ASTM D4626 Practice for Calculation of Gas Chromatographic Response Factors
4. Summary of Practice
4.1 Individual C6 to C11 n-paraffins are precisely weighed and combined in an inert, tight-sealing glass vial. Different concentration levels of the blend components to cover concentration ranges of interest may be obtained by dilution with a suitable solvent. As diluent, a n-paraffin, such as n-dodecane, that is, higher boiling than the blend components is suitable. The quantitative blends are analyzed, in duplicate, by gas chromatography using either thermal conductivity, flame-ionization or other forms of detection. From the mass or volume composition of the blend and the raw area or peak height measurements, mass or volume response or relative response factors for each blend component are calculated.
5. Significance and Use
5.1 ASTM standard gas chromatographic methods for the analysis of petroleum products require calibration of the gas chromatographic system by preparation and analysis of specified reference mixtures. Frequently, minimal information is given in these methods on the practice of calculating calibration or response factors. Test Methods D2268, D2427, D2804, D2998, D3329, D3362, D3465, D3545, and D3695 are examples. The present practice helps to fill this void by providing a detailed reference procedure for calculating response factors, as exemplified by analysis of a standard blend of C6 to C11 n-paraffins using n-C12 as the diluent.
5.2 In practice, response factors are used to correct peak areas to a common base prior to final calculation of the sample composition. The response factors calculated in this practice are "multipliers" and prior to final calculation of the results the area obtained for each compound in the sample should be multiplied by the response factor determined for that compound.
5.3 It has been determined that values for response factors will vary with individual installations. This may be caused by variations in instrument design, columns, and experimental techniques. It is necessary that chromatographs be individually calibrated to obtain the most accurate data.
