Sampling quality control issues

As an important parameter for surface quality, roughness is discussed in almost every article on cleaning and etching. However, in most cases it is treated as a quality control issue. As a result, the data on surface roughness reported in the literature for silicon surfaces are obtained under diverse conditions and are generally not comparable due to the fact that data are often reported without clear definition of the methods of determination and the area of sampling. 

There are samples or crude extracts containing the analyte of interest but whose concentration has not been accurately established. For marine biotoxins, such materials may be frozen homogenates of naturally contaminated seafood, crude or partially purified extracts of such seafood, or of harmful algae. Digestive glands of contaminated shellfish are a source of concentrated toxins and their metabolites. Such materials cannot be used to calibrate methods of analysis but can serve very useful functions in method validation and quality control, especially when they contain rare toxins not readily available elsewhere (i) Retention times and spectral properties can be established on a routine basis for LC-UV, LC-FL, or LC-MS methods (ii) Partially purified extracts can be used for fortification experiments during method validation and thus establish recovery and precision data (iii) If concentrations of toxins can be established by reference to CRMs, then the materials can be used as in-house or interlaboratory reference materials for quality control. Issues such as toxin stability and homogeneity then become more important. ... 

As speciation methodology has developed over the past 40 years, it has become clear that quality control issues such as sampling, sample preparation, and calibration are critical to obtain meaningful results regarding environmental samples. Many early studies were flawed by errors in these methodologies that produced inaccurate data. Here some of the major issues in sample handing and treatment are discussed. 

Several method performance indicators are tracked, monitored, and recorded, including the date of analysis, identification of equipment, identification of the analyst, number and type of samples analyzed, the system precision, the critical resolution or tailing factor, the recovery at the reporting threshold level, the recovery of a second reference weighing, the recovery for the control references (repeated reference injections for evaluation of system drift), the separation quality, blank issues, out of spec issues, carry over issues, and other nonconformances. The quantitative indicators are additionally visualized by plotting on control charts (Figure 23). 

Fig. 13.3 The quality of commercial compounds. In general, quality control by the compound brokers has improved significantly over the past decade. Sample identity and purity is now less of an issue, but still bears watching. The graph shown above summarizes the historical data gathered over a period oftime over which vendor performance was monitored. In recent years, more than 90% of preferred vendors have provided accurate and highly pure samples.

A number of issues were addressed in the general sessions that were common to all six of the proposed protocols. These included definitions of each of the sample media, limitations of the protocols, guidelines for the fractionation of samples found to be toxic in the Salmonella assay, and analytical quality control considerations. 

The objective of this book is to provide an overview of a variety of sample preparation techniques and to bring the diverse methods under a common banner. Knowing fully well that it is impossible to cover all aspects in a single text, this book attempts to cover some of the more important and widely used techniques. The first chapter outlines the fundamental issues relating to sample preparation and the associated quality control. The... 

It is critical to minimize the component manufacturing variations in order to build a reliable PEM fuel cell system. We demonstrated that even within the same commercial MEA sample, the thicknesses of the electrode layers and membrane could vary greatly from one region to another. With the current scale of PEM fuel cell production, commercial-grade fuel cell components often display substantial deviations from their product specifications. Such component manufacturing issues hamper the overall effort toward improving commercial PEM fuel cell system reliability. Without adequate MEA quality control, it is difficnlt to interpret antopsy resnlts and to link apparent membrane/electrode problems of nsed MEAs to a particnlar failnre mechanism. Part of the problem is the lack of a nondestrnctive in-line MEA qnality control method to ensnre batch-to-batch consistency. 

Sample requirement and specimen collection Preparation of analytical device— machine and/or consumables Performance of test Performance of quality control Documentation of test result and quality control result Reporting of test result to appropriate personnel Interpretation of result and sources of advice Health and safety issues e.g disposal of sample and test device, cleaning of machine and test area)... 

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