Peaks assessment

As another example, PL from GaP N at 77 K is a convenient way to assess nitrogen concentrations in the range cm by observing the ratio of the peak... 

The so-called flow temperature cannot be considered to be either the processing temperature or the maximum service temperature. It is obtained using the highly arbitrary Rossi-Peakes flow test (BS 1524) and is the temperature at which the compound is forced down a capillary of fixed dimensions by a fixed load at a specified rate. It is thus of use only for comparison and for quality control purposes. Since the rates of shear and temperatures used in processing are vastly different from those used in this test, extreme caution should be taken when assessing the result of flow temperature tests. 

Analytical information taken from a chromatogram has almost exclusively involved either retention data (retention times, capacity factors, etc.) for peak identification or peak heights and peak areas for quantitative assessment. The width of the peak has been rarely used for analytical purposes, except occasionally to obtain approximate values for peak areas. Nevertheless, as seen from the Rate Theory, the peak width is inversely proportional to the solute diffusivity which, in turn, is a function of the solute molecular weight. It follows that for high molecular weight materials, particularly those that cannot be volatalized in the ionization source of a mass spectrometer, peak width measurement offers an approximate source of molecular weight data for very intractable solutes. 

To day peak widths are rarely used in chromatographic analysis except for the purpose of calculating peak areas. Peak widths, however, can provide a means of measuring the diffusivity of a solute which is a function of the molecular weight. Consequently, if a reliable relationship between diffusivity and molecular weight can be identified, then the molecular weight of the solute can be assessed. Peak widths of solutes eluted from an open tube can give very precise values of diffusivity. There are a number of equations that purport to relate diffusivity to... 

Finally, for situations in which it is not clear that exposure is and will continue to be below the limit values, a detailed survey with a measurement strategy is required. The methods used are based mostly on instruments for sampling the environment in order to obtain reliable measurements of workplace air concentrations. In general, the measurement strategy must consider the most efficient use of resources for the purpose of obtaining quantitative data on exposures by having a clear idea of what the data will be used for or whether it meets the specified need. For example, if the data pertain to peak exposures, these peaks have to be assessed according to the STEL requirements, if any. 

The flue gases analyzed will be one or more of carbon dioxide, carbon monoxide and oxygen. If carbon dioxide alone is measured, it is possible to draw erroneous conclusions, as the level will peak at stoichiometric and reduce in both the excess air and air deficiency regions. It is essential to measure another flue gas to obtain a reliable assessment of burner performance. 

The effectiveness of the various protective measures adopted should be assessed by making shut-down tests and comparing the results with tests made during peak-load periods (see Fig. 10.36). 

The number and amount of daily insulin doses, times of administration, and diet and exercise requirements require continual assessment. Dosage adjustments may be necessary when changing types of insulin, particularly when changing from the single-peak to the more pure Humulin insulins. 

The infra-red measurements were of two types, normal-film measurements with the sample sandwiched between KBr plates, and tilted-film experiments with the sample sandwiched between 45° prisms of KBr, in each case with layers of Nujol to provide optical matching. Whereas the 1616 cm 1 Raman line occurs in a region well clear of other lines so that it was satisfactory to measure peak intensities, the infra-red spectrum of PET shows many overlapping bands. Accurate assessment of absorption intensities therefore requires the computer separation of the spectrum into a set of overlapping peaks (shown to be Lorentzian in profile) and a linear background. The procedures adopted and the band assignments are discussed in detail by Hutchinson et al. 6). 

The above considerations apply to samples where all the components are of interest and all need to be separated and quantitatively assessed. In practice, for many samples, only specific components of the mixture are important and only those need to be separated from the matrix and be analyzed. The components of the matrix need not be resolved and they are of no interest. It follows, that under these circumstances the critical pair will be comprised of the component of interest that has the closest neighbor and the neighbor itself. Such a situation usually greatly simplifies the separation problem but it should be noted that the last peak must still be eluted before the next analysis can be carried out and so the analysis time may not be significantly reduced. 

This value appears to be in reasonable agreement with the peak capacity demonstrated by the chromatogram shown in figure 2. It is seen that the micro-reticulated gel gives separations as good as, if not better than, those obtained on silica gel and all the solutes are adequately separated for quantitative assessment. 

It would appear that a peak capacity close to 15 is probably realized and the separation is quite adequate for accurate quantitative assessment. 

Marks (1978) reviewed published reports of benzodia2epine dependence in the literature from 1961 to 1977 and estimated that benzodiazepine dependence occurred in one case per 50 million patient-months of use. His assessment of risk has been criticized, however, because published case reports tend to occur less frequently than the phenomenon they describe. Benzodiazepine dependence case reports peaked between 1969 and 1973, about 10 years after the introduction of the drugs (Petursson and Lader 1981a). 

The factors chosen for study were the concentration of the ion-pairing reagent, the solution pH ( quantitative factors) and the acid chosen for pH adjustment (formic, acetic, propionic and trifluoroacetic acids) ( quahtative factor). The effect of these factors was assessed by using responses that evaluated both the HPLC (the number of theoretical plates and the retention time) and MS performance (the total peak area and peak height) for each of the four analytes studied, i.e. 1-naphthyl phosphate (1), 1-naphthalenesulfonic acid (2), 2-naphthalenesulfonic acid (3) and (l-naphthoxy)acetic acid (4). 

Histamine is a critical mediator in anaphylactic reactions. It is a diamine produced by decarboxylation of the amino acid histidine in the Golgi apparatus of mast cells and basophils. Once secreted, it is rapidly metabolized by histamine methyltransferase [2]. Plasma histamine levels are elevated in anaphylaxis, reaching a concentration peak at 5 min and declining to baseline by 30-60 min [3]. Therefore, histamine samples for assessing an anaphylactic reaction should be obtained within 15 min of the onset of the reaction. Urinary metabolites of histamine may be found for up to 24 h. 

A DSC instrument was used to assess the possible consequences of a potential thermal runaway using post-nitration mixtures for evaluations (see Fig. 5.4-65). For the solvent process two minor peaks between 150 and 220 °C appeared, which correspond to thermal effects of -15 kJ/kg and -9 kJ/kg. In contrast, a large thermal effect (-730 kJ/kg) was observed for the reaction mixture from the water process, located between 90 and 160 °C. Based on these data the risk of a thermal runaway for both processes was assessed. 

Use of densitometric detection provides an insight into the concentration profiles of chromatographic bands, thus furnishing an indispensable prerequisite, needed for proper assessment of the retention mechanisms in the preparative adsorption TLC. Figure 2.4 shows three types of the band eoncentration profiles. The Gaussian peak (a) in this figure represents the linear isotherm of adsorption of a given species, peak... 

In some cases a principal components analysis of a spectroscopic- chromatographic data-set detects only one significant PC. This indicates that only one chemical species is present and that the chromatographic peak is pure. However, by the presence of noise and artifacts, such as a drifting baseline or a nonlinear response, conclusions on peak purity may be wrong. Because the peak purity assessment is the first step in the detection and identification of an impurity by factor analysis, we give some attention to this subject in this chapter. 

In pharmaceutical analysis the detection of impurities under a chromatographic peak is a major issue. An important step forward in the assessment of peak purity was the introduction of hyphenated techniques. When selecting a method to perform a purity check, one has the choice between a global method which considers a whole peak cluster (from the start to the end of the peak), and evolutionary methods, which consider a window of the peak cluster, which is... 

F.C. Sanchez, J. Toft, B. van den Bogaert and D.L. Massart, Orthogonal projection approach applied to peak purity assessment. Anal. Chem., 68 (1996) 79-85. 

F. Cuesta Sanchez, M.S. Khots, D.L. Massart and J.O. De Beer, Algorithm for the assessment of peak purity in liquid chromatography with photodiode-array detection. Anal. Chem., 285 (1994) 181-192,... 

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