Peak ratio

TABLE 21.4 Peak Resolution Parameters Valley-to-Peak Ratios, v, and Peak Separation Parameters, P, for Batch 52 Gel... 

The final step in the process of standardizing our columns was to try and maintain the high quality of columns from batch to batch of gel from the manufacturer. This was done by following the basic procedures outlined earlier for the initial column evaluation with two exceptions. First, we did not continue to use the valley-to-peak ratios or the peak separation parameters. We decided that the D20 values told us enough information. The second modification that we made was to address the issue of discontinuities in the gel pore sizes (18,19). To do this, we selected six different polyethylenes made via five different production processes. These samples are run every time we do an evaluation to look for breaks or discontinuities that might indicate the presence of a gel mismatch. Because the resins were made by several different processes, the presence of a discontinuity in several of these samples would be a strong indication of a problem. Table 21.5 shows the results for several column evaluations that have been performed on different batches of gel over a 10-year period. Table 21.5 shows how the columns made by Polymer Laboratories have improved continuously over this time period. Figure 21.2 shows an example of a discontinuity that was identified in one particular evaluation. These were not accepted and the manufacturer quickly fixed the problem. 

Additional information on the rates of these (and other) coupled chemical reactions can be achieved by changing the scan rate (i.e., adjusting the experimental time scale). In particular, the scan rate controls the tune spent between the switching potential and the peak potential (during which the chemical reaction occurs). Hence, as illustrated in Figure 2-6, i is the ratio of the rate constant (of the chemical step) to die scan rate, which controls the peak ratio. Most useful information is obtained when the reaction time lies within the experimental tune scale. For scan rates between 0.02 and 200 V s-1 (common with conventional electrodes), the accessible... 

An example of such a catalytic EC process is the oxidation of dopamine in the presence of ascorbic acid (4). The dopamine quinone formed in the redox step is reduced back to dopamine by the ascorbate ion. The peak ratio for such a catalytic reaction is always unity. 

This an excellent example of the value of the diode array detector. If the chromatogram shown in figure 3 was monitored at two different wavelengths, then a peak ratio curve would immediately disclose the presence of the second peak (see page 175) and it would no longer be necessary to resort to changes in mobile phase composition to establish the presence of the impurity. 

The relative product yields depend on the CHa to Cl ratio on the surface. In the studies reported here, this ratio has been adjusted to 1 1 (consistent with the CHa Cl stoichiometry in CHaCl) on the basis of a Cl(181 eV) C(272 eV) Auger peak ratio of 6.5 which is the same as that measured for physisorbed monolayers of dimethyldichlorosilane. Monolayer coverages of CHa + Cl having 1 1 stoichiometry were obtained by a 20 L exposure from the methyl radical source (approximately sahiration coverage) followed by a 9.5 L dose of CI2. 

In all of the studies described above, the CuaSi samples were prepared by ion bombardment at 330 K followed by cooling of the surface to 180 K before adsorbing the methyl radicals and chlorine. AES studies as well as ion scattering results in the literature [7, 15] show that this procedure produces a surface that is enriched in silicon compared with the Cu3Si bulk stoicWometry. We have found that surfaces with less Si enrichment (possibly even copper enriched relative to the bulk stoichiometry) can be prepared by ion bombardment at temperatures below 300 K. Specifically, Cu(60 eV)/Si(92 eV) Auger peak ratios of 1.2 - 1.7 compared with a ratio of 0.5 at 400 K can be obteiined by sputtering at 180 K. 

The 1H and 13C NMR spectra of the three fluorides are given in Figures 4 and 5 respectively. The peak assignments for various groups in each compound are given in Tables II and III, while calculated and observed peak ratio values are given in Tables IV and V. 

Variations on the spectral peaks from different species of the same genus were also observed. Three species of Pseudomonas produced the spectra shown in Figure 14.2. These spectra are clearly unique and were used to correctly identify unknown samples. Because of peak ratio reproducibility issues in bacterial protein profiles obtained by MALDI MS,11 a fingerprint approach that had been used for other mass spectrometry approaches has not been used. The profile reproducibility problem was first recognized by Reilly et al.12,13 and later researched by others in the field.14,15 As a later alternative, a direct comparison of the mass-to-charge ratio (m/z) of the unknown mass spectral peaks with a database of known protein masses has been used to identify unknown samples.14... 

Rule 3). The size of the M + 2 peak indicates the absence of sulphur and halogens and the empirical formula C9H10O2 given in Beynon s tables best fits the isotope peak ratios. The number of saturated sites is 9 + 1 - 5 = 5, i.e. one ring and four double bonds. 

The excellent, high-resolution y- and X-ray spectra which can be obtained from semiconductor detectors make the detectors very important in modern instruments. A typical spectrum is shown in Figure 10.11(b) which may be compared with the much broader peaks from a scintillation detector (Figure 10.11(a)). The spectra are not immune from the problem of Compton scattering (p. 461) but a good quality modem detector will have a photopeak to Compton peak ratio of 50 1 or better. Computer-aided spectrum analysis also serves to reduce the interference from the Compton effect. 

Shown in Figure 6-A are EELS spectra of the entire series of pyridine carboxylic acids and diacids adsorbed at Pt(lll) from acidic solutions at negative electrode potential. Under these conditions all of the meta and para pyridine carboxylic acids and diacids exhibit prominent 0-H vibrations (OH/CH peak ratio near unity). In contrast, at positive potentials only the para-carboxylic acids display pronounced 0-H vibrations, Figure 6-B. All of the 0-H vibrations are absent under alkaline conditions, Figure 6-C. This situation is illustrated by the reactions of adsorbed 3,4-pyridine dicarboxylic acid ... 

Interpretation/report The GC retention time of a naphthalene standard and the mass spectrum of this peak confirm its presence. Because of the complexity of the chromatograms of the petroleum products and the pesticide sample, you find it impossible to examine the chromatogram of each. However, a comparison of the GC fingerprints (i.e., the matching of chromatographic peaks and comparison of peak ratios) clearly shows that the sample consists of naphthalene dissolved in kerosene. 

Karen Skinner determined the yeast glycogen content for beer production using MIR.20 While not widely accepted as an important parameter for beer production, glycogen content is most often determined. Because all process applications, even raw material measurements, speed up the production of the final product, this application qualifies as a process measurement. Peak ratios were used to quantify the glycogen content of samples made into potassium... 

The exciplex intensity showed quite different behavior as the setting proceeded. A comparison of the (monomer peak/monomer peak) ratio to the (exciplex peak/monomer peak) ratio was quite illuminating. We considered the initial maximum wavelength of the exciplex emission at 540 nm, and compared its intensity to the monomer intensity at 405 nm as the dissolution/ polymerization proceeded. A substantial decrease in exciplex intensity, compared to monomer intensity, was observed over the first 40 min of the cure. The ratio then leveled off, indicating that the local viscosity had reached a maximum after 40 min and that the dissolution/polymerization was considered to have reached completion at the ambient temperature of the laboratory. Since the working time for the cement was considerably less than the 40-min time period over which the exciplex/monomer intensity ratio was steadily decreasing, the intensity ratios served as in situ monitors of the cure. 

G2 and G3 are in an equilibrium state, since thermal treatment (120°C, 30 min) did not result in any modification of the relative peak ratios (chromatograms not shown). 

The major assumption in the fitting procedure was that the basis spectra (i.e., spectra for individual molecular components) are independent of flow tube temperature. This approximation was tested by running mass spectra of stable molecules such as toluene and st3Tene over the full range of flow tube temperatures, and the peak ratios in these spectra change by no more than l%-2%. Based on this result and the signal-noise ratio in the experiments, the fitting uncertainty was estimated at about 5%. 

Scheme 4 Scrambling of He-containing Cgo between Cgo and C120 under HSVM integrated peak ratio of He C6o and He Ci2o=7 3 by He NMR...

FIGURE 17.8 Peak ratio of rac-r/j-verapamil at a constant concentration (60ng/mL) as a fnnction... 

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