Detector response, correction

Post-column on-line derivatisation is carried out in a special reactor situated between the column and detector. A feature of this technique is that the derivatisation reaction need not go to completion provided it can be made reproducible. The reaction, however, needs to be fairly rapid at moderate temperatures and there should be no detector response to any excess reagent present. Clearly an advantage of post-column derivatisation is that ideally the separation and detection processes can be optimised separately. A problem which may arise, however, is that the most suitable eluant for the chromatographic separation rarely provides an ideal reaction medium for derivatisation this is particularly true for electrochemical detectors which operate correctly only within a limited range of pH, ionic strength and aqueous solvent composition. 

If the detector response differs, make up by weight a 1 1 mixture of each of the separate components (I, II, and III) with compound (IV). Inject a 0.1 pL sample of each mixture, measure the corresponding peak area, and hence deduce the factors which will correct the peak areas of components (I), (II), and (III) with respect to the internal standard (IV). 

Theory. We will outline theory developed earlier (11,12) for converting the detector response F(v) from a turbidity detector into particle size information. F(v) is related to the dispersion-corrected chromatogram W(y) by the integral equation... 

Faraday collector, simultaneously with U, U and U during the first sequence. This shortens the analysis routine, consuming less sample. Ion beam intensities are typically larger in MC-ICPMS than in TIMS due to the ease with which signal size can be increased by introducing a more concentrated solution. While this yields more precise data, non-linearity of the low-level detector response and uncertainties in its dead-time correction become more important for larger beam intensities, and must be carefully monitored (Cheng et al. 2000 Richter et al. 2001). 

To allow for this, before the peak areas are normalised we must first correct each area so as to get the area we would have obtained had the detector response been the same for each of the three compounds. We will now use the results from our mixture to determine calibration factors (relative response factors) for the detector, and then use these for the analysis of a commercial tablet. 

Some commercial detectors come with built-in procedures and software that automatically corrects for a flat detector response of every pixel4. For other detectors the necessary correction has to be carried out by the user. 

Sulfur dioxide in the sample causes a negative interference of approximately 1 mole of ozone per mole of sulfur dioxide, because it reduces the iodine formed by ozone back to potassium iodide. When sulfur dioxide concentrations do not exceed those of the oxidants, a method commonly used to correct for its interference is to add the amount of sulfur dioxide determined by an independent method to the total detector response. A second method is to remove the sulfur dioxide from the sample stream with solid or liquid chromium trioxide scrubbers. Because the data on the performance or these sulfur dioxide scrubbers are inadequate, the performance for each oxidant system must be established experimentally. 

To determine the correction factors, an internal standard is generally added to each of the mixtures and the detector response measured relative to the internal standard. If the ratio of a monosaccharide to the internal standard decreases after hydrolysis of a test mixture of monosaccharides, decomposition has occurred and a recovery factor should be determined. The internal standard must either be resistant to decomposition during hydrolysis or should be added after hydrolysis it is usually better to add the internal standard after hydrolysis, to be on the safe side. The internal standard must not appear in the samples and must be resolved from other components in the sample, as with any internal standard. 

Mass recovery of MA samples was checked by using the concentration (DRl) detector response (mass/area ratio) of the corresponding LB arm it was assumed that the detector response was identical for compositionally similar samples. Corrections for 38% and 9% sample loss were applied to the "mass injected" in the SEC/LALLS data for (Sl-1) DVB and (Sl-2) DVB, respectively. 

The contribution of slow detector response can be ne ected when the base peak width is at least 40 times larger than r [cf. Eq. 3)]. In practice it is difficult to correct for such distortion because the time constant concept is only an approximation. It is not very reproducible and is sensitive to changes in the characteristics of the various elemehts of the electronics. Furthermore, detectors, amplifiers, and record are not first-order systems mid their response is only iippruxinntted by an exponential function (44). The response time is therefore defined by the time neces-... 

With enantiomer analysis, however, a linear detector response is indispensible. Thus, for the correct determination of. say, 0.1 % of an enantiomeric impurity, linearity within a concentration range of at least three orders of magnitude is required. It is generally accepted that the flame ionization detector (FID) does fulfill this requirement, but it is recommended that the linear detector response is verified via dilution experiments31. In contrast, the linear response range of the electron capture detector is low, being only two to three orders of magnitude. 

IFS66-FRA-106 FT-Raman spectrometer equipped with a liquid-Nj cooled Ge-diode detector. Samples were in small glass capillary tubes at 23°C. The spectra were calculated by averaging -200 scans followed by apodization and fast-Fourier-transformation to obtain a resolution of -2 cm and a precision better than 1 cm . The spectra were not corrected for (small) infensity changes in detector response versus wavelength. 

Fig.l. Normalized steady-state fluorescence spectra of the PSBR in methanol, ethanol and octanol. The fluorescence spectra are corrected for detector response and converted onto an energy scale. Note that absorption and emission are lacking mirror symmetry. The total Stokes shift is 6.870 cm 1 octanol and 7.900 cm 1 in methanol. 

Fig. 2. Time resolved fluorescence spectra of all-trans PRSB in methanol (black) and octanol (grey) for a) t<50 fs and b) t>50 fs. The intensity of the octanol spectra is adjusted the methanol spectra. The spectra are not corrected for self-absorption (for >19.500 cm 1), or for the detector response function. A residual signal appearing at energies <14.000 cm"1 is due to incomplete background subtraction (see above).

Experiment C is the same as B. but the split vent was opened after 30 s to rapidly purge all vapors from the injection liner. The bands in chromatogram C would be similar to those in B, but the bands are truncated after 30 s. Experiment D was the same as C, except that the column was initially cooled to 25 °C to trap solvent and solutes at the beginning of the column. This is the correct condition for splitless injection. Solute peaks are sharp because the solutes were applied to the column in a narrow band of trapped solvent. Detector response in D is different from A-C. Actual peak areas in D are greater than those in A because most of the sample is applied to the column in D. but only a small fraction is applied in A. To make experiment D a proper splitless injection, the sample would need to be much more dilute. 

At this time the peak areas in the unknown can be corrected for individual variation in detector response by dividing each area by the response factor for that component. The result is then a corrected peak area. The weight percent is then determined by dividing the corrected area by the total corrected area and multiplying by 100. 

Thermal conductivity detectors used in gas chromatographs do not respond equally to all FAMlis. To correct for varying detector sensitivity, peak area for each FAME should be multiplied by the proper response correction factor (RCF) (Table E6.2). If extra time is available, you may want to calculate your own response correction factors for the fatty acid methyl esters. The factors are experimentally determined on a gas chromatograph by comparing the area under a GC peak due to a known amount of compound to the area under a GC peak represented by a reference compound. 

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