Parallel chromatograms

More interesting is the use of two different detectors in parallel at the exit of a GC column—so called dual channel detection. The detectors chosen should have major differences in sensitivity for different classes of compounds. Both signals are recorded simultaneously producing parallel chromatograms like those shown in Figure 8.2. Identifications can be made... 

The second group of determinations based on complex-formation is represented by the determination of amino acids. The a-amino acids react at a controlled pH with an excess of an insoluble cupric compound. The copper taken into solution as the 1 2 copper-amino acid complex is then determined polaro-graphically.< 2) A preliminary separation is necessary because the half-wave potentials of the complexes of individual amino acids do not differ very much. Paper-chromatography has been suggested for this purpose. ) The paper with the spot, the position of which is determined on a parallel chromatogram with ninhydrin, is cut... 

As the film thickness decreases, k or retention factor also decreases at constant temperature, column length, and inner diameter. Conversely, with an increase in film thickness in a series of columns having the same dimensions, retention increases under the same temperature conditions. This effect of film thickness on separation is demonstrated in the series of parallel chromatograms appearing in Figure 3.31. Column diameter limits the maximum amount of stationary phase that can be coated on its inner wall. Small-diameter columns usually contain thinner films of stationary phase, while thicker films can be coated on wider-bore columns. The concept of phase ratio allows two columns of equal length to be compared in terms of sample capacity and resolution. 

Figure 15.10 Primary (a) and secondary (b) separation of unleaded gasoline, where (a) shows the IRD chromatogram, and (b) shows the MSD total ion chromatogram of heart cut c. Adapted from Analytical Chemistry, 65, N. Ragunathan et al., Multidimensional gas chromatography with parallel cryogenic tr aps , pp. 1012-1016, copyright 1993, with permission from the American Chemical Society.

Certain assays may benefit from staggered parallel chromatography, for example, when (1) the same assay must be performed for a large number of samples in a short time and (2) if the analytes of interest that elute in a narrow window account for only a fraction of a chromatogram. 

For comparison of the different ionisation methods and detection modes, the results obtained as FIA overview spectra are presented in Figs. 2.11.7 and 2.11.8. Reconstructed ion chromatograms (RIC) of APCI and ESI combined with selected mass traces of all LC separations and, in parallel, the selected standardised mass traces of the C42 and C14 homologues containing three ethoxy chain links recorded in the negative mode are presented in Fig. 2.11.9. These results again demonstrate the quite large variation in the ionisation efficiency of... 

Electron capture detectors are extremely sensitive (1 X 10 12 mol) but are specific for electrophilic compounds. However, they can be used in parallel with flame ionization detectors to identify specific peaks in a chromatogram. 

LOD and LOQ were measured to assess the sensitivity of the FID, ECD and TSD detectors for GC analysis of various nitroaromatic compounds. A parallel connection of the three detectors at the end of a single narrow-bore capillary column enabled direct comparison of the chromatograms. Structural effects on the response were evaluated and detection mechanisms were discussed. Recommendations were made for identification purposes and for analysis of environmental samples of nitro- and chloro-nitro-benzenes in a wide range of concentrations451. 

Figure 5 is the case of a mixture NBS 706 (98.5 %) and PS 411000 (1.5 %). The value of M of the mixture l s about 8 % higher than that of NBS 706, bu both values of M are nearly the same. Both normalized chromatograms have similar shapes as in the case of Figure 1. However, the sequential U test (Figure 6) revealed after the third pair of parallel measurements that the MWD of the mixture is different from that of NBS 706.

Figures 7 and 8 show the normalized chromatograms of NBS 706 and of the mixture of NBS 706 and ESBRITE. Molecular weight averages of each pair of runs can be regarded as Identical within the experimental errors. The chromatograms in Figure 7 were judged to be Identical by the sequential U test of four pairs of parallel measurements. Only two pairs of runs were necessary for the decision of disagreement in the case of Figure 8.

In conclusion, the sequential U test is useful for the judgement of identity between MWDs of a pair of polymer samples whose molecular weight averages are Identical within the experimental errors. Identity of MWDs of the two polymer samples was established with more than four pairs of parallel measurements, and the disagreement of MWDs with two to four pairs of parallel measurements. Though this statistical treatment is useful for the identification or differentiation of the MWDs of the pair of polymers, it can not detect small differences in shapes of the both chromatograms. 

Figure 6.29 shows mass spectra recorded during elution reduced to a two-dimensional contour plot. Each point is produced from pseudo-molecular ions, cluster formation or fragmentation. AU ions eluting in parallel with respect to time, at c. 29 min are assumed to belong to the main component, but there are some points clearly seen on the front edge of the main peak that indicate the presence of an impurity. This was confirmed by the production of a mass chromatogram of miz 486. 

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