Response factors calculation

If standard mixtures of known weight ratios of components do not give the same ratio of areas, the detector is not responding equivalently to each component. In this case a quantitative analysis of the mixture requires preliminary experimentation. One method is the use of an internal standard (for a more detailed discussion of other procedures, specialist texts should be consulted65,66). Thus for a two-component mixture (A + B), a third component C is selected as the internal standard. Mixtures of A + C and B -I- C are prepared in which the weights of each component in each mixture are known. The relevant chromatogram is recorded and the detector response factors calculated from the following relationships ... 

Finally, these relative heights or areas are compared with equivalent values obtained from standards curves prepared from known amounts of target compounds to yield values for the amount of each target compound present in the chromatographic injection. Unknowns in the chromatogram can be identified with relative retention times, areas, and heights, but the amount of each present cannot be determined until they are identified, standard curves run, and response factors calculated for each compound. 

Calculate the response factors of the standards by dividing their concentrations by their peak areas. Calculate the concentration of each component in the sample by multiplying the individual peak areas corresponding to each component by the appropriate response factor calculated for its standard, giving the concentration in w/w percent. A comparison of sorbitol and dextrose peak areas shows that at least 95% of the sum of these peak areas is sorbitol. A similar comparison of maltitol and maltose peak areas shows that at least 95% is maltitol. Neither sorbitol nor maltitol fractions comprise more than 50% of the sample. 

From the relative response factors calculated in the first experiment as well as from the known concentration of the internal standard within the sample, C(s, this leads to ... 

Repeatability. In order to achieve a highly reliable compositional analysis, the error of each component shall be less than 1%, derived from the maximum and minimnm response factor of the consecutive analysis runs. Table 2 shows an example of the response factor calculation. 

Notice that the response factors calculated in this example are molar response factors. It is necessary to correct these values by the relative molecular weights of each substance to obtain weight response factors. 

Under the conditions given in Table 7.11 chromatograph 5 ul of the sample and from the chromatogram decide on a suitable internal standard, eg n-butyl benzene. Prepare an accurate w/w solution of the chosen internal standard in the sample and chromatograph 5 ul of the solution under the conditions given in Table 7.11. Determine the peak areas of the standard and of the relevent impurity peaks and, knowing the concentration of the standard and assuming that all components have the same response factor, calculate the results ... 

Assuming that all the components have the same response factor, calculate the... 

Using the relative response factors calculate the concentration in mol percent of each of these components in accordance with the following equation (see Table 3) ... 

A 1.1 Referring to Section on Summary of Method, it is noted that the test method is based on response factors calculated from a selected reference standard using peak area measurements. Liquid reference standards are difficult to prepare and are subject to change in composition during use. Hence it is virtually mandatory that the reference standard be authenticated in some manner when received and periodically during use. One simple approach is described as follows ... 

Difference from Calibration Mixture—Multiply the area of each peak in the calibration mixture by the liquid volume response factor calculated in 11.2, and normalize the volume percent of each compound so that the volumes of all compounds heavier than n-butane add up to 100.0. Compare the volume percent of each compound heavier than n-butane... 

Analyze the linearity standard described in 7.5 and calculate the relative mass response fiictors according to Practice D4626. Response factors calculated relative to hexadecane must be between 0.90 and 1.10. 

Because some of the impurities identified in AMS are not available commercially, this test method is based on the use of theoretical response factors calculated with the use of effective carbon numbers (see Table 2). ... 

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