Interpretation of analytical results

Correct interpretation of the analytical results in the field of residue analysis is a matter of major importance. Truly positive, false-violative, false-positive, falsenegative, and truly negative are all types of test results that may be produced during food monitoring for drug residues. Truly positive is a positive test result 

A different method of interpretation is frequently observed between inspection services and analytical laboratories. This is because inspection services are interested mainly in a yes/no answer to questions, such as Has the animal been treated with anabolics or Does the food commodity contain residues above their MRL , in order to proceed to such action as rejection of the food commodity or removal of the test-positive animals from the farm. On the other hand, laboratories mainly use quality criteria to convert analytical results into yes/no answers. This conversion, however, is often obscured by inherent analytical difficulties including estimation of the impact of systematic and random errors and the way of sampling. 

Many screening tests, for example, are dichotomous yes/no tests. If this is the case and the test is designed to indicate the presence or absence of an analyte, the limit of detection must be known so that the lower concentration level of what will be detected is known. A negative result, however, does not prove that the analyte is absent from the sample, because its concentration might be below the limit of detection. 

If the purpose of the test is to establish whether tlie analyte exceeds or meets some established level, the limit of detection becomes of minor importance, whereas the performance of the test at the level of interest determines actually the reliability of the results. Ideally, screening tests should give no positive results when there are drug residues below the tolerance/MRL level. Equally desired is for the tests to give a positive result 100% of the time when the drug concentration 

Useful information about the characteristics of screening tests can be obtained by development of the characteristic operating curve (32). In this technique, a panel of test samples is produced by fortifying control matrix at several levels with the analyte of interest. The test is run on each sample witli 15-20 replicates at each concentration level. For rapid screening tests this should not represent an undue analytical burden. The results are plotted as the percentage of samples that are positive at each concentration level. 

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Thus, a good source of potential revenue for products and services exists in the multitude of smaller boiler-houses to be found operating around the globe. It is here that practical advice is most often needed concerning the suitability and correct application of chemical treatments, the regular interpretation of analytical results obtained, and the strategies to be employed to maximize efficiency and reduce costs. 

Cluster analysis is important in all situations where homogeneity of data on the one hand and latent structures on the other hand play a significant role in evaluation and interpretation of analytical results. This applies in particular for single objects with extreme properties like outliers, hot spots etc that can easily be recognized being singletons among clusters. 

Because sulfide is a very reactive component that is easily oxidized or reacts with heavy metals to produce precipitates, and because hydrogen sulfide is also easily emitted from the water phase, precautions must be taken under sampling, and the interpretation of analytical results must be careful. 

Water and hydrocarbons occurring together, in shallow aquifer systems, may be considered immiscible for flow calculation purposes however, each is somewhat soluble in the other. Since groundwater cleanup is the purpose behind restorations, it receives greater attention. Definition of water quality based on samples retrieved from monitoring wells relies heavily upon the concentration of individual chemical components found dissolved in those samples. An understanding of the processes that cause concentration gradients is important for the proper interpretation of analytical results. 

Mandel, J. Accuracy andPrecision Evaluation and Interpretation of Analytical Results , InTreatise on Analytical Chemistry, ed. by I.M Kolthoff and PJ. Elving, 2nd edn., Vol. 1. New York, Wiley and Sons, Inc., 1978. 

The primary source of variation in an assay system is usually the sample itself. This is the reason to have an assay in the first place. However, there may be variations in sample composition other than those toward which the assay is directed, and those variations may detract from the performance and reproducibility of the assay. Eliminating, or at least controlling, these influences can significantly improve resolution and sensitivity, as well as reproducibility. An important example is the ability of proteins to form stable complexes with a wide range of other solutes. Such complexes exhibit a range of aberrant retention behaviors that can confound interpretation of analytical results. 

Since the term total petroleum hydrocarbons (total petroleum hydrocarbons) includes any petroleum constituent that falls within the measurable amount of petroleum-based hydrocarbons in the enviromnent the information obtained for total petroleum hydrocarbons depends on the analytical method used. Therefore, the difficulty associated with measurement of the total petroleum hydrocarbons is that the scope of the methods varies greatly (Table 8.1). Some methods are nonspecific, whereas others provide results for hydrocarbons in a boiling-point range. Interpretation of analytical results requires an understanding of how the determination was made (Miller, 2000, and references cited therein Dean, 2003). 

Due either to the appeal of analytical applications or the complex mechanistic pathways, one can envisage why most articles on peroxyoxalate in the literature involve analytical subjects while only a fraction focus on the mechanistic aspects of this transformation. Even so, it is obvious that unequivocal knowledge about the mechanism involved in the generation of electronically excited states in this complex transformation is of fundamental importance, not only from the academic point of view but also, and far more, for the rational design of analytical application and the interpretation of analytical results . ... 

Another issue of relevant importance to the interpretation of analytical results is the analytical specificity of the test, particularly when in an immunobased assay. Specificity is exquisite in immunochemical assays but, at the same time, it can be exquisitely troublesome. For example, when an immunochemical assay for the penicilloyl group is used to monitor the pharmacokinetics of penicillin elimination from the serum of treated animals, the measured levels remain high for at least several weeks, although the antibacterial activity was all eliminated from bovine serum within 24 h after injection. This is because the immunochemical assay measured not only the free drug but also the penicilloyl groups covalently bound to proteins in serum. The half-life of these bound residues is roughly equal to the half-life of the proteins in the circulation. 

Interpretation of Analytical Results—Tritium. The locations of transects in the Sedan ejecta field at which samples were collected are shown in Figure 1. The distribution of tritium with depth at five sites on Sedan crater lip is shown on Figure 2. Except for the 9A area, the various sectors of the crater lip have very similar tritium depth profiles. The 9A area is a unique sector of the crater lip. A large mass of earth lifted by the detonation fell back to the crater in the 9A area earlier than the rest of the crater ejecta. Part of this material slumped into the crater, and the rest remained on the crater lip forming a prominence on the crater profile. Missile ejecta is thinner on this high point, and open-field radiation levels are lower. Tritium concentrations in the ejecta or slumped material at 9A are lower than in the rest of the crater lip mass. 

The hydrolysis of esters by esterases in the blood has been considered above, but even more importhydrogen sulphide, and hy(frogen cy[Pg.115]

The relationship between drug action and the processes of absorption, distribution, and elimination has been successfully applied in clinical pharmacology for the optimisation and individualisation of therapy. In clinical and forensic toxicology, similar relationships are applied in the interpretation of analytical results. 

An accurate interpretation of analytical results requires the use of a specific immunoassay, or identification and quantification with a chromatographic technique. 

In the EU, and also in other countries that have adopted regulations or guidelines based on the EU approach, the interpretation of analytical results and regulatory decisions is made on the basis of those results that depend on the method performance characteristics known as the detection capability and the decision limit. The detection capability (CCfi) is defined in point 1.12 of the Annex to Commission Decision 2002/657/EC. CCP as the smallest content of the analyte that may be detected, identified, and/or quantified in a sample with an error probability of p. The P error is the probability that the tested sample is truly non-compliant even though a compliant measurement has been obtained. For screening tests the P error (the false-compliant rate) should be <5%. 

Clinical chemistry a subject bridging natural science and medicine, and now established as an independent discipline. It is defined by M.CSanz and P.Lous (IFCC News Letter, N0.6, p.l) as follows Clinical chemistry encompasses the study of the chemical aspects of human life in health and illness and the application of chemical laboratory methods to diagnosis, control of treatment and prevention of disease. In praetiee, C.c. involves investigation of patient material with established analytical chemical or biochemical methods, for the purpose of diagnosis and therapy monitoring, as well as the development of new analytical methods and research into biochemical aspects of disease (pathobiochemistry). The clinical chemist usually operates from a centralized hospital laboratory, and must often also provide a medical interpretation of analytical results in consultation... 

Mandel, J. Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The Treatment of Outliers. In Treatise On Analytical Chemistry, 2nd ed., V0I.I, edited by I. M. Kolthoff and P. J. Elving. New York John Wiley and Sons, 1978. pp. 282-285. 

Based on the above evaluation, the following data quality objectives (DQOs) should facilitate interpretation of analytical results. 

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