Chromatography overlapping peaks

This present chapter will not focus on the statistical theory of overlapping peaks and the deconvolution of complex mixtures, as this is treated in more detail in Chapter 1. It is worth remembering, however, that of all the separation techniques, it is gas chromatography which is generally applied to the analysis of the most complex mixtures that are encountered. Individual columns in gas chromatography can, of course, have extremely high individual peak capacities, for example, over 1000 with a 10 theoretical plates column (3), but even when columns such as these are... 

Foley, J. R, Systematic Errors in the Measurement of Peak Area and Peak Height for Overlapping Peaks, Journal of Chromatography 384, 1987, 301-313. 

J. Chen and S.C. Rutan, Identification and quantification of overlapped peaks in liquid chromatography with UV diode array detection using an adaptive Kalman filter. Anal. Chim. Acta, 335(1996) 1-10. 

MS detection does not necessarily require as highly resolved GC separations as in the case of selective detectors because the likelihood of an overlapping mass spectral peak among pesticides with the same retention time is less than the likelihood of an overlapping peak from the same element. Unfortunately, this advantage cannot always be optimized because SIM and current gas chromatography/tandem mass spectrometry (GC/MS/MS) methods, it is difficult to devise sequential SIM or MS/MS retention time windows to achieve fast GC separations for approximately > 50 analytes in a single method. 

Fraga, C.G., Corley, C. A. (2005). The chemometric resolution and quantification of overlapped peaks from comprehensive two-dimensional liquid chromatography. J. Chromatogr. A 1096, 40-49. 

A typical application can be found in chromatography. A group of components elute in a strongly overlapping peak cluster. We suspect that a particular chemical, for which we know the spectrum, might be in the unknown mixture, but due to overlap, its spectrum does not appear pure in the matrix Y. 

Fig. 15.5 Illustration of how two overlapping peaks S and ip emerging from the first colmnn (a) are resolved in GCxGC after passage to the second column (b) [31]. Reprinted from Marriott, R, Shellie, R., Principles and applications of comprehensive two-dimensional gas chromatography. Trends Anal. Chem. (2002), 21 573-583 with permission from Elsevier...

Figure 1 shows ion chromatrogram of the test solution added with EDTA or TEA. It was difficult to determine SO due to the overlapping peaks of EDTA and SO. However, TEA was found to be suitable for determination of anions present in rain water by ion chromatography. 

In contrast to analytical chromatography, where it is possible to deconvolute overlapping peaks and to obtain even quantitative information from non-resolved peaks,... 

In contrast to analytical chromatography, where it is possible to deconvolute overlapping peaks and to obtain even quantitative information from nonresolved peaks, preparative chromatography typically requires complete peak resolution if the components of interest are to be isolated with 100% purity and yield. Chromatographic resolution is a measure of how well two adjacent peak profiles of similar area are separated. is mostly defined as (Equation 2.43)... 

Goodman K. J., and Brenna, J. T (1994). Curve fitting for restoration of accuracy for overlapping peaks in gas chromatography/combustion isotope rato mass spectrometry. Anal Chem. 66, 1294-1301. 

The simplest description of retention behaviour considered previously suggests that all molecules of a particular analyte should travel down the column at the same rate and emerge at exactly the same time. If this were the case, chromatography would be easy and poor resolution due to overlapping peaks would be very rare. 

TOP analyzers are particularly useful when interfaced with chromatography where peak widths are measured in seconds it is important to obtain as much MS and MS/MS data as possible during that time period to fully characterize each individual chromatographic peak. In addition, the rapid acquisition of spectra at high resolution enables the collection of all data in accurate mass measuranent mode that can be further interrogated, e.g., to assist in the deconvolution of the components of overlapping LC peaks. 

Kiesswetter R, Brandi F, Kasmer-Pustet N, and Mann-schreck A (2003) Chiroptical detection during liquid chromatography deconvolution of overlapping peaks of enantiomers and its applications. Chirality 15 40-49. 

A variety of chromatography data software, which also includes well-known names, still do not use deconvolution. In the example as well as in other studies [5] it has already been shown that the use of deconvolution results is a clear optimization for the separation of overlapped peaks. The area and height and retention time determinations are clearly more accurate. Even at the deconvolution the made error depends on the resolution. The lower the resolution, the larger the error. 

To evaluate and optimize separation methods for overlapping peaks, there is a software tool called hilchromet. With hi chromet, the analyst has a tool for determining how well the chosen separation method in his chromatography data system really is it deals with symmetric as well as a symmetric peaks. 

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