Sample comparison

Where it is necessary to compare a sample S against a second standard B, other simple equations can be used (Figure 48.4). If one analyst has used standard A for sample comparison but wants to compare the sample against another standard B, it is only necessary to know the relative delta values of the two standards (S b) and to apply the equations shown in Figure 48.4. 

Areal Variation. One objective of the sampling comparison studies was to determine the variation in TCDD concentration over a small area to estimate the error associated with a grab sample concentration. Accordingly, a one-square-yard area was selected adjacent to a previously sprayed road. The center of the test area was about 6 feet from a sprayed road shoulder. This one-square-yard area was divided into nine one-square-foot areas. Using clean spoons and knives, a single scoop was collected from the center of each one-square-foot area down to a depth of 2 inches. The data are presented in Figure 1. 

In this instance, the standard addition of a surfactant to the real sample is an appropriate alternative, i.e. along with the analysis of the original sample, where a second sample is amended with a known concentration of the pure standard material, preferably at a similar level, and prepared for analysis alongside the authentic sample. Comparison of the analytical results provides information on both the extraction efficiencies and possible ion suppressions in the interface. 

However, the procedure for sample comparison by bioinformatics analysis differs. The main differences are that (1) the samples from each chnical subject are treated separately during the first two phases of analysis, and (2) the method to compare samples is different ... 

Oostdyk TS, Grob RL, Snyder JL, et al. 1994. Solid phase extraction of primary aromatic amines from aqueous samples comparison with liquid-liquid extraction techniques. J Environ Sci Health... 

The most frequently used tests in quality control in the flavour industry are paired-sample comparison tests, and triangle tests, which are often combined with the description of deviation from a reference item. For the selection and training of panellists, further test methods are used, for example ranking tests for colour, taste and odour, threshold detections (taste, off-flavour), colour blindness tests and odour identification tests [6]. 

Radiation damage Desolvation reactions Solid-gas reactions Thermal stability Oxidative stability Curie point determinations Purity determinations Sample comparison... 

One of the best checks of the counting method is sample comparison with other laboratories and reproducibility in counting standards and background. Table III shows such comparison. The counting efficiency for the tritium window used is 76%. All samples and background were measured at 400 cm. Hg pressure, using a 3 1 H2 CH4 counting gas mixture. 

Gas chromatography (GC) for amino acid analysis is the alternative to HPLC that has found the greatest acceptance. It requires the preseparation derivatization of the amino acids to render them volatile. For this purpose, amino acids are frequently converted into acylated esters. N-Trifluoroacetyl-n-butyl esters and /V-heptafluorobutyrylisobutyl esters are most commonly employed. There have been comparative studies (3,4) that document similar (if not equivalent) analytical results for GC and the classic ion-exchange chromatographic method applied to a variety of food samples. Comparison (5) of GC to the reversed-phase HPLC determination of amino acids (phenylisothiocyanate derivatized) also shows excellent agreement. 

Bromine-82 has a half-life of about 36 hours this is not sufficient for the isotope to be used conveniently in tracer work especially if labelled reagents have first to be prepared and purified. Low concentrations of bromine in small specimens of organic materials, such as polymers, can be determined by the method of neutron activation analysis (2). The various substances are prepared using ordinary bromine and then samples are bombarded with thermal neutrons so that the nuclear reaction 81Br(n, y)82Br occurs. Activity is therefore induced in the samples comparison with standards treated similarly permits determination of the bromine contents of the unknowns. For this technique to be applicable, it is necessary to have access to a powerful source of thermal neutrons. Neutron activation analysis can be used for the determination of very low concentrations of many elements and its general features have been fully discussed (3). 

Using a urine sample spiked with omeprazole and its metabolites as an example, Table 6.4, part (a) shows the control sample comparison results of the MDF data. The urine sample was obtained by a 1 50 dilution of the omeprazole HLM mixture with... 

TABLE 6.4. Results of Control Sample Comparison Between Urine Sample and Urine Sample Spiked with Omeprazole HLM Metabolites... 

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