Counting methods contamination

Other analytical methods of quantifying the degree of contamination are based on counting the contaminants in the melt, in cast films or in solution of the... 

The most important issue in food quality analysis is food safety. Therefore, the development of rapid methods for the identification and quantification of bacterial contamination in foods is of utmost importance. Thus, a CE method with UV detection was proposed for the identification and quantification of bacterial contamination in food samples. The proposed method allowed for the effective separation of eight different types of bacteria in only 25 min. Electrophoretic resolution was improved by using cations in phosphate buffer (pH 7.0) that interacted with the bacterial surfaces changing its electrical properties and electrophoretic mobility. The validity of the method was established by comparison with the standard plate counting method, where bacterial cells were separated as... 

Picer et al. [49] described a method for measuring the radioactivity of labelled DDT contaminated sediments in relatively large volumes of water, using a liquid scintillation spectrometer. Various marine sediments, limestone and quartz in sea water were investigated. External standard ratios and counting efficiencies of the systems investigated were obtained, as was the relation of efficiency factor to external standard ratios for each system studied. 

Modern polymer technology is founded on catalysis, and catalytic methods are extensively used in the production of plastics. Catalysts, since they only catalyse reactions, do not count as polymer constituents but may be present as impurities in the polymeric material. Table 22 lists the usual catalysts used for the polymerization of the polymers mentioned above, which can be found as contaminants in formulations stored in plastic containers. 

A comparison of 1966-1981 fetal mortality rates for Michigan counties with a high percentage of quarantined farms (6.8-20.4%) w ith those of Michigan counties with no quarantined farms did not conclusively establish differences in rates or trends after the 1973 contamination episode (Humble and Speizer 1984). This study is difficult to interpret because the exposure status method was imprecise, the collected data included only spontaneous abortions occurring after 20 weeks of gestation (early trimester abortions were not counted), and the two populations displayed different pre-1973 trends for fetal mortality rates. 

Neutron activation has been used to determine the concentrations of trace elements in polyethylene. A procedure has been optimized which involves three irradiations with a SICWFOKE nuclear reactor and four counts with a gamma-ray spectrometer. Phosphorus is determined with beta-ray spectrometry. The detection limits, most of which are below one ppm, have been determined for 42 elements. The merits of the method are discussed in terms of sensitivity, accuracy, ease of use, interferences, and freedom from contamination. 

For those who have access to the necessary equipment, neutron activation analysis is a convenient method for the determination of the average concentrations of trace elements in polymers. The fact that very little sample preparation is necessary contributes to its high reliability and reduces the risk of contamination to a minimum. Accuracies of 5% or better can be achieved when the concentrations are well above the detection limits. Analysis for about a dozen elements can be completed in less than an hour. To detect the elements with long-lived radioactive isotopes, about ten days are needed. If a number of samples are to be analysed, they can be irradiated simultaneously and counted sequentially using an automatic sample changer. 

Although our initial concerns about possible interferences due to chemiluminescence and quenching effects have been somewhat mitigated by recent disclosures of Blank and Kidwell s tritium counting procedures, an entirely different problem exists concerning their isotopic method, one that in our opinion casts serious doubt upon the general suitability of their approach for doing hair contamination/decontamination studies. 

January 13 to February 14, 1999 March 17, 1997 Failure to investigate contamination Failure to maintain equipment Failure to maintain documents Failure to maintain an accurate label count Inadequate methods to describe procedures fully Failure to record all data collected... 

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