Interface liquid chromatography-infrared

Detection in SFC can be achieved in the condensed phase using optical detectors similar to those used in liquid chromatography or in the gas phase using detectors similar to those used in gas chromatography. Spectroscopic detectors, such as mass spectrometry and Fourier transform infrared spectroscopy, are relatively easily interfaced to SFC compared to the problems observed with liquid mobile phases (see Chapter 9). The range of available detectors for SFC is considered one of its strengths. 

D Commercial COTS controlled by external computer Hybrid systems such as automated dissolution workstation with high-performance liquid chromatography (HPLC) or ultraviolet-visible (UV-Vis) interface Liquid chromatographs, gas chromatographs, UV/Vis spectrophotometers, Fourier transform infrared (FTIR) spectrophotometers, near-infrared (NIR) spectrophotometers, mass spectrometers, atomic absorption spectrometers, thermal gravimetric analyzers, COTS automation workstations... 

Castles, M.A. Azarraga, L.V. Carreira, L.A. Continuous on-line interface for reversed-phase microbore high performance liquid chromatography/diffuse reflectance infrared fourier transform analysis. Appl. Spectrosc. 1986, 40, 673-680. 

Romanach and de Haseth [3] have used, in CCC, a how cell for LC-FTIR (liquid chromatography-Fourier transform infrared) spectrometry. The main difflculty is the absorbance of the liquid mobile phase. This problem is exacerbated in EC by low solute-to-solvent ratios in the eluates. On the contrary, CCC leads to a high solute-to-solvent ratio so that it can be used with a very simple interface with a CCC column, without any complex solvent removal procedures. High sample loadings are possible by using the variable path length of the IR detector (from 0.025 to 1.0 mm). 

DiNunzio, J. E. Pharmaceutical applications of high-performance liquid chromatography interfaced with Fourier transform infrared spectroscopy. Journal of Chromatography. 626 97-107, 1992. 

A variation on the GC-MS technique includes coupling a Fourier transform infrared spectrometer (FT-IR) to a gas chromatograph. The substances that elute from the gas chromatograph are detected by determining their infrared spectra rather than their mass spectra. A new technique that also resembles GC-MS is high-performance liquid chromatography-mass spectrometry (HPLC-MS). An HPLC instrument is coupled through a special interface to a mass spectrometer. The substances that elute from the HPLC column are detected by the mass spectrometer, and their mass spectra can be displayed, analyzed, and compared with standard spectra found in the computer library built into the instrument. 

Compared to GC-IR, liquid chromatography (LC)-IR measurements are often more challenging because mobile phases are not necessarily infrared transparent. Due to the fact that mobile phase concentration greatly exceeds that for mixture components in LC effluent, even mobile phases that have weak IR ab-sorptivities can present significant problems. LC-IR interfaces can be categorized as flow cell or mobile phase elimination. Figure 2 illustrates the three LC-IR interfaces described in the following sections. 

Several researchers have combined the separating power of supercritical fluid chromatography (SFC) with more informative spectroscopic detectors. For example, Pinkston et. al. combined SFC with a quadrupole mass spectrometer operated in the chemical ionization mode to analyze poly(dimethylsiloxanes) and derivatized oligosaccharides (7). Fourier Transform infrared spectroscopy (FTIR) provides a nondestructive universal detector and can be interfaced to SFC. Taylor has successfully employed supercritical fluid extraction (SFE)/SFC with FTIR dectection to examine propellants (8). SFC was shown to be superior over conventional gas or liquid chromatographic methods. Furthermore, SFE was reported to have several advantages over conventional liquid solvent extraction (8). Griffiths has published several... 

One variant, close to LC, that has been successfully interfaced to infrared spectroscopy, is supercritical fluid chromatography (SFC). In this case, one of the key mobile phases, super critical carbon dioxide, is virtually transparent for most of the mid-IR region. This may be operated directly on-line with a high-pressure liquid flow cell. 

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