Determination of Peak Areas

According to Kucera [13] and Grushka [14], the area of peak i corresponds to the zero moment, Wo of the distribution function describing the peak. 

The first moment normalized to Wq corresponds to the retention time  

The second moment, W2 of a peak i with the distribution function y,(t) is related to the retention time, Wi, and as the central moment m i represents the 

The interpretation of the retention time as the first moment, mu is more comprehensive than the use of the peak time (fmax) ffi indicates the position of the peak center on the timescale. In the case of unsymmetric peaks, that position may deviate significantly from the position of the peak maximum. The thermodynamically correct retention time is actually derived from the position of the Gaussian component in a deconvoluted total peak profile. According to the more recent opinion of Jonsson [15], the correct retention time equals the median value of the peak. 

There are several approaches (Foley and Dorsey [16] Yau [17] Grushka [14]) to determining moments using the exponential peak function (retrievable from chromatography data systems) that yield slightly different results. 

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GC-MS runs were stored as files by the data system on discs FORTRAN routines were written to compare selected parameters in file sets and to reduce the data to summary tables for hard copy output. These routines facilitated the determination of peak areas of components in extracted ion current profiles (EICP) for both total and selected ion chromatograms, calculated the removal of components of interest (e.g., those containing halogen isotopes) by treatment processes (GAC, CI2) or derivatization, summarized the occurrence of new components of interest in treatment or derivatization, and calculated the percent of the total ion current represented by a given component. The programs allowed operator discrimination between major and minor components in a file set by preselection of an ion current threshhold for data reduction. For data summarized herein, components were >4000 ion counts, which corresponds to a level >5 of the internal standard (decachlorobiphenyl) response. 

Differential thermal analysis was performed with the DuPont 900 differential thermal analyzer the heating rate was usually 10°C. per minute. To determine heats of reaction, the calorimeter attachment to the Du Pont instrument was employed. Planimeter determinations of peak areas were converted to heat values by using standard calibration curves. For the infrared spectra either a Beckman IR5A instrument or a Perkin Elmer 521 spectrophotometer with a Barnes Engineering temperature-controlled chamber, maintained dry, was used. Specimens for infrared were examined, respectively, as Nujol mulls on a NaCl prism or as finely divided powders, sandwiched between two AgCl plates. For x-ray diffraction studies, the acid-soap samples were enclosed in a fine capillary. Exposures were 1.5 hours in standard Norelco equipment with Cu Ko radiation. For powder patterns the specimen-to-film distance was 57.3 mm. and, for long-spacing determinations, 156 mm. 

Internal Standard (IS) The internal standard (IS) is a compound added in a fixed, known amount to every quantitation sample to serve as an internal control for the analysis. Most commonly, the IS is used to normalize response through determination of peak area ratio as described above. The ideal IS will track with the analyte(s) through the extraction, chromatography, and mass spectrometry to account for variable recovery, minor spills, and changes in response over time. Stable-isotope versions of the analytes are ideal IS for LC-MS quantitation, but in many cases structural analogs exhibit sufficiently similar chemistry to be useful in this role (Jemal et al., 2003 Wieling, 2002 Stokvis et al., 2005). 

The hydrogen distribution computed using the determined values of a = 1/900 and b = 1/800 are shown in Table II. In the present in vestigation it was felt that the determination of peak areas rather than peak intensities would be the more accurate method for determining quantitative functional group concentration. For comparison to other infrared investigations, useful relations are... 

Manual Determination of Peak Areas and Peak Heights 331... 

Data handling in HPLC protein analysis has been limited to the determination of peak areas/heights, retention times, and, in the case of gel-permeation, molecular size. Commercial equipment is available for this. 

Since the determination of peak areas, peak detection, and baseline correction are well established methods, the determination of concentration is a smaller problem and results in values with small standard deviations. Nevertheless, TLC is not suitable for automation in its application to photokinetics since the photoactivation of the sample by the chromatographic material is not negligible [108]. The light paths for reflection and fluorescence measurements are given in principle in Fig. 4.27. 

In Mossbauer spectroscopy, as in other spectroscopic methods, quantitative analysis is based upon the determination of peak areas. 

Determination of Peak Areas 555 Table 8-1. Survey of various methods for calculating peak areas. 

Peak tracking is performed by diode-array detection, determination of peak areas and retention times, and most importantly by mass spectrometry. 

X-ray photoelectron spectra (XPS) of catalysts were recorded using a Leybold Heraeus LHS-11 apparatus equipped with a computer system, which allowed the determination of peak areas. The excitation radiation was the Alka line (E = 1486 eV). All the samples were grounded and then pressed into the sample holders before the analysis. Signals corresponding to Al2p, Al s °3p" 2p 2s levels were recorded. The energy... 

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