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B

olong

et al

.:

J

ournal of

AOAC I

nternational

V

ol

.

99, N

o

.

1, 2016 

201

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

Matrix

a

Results

b

Interday

mean

Mean

RSD

r

, % RSD

iR

, %

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Adult RTF, high fat

c

 Mean, mg/100 g

159

156

161

166

169

160

162

 RSD

r

, %

1.66

1.82

1.02

1.82

1.26

0.44

1.34 3.04

SRM 1849a (701±17 mg/100 g)

 Mean, mg/100 g

716

706

713

705

705

711

709

 RSD

r

, %

0.23

1.22

0.56

0.44

0.70

0.20

0.56 0.80

Pediatric powder

 Mean, mg/100 g

342

342

340

350

347

344

344

 RSD

r

, %

0.98

1.24

0.13

0.55

1.22

0.82

0.82 1.23

Adult powder, milk-protein-based

 Mean, mg/100 g

321

312

311

325

318

319

318

 RSD

r

, %

1.05

0.89

0.26

1.80

1.11

0.89

1.00 1.77

Infant powder, soy-based

 Mean, mg/100 g

516

521

509

524

517

518

517

 RSD

r

, %

0.76

0.23

1.09

0.10

0.14

0.27

0.43 1.01

Infant RTF, milk-based

 Mean, mg/100 g

44.9

45.3

46.5

45.5

45.6

46.3

45.7

 RSD

r

, %

0.16

1.58

1.14

1.03

1.24

0.46

0.94 1.45

Adult powder, low-fat

 Mean, mg/100 g

354

339

347

366

355

359

353

 RSD

r

, %

0.13

1.69

1.14

0.43

1.80

0.99

1.03 2.66

Adult RTF, high protein

 Mean, mg/100 g

153

157

156

160

160

157

157

 RSD

r

, %

0.35

1.47

1.45

1.93

0.44

1.36

1.17 1.78

Infant powder, elemental

 Mean, mg/100 g

360

353

354

373

367

371

363

 RSD

r

, %

0.49

1.26

0.60

0.99

0.96

0.38

0.78 2.34

Infant powder, partially hydrolyzed soy-based

 Mean, mg/100 g

419

415

413

427

428

421

421

 RSD

r

, %

0.21

1.57

0.24

0.42

0.66

0.67

0.63 1.53

a

 Two samples each of the 10 SPIFAN matrixes were tested.

b

 Concentrations on an “as-is” basis.

c

 RTF = Ready-to-feed.

Accuracy/Recovery

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.

LOQ

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).

83