Electronic Peak Area Determination

For the electronic evaluation of chromatographic data, one uses dedicated systems, integrators, or personal computers equipped with appropriate software. 

A survey of methods for determining peak areas and quantities proportional to peak area is given in Table 9.1. 

Method Required time Max. precision In routine operation 7 [%] Accuracy Applicability to unsymmetric peaks 

Peak height measurement Small 0.5 (depending on peak symmetry) Good (with symmetric peak shape) Not suited 

Peak height X half width Small 2 Good (with constant and almost symmetric peak shape) Rather unsuited 

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An intergrator may be regarded as a device that essentially facilitates simultaneous measurement of areas under the chromatographic peaks in the chromatogram either by mechanical or electronic means. It is, however, pertinent to mention here that manual techniques for determining peak areas are known, such as ... 

The most accurate measurements of peak areas are those obtained by means of electronic data reduction with integrators or computers. The vast majority of laboratories now have electronic or computer methods for determining peak areas. Two main features are required for electronic processing of chromatographic data accurate digitization of the analog signal and software. The software is required for the detection of peaks, correction for baseline drift, calculation of peak areas, retention times, and concentrations of components in the sample, and production of the final report.5... 

Mossbauer spectrum, the positions and separations of which depend on the oxidation state, electronic configuration, magnetic ordering, coordination number and symmetry of the iron atoms in a mineral structure. Computed peak areas enable Fe3+/Fe2+ ratios and site populations of Fe2+ ions in crystal structures to be readily determined for several minerals without interference from coexisting Mn, Cr and other transition elements. 

Using split injection mode, inject 1 to 5 xL of the standards into the chromatograph. Determine the peak areas by electronic integration. Plot peak area against concentration for each analyte corrected for the blank to construct a standard curve. Determine the concentration of additives and byproducts by comparison to the standard curve. The sum of the concentrations of the impurities and stabilizers is less than 1.0%. The order of elution and approximate retention times, in minutes, are as follows methyl chloride 2.8 vinyl chloride 3.0 ethyl chloride 3.5 propylene oxide 4.1 2-methyl-2-butene 4.5 vinylidene chloride 4.6 dichloromethane 5.3 trans-1,2-dichloroclhylene 5.9 chloroform 8.7 cyclohexane 10.5 and carbon tetrachloride 12.0. 

For example, little is known about the isotopic composition of formaldehyde in the atmosphere. Formaldehyde is a chemical intermediate in hydrocarbon oxidation. The carbon (8 C) and hydrogen (8D) isotopic composition of atmospheric formaldehyde is analyzed using continuous flow gas chromatography isotope ratio mass spectrometry." Isotope ratios were measured using GC-IRMS (Finnigan MAT 253 stable isotope ratio mass spectrometer, single-sector field with electron impact ion source and multiple ion collection) with a precision of 1.1 and 50%(lo ) for 8 C and 8D, respectively. The accuracy of the online continuous flow isotope technique was verified by calibrating three aliquots of the gas phase standard via the offline dual inlet IRMS technique. The concentration of formaldehyde in ambient air was determined on IRMS major ion peak areas (i.e., mass 44 for 8 C and mass 2 for 8D)." ... 

Integration of peak areas in routine analysis is mostly achieved with electronic integrators. Two main problems arise from this evaluation technique first the definition of the baseline, and second, the determination of the time constant of the TLC-scanner and the integrator electronics. 

The glass column used for the separation was packed with 10% Carbo-wax 20M and 2% KOH coated on a Chromosorb W support. The attenuation was adjusted such that all of the samples could be run on the same scale and the corresponding peak areas were determined by an electronic integrator. 

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