AOAC Methods in Codex STAN 234 (Preliminary Methods Review)

-

'

857

BARBANO ET At.: J. ASSOC. OFF. ANAL. CHBM. (VOL. 73, NO. 6, 1990)

Teble 4. Percent protein determined by KJeldahl method on ,aw milk eamplN, aecond lrlal of collaborallve ttuCly (dlgeeted 1.5 h after clearlng) Laboratory•

Materlal mean 3.S12

K" 3.541 3.571 3.457 3.495 3.574 3.566 3.366 3.403 3.777 3.795 3.195 3.227 3.280 3.268 3.421 3.413 3.236 3.249

F 3.513 3.519 3.435 3.453 3.538 3.540 3.354 3.359 3.742 3.563 3.171 3,183 3.259 3.262 3.369 3.383 3.208 3.198

H

J 3.499 3.517 3.466 3.456 3.534 .3.5.24 3.327 3.345 3.734 3.722 3.183 3.187 3.264 3.266 3.358 3.377 3.195 3.203

0 3.556 3.540 3.452 3.405 3.539 3.542 3.372 3.362 3.757 3.731 3.192 3.163 3.279 3.275 3.399d 3.183d

C 3.480 3.482 3.433 3.435 3.540 3.522 3.336 3.335 3.724 3.727 3.188 3.172 3.250 3.257 3.352, 3.353 3.184 3,180

A 3.504 3.499 3.462 3.442 3.53t 3.636 3.343 3.349 3.715 3.716 3.367c 0,602c 3.239 3.265 3.368 3.360 3,20t 3.201

E 3.497 3.500 3.444 3.445 3.524 3.535 3.338 3.343 3,733 3.730 3.169 3.167 3.252 3.254 3.360 3.359 3.195 3.187

Q

B

Matsrlal

3.514 3.535 3.437 3.464 3.535 3.536 3.338 3.349 3.671 3.741 3.183 3.170 3.238 3.252 3.375" 3.328e 3.125· 3.203·

3.523 3.529 3.461 3.471 3.558 3.547 3.353 3.360 3.748 3.748 3.183 3.182 3.265 3.266 3.384 3.377 3.203 3.201

3.510 3.496 3.449 3.444 3.534 3.510 3.324 3.342 3.716 3.690 3.161 3_164 3.245 3.251 3 ,357 3.321 3.170 3.196

3.447

2

3.535

3

3.346

3.725

5

3.175

6

3.258

7

3.363

8

3.199

3.231 3.231

9

' l.$oratory I could not participate because of broken equipment. 11 1nvalld data (laboratory did not use class A buref). 'Invalid data (not enough alkali was delivered during distillatlon). 1 Statistical outlier (Cochran test). 11111alld data (samples cryste,lllzed Immediately after removal from dlgestOf).

equipment for the second collaborative study are reported in Table 4. Blind duplicates were paired for each sample mate– rial. The difference in ana.lytical procedure in trial l vs trial 2 is that the digests were boiled for 1.5 h (an additional 0.5 h) after clearing in trial 2. As in trial I, laboratories A, C, D, E, and G used block digestor plus steam distillation equipment. The remaining laboratories (B, f, H, J, and K) used tradi– tional KjeldaM equipment. There was l invalid data point in laboratory A because of failure of the alkali pump and delivery of a very low amount of sodium hydroxide for distillation of the sample. There were 2 invalid data in laboratory G because the samples crystallized immediately after digestion (indicating too little residual acid remaining at the end of digestion and a possible

,y to laboratory. The relative normality never djffered from dl:$ired normality by greater than 0.0004N, which is within the tolerance specified in the method. Protein test values for all samples in all laboratories were recalculated using the ,elative normalities (instead of the reported normalities). fhe data set calculated using relative normalities had SR and R values of 0.0205 and 0.0579, respectively. Thus, account– ing for normality of titrant did not improve the reproducibili- 1y of the test (comparing to Table 2 mean SR and R values of

U.020 and 0 .057, respectively). RHUlls or Collaborative Trial 2

All of the data collected for total nitrogen determination ~y the Kjeldahl method from traditional and block digestor

Table 5. AOAC etatletlcal parameters by sample material for percent protein detefflllned by Kleldahl method In second trlal of collaborallve etudy (digested for 1.5 h after clearlng)

Material

8

7

5

8

9

4

3

2

All data

Outliers excluded

Statistic

s

8

7

9

8

9

9

!}

Codex Trial Method Review 18 3.717 0.048 1.242 0.043 1.168 0.131 0.123 'Ml.Wins ara based on data from &le material 8 with outliers excluded. No. of labs No. of accepted values Mean,% e, RSD,, % 8fl RSDR, % rValue RValue 9 18 3.512 0.009 0.247 0.020 0.580 0,025 0.058 9 18 3.447 0.015 0.429 0.016 0.457 0.042 0.045 18 3.535 0.008 0.239 0.011 0.297 0.024 0.030 18 3.346 0.008 0.225 0.013 0.380 0.021 0.036

16 3.354 0.055 1.643 0.048 1.438 0 156 0.136

14 3.363 0.012 0.347 0.016 0.485 0.033 0.046

16 3.199 0.008 0.239 0.016 0.512 0.022 0.046

16 3.175 0.009 0.274 0.010 0.304 0.025 0.027

18 3.258 0,007 0.226 0.012 0.352 0.021 0.032

3.395 0.014 0.385 0017 0.504 0.038 0.049