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R Albert

Publications and source records attributed to R Albert.

79 records · Page 5Linked to original sources
PubMedDate not supplied

Performance characteristics of methods of analysis used for regulatory purposes. I. Drug dosage forms. B. Gas chromatographic methods.

Gas chromatographic methods for the analysis of drug dosage forms consist of a simple extraction, dilution with an internal standard solution, and injection, or, even simpler, dilution with the internal standard solution and injection. These methods were used in 7 collaborative studies of the determination of 12 pharmaceuticals, published in the Journal of the AOAC during 1973-1983. A total of 43 individual materials consisting of various dosage forms were each analyzed, usually in duplicate, by an average of 8 laboratories, with a total of 582 reported determinations. The average within-laboratory coefficient of variation (CVo) was 1.25% and the average among-laboratories coefficient of variation (CVx) was 2.41%, for a CVo/CVx ratio of 0.52, at an average outlier rate of 1.4% of the reported values. The line of best fit for CVx plotted against concentration increases with decreasing concentration, extending from a CVx of approximately 1.8% at 100% concentration to a CVx of approximately 3.2% at 1% concentration. The change in CVx for a 10-fold decrease in concentration is approximately 0.7% CVx, independent of analyte and matrix.

Chromatography, Gas↗
PubMedDate not supplied

Reliability of mycotoxin assays--an update.

The precision parameters of the method-performance (collaborative) studies for mycotoxins published in the literature through 1991 have been recalculated on a uniform basis by following the International Union of Pure and Applied Chemistry protocol. About 80% of the 793 accepted assays for mycotoxins, almost all of which have been conducted by thin-layer chromatography (TLC), liquid chromatography (LC), and enzyme-linked immunosorbent assays (ELISA), exhibit relative standard deviations among laboratories (RSDR) that are less than 2 times the values predicted from the Horwitz equation: RSDR, % = 2(1-0.5log10C) where C is the concentration expressed as a decimal fraction. The precision of TLC and LC methods is about the same, but that of ELISA is somewhat poorer. For those commodities for which sufficient data exist to provide a meaningful comparison, the methods applied to cottonseed products have the best precision and corn the worst, with peanuts intermediate. Overall, however, the primary factor affecting RSDR is concentration, more or less independent of analyte, method, matrix, and age of the study. If it is assumed that the test results are normally distributed and that an RSDR of 50% is the point where effective control of the results begins to be lost (a value equivalent to the production of 2% false-negative values), then relying on the Horwitz curve, the limit of quantitative measurement is the single digit, i.e., 5, micrograms/kg (10(-9); ppb) concentration for solid food commodities. Such a value must be considered as a limit applicable to a single analyte, aflatoxin B1, and not as a mean, and not applicable to the sum of the individual components, each of whose associated standard deviation would lie in the unacceptable region. Enforcement of a 5 micrograms aflatoxin B1/kg limit, under the assumptions made, requires that a responsible manufacturer and a prudent regulator operate at opposite extremes of tolerance limits: e.g., the producer at 2 micrograms/kg and the consumer at 10. A proposed Codex "maximum level" of 0.05 micrograms aflatoxin M1/kg milk cannot be supported by the available data applied in an interlaboratory enforcement environment. These conclusions are also supported by an examination of the reported data from the ongoing, large-scale proficiency studies routinely performed by the American Oil Chemists' Society and the International Agency for Research on Cancer.

Databases, Factual↗
PubMedDate not supplied

Reliability of the determinations of polychlorinated contaminants (biphenyls, dioxins, furans).

Precision performance parameters from results of 34 interlaboratory performance studies of polychlorinated aromatic ring compounds (biphenyls, dioxins, and furans) (PCCs) have been recalculated by using the international Union of Pure and Applied Chemistry-1987 harmonized protocol. Most studies of 1052 test samples, 56 analytes, 19 matrixes, and 2 types of detectors (electron capture and mass spectrometers) provide among-laboratories relative standard deviations (RSDRS), that are considerably better than those predicted from the Horwitz equation at fractional concentrations of 10(-5) down to 10(-15). The explanation suggested is that supplying common reference calibration solutions, as was done in many of these studies, does not reflect realistic operating conditions. Furthermore, the ability to repeat, discuss, and reassess aberrant reported values results in underestimating the true RSDR. The commonly reported problems of preparation of standard calibrating solutions, instability of the detection system, and failure to follow quality control instructions and good laboratory practices may be important sources of interlaboratory variability in PCC determinations.

Benzofurans↗
PubMedDate not supplied

Variability associated with analytical methods used to measure aflatoxin in agricultural commodities.

A total of 1019 analytical precision estimates obtained from method-performance (collaborative) studies for mycotoxins published through 1991 were sorted by type of variance measurement, type of analytical method, and type of agricultural commodity. Precision estimates for total aflatoxin were sorted into 2 precision measurements (among-laboratories and within-laboratory), 3 analytical methods (thin-layer chromatography [TLC], liquid chromatography [LC], and enzyme-linked immunosorbent assay [ELISA]), and 11 agricultural commodities. Sufficient data existed to study the analytical variability (precision) associated with 36 sorted combinations (of a possible 66). In all but one combination (within-laboratory, barley, and TLC), the variance (V) was a function of total aflatoxin concentration (C). A power function of the form V = aCb, where a and b are constants, describes the relationship between variance and aflatoxin concentration. The coefficients a and b were determined from regression analysis. When results were pooled across all agricultural commodities, LC had the lowest analytical variability while ELISA had the highest. For a given method, among-laboratories variability was approximately double the within-laboratory variability. These analytical variability estimates can be coupled with previously determined variability estimates of sampling and sample preparation to determine the performance associated with specific test procedures used to inspect agricultural commodities for aflatoxin.

Aflatoxins↗