Area-normalization method

Salient features of Area Normalization Method are as follows ... 

Also, because of the additional substances present in adulterated samples, the peak area normalization method is applied only to those peaks due to heroin processing, including opium alkaloids, if present. 

If a calibration curve is not made and a data system is used to make the calculations, a slightly different procedure is followed. A calibration mixture prepared from pure standards is made by weight and chromatographed. Absolute calibration factors, equal to the grams per area produced, are stored in the data system for each analyte. When the unknown mixture is run, these factors are multiplied times the respective areas of each analyte in the unknown resulting in a value for the mass of each analyte. This procedure is a one-point calibration, as compared to the multipoint curve described before, and is somewhat less precise. Note also that these calibration factors are not the same as the relative response factors used in the area normalization method. 

Matisova and co-workers11 have suggested that the need for a reproducible sample volume can be eliminated by combining the standard addition method with an in situ internal standard method. In the quantitative analysis of hydrocarbons in petroleum, they chose ethyl benzene as the standard for addition, but they used an unknown neighboring peak as an internal standard to which they referenced their data. This procedure eliminated the dependency on sample size and provided better quantitation than the area normalization method they were using. 

Determine the composition of the sample, using the area normalization method, by the formula... 

Peak areas and relative detector responses are to be used to determine the concentration of the five species in a sample. The area-normalization method described in Problem 31-20 is to be used. The relative areas for the five gas-chromatographic peaks are given in the table. Also shown are the relative responses of the detector. Calculate the percentage of each component in the mixture. 

Another approach that avoids the uncertainties associated with sample injection is the area-normalization method, ( ompicte elution of all ci)mponents of the sample is required. In the normalization method, the areas of all eluted peaks are computed after correcting these areas for differences in the detector response to different c<>ni]K)und types, the concentration of the analyte is found from the ratio of its area lo the tola area of all peak.s. The f( llo ing e.xample illustrates the procedure. 

Unfortunately, it is often not practical to arrange conditions so that all of the components of a mixture arc eluted from a column in a reasonable period. As a result, the area-normalization method has limited applications. 

Calculations for the internal standard method are similar to those mentioned above for the external standard. More detailed information concerning the external and internal standard methods, as well as other methods of evaluation Je.g., area normalization method (100% method), addition method] is given in [11]. 

The area normalization method was applied to the determination of normal-, secondary-, iso-, and tertiary-butyl alcohol. To determine the relative response factor for the alcohols, a standard solution of the alcohols was prepared and its gas chromatogram observed. The results were as follows ... 

SI 27-25 One method for quantitative determination of the concentration of constituents in a sample analyzed by GC is the area-normalization method. Here, complete elution of all of the sample constituents is necessary. The area of each peak is then measured and corrected for differences in detector response to the different eluates. This correction involves dividing the area by an empirically determined correction factor. The concentration of the analyte is found from the ratio of its corrected area to the total corrected area of all peaks. For a chromatogram containing three peaks, the relative areas were found to be 16,4, 45.2, and 30,2 in the order of increasing retention time. Calculate the percentage of each compound if the relative detector responses were 0,60, 0.78, and 0.88, respectively. 

Comparison of internal standard, external standard, and area normalization methods... 

Simultaneous running of appropriate standards is required. No area normalization method can be used for quantitation. 

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