AOAC Methods in Codex STAN 234 (Preliminary Methods Review)

856

BARBANO ET AL.: J. ASSOC. OFF. ANAL. CH!'.M. (VOL. 73, NO. 6, 1990)

Table 2. AOAC 11tallstlcal parameters by sample materlal for percent protein determined by KJeldahl m.thod In fltsl lrtal or collaborallve study (digested for 1 h aNer cl.arlng) Material

7

4

5

9

2

3

6

8

All

All

Outlier

Outlier

Mean•

date

data

StatlltJc

••eluded

excll.ldlJd

II

9

9

10

10

10

10

10

9

10

No. of labs

9

No. of accepted values

18

18

20

20

18

18

20

16

20

20

20

3.367 0.021 0.810 0.024 0.706 0.058 0.087

3.396 0.011 0.336 0.015 0.441

3.086 0.007 0.237 0.016 0.529 0.021 0,048

3.610

3.082

3.091 0.025 0.817 0.023 0.737 0.071 0 .084

3.140 0.007 0.225 0.012 0.387

3.259 0.013 0,385 0.019 0.587

3.379 0.046 1.359 0.054 1.588 0.130 0.152

3.266 0.018 0.540 0.020 0.611 0.050 0.058

3.296 0.015 0.446 0.020 0.611 0.042 0.057

3.446 0.013 0,384 0.026 0.739

Mean,%

s,

0.018 0.045

1.445 0.046 1,479 0.126 0.129

0.490 0.027 0.760 0.050 0.078

RSD,, %

SR

RSDA, % r Value R Value

0.020 0 ,036

0.035 0.032

0.054

0.042

0.034

0.072

• Means are baaed on dal.a from sample rne.terlals 5 and 8 with outllers excluded.

regression.~ of percent protein vs each AOAC statistical pa· rametcr for each type of equipment found no significant influence of protein concentration on any of the traditional equipment AOAC statistical parameters but there was a significant (P < 0.05) influence of protein concentration on SR and R values for the block digcstor equipment. One factor that may cause block digestors in different laboratories to display different recovery of nitrogen on high protein samples at the end of a fixed (I h) time of boiling after clearing may be laboratory-to-laboratory variation in line voltage. Differences in line voltage can resuit in different block temperature recovery times, as indicated by the manu– facturer {P. Calvi, Tecator, Inc., personal communication). The provisional JDF procedure requires that boiling be con– tinued for 1.5 h after clearing (the method for our first

collaborative study trial was I h after clearing). If digestion heating conditions differed between laboratories usmg block digestors, digestion could be more complete in some labora– tories than in other laboratories. We hypothesized that sam– ple digestion may not have been complete in all laboratories using block digestors. This could explain the increase in the laburatory-to-Jaboratory varjability of test results with in– creasing protein content in the first trial. Thus, a second trial in the collaborative study was conducted to determine if a boiling time of I .5 h after clearing would eliminate the corre- lation between protein concentration and reproducibility sta- tistics. Relative normality of the titrant used in each laboratory I d d . .f . . Ii was eva uate to etermine 1 errors in htrant norma ty contributed to differences in mean test results from Jaborato-

Tabte 3. Linear regr...ion ot ,,, RSD,, •R, ASDR, r value, and R value va percent proteJn (all ragrealone comprised 9 test t values with 7 d99,.., of freedom) tor flm trlal In collaboratlve 1tudy

Corr. coetf., %

.,

Mean

Eq\llpment

S1atlstic

Slope

Intercept

~Value

b

0.015 0.445 0.020 0.811 0.042 0.057 3.296 0.015 0.449 0.018 0.545 0.042 0.051 S.292 0.013 0.388 0.022 0,663 O.G36 0.062 3.302

0.0051 0.0158 0.0176 0.3347 0.0145 0.0-499 0.0105 0.1679 0.0346 0.8640 0.0294 0.0979

-0.0021

All

2.19 0.02

0.396 0 .039 2.034 1.282 0.396 2.034 0.732 0.383 2.784· 2.300 0.732 2.784·

RSD,, %

0.3927

-0.0379 -0.4922 -0.0061 -0.1072

37.15 18.52

8A

RSDA, %

r value R value

2.18

37.15

% protein

a,.

-0.0190 -0.1040 -0.0950 -2.2990 -0.0540 -0.2710

7.10 2.04

Block

RSD,, %

52.54 43.03

8R

RSOn, %

r value R value

7.10

N N

52.54

% protein

., R Sf!

M

- 0.0104 -0.4223

0.0473 1.7819 0.0097 0.9872 0.1 338 0.0274

4.72 7.60 4.12 3.03 4.72 4.12

-0.589 -0.759

Tredlllonal

Sr

ASD,, %

0.0037

0.549

Bil

-0.0IIBO -0.0296

-0.468 -0.589

RSOR, %

AS r V R i;

r value R value

0.0104

0 ,549

% protein

Codex Trial Method Review • Significant at a • o.os.