6. AOACSPIFANMethods-2018Awards

162

Pacquette & Thompson: J ournal of AOAC I nternational V ol. 98, N o. 6, 2015  1707

Table 3. SLV intermediate precision data for Cr, Mo, and Se (from 8 independent days of testing in duplicate, 4 days per each analyst using two different Agilent ICP/MS units) a

Sample type

Cr Mean

RSD IP

Mo Mean

RSD IP

Se Mean

RSD IP

Infant powder milk Infant powder soy

4.9 (

7.7 5.2

17.7 (

8.2 4.5 4.0 3.6 3.0 4.9 5.1 7.5

25.6 (

6.5 3.3 2.7 4.1 3.2 2.8 2.9 2.8 2.9 3.0

Infant powdered milk partially hydrolyzed 2.4 (

20

9.2 1.3 5.0 1.3 6.3

Adult powder low fat Adult powdered milk Child formula powdered Infant elemental powdered

47.6

62.7

29.7

15.8 (

32.6 (

24.3 (

30.2 23.9

30.0 17.8

23.7 23.2

Infant RTF milk

7.6 (

53

16.9 (

10

29.6 (

Adult RTF high protein

130 141

2.9 1.8

154 193

3.2 2.6

92.6 133

Adult RTF high fat 3.6 a  Units of concentration are µg/kg as RTF with powders reconstituted 11.1% (w/w). Note that several of the means are designated as

solutions at concentrations that are representative of nutritional products in samples for ICP/MS analysis. The typical H 2 gas mode for Se, and He gas mode for Cr and Mo, were used. (f)  Accuracy .—Accuracywas demonstratedby analyzing three NIST SRMs on 2 independent days, measuring spike recoveries in 10 nutritional products on 3 different days, and comparing results for 10 nutritional products obtained by this method to results obtained by other in-house validated ICP-atomic emission spectrometry and atomic fluorescence spectrometry methods. The spike levels of the analytes added to the products were between 50 and 200% of the analyte concentrations in each product. (g)  Precision .—Both within-day and between-day RSD values were determined by analyzing two in-house laboratory control samples. Within-day precision was determined by analyzing the laboratory control samples in duplicate on each day, and between-day precision was measured by using the mean Table 4. SLV overspike recoveries (mean from 3 days, in triplicate each day) from SPIFAN matrixes at 50–200% of native levels a

results of the duplicate samples analyzed on each day on 10 different days. (h)  Ruggedness and robustness .—To determine the ruggedness of the method, laboratory control samples were analyzed by two analysts on 10 different days. Also, NIST SRM 1849 was analyzed in triplicate with varying sample weights and with different ISs. (i)  Reproducibility .—Eight laboratories completed a multilaboratory testing protocol with this method on seven samples submitted as blind duplicates (14 total samples analyzed plus the SRM1849a control, which was not blinded). Represented were four countries and five ICP/MS instrument models from three major vendors. Results showed an average RSD R of 9.3% for Cr, 5.3% for Mo, and 6.5% for Se, with an average HorRat ratio of 0.35 across all three analytes and samples. The SLV data were not published with the method above; they will be briefly summarized here. Table 3 shows the intermediate precision for each of the SPIFANmaterials across 8 different days of results using two different analysts and two Agilent ICP/MS units, a model 7500 and a model 7700. As noted previously, the infant formulas contained no added Cr or Mo, so they were mostly not included in the MLT. For levels above the PLOQ, Table 5. SRM 1849a results during SLV ( n = 16, two analysts, two Agilent instruments) and collaborative study (run once in duplicate as a known sample by each laboratory, together with other blinded samples) SLV Data

Product

Cr

RSD Mo RSD Se RSD

Infant powder milk Infant powder soy Infant powdered milk partially hydrolyzed Infant powdered soy partially hydrolyzed Adult powder low fat Adult powdered milk

109 10.0 92.5 2.5 106 4.7 108 1.5 93.1 1.2 103 6.0 90.1 1.1 95.2 5.7 99.5 2.3

91.0 3.0 108 1.0 101 2.3

101 4.8 95.4 8.1 99.3 3.3

104 1.6 97.4 4.6 103 4.1 Child formula powdered 102 2.5 96.2 2.1 104 4.8 Infant elemental powdered 102 8.8 96.9 2.7 106 4.6 Infant RTF milk 103 6.1 92.3 5.4 101 4.9 Adult RTF high protein 98.0 2.5 92.0 2.7 104 4.9 Adult RTF high fat 98.0 2.8 93.3 3.1 105 7.0 a  Native levels that are below the PLOQ and other concentrations can be found in Table 3.

Cr

Mo

Se

Mean SLV, µg/kg, n = 16

105

166

82.7

RSD SLV, %

1.4

1.1

1.8

Certified interval, µg/kg Mean MLT (not including SLV), µg/kg RSD MLT, % (eight labs)

104.0–110.4 166.7–174.7 78.3–84.1

106

167

82.6

2.4

2.8

1.5