Height, peak, definition

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 ... 

An alternative definition of peak distortion is peak fidelity or the ratio of the output peak height to the input peak height. Peak fidelity (f) can be approximated by ... 

When the analyst is not so fortunate and no comparable published method is available, a completely new method may need to be developed. In either instance, the process of method optimization is necessary. Note that the analyst determines the definition of the term optimization. To begin the optimization process, criteria [i.e., minimal (value must be >A ), maximal (value must be <7), or bounded (between X and T)] are established for any or all of the following peak shape, peak height, peak separation, run time, and overall analysis time (and therefore sample throughput). For the last listed criterion, remember that in gradient separations the re-equilibration time must be considered as part of the analysis time since a subsequent injection cannot occur until after the system has reached equilibrium with the initial solvent... 

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]. 

Resolution 10% valley definition, m/Am. Let two peaks of equal height in a mass spectrum at masses m and m/Am be separated by a valley that at its lowest point is just 10% of the height of either peak. For similar peaks at a mass exceeding m, let the height of the valley at its lowest point be more (by any amount) than 10% of either peak height. Then the resolution (10% valley definition) is m/Am. It is usually a function of m therefore, m/Am should be given for a number of values of m. 

FIG. 16-32 Exponentially modified Gaussian peak with Xq/Gq = 1.5. The graph also shows the definition of the peak asymmetry factor at 10 percent of peak height. 

Resolution (10% valley definition) Let two peaks of equal height in a mass spectrum at masses m and (m - Am) be separated by a valley that at its lowest point is 10% of the height of the peaks. 

The simplest definition of sensitivity is the signal-to-noise ratio. One criterion for judging the sensitivity of an NMR spectrometer or an NMR experiment is to measure the height of a peak under standard conditions and to compare it with the noise level in the same spectrum. Resolution is the extent to which the line shape deviates from an ideal Lorentzian line. Resolution is generally determined by measuring the width of a signal at half-height, in hertz. 

Pigur 1.6 The 10% peak height definition of the asymnetry factor. The asynetry factor is equal to the ratio A/B. 

The term resolution essentially describes the same the small difference being that its definition is based on the resulting signals. The resolution R is defined as the ratio of the mass of interest, m, to the difference in mass. Am, as defined by the width of a peak at a specific fraction of the peak height. [1]... 

Two neighboring peaks are assumed to be sufficiently separated when the valley separating their maxima has decreased to 10 % of their intensity. Hence, this is known as 10 % valley definition of resolution, Rio%- The 10 % valley conditions are fulfilled if the peak width at 5 % relative height equals the mass difference of the corresponding ions, because then the 5 % contribution of each peak to the same point of the m/z axis adds up to 10 % (Fig. 3.16). 

Fig. 3.16. Illustration of the 10 % valley and of the Ml width at half maximum (FWHM) definitions of resolution. Peak heights are not to scale.

In qualitative analysis, the unknown spectrum is compared with a known spectrum in a library. Each gas is definitively determined by its spectrum. The comparison with library data is a simple pattern recognition process. Depending on the availability, the comparison may be made using any of a number ancillary aids. So, for example, in accordance with the position, size and sequence of the five or ten highest peaks. Naturally, comparison is possible only after the spectrum has been standardized, by setting the height of the highest line equal to 100 or 1000 (see Table 4.5 as an example). 

Peak Width. Peak width depends on the mass resolution. A resolution of 1 mass unit is sufficient to distinguish ions in most qualitative/quantitative small molecule applications. A typical definition of unit resolution is when the peak width at half-height is about 0.6 to 0.8 mass unit. The profile scan of ions on a typical benchtop LC-MS has a bandwidth of about 1 mass unit (Figure 13.1). 

This is an even function that has a maximum of 0.399 for x = 0. The function also has two inflection points x — 1 with a corresponding ordinate value of 0.242, which represents 60.6% of the maximum value of the function. The width of the function at the inflection points is approximately 2er (er = 1). In modern chromatography, Wj/2 represents the width of the peak at the half-height (wi/2 = 2.35er) and a2 the variance of the peak. The width of the peak at the base, w, is measured at 13.5% of the height. At this position, if the curve is Gaussian, w = 4a by definition. 

Resolution measures the ability to separate two closely spaced peaks. The greater the resolution, the smaller is the difference (AX.) between two wavelengths that can be distinguished from each other. The precise definition (which is beyond the scope of this discussion) means that the valley between the two peaks is about three-fourths of the height of the peaks when they are just barely resolved. The resolution of a grating is given by... 

In rubber testing, the surface finish of metals is of importance, for example on mould surfaces and compression set plates. There are a number of standards in the ISO Geometric Product Specification series but the most relevant is ISO 428729 which covers terms, definitions and surface texture parameters relating to the profile method of measuring surface finish. There are apparently over 1000 different parameters to characterize surface finish30 but only a few are generally encountered. The most commonly found is Ra (previously called CLA) which is the mean deviation of the surface profile above and below the center line, followed by Rz, a measure of the peak to valley height. For example, the arithmetic mean deviation (Ra) of the compression plates for compression set tests must be better than 0.2 m. 

FWHM Full width at half-maximum. Mass resolution is often difficult to determine at or near the base of a peak due to baseline noise and peak overlap. It is more common to measure the width of the peak halfway to the peak maximum, where a clean measurement is possible. The most common alternative to FWHM was the 10% valley definition, in which the peak width at 10% of height was examined. This latter definition is common in the literature, especially for magnetic sector mass spectrometers, but is currently used much less frequently than FWHM. The choice of FWHM or 10% valley has an impact on the calculation of resolving power. 

Figure 8. C q isoprenoid tiophenes as indicators of palaeosalinity structures, definition of the isoprenoid thiophene ratio (ITR) and some typical distributions (based on peak heights in m/z 308 mass chromatograms) in sediments and petroleums. Description of the samples is given elsewhere (16).

Three definitions of peak-valley ratios are illustrated in figure 4.2. All of them express the extent of separation as some measure of the depth of the valley between two peaks divided by some measure of the peak height. The first criterion (P) measures the depth of the valley relative to the interpolated peak height as shown in figure 4.2.a. The corresponding expression is ... 

For Gaussian peaks of equal height the value of the peak-valley ratio (then the same according to all three definitions) can readily be expressed in terms of Rs. This can be done by relating the parameters f, g and v (see figure 4.2) to the parameters that describe a Gaussian peak (trand h). For the first of a pair of Gaussian peaks (peak A) we can write... 

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