William Horwitz

Heated fats. I. Studies of the effects of heating on the chemical nature of cottonseed oil

When cottonseed oil was heated at 225°C. in the presence of air for long periods of time, nonurea adduct-forming monomers and dimers were formed which were toxic to rats. Analyses showed that the toxic fractions contained moderate amounts of carbonyl and hydroxyl and that they contained unsaturation difficult to remove by hydrogenation. Cyclic structures appeared to be present in the dimer fraction. The production of nonurea adducting monomers and dimers is associated with polymerization and other reactions of linoleic acid.

Quality IssuesThe Concept of Uncertainty as Applied to ChemicalMeasurements

The calculation of uncertainty as recommended for physical measurements cannot be transferred readily to chemical measurements. Physical measurements and chemical measurements have entirely different error patterns that behave differently on replication. Correctable local bias predominates in physical systems and random error is minor; random error predominates in chemical systems and bias is difficult to identify and eradicate. Therefore bias must be monitored by randomizing in the interlaboratory environment, a concept not handled by the conventional ISO treatment of uncertainty.

Precision in analytical measurements: Expected values and consequences in geochemical analyses

Over the years the authors have developed an empirical formula for the relative standard deviation among laboratories (RSDR, %) as a function of concentration C, expressed as a decimal fraction: RSDR=2(1−0.5log C)≈2C(−0.1505). This formula predicts that starting with a concentration of 100% (pure materials; C=1.00), RSDR will be 2%, increasing by a factor of 2 for each decrease in C of 2 orders of magnitude. It has been a useful guide to acceptable precision in the fields of agricultural, pharmaceutical, and nutritional chemical analysis. It has now been found that this formula is also useful for interpreting the quality of reported analyses of various reference materials available to geochemists. If a ratio is calculated of the found RSDR value to the RSDR value calculated from the formula, an easily interpreted limiting parameter is generated. A ratio >2 provides a rational reference point for interpreting the uncertainty of the analytical portion of the total variability of geochemical concentration estimates. Such a high ratio indicates excessive among-laboratories precision, reflecting large systematic errors on the part of one or more laboratories. The formula quantitates the concept of the transformation of the individual systematic errors of the laboratories into the random error of the group.

The examination of fats and fatty acids for toxic substances.

The chick edema disease factor was found to be present in a number of distillates and residues that were obtained during the production of commercial fatty acids. The raw materials from which the toxic samples were produced included inedible animal tallows, acidulated vegetable oil foots, and oils recovered from tin plate manufacture. The chick edema factor was found to be present in several oleic acids and in a triolein. Twenty stearic acid samples which were examined were nontoxic.The nonurea adduct-forming fatty acids that were isolated from commercial oleic acids and various distillates and residues from the manufacture of commercial fatty acids were found to be toxic to weanling rats even after hydrogenation. Analysis of the nonurea-adducting monomers that were isolated from a fatty acid by-product distillate indicated the presence of cyclic structures.

Studies of the chick edema factor. II. Isolation of a toxic substance

A crystalline halogen containing material producing chick edema symptoms at 0.1 part per million in the diet has been isolated from a sample of triolein which was toxic to monkeys. This material is similar to that reported by Harmanet al. (4) but differs somewhat in ultraviolet speetral properties.

THE INEVITABILITY OF VARIABILITY IN PESTICIDE RESIDUE ANALYSIS

Abstract – All scientific measurements are inherently variable. In analytical chemistry, usually the lower the concentration sought, the greater the variability. There are four major sources of variability in the analytical sequence: sampling, method, analyst, and misinterpretation of the results of the analysis. In general, the major source of variability in pesticide residue analysis is from sampling, which may contribute a relative error, in terms of coefficient of variation, of 20% or more. Sampling error can be reduced only by collecting and analyzing more and larger samples. Many of the commonly used pesticide residue analytical methods used at tolerance levels are equivalent in reliability; thus a choice among them must be based upon such qualitative factors as applicability to a wide range of pesticides and commodities, speed and cost, and availability of reagents and equipment. The coefficient of variation due to methods (from interlaboratory collaborative study data) is about 15%, which when combined statistically with the sampling error, can produce a total “normal” error in pesticide residue analysis of about 25%. Control of the analyst variability, which is included in the sampling and method estimates, requires the use of a continuous program of quality assurance. Errors from the misinterpretation of the results of analysis are controllable by intelligent laboratory administration.