Chromatographic applicability spectrum

CHROMATOGRAPHIC APPLICABILITY SPECTRUM 1.8.1 Analysis of Amino Acids and Derivatives... 

Certain compounds, whether present in solution or in solid state (as molecular or ionic crystals) emit light when they are excited by photons in the visible or near ultraviolet domain of the spectrum. This phenomenon, called luminescence, is the basis of fluorimetry, a very selective and sensitive analysis technique. The corresponding measurements are made with fluorimeters or spectrofluorimeters and, for chromatographic applications, with fluorescence detectors. 

In gas chromatography/mass spectrometry (GC/MS), the effluent from a gas chromatograph is passed into a mass spectrometer and a mass spectrum is taken every few milliseconds. Thus gas chromatography is used to separate a mixture, and mass spectrometry used to analyze it. GC/MS is a very powerful analytical technique. One of its more visible applications involves the testing of athletes for steroids, stimulants, and other performance-enhancing drugs. These drugs are converted in the body to derivatives called metabolites, which are then excreted in the... 

Figure 4.18 Electrospray spectrum from a single chromatographic response in the LC-MS analysis of a tryptic digest. From applications literature published by SCIEX, Concord, Ontario, Canada, and reproduced by permission of MDS SCIEX, a division of MDS Inc.

A particular problem with GRAFA and RBL is the reproducibility of the retention data. The retention time axes should be perfectly synchronized. Small shifts of one time interval (thus the ith spectrum in X, corresponds with the i+lth spectrum in X ) already introduce major errors (> 5%) when the chromatographic resolution is less than 0.6. The results of an extensive study on the influence of these factors on the accuracy of the results obtained by GRAFA and RBL have been reported in Ref. [37]. Although some practical applications have been reported [38,39], the lack of robustness of RBL and GRAFA due to artifacts mentioned above has limited their widespread application in chromatography. 

As noted, IR instruments fall into several categories that range from simple photometers (single or multiple filter devices) to relatively complex full-spectrum devices, such as FTIR instruments. Today s process engineers often prefer optical methods of measurement rather than the traditional chromatographs because of perceived lower maintenance and ease of implementation. However, the final selection is often based on the overall economics and the practicality of the application. 

The use of a fixed wavelength UV detector for liquid chromatographic separations was first described by Horvath and Lipsky in 1966 [1], and is possibly the most popular HPLC detector in general use today. Although other detection techniques are more sensitive, the UV detector provides a simple and universal answer to the majority of HPLC applications [2]. Developed in 1982, the diode array UV detector measures the full absorption spectrum of each analyte peak, and was a... 

Principal component analysis is most easily explained by showing its application on a familiar type of data. In this chapter we show the application of PCA to chromatographic-spectroscopic data. These data sets are the kind produced by so-called hyphenated methods such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) coupled to a multivariate detector such as a mass spectrometer (MS), Fourier transform infrared spectrometer (FTIR), or UV/visible spectrometer. Examples of some common hyphenated methods include GC-MS, GC-FTIR, HPLC-UV/Vis, and HLPC-MS. In all these types of data sets, a response in one dimension (e.g., chromatographic separation) modulates the response of a detector (e.g., a spectrum) in a second dimension. 

The selective application of MS/MS and MS/MS/MS experiments has been used to assist in the tentative identification of structures. For example, the ions with m/z 456, corresponding to acetylechimidine-N-oxide or acetylvulgarine-N-oxide (Figure 13.12) have been selected from the total ion spectrum derived from directly infusing an extract of E. vulgare into the ESI source (Figure 13.13). Without a chromatographic... 

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