Supercritical fluid chromatography instrumentation used

Supercritical fluid chromatography (SEC) was first reported in 1962, and applications of the technique rapidly increased following the introduction of commercially available instrumentation in the early 1980s due to the ability to determine thermally labile compounds using detection systems more commonly employed with GC. However, few applications of SEC have been published with regard to the determination of triazines. Recently, a chemiluminescence nitrogen detector was used with packed-column SEC and a methanol-modified CO2 mobile phase for the determination of atrazine, simazine, and propazine. Pressure and mobile phase gradients were used to demonstrate the efficacy of fhe fechnique. 

In supercritical fluid chromatography, fluids above their critical point are used as mobile phases. This chapter discusses the principles of operation, mobile phase considerations, parameters that can be adjusted in method development as well as an overview of instrumentation required and a few pertinent examples from current literature. Not everything can be illustrated, but the advantages of this diverse technology will be highlighted. 

Another technique is supercritical fluid chromatography (SFC), which is a chromatographic technique that in many ways is a hybrid of GC and HPLC. It is recognized as a valuable technique for the analysis of thermolabile compounds, which would not be amenable to analysis by GC or HPLC. Few applications have been reported for SFC in the field of OCP and OPP determination (16). The advantages reported for SFC are versatility in separation (by the addition of modifier or the choice of stationary phase) and detection (with LC or GC detectors). However, SFC is a little-used technique because it still presents a wide range of instrumental problems (14-16). 

Most FTMS instrument and method development research has been focussed on demonstration experiments. Examples include coupling FTMS with various sample introduction schemes (e.g., GC, LC, supercritical fluid chromatography), sample ionization (e.g., LD, pulsed SIMS, Cf-252 PDMS, etc.), and demonstrating application to various interesting classes of chemical compounds. These demonstrations are useful because they are indications of the potential of the technique. However, few reports of the routine use of FTMS for trace analysis, for accurate mass, and for structure determination of unknowns have yet appeared. One reason is that FT mass spectrometers are not widely spread in the hands of users. Another is that FTMS is not yet routine. Most of the demonstration experiments have been done in expert laboratories by committed and highly focussed graduate students and postdoctoral researchers. 

Supercritical fluid chromatography (SFC) is a column chromatographic technique in which a supercritical fluid is used as a mobile phase. A supercritical fluid is a gas or liquid brought to a temperature and a pressure above its critical point. The first report of SFC dates back to 1962 when Kesper et al. [1] used supercritical fluid chlorofluorocarbons as a mobile phase for the separation of metal porphyrins. It was not until the early 1980s that an important breakthrough of the technique occurred. This was the introduction of capillary SFC and the availability of commercial instrumentation. These became major factors in the recent rise in popularity of SFC. According to the latest estimation, approximately 100 SFC articles are published in major journals every year. 

Prior to the commercialisation of LC-MS instruments, supercritical fluid chromatography (SFC) was mainly used for the analysis of oligomers. As the range of LC-MS instruments can be extended up to 4000 dal tons this capability makes them ideal to characterise oligomers. For example, it has been shown that silicone oligomers can be detected by LC-MS in food simulants. ... 

Supercritical fluid chromatography (SFC) with open-tubular columns was first demonstrated in 1981 by Novotny and co-workers [1]. This technique, known as capillary SFC, was made available to the analytical community through the introduction of several commercial instruments in 1986. Initially difficult to use, improvements in instrumentation and hardware, coupled with a wider array of columns and restrictor options designed specifically for the technique, becoming available, have led to a general acceptance of the method in many laboratories. Not only useful as a research tool, capillary SFC is firmly established as an essential analytical method for production support and quality control in many industries. Some of these include chemical and petroleum manufacturing, pharmaceuticals, polymers, and environmental monitoring. 

Supercritical fluid chromatography are more complex that HPLCs. One of the fluids is usually a liquefied gas at high pressure. The instrument cannot use a single high pressure pump and a gradient valve to mix such fluids with normal liquids. Consequently, one always requires at least two high pressure... 

Supercritical fluid chromatography can be used as a qualitative or quantitative technique. Qualitative information allows a substance to be identified on the basis of retention time comparisons between a standard and the sample. When used quantitatively, the SFC can employ external or internal standards to generate a standard curve. Then, the peak area of the sample peak on the chromatogram can be used to obtain a concentration. An example of an SFC instrument is shown in Figure 3.35. 

---