Peaks definition

Figure 6. A porHon of the database for vinylidene chloride isobutylene copolymer. Boxed entries are required input from the user. The peak definition for the first peak is shown.

Digital resolution The distance, in hertz, between successive data points determines the extent of peak definition by the data points. 

Partition coefficient, 9, 10 Partition ratio, 11 time optimization of, 57-58 Peak, definition of, 69 Peak capacity, 18, 19 Pellicular supports, 157 Permeability, 63-64 Phase selection diagrams, 218-219 Phase volume ratio, 11 Pinkerton (ISRP) columns, 225-226 Plate height, 17 Plate number, 14-16 Plate theory, 3, 28 Polarity index, 210, 211 Pore size of LC supports, 157 Porosity, 27 Precision, 99-100 Preparative scale ... 

By selecting frequencies of well-resolved peaks definitely assignable to the separate polymers (e.g., the 1657 cm band of uridine and the 1625 cm band of adenosine) these workers were able to demonstrate through the coincidence of the melting curves (Fig. 12.14) that the spectral changes specifically reflect an interaction between poly A and poly U and not, for example, independent structural changes in the separate polymers. 

L4.3.1 Chromatography Although the final detection is based on the mjz ratios, optimized chromatographic separation is crucial to obtain high-quality data since it is directly related to peak definition and subsequent data... 

Figure 8.12 illustrates the cyclic voltammetry and the transmittance of the window. The feasibility of the electrochromic system is confirmed by the excellent peak definition and low peak separation, as well as by the large transmittance variation upon cycling. One problem associated with the use of lithiated nickel oxide counter-electrodes remains the low diffusion of the Li" ions (calculated to be of the order of 10 cm s [24]), which may lead to long response times. However, this problem may be alleviated by optimizing the morphology of the electrode. 

In situ thermal transitions were also described by Taylor et al., who examined the isothermal dehydration behavior of trehalose dihydrate [29]. For small particle size fractions (<45 fjLm), heating at 80°C caused loss of peak definition until, at 210 min, amorphous material was present. In contrast, a larger particle size fraction (>425 fim) converted to the crystalline anhydrous form of the material. The kinetics of this conversion was probed from the Raman data using peak height ratios with time a two-stage rearrangement was indicated. A broader consideration of pharmaceutical hydrates, including their characterization by several techniques (NMR, Raman spectroscopy, and isothermal calorimetry) can be found in the literature [30] as can a review of the use of spectroscopic techniques for the characterization of polymorphs and hydrates [31]. 

In order to provide a representative and reproducible GC peak integration, the total MID cycle time on the chromatographic time scale should allow for the acquisition of 8-10 data points over a chromatographic peak (Figure 2.232). The cycle time has a direct influence on the available measurement time for each ion (dwell time). If the MID cycle time is too short, the sensitivity of the instrument is compromized too high values lead to a poor GC peak definition. 

With regard to existing analysis procedures, for target compound quantitation, high speed and flexibUity in the choice of precursor ions is necessary. For the analysis with internal standards (e.g., deuterated standards) and multi-component methods, the fast switch between multiple precursor ions is necessary to achieve a sufficiently high data rate for a reliable peak definition of all coeluting compounds, in particular for SRM quantitations. 

Figure7.14 Peak definition for different dwell time settings.(Reproduced by permission of the Royal Society of Chemistry.)...

As a rule, a GC peak should he defined by at least 15 points to offer good peak definition. Thus, in a GC peak of 3 s base width, each isotope should be measured in an interval of a maximum of 200 ms. Provided that three different isotopes are measured, a maximum dwell time of 66 ms per isotope should be applied. Consequently, for narrower peaks and/or more isotopes to be measured, dwell times must be reduced. Thus, in GC-ICP-MS, GC parameter optimisation should not aim for extremely narrow peaks. 

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