in b ( 1 ). Wash the MDO glass volumetric flasks in a laboratory washing machine or soak overnight in a water bath with HNO 3 (30%, v/v). Rinse withH 2 O to avoid or tominimize risk of iron contamination. Dry MDC vessels at 60°C in drying oven for 1 h. Detection E. Principle Digested test solution or an appropriate dilution is presented to the inductively coupled plasma-optical emission spectrometry (ICP-OES) instrument. The instrument is calibrated with acid(s) matched standard calibrant solutions. An ionization buffer (cesium) and internal standard(s) (chromium, indium, strontium, and yttrium) are used with or without appropriate in-line addition to
Table 2011.14E. Interlaboratory study results for magnesium 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
1746.74 439.31 859.48
98 99 98
38.46
2.20 1.27 3.91 3.32
51.03 13.37 35.38 73.68
2.92 3.04 4.12 4.30
0.56 0.48 0.71 0.82
8 9 7 8
2SG NS g
5.57
Infant cereal
33.62
2, 6DG
Peanut butter NIST SRM 2387 1714.02 (1680) h
102 56.83
2SG
Wheat gluten NIST RM 8418
482.05 (510) h
95
8.52
1.77
16.53
3.43
0.54
9
NS
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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