Application of a special in-house validation procedure for environmental–analytical schemes including a comparison of functions for modelling the repeatability standard deviation

Abstract Sample size formulas are developed to estimate the repeatability and reproducibility standard deviations (sr and sR) such that the actual error in (sr and sR) relative to their respective true values, σr and σR, are at predefined levels. The statistical consequences associated with AOAC INTERNATIONAL required sample size to validate an analytical method are discussed. In addition, formulas to estimate the uncertainties of (sr and sR) were derived and are provided as supporting documentation.Formula for the Number of Replicates Required for a Specified Margin of Relative Error in the Estimate of the Repeatability Standard Deviation

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Colorimetric Method for Carbadox in Feeds: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/60.5.1059 ◽

1977 ◽

Vol 60 (5) ◽

pp. 1059-1063

Author(s):

John T Goras

Keyword(s):

Standard Deviation ◽

Stannous Chloride ◽

Collaborative Study ◽

Colorimetric Method ◽

Feed Supplement ◽

Colored Complex ◽

Feed Supplements ◽

Repeatability Standard Deviation ◽

Standard Additions ◽

The Mean

Abstract A colorimetric method for determining carbadox in complete swine feeds and feed supplements was collaboratively studied. Carbadox is separated from feed with CHCl3-methanol (3+1) and then separated from interfering materials by a series of solvent-solvent extractions. The drug is isolated as a dry residue, reconstituted, and reacted with stannous chloride to form a colored complex that is measured at 520 nm. The method of standard additions is used to compensate for a feed or feed supplement matrix effect. Twenty-seven laboratories assayed feeds containing 0.0013, 0.0053, and 0.0242% carbadox. The repeatability standard deviation (σ0) and reproducibility standard deviation (σx) were σ0 = 0.00014%, σx = 0.00035% (29% of grand mean) for 0.0013% carbadox in feed; σ0 = 0.00025%, σx = 0.00037% (6.7% of grand mean) for 0.0053% carbadox in feed; and σ0 = 0.0019%, σx = 0.0024% (9.6% of grand mean) for 0.0242% carbadox in feed. The between-laboratory variance ratio was not significant for feeds containing 0.0013 and 0.0053% carbadox, but was significant for feeds containing 0.0242% carbadox. The mean recovery values for feeds containing 0.0013, 0.0053, and 0.0242% carbadox were 92, 104, and 103%, respectively. The method was adopted as official first action for feeds having a guaranteed potency of 0.0055% carbadox or higher.

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Experimental Designs for Interlaboratory Precision Experiments: Comparison of ISO 5725 with Draft NEN 6303

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/72.1.34 ◽

1989 ◽

Vol 72 (1) ◽

pp. 34-37 ◽

Cited By ~ 1

Author(s):

J Zaalberg

Keyword(s):

Standard Deviation ◽

Edible Oils ◽

Collaborative Study ◽

Experimental Designs ◽

Interlaboratory Experiments ◽

Interlaboratory Studies ◽

Repeatability Standard Deviation ◽

Level Design ◽

Iso 5725

Abstract To determine the precision of standardized analytical methods, interlaboratory experiments are carried out in which several laboratories analyze identical samples from well homogenized batches of material. From the test results, estimates of the standard deviations under repeatability as well as under reproducibility conditions are calculated. In the present work, the experimental designs recommended in the International Standard ISO 5725 have been compared with a design proposed in the draft Netherlands Standard NEN 6303. This has been done by comparing their mathematical models as well as by applying them to the results of a recent collaborative study on the determination of heavy metals in edible oils and fats. The reproducibility standard deviation is estimated equally well with both Standards, but it appeared that the designs given in ISO 5725 can lead to serious underestimation (uniform-level design) or overestimation (split-level design) of the repeatability standard deviation. By using the design proposed in NEN 6303, these biases can be avoided. Hence, it is recommended that interlaboratory studies be organized according to the design of NEN 6303.

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Modified Method for Carbadox in Feeds: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/62.5.982 ◽

1979 ◽

Vol 62 (5) ◽

pp. 982-984

Author(s):

John T Goras

Keyword(s):

Standard Deviation ◽

Room Temperature ◽

Collaborative Study ◽

Variance Ratio ◽

Modified Method ◽

Repeatability Standard Deviation ◽

Standard Solution ◽

The Mean ◽

Optimum Working ◽

Statistical Results

Abstract The official first action method for carbadox in swine feed, 42.C01-42.C04, was modified in 2 respects. First, the samples were leached overnight at room temperature instead of boiled for 1 hr. This change avoided problems with overheating and excessive evaporation. Second, the dilution scheme for samples spiked with carbadox standard solution was changed to give absorbance values that were within the optimum working range of all types of spectrophotometers. The modified procedure was collaboratively studied by 21 laboratories. The repeatability standard deviation (σo) and reproducibility standard deviation (σo) were σ0 = 0.00029% and σx = 0.00056% (8.9% of grand mean) for feeds containing 0.00617% carbadox; and σo = 0.0012% and σx = 0.0019% (9.3% of grand mean) for feeds containing 0.0198% carbadox. The between-laboratory variance ratio was significant for feeds containing 0.0198% carbadox. The mean per cent of intent values for feeds containing 0.00617% carbadox and 0.0198% carbadox were 102% and 104%, respectively. In general, the statistical results were comparable to those previously obtained for the official first action method. Consequently, the modified procedure is not recommended as a replacement for the official first action method.

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Evaluation of the Babcock Method for the Determination of Milk Fat

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/58.5.949 ◽

1975 ◽

Vol 58 (5) ◽

pp. 949-956

Author(s):

Myron R Mckinley ◽

Richard E Arnold ◽

John B Rosenbury ◽

Earl C Born ◽

Chapman E Dunham ◽

...

Keyword(s):

Sulfuric Acid ◽

Standard Deviation ◽

Milk Fat ◽

Collaborative Study ◽

Tempering Temperature ◽

Coefficients Of Variation ◽

Sample Composition ◽

Significant Difference ◽

Repeatability Standard Deviation ◽

Milk Solids

Abstract The Babcock test for fat in milk was evaluated to study the effects of variables such as glassware calibration, sample preparation, sample composition, reagents, tempering conditions, procedural variations, and analyst. Certain test bottles yielded significantly different results; however, there was little indication of pipet variation. Analysis of the various techniques for tempering and mixing indicated that samples tempered at 68°F (20°C), containing an airspace of approximately 25% of the total container, and mixed by inversion 5–10 times or poured from one container to another gave the most consistent results. Sample composition did not affect results, provided all milk-solids-notfat were digested by the sulfuric acid. A pipet draining time of 10 sec followed by blowing out the pipet was sufficient to yield reproducible results. Differences between lots of sulfuric acid affected results. Results were 0.027% less when the final test tempering was 130°F (54.5°C) compared to 140°F (60°C); however, a final tempering for a minimum of 3 min gave satisfactory results. Variations in reading results between individual analysts were negligible. The Babcock method for fat in milk, modified to include the optimum parameters as determined in this study, was subjected to a collaborative study. Nine laboratories analyzed 10 samples in duplicate. Statistical analysis of collaborative data indicates a significant difference between laboratories (p <0.01 ). The repeatability standard deviation of the method is 0.0183%. The reproducibility standard deviation is 0.0407%. The repeatability and reproducibility coefficients of variation are 0.53 and 1.17%, respectively. On the basis of the collaborative results, the following changes have been incorporated into the official final action method: specifications for the reading light; sample draining time; tempering temperature of the acid; tempering procedure for reading the test bottle.

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Mass Loss on Drying for Instant Coffee: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/63.2.178 ◽

1980 ◽

Vol 63 (2) ◽

pp. 178-179

Author(s):

William P Clinton ◽

Paul H Manni ◽

John M Ferry

Keyword(s):

Standard Deviation ◽

Mass Loss ◽

Coefficient Of Variation ◽

Collaborative Study ◽

Instant Coffee ◽

Reproducibility Standard Deviation ◽

Repeatability Standard Deviation ◽

Working Method

Abstract A collaborative study was undertaken to define an acceptable routine working method for determination of mass loss in instant coffee. Fourteen laboratories of 24 invited to participate submitted results. The repeatability standard deviation and coefficient of variation were 0.026 and 0.7%, respectively. The reproducibility standard deviation and coefficient of variation were 0.153 and 3.8%, respectively. The method has been adopted as official first action.

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Determination of Total Nitrogen in Urine by Pyrochemiluminescence: Collaborative Study

Journal of AOAC International ◽

10.1093/jaoac/78.2.301 ◽

1995 ◽

Vol 78 (2) ◽

pp. 301-306 ◽

Cited By ~ 3

Author(s):

Kristi A Boehm ◽

P Frank Ross

Keyword(s):

Standard Deviation ◽

Total Nitrogen ◽

Collaborative Study ◽

Urine Samples ◽

External Control ◽

Severe Stress ◽

Average Recovery ◽

Oxidative Pyrolysis ◽

Repeatability Standard Deviation

Abstract Twelve collaborating laboratories analyzed 5 blind duplicate samples of human urine for total nitrogen using a pyrochemiluminescence method. The nitrogen content ranged from low (650 mg/L) to high levels (8800 mg/L) in urine samples of people under moderate to severe stress. In addition to test samples, collaborators also received a certified standard (sodium nitrite in water) as an external control. The pyrochemiluminescence assay was performed on urine samples diluted in water within a range of 1:50 to 1:100. The method detects total nitrogen by reaction of the product of high temperature oxidative pyrolysis and ozone. Repeatability standard deviation values (RDSr) ranged from 1.49 to 3.91% and reproducibility standard deviation values (RSDR) ranged from 3.66 to 9.57%. The average recovery of total nitrogen was 99.9%. The pyrochemiluminescence method for determination of total nitrogen in urine was adopted first action by AOAC INTERNATIONAL.

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Protein Nitrogen Unit Precipitation Procedure for Allergenic Extracts: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/64.6.1435 ◽

1981 ◽

Vol 64 (6) ◽

pp. 1435-1438

Author(s):

Joan C May ◽

Jenny T C Sih ◽

◽

Allergy Laboratories ◽

J Best ◽

...

Keyword(s):

Standard Deviation ◽

Coefficient Of Variation ◽

Collaborative Study ◽

Precipitation Method ◽

Protein Nitrogen ◽

Accuracy And Precision ◽

Precipitation Procedure ◽

Allergenic Extracts ◽

Kjeldahl Method ◽

Repeatability Standard Deviation

Abstract Protein nitrogen unit (PNU) determination is one of the methods used to test and label the concentration of allergenic extracts. This recently standardized method is applicable to all allergenic extracts. One PNU/mL is equivalent to 1 × 10−5 mg nitrogen determined to be in the material precipitated from 1 m l allergenic extract by phosphotungstic acid (PTA), a protein precipitant. The nitrogen is quantitated by the Kjeldahl method or another analytical method of equivalent accuracy and precision. A collaborative study of the optimized PNU precipitation method in which 6 samples were analyzed in duplicate by 6 laboratories using the Kjeldahl method for the determination of nitrogen yielded a mean of 0.1358 mg N/ml, a repeatability standard deviation and coefficient of variation of 0.0071 mg N/mL and 5.23%, respectively, and a reproducibility standard deviation and coefficient of variation of 0.0188 mg N/mL and 13.84%, respectively. The method has been adopted official first action.

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Microdiffusion and Fluoride-Specific Electrode Determination of Fluoride in Infant Foods: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/64.4.1021 ◽

1981 ◽

Vol 64 (4) ◽

pp. 1021-1026

Author(s):

Robert W Dabeka ◽

Arthur D Mckenzie ◽

◽

R A Baetz ◽

D W Bingham ◽

...

Keyword(s):

Standard Deviation ◽

Collaborative Study ◽

Variance Analysis ◽

Infant Foods ◽

Reproducibility Standard Deviation ◽

Coefficients Of Variation ◽

Repeatability Standard Deviation

Abstract Twelve laboratories analyzed (1 replicate) 12 samples of infant foods – milk, pears, and peas – containing 0.2-5 ppm F. There was one laboratory outlier. Mean coefficients of variation were 7.06% for intralaboratory determination of 3 sets of blind duplicates and 21.6% for interlaboratory determination of 12 samples. Variance analysis for all samples yielded a reproducibility standard deviation of 0.41 ppm; for 3 sets of blind duplicates, repeatability standard deviation was 0.26 ppm and reproducibility standard deviation was 0.32 ppm.

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High Pressure Liquid Chromatographic Determination of Bacitracin in Premix Feeds and Finished Feeds: Collaborative Study

Journal of AOAC INTERNATIONAL ◽

10.1093/jaoac/65.5.1178 ◽

1982 ◽

Vol 65 (5) ◽

pp. 1178-1185 ◽

Cited By ~ 2

Author(s):

John B Gallagher ◽

Paul W Love ◽

Linda L Knotts ◽

◽

M Allred ◽

...

Keyword(s):

Standard Deviation ◽

Collaborative Study ◽

Chromatographic Determination ◽

Chromatographic Technique ◽

Reverse Phase ◽

High Pressure Liquid Chromatographic ◽

Repeatability Standard Deviation ◽

Liquid Chromatographic Determination ◽

Liquid Chromatographic

Abstract A liquid chromatographic technique for the determination of bacitracin in finished feeds and premix feeds consists of an isocratic reverse phase, ion-suppressed technique. The chromatography can be completed in less than 25 min. In a collaborative study involving 9 laboratories and 3 samples of bacitracin methylene disalicylic acid and 3 samples of bacitracin zinc premixes covering the range of 10-50 g/lb, the repeatability standard deviation was 0.55, and the reproducibility standard deviation was 1.35. The average recovery of the bacitracin was 102.0%. The method has been adopted official first action for bacitracin in premix feeds.

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