Evaluation of Analytical Methods Used for Regulation

1982 ◽  
Vol 65 (3) ◽  
pp. 525-530 ◽  
Author(s):  
William Horwitz
Keyword(s):  
Relative Importance ◽  
False Negatives ◽  
Methods Of Analysis ◽  
Collaborative Studies ◽  
Limit Of Determination ◽  
Regulatory Analysis ◽  
Criteria For Evaluation ◽  
Reproducibility Limit ◽  
Action Levels ◽  
Evaluation Of Methods

Abstract Regulatory analysis requires methods for analysis for 3purposes: surveillance, to detect problems; monitoring, to follow trends; and compliance, to enforce specifications (standards, action levels, tolerances). Each purpose requires a different weight to be assigned to the relative importance of the scientific characteristics of methods of analysis: systematic error, repeatability, reproducibility, limit of determination, and specificity. Evaluation consists of balancing the level of scientific requirements against the practical considerations of cost, time, and level of (raining required. In trace analysis, FDA utilizes recovery limits of 80-110% at ≥0.1 ppm and 60-100% below. The criterion for acceptable reproducibility (total of between- and within-laboratories) of methods of analysis can be represented by a relationship between coefficient of variation and concentration. The results of collaborative studies show that 10% outliers must be tolerated, but above 20% is excessive. Other new, important criteria for evaluation of methods at trace levels are % false positives, false negatives, and the magnitude of the blank.

Bacitracin Determination in Feeds: Evaluation of Methods

1981 ◽  
Vol 64 (4) ◽  
pp. 980-990
Author(s):  
Hussein S Ragheb
Keyword(s):  
Contributing Factors ◽  
Plate Method ◽  
Large Variability ◽  
Collaborative Studies ◽  
Different Types ◽  
Test Organisms ◽  
Sources Of Variation ◽  
Zinc Bacitracin ◽  
Many Sources ◽  
Evaluation Of Methods

Abstract Assay of bacitracin activity in feeds is subject to many sources of variation. Bacitracin standards are complex mixtures and may contain various amounts of less active forms of bacitracin. Test organisms may respond differently to these mixtures. Collaborative studies should involve the use of one standard, perhaps USP zinc bacitracin. The use of different types of bacitracin standards (regular or zinc) in a laboratory may contribute to variation in sample potency. The pyridine extraction method is subject to serious operational difficulties. Among the contributing factors are incomplete evaporation of pyridine (causing positive bias), allowing the temperature to increase too much during evaporation (causing negative bias), and the numerous manipulative steps in the technique (causing large variability). Because of these factors and the toxic properties of pyridine, the method finds little use. Methanol extraction offers a better substitute for determining zinc or methylene disalicylate bacitracin in premixes and complete feeds by the plate method.

scholarly journals The Horwitz Ratio (HorRat): A Useful Index of Method Performance with Respect to Precision

2006 ◽  
Vol 89 (4) ◽  
pp. 1095-1109 ◽  
Author(s):  
William Horwitz ◽  
Richard Albert
Keyword(s):  
Standard Deviation ◽  
Relative Standard Deviation ◽  
The European Union ◽  
Method Performance ◽  
Actual Performance ◽  
Methods Of Analysis ◽  
Limit Of Determination ◽  
Relative Standard ◽  
Method Optimization ◽  
Acceptability Criteria

Abstract The Horwitz ratio (HorRat) is a normalized performance parameter indicating the acceptability of methods of analysis with respect to among-laboratory precision (reproducibility). It is the ratio of the observed relative standard deviation among laboratories calculated from the actual performance data, RSDR (%), to the corresponding predicted relative standard deviation calculated from the Horwitz equation PRSDR (%) = 2C0.15, where C is the concentration found or added, expressed as a mass fraction. It is more or less independent of analyte, matrix, method, and time of publication (as a surrogate for the state of the art of analytical chemistry). It is now one of the acceptability criteria for many of the recently adopted chemical methods of analysis of AOAC INTERNATIONAL, the European Union, and other European organizations dealing with food analysis (e.g., European Committee for Standardization and Nordic Analytical Committee). The origin and applications of the formula are described. Consistent deviations from the ratio on the low side (values <0.5) may indicate unreported averaging or excellent training and experience; consistent deviations on the high side (values >2) may indicate inhomogeneity of the test samples, need for further method optimization or training, operating below the limit of determination, or an unsatisfactory method.

scholarly journals VI. The analysis of tidal observations

1928 ◽  
Vol 227 (647-658) ◽  
pp. 223-279 ◽  
Keyword(s):  
Shallow Water ◽  
Sea Level ◽  
Great Increase ◽  
A Priori ◽  
Relative Importance ◽  
Higher Harmonics ◽  
Methods Of Analysis ◽  
Tidal Oscillation

The Tidal Institute was founded in the year 1919 and researches on tidal problems have since been continuously carried out. It was early shown that certain methods of analysis were incomplete and that the harmonic constituents taken into account do not fully represent the tidal oscillation. Special attention was called to the great increase required in the number of higher harmonics (“overtides” and “compound tides”) needed to represent tidal oscillations in shallow water. An investigation on the variations of “constants” obtained from yearly batches of observations provided additional evidence concerning the defects of analysis, and it was shown that the constants for important constituents are considerably perturbed by contributions from other constituents. In the year 1921 was published a very thorough expansion of the tide-generating potential, and many new constituents were indicated as being worthy of attention. Meteorological perturbations of sea-level and tides have also been studied, but much yet remains to be done, and such investigations require exact and complete methods of analysis. A tidal record may be assumed to consist of three parts:— (1) Oscillations of known periods and whose relative importance is known; (2) Oscillations whose periods are not known a priori, though exact periods may be deduced from considerations of causes, if such become known; (3) Oscillations of no persistent periodicity or amplitude and which may be regarded as sources of “casual errors" such as may be attributable to meteorological variations.

Evaluation of methods of analysis for dietary fibre using real foods and model foods

2013 ◽  
Vol 140 (3) ◽  
pp. 568-573 ◽  
Author(s):  
Klaus Englyst ◽  
Michael Quigley ◽  
Hans Englyst ◽  
Bhavna Parmar ◽  
Andrew Damant ◽  
...  
Keyword(s):  
Dietary Fibre ◽  
Methods Of Analysis ◽  
Evaluation Of Methods

Determination for and from Analyst Performance Standards: Collaborative Studies

1982 ◽  
Vol 65 (6) ◽  
pp. 1333-1338
Author(s):  
Anthony J Malanoski
Keyword(s):  
Quality Assurance ◽  
Performance Standards ◽  
Performance Standard ◽  
Collaborative Studies ◽  
Regulatory Analysis

Abstract With the increased emphasis on quality assurance in all phases of regulatory analysis, it has become necessary to establish standards of performance for the analyst. The technique discussed is one that should be considered for use and the performance standard should become an integral part of the method.

A Review of Sampling Plans and Collaboratively Studied Methods of Analysis for Aflatoxins

1976 ◽  
Vol 59 (6) ◽  
pp. 1315-1343 ◽  
Author(s):  
Pieter L Schuller ◽  
William Horwitz ◽  
Leonard Stoloff
Keyword(s):  
Concentration Level ◽  
Screening Methods ◽  
Food Contaminants ◽  
Sampling Plans ◽  
Methods Of Analysis ◽  
Collaborative Studies ◽  
Coefficients Of Variation ◽  
Practical Operation ◽  
Confirmatory Tests ◽  
Order Of Magnitude

Abstract Aflatoxins are the only food contaminants being monitored routinely on an international scale with methods operating at the order of magnitude of 10 μg/kg. At this concentration level, methods of analysis which can achieve coefficients of variation of 30–40% with recoveries of 70% or greater in interlaboratory collaborative studies can be considered eligible for referee status. In most cases, sample reproducibility is the variable limiting the reliability of methods of analysis. The inherent uncertainty of the identity of chromatographically separated entities requires the application of confirmatory tests to verify that the characteristic measured results from the presence of aflatoxin. The methods are also inoperable without a verification of the identity, purity, and concentration of the reference standards used. Screening methods which reliably eliminate negative samples from further consideration are indispensible for the practical operation of monitoring programs.

Performance Characteristics of Methods of Analysis Used for Regulatory Purposes. I. Drug Dosage Forms. C. Automated Methods

1985 ◽  
Vol 68 (1) ◽  
pp. 112-121
Author(s):  
William Horwitz ◽  
Richard Albert
Keyword(s):  
Computer Program ◽  
Drug Dosage ◽  
Dosage Forms ◽  
Performance Characteristics ◽  
Methods Of Analysis ◽  
Collaborative Studies ◽  
Relative Standard ◽  
Standard Deviations ◽  
Best Fit ◽  
Automated Methods

Abstract For analysis of drug dosage forms, precision measures of AOAC approved automated methods, usually containing a spectrophotometric or fluorometric measurement step, were recalculated on a consistent statistical basis, using a computer program "FDACHEMIST." Ten collaborative studies of 14 compounds in 38 materials, consisting of various dosage forms, usually in 10 replications by an average of 7 laboratories, with a total of 2461 determinations, were reviewed. The average relative standard deviations within-laboratory (RSD0) and among-laboratories (RSDX) were 1.1 and 1.9%, respectively, and the ratio of RSD„/RSDX was 0.57, with an average outlier rate of 0.57% of the reported values. The line of best fit for RSDX plotted against — log concentration increases slightly with decreasing concentration, extending from an RSDX of about 1.6% at 100% concentration to an RSDX of 2.2% at 0.1% concentration, a change in RSDX of about 0.2% for a 10-fold decrease in concentration, independent of analyte and matrix.

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