Relative detector response

By assuming that a proportional increase in the amount of sample injected results in a proportional increase in the detector response for the solute band of interest, the detector response for chromatogram I in Figure 7 will increase 14 times when the maximum sample volume of 7 /xL is injected. However, for the 4.6-mm i.d. column, the detector response will increase 400 times when the maximum sample volume of 200 (lL is injected. By taking into account the relative detector responses for the 0.5-/xL injection, at the maximum sample injection volumes, the 4.6-mm i.d. column with the 20-/liL detector flow cell will produce approximately five times the detector response of the 1-mm i.d. column with the 5-/zL flow cell. In most cases, studies can be designed to provide excess sample because aqueous environmental samples are seldom limited with respect to volume. 

Fig. 16.4 shows the capillary gas chromatograms obtained for a fraction. Fig. 16.4(b) shows the total ionisation chromatograms for the fraction obtained from the high resolution mass spectral data set. In general, the correlation between the total ionisation chromatogram profile and the flame ionisation detector profile is low due to both the differing relative detector responses and the consideration of scan cycle time (9.6s) with respect to chromatographic peak elution time ( 20s). 

One method for the quantitative determination of the concentration of constituents in a sample analyzed by gas chromatography is area normalization. Here, complete elution of all 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 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. 

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. 

Compound Relative Peak Area Relative Detector Response... 

Accurate g.l.c. analysis of mixtures of substances with a flame ionization detector (f.i.d.) depends upon a knowledge of the relative detector response of each compound. Variations in the f.i.d. responses of steroids in molar terms have now been put on a quantitative basis. There is a good linear relationship between molar f.i.d. response and the effective carbon number , which is the number of carbon atoms per molecule less half the number of oxygen atoms (over the ranges Ci8—C31, and Oo—O4). This behaviour parallels earlier conclusions for paraffin hydrocarbons, alcohols, and esters. G.l.c. data are reported for the trimethylsilyl ethers of 49 plant sterols on eight different columns. ... 

The experiment can readily be extended to other systems, for example, a nitric acid/nitrogen oxide vapour produced by adding concentrated nitric acid to copper. The quantitative exercise could simply be carried out with flame ionisation detection however, if both detection systems are available this forms the basis for a study and comparison of relative detector response using both total ion and selected ion monitoring. 

A mixture of the methyl ethanoate (A), methyl propanoate (B) and methyl butanoate (C) was analysed by GC. The area of each peak and the relative detector responses are given in Table 10.7. Use this information to determine the percentage of each compound in the mixture. 

A mixture of three volatile compounds (J, B and C) was analysed by GC using a column of 50 cm length. The retention time (/r), the peak width at base line (wj,), the area under each peak and the relative detector response factor, are given in Table 10.17. Under the same conditions a compound with no affinity for the stationary phase took 2.3 min to be eluted. 

The PID is nondestructive, relatively inexpensive, of rugged construction and easy to operate. The linear range is approximately 10. For favorable compounds the PID is 5 to 50 times more sensitive than the FID [280,286]. In other cases it may not respond at all or respond poorly determined by the ionization potential of the compound and the photon energy and flux. On an individual compound basis relative detector response factors vary over a wide range allowing the PID to be used as a selective detector for some applications. Major applications of the PID are the analysis of volatile organic compounds from environmental samples and in field-portable gas chromatographs [292]. 

Determine the concentration of species in a sample using the peak areas and relative detector responses for the five gas chromatographic peaks given in the fi l-lowiiig table, L se ihc area-norinaliz.aiion method described in Problem 27-25,... 

Jane et al have recorded retention (125x5 (i.d.) mm Spherisorb S5W Silica column) and relative detector response data (EC (V25 grade GCE, -1-1.2 V V5 Ag/ AgCl) and UV absorption (254 nm)) for 462 basic drugs and quaternary ammonium compounds using methanolic ammonium perchlorate (10 mmol L pH 6.7) as... 

Figure A.1 Comparison of retention (k) and relative detector response (EC (V25 grade...

Table A.l Comparison of retention and relative detector response data for basic drugs (Jane et al. (A) and Jane and McKinnon, unpublished (B)) Data excluded from the regression analysis (Figure A.l) as outliers . (N.B. Data in italics not shown in Figure A.l)...

This method can be used to determine the relative amount of components in a sample, assuming that all components elute at the given conditions. When the relative detector response of the components is not known, only semiquantitation relative to one compound can be obtained (assuming identical response factors). If the relative response of the components is known, their percentage ratio in the sample can be found. Their response factor can be determined by establishing a curve where detector response is plotted as a function of their concentration. The slope of the curve represents the response factor. 

Comparison of the relative detector response from two or more detectors can aid in the identification or classification of an unknown component. Generally the component is chromatographed on one column and the effluent split and fed to two or more detectors. Commonly used pairs of detectors are the phosphorus... 

Relative detector response factor also frequency Frequency... 

From Figure 107 it is obvious that the graph is linear for low sample volumes, but above 2.5 y1, the thermal conductivity response is no longer linear. (Jamieson ) The relative detector responses to a number of compounds are given in Table 102. 

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