Reliability of identification

When the analytical laboratory is not responsible for sampling, the quality management system often does not even take these weak links in the analytical process into account. Furthermore, if sample preparation (extraction, cleanup, etc.) has not been carried out carefully, even the most advanced, quality-controlled analytical instruments and sophisticated computer techniques cannot prevent the results of the analysis from being called into question. Finally, unless the interpretation and evaluation of results are underpinned by solid statistical data, the significance of these results is unclear, which in turn greatly undermines their merit. We therefore believe that quality control and quality assurance should involve all the steps of chemical analysis as an integral process, of which the validation of the analytical methods is merely one step, albeit an important one. In laboratory practice, quality criteria should address the rationality of the sampling plan, validation of methods, instruments and laboratory procedures, the reliability of identifications, the accuracy and precision of measured concentrations, and the comparability of laboratory results with relevant information produced earlier or elsewhere. 

When identification is carried out by Py-GC the most important factors are the presentation of the experimental results and selection of the parameters used to compare different samples. In order to simplify the evaluation of the results and increase the reliability of identification, it is advisable to limit the number of characteristics used for identification. For Instance, in the above example of identification of paints produced at two factories, the characteristic value was the height ratio of only two peaks (acrolein and methacrolein) in the pyrolysis products. 

Sample components on the plate are identified by comparing the obtained colors with a specific standard. To increase the reliability of identification, several reactants can be used, which yield products of various colors characteristic of a given CWA. 

Identification of known compounds is less demanding than the structure determination of an unknown. It is also based on molecular characterization, e.g., spectral features (as discussed earlier), chromatographic retention time, and comparison with standards of known structure. The reliability of identification is a critical issue. Several decades ago the chromatographic retention time itself was often accepted as proof of identification of a compound. It is no longer the case, as various examples of false-positive and false-negative results were found. The current trend is to require more and more detailed and specific information before identification of a compound is accepted. For example, besides retention time, mass spectra and/or accurate mass measurements are also needed. 

Examination of skeletons of modem penguin species held in any collection will reveal - even to a non-expert - a high degree of intraspecilic variation in postcranial bones (Simpson, 1946 Zusi, 1975). Character polymorphism is also common (Walsh and Suarez, 2006), making character-based taxonomic identification of isolated material (e.g. from abandoned rookeries Emslie and Woehler, 2005) problematic. This observation does not bode well for the reliability of identifications of fossil material, which on the whole has been (and continues to be) diagnosed on the basis of aspects of... 

Some of the features of GO (EPRI NP-3123) are given in Table 3.4.6-2. A GO model is networks GO operators to represent a system. It can be constructed from engineering drawings by replacing system elements (valves, switches, etc.) with one or more GO symbols. The GO computer code quantifies the GO model for system reliability, availability, identification of system fault sequences, and relative importance in rank of the constituent elements. 

Segregation may also be necessary in the packaging of products not only to prevent visible damage but electrical damage, as with electrostatic-sensitive devices. Segregation may be the only way of providing adequate product identity, as is the case with fasteners. While a well-equipped laboratory can determine the difference between products and materials the consumer needs a simple practical method of identification and labeled packets are often a reliable and economic alternative. 

The limit of detection is the smallest amount of an analyte that is required for reliable determination, identification or quantitation. More mathematically, it may be defined as that amount of analyte which produces a signal greater than the standard deviation of the background noise by a defined factor. Strictly for quantitative purposes, this should be referred to as the limit of determination . The factor used depends upon the task being carried out and for quantitative purposes a higher value is used than for identification. Typical values are 3 for identification and 5 or 10 for quantitation. 

As is well known the difficulty of analysis of a sample increases as its complexity increases. Analysis usually commences with a rather nonspecific clean-up step and requires that the separation step that follows be highly selective and depends on a detection step that is as specific as possible. As the selectivity of detection increases there is also an increase in the reliability of the identification and it is possible to reduce the demands made on the selectivity of the preceding separation method. This is the case for radiometric and enzymatic methods and also explains the popularity of fluorescence measurements. The latter obtain their selectivity from the freedom to choose excitation and measurement wavelengths. 

Containers and closures shall be tested for conformance with all appropriate written procedures. In lieu of such testing by the manufacturer, a certificate of testing may be accepted from the supplier, provided that at least a visual identification is conducted on such containers/closures by the manufacturer and provided that the manufacturer establishes the reliability of the supplier s test results through appropriate validation of the supplier s test results at appropriate intervals. 

The reliability of the identification can be improved if that protein can be cleaved to two or more polypeptides.77 79... 

Rhodes A, Jasani B, Balaton AJ, et al. Study of interlaboratory reliability and reproducibility of estrogen and progesterone receptor assays in Europe documentation of poor reliability and identification of insufficient microwave antigen retrieval time as a major contributory element of unreliable assays. Am. J. Clin. Pathol. 2001 115 44-58. 

The habit of pharmaceutical compounds has been used for purposes of identification, although the method can only be reliably used when the crystallization solvent used to generate the test crystals is carefully controlled. Since the faces of a crystal must reflect the internal structure of the solid, the angles between any two faces of a crystal will remain the same even if the crystal growth is accelerated or retarded in one direction or another. Toxicologists have made extensive use of microscopy following multiple recrystallization, and they have developed useful methods for compound identification [5]. 

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

For identification purposes, the higher the number of peptides and the longer the sequence of known fragments, the higher the reliability of protein identification. 

There are some inherent methods to increase the reliability of a MALDI mass mapping identification. If trypsin was used as an enzyme for digestion, the sequences. . . RR.. . , . . . RK.. . , . . . KR.. . , or. . . KK.. . often produce ragged ends owing to partial cleavage behind the first lysine or arginine. This can be used to increase the confidence of an identification (Jensen et al., 1996). 

HSPD - 12 Policy for a Common Identification Standard for Federal Employees and Contractors. Establishes a mandatory, government-wide standard for secure and reliable forms of identification issued by the federal government to its employees and contractors (including contractor employees). 

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