Applications of SFC

Another application of SFC-GC was for the isolation of chrysene, a poly aromatic hydrocarbon, from a complex liquid hydrocarbon industrial sample (24). A 5 p.m octadecyl column (200 cm X 4.6 mm i.d.) was used for the preseparation, followed by GC analysis on an SE-54 column (25 m X 0.2 mm i.d., 0.33 p.m film thickness). The direct analysis of whole samples transferred from the supercritical fluid chromatograph and selective and multi-heart-cutting of a particular region as it elutes from the SFC system was demonstrated. The heart-cutting technique allows the possibility of separating a trace component from a complex mixture (Figure 12.21). 

SFC-FID is widely used for the analysis of (nonvolatile) textile finish components. An application of SFC in fuel product analysis is the determination of lubricating oil additives, which consist of complex mixtures of compounds such as zinc dialkylthiophosphates, organic sulfur compounds (e.g. nonylphenyl sulfides), hindered phenols (e.g. 2,6-di-f-butyl-4-methylphenol), hindered amines (e.g. dioctyldiphenylamines) and surfactants (sulfonic acid salts). Classical TLC, SEC and LC analysis are not satisfactory here because of the complexity of such mixtures of compounds, while their lability precludes GC determination. Both cSFC and pSFC enable analysis of most of these chemical classes [305]. Rather few examples have been reported of thermally unstable compounds analysed by SFC an example of thermally labile polymer additives are fire retardants [360]. pSFC has been used for the separation of a mixture of methylvinylsilicones and peroxides (thermally labile analytes) [361]. 

Yang et al. [389] rapidly distinguished compounds extracted from paper, using on-line SFE-SFC-FHR in conjunction with principal component analysis. The quantitative determination of the surfactant mixture Triton X-100 and other complex oligoether surfactants by means of cSFC-FTIR flow-cells has been reported [390,391]. Practical applications of SFC-FTIR include the determination of nonvolatile compounds from microwave-susceptible packaging that may migrate into heated food. Another application is the analysis of fibre finishes on fibre/textile matrices. 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

Supercritical fluid chromatography (SFC) is a relatively recently developed chromatographic technique. Because of its ability to deal with compounds that are either polar or of high molecular weight, much attention has recently focused on applications of SFC to the analysis of different analytes using a variety of fluids or fluid mixtures to provide differing solvent capabilities and select vities. As a result there is a large amount of research currently underway both in SFC method development and in hardware development. 

Acrylic Macromers. Thus far we have shown applications of SFC to the characterizations of monomers and crosslinkers. The next couple applications will focus upon the analysis of oligomeric methacrylates, specifically methacrylate macromers. Methacrylate macromers are frequently used as building blocks for larger architecturally designed polymers. Unfortunately, macromers far exceed the capability of GC and do not possess a chromophore for HPLC analysis. Hatada et. al. has used packed column SFC to analyzed the stereoisomers of oligomeric methylmethacrylate (MMA) prepared by anionic polymerization (13). 

Promising applications of SFC include group separations (paraffins, olefins and aromatics) in petrochemical samples, monitoring of supercritical extraction processes (caffeine from coffee, nicotine from tabacco) and oligomer separations. However, it is in the field of applications that SFC has yet to prove its value. Unique separations that can be accomplished with SFC, but not with either GC or LC, have yet to be demonstrated. 

Several applications of SFC-ICP-MS in organotin have been reported. The SFC mode is particularly suitable for tri- and tetraorganotin species and this technique enables better sensitivity when compared with LC (better transport efficiency to plasma). A comprehensive review is available. ... 

Some applications of SFC outside the pharmaceutical industry employ oven temperatures up to 200 °C and use the flame ionization detector (FID) from GC. The FID is not generally used in the pharmaceutical industry because polar solutes will not elute without a modifier, and modifiers give a response in the detector. However, a mass spectrometer is often mounted in the same manner as an FID. A small fraction of the total flow is split off through a tee to a fixed restrictor mounted in the inlet to the MS. The bulk of the flow proceeds through to the back-pressure regulator. Column outlet pressure is controlled by the BPR. 

Until now applications of SFC have been limited to product analysis of, e.g., nonionic surfactants but here with great success.No reports on the determination of surfactants in environmental matrices using SFC is known to the authors. 

SKC is also very useful for achiral separations. Fig ures 2 -7.29-8, and 29-9 illustrate three lypical and tli-versc applications of SFC. Figure 29-7 shows the separation of a scries of dimcihylpolysiloxanc oligomers... 

Decomposition is probably occurring in the source or in the interface. Additional experiments, in which both the source and SFC-MS interface temperatures are varied, will be required to establish the site of decomposition. It is clear, however, that the application of SFC-MS to thermally-labile materials will ultimately be limited, not by the SFC, but by the interface-detector combination. 

Application of SFC-MS to a Drug-Related Problem. Tergitol nonionic surfactant-9 (USP name Nonoxynol-9 abbreviated here TNS-9) is an important active ingredient and surfactant in a number of drug formulations. 

Capillary SFC-MS Development and Applications. The initial applications of SFC have stressed thermally labile and higher molecular weight mixtures not amenable to GC. Many of the early applications of capillary SFC have utilized carbon dioxide as the mobile phase, but the extension to alternative fluids is being actively pursued. 

A potentially important application area for capillary SFC and SFC-MS is in the analysis of thermally labile molecules not readily amenable to gas chromatography, such as mycotoxins of the trichothecene group (48,49). Figure 14 shows a fast separation of four trichothecenes on a short 0.8 m x 25 pm column at 100 C with supercritical CO2 as the mobile phase. Diacetoxyscirpenol (DAS) and T-2 toxin are easily resolved while the two macrocyclic compounds, roridin A and verricarin J, are not well separated. However, even this level of separation is often sufficient given a highly selective detector such as the mass spectrometer. Application of SFC-MS to these compounds is described in detail elsewhere ( ). 

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