OMB Meeting Book - Jan. 11, 2018

B olong et al .: J ournal of AOAC I nternational V ol . 99, N o . 1, 2016  201

Accuracy/Recovery

LOQ

Accuracy was demonstrated in the precision study with the use of SRM 1849a (Table 4). All results obtained fell within the certified concentration range of the method. The accuracy values ranged from 99.9 to 102.3%, meeting the requirements of SMPR 2014.015. Samples of 10 SPIFAN matrixes spiked at two levels (50 and 100% overspikes) were prepared and tested in duplicate on 3 days for recovery. Results are presented in Table 5. Within-day recoveries across the matrixes varied between 100.3 and 103.3%, and among-day recoveries varied between 100.9 and 102.5%, all within the 95 to 105% requirement.

The minimum silver nitrate consumption end point volume that can be evaluated by the Metrohm potentiometric titration system is in the range 0.0 to 0.05 mL, depending on the instrument sensitivity conditions and day-to-day variation. A 0.05 mL minimum silver nitrate consumption end point volume is more stable than a 0.02mLcondition and is able to be validated via appropriate dilution of the NaCl SS. This translates to an estimated LOQ of 20 mg/100 g chloride on a powder basis and a 2.2 mg/100 mL chloride result on a ready-to-feed basis (25 g milk powder reconstituted to total 225 g).

Table 4. Precision in SPIFAN matrixes and NIST SRM 1849a

Results b

Interday mean

Mean

Matrix a

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

, % RSD iR

, %

RSD r

Adult RTF, high fat c  Mean, mg/100 g

159 1.66

156 1.82

161 1.02

166 1.82

169 1.26

160 0.44

162

, %

1.34 3.04

 RSD r

SRM 1849a (701±17 mg/100 g)  Mean, mg/100 g

716 0.23

706 1.22

713 0.56

705 0.44

705 0.70

711

709

, %

0.20

0.56 0.80

 RSD r

Pediatric powder  Mean, mg/100 g

342 0.98

342 1.24

340 0.13

350 0.55

347 1.22

344 0.82

344

, %

0.82 1.23

 RSD r

Adult powder, milk-protein-based  Mean, mg/100 g

321 1.05

312 0.89

311

325 1.80

318 1.11

319 0.89

318

, %

0.26

1.00 1.77

 RSD r

Infant powder, soy-based  Mean, mg/100 g

516 0.76

521 0.23

509 1.09

524 0.10

517 0.14

518 0.27

517

, %

0.43 1.01

 RSD r

Infant RTF, milk-based  Mean, mg/100 g

44.9 0.16

45.3 1.58

46.5 1.14

45.5 1.03

45.6 1.24

46.3 0.46

45.7

, %

0.94 1.45

 RSD r

Adult powder, low-fat  Mean, mg/100 g

354 0.13

339 1.69

347 1.14

366 0.43

355 1.80

359 0.99

353

, %

1.03 2.66

 RSD r

Adult RTF, high protein  Mean, mg/100 g

153 0.35

157 1.47

156 1.45

160 1.93

160 0.44

157 1.36

157

, %

1.17 1.78

 RSD r

Infant powder, elemental  Mean, mg/100 g

360 0.49

353 1.26

354 0.60

373 0.99

367 0.96

371 0.38

363

, %

0.78 2.34

 RSD r

Infant powder, partially hydrolyzed soy-based  Mean, mg/100 g

419 0.21

415 1.57

413 0.24

427 0.42

428 0.66

421 0.67

421

, %

0.63 1.53

 RSD r

a  Two samples each of the 10 SPIFAN matrixes were tested. b  Concentrations on an “as-is” basis. c  RTF = Ready-to-feed.

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