Carbon dioxide, as mobile phase

NG, 2,6-DNT, 2,4-DNT, 2,4,6-TNT and PETN SGC using packed capillary columns and neat carbon dioxide as mobile phase 740°C Low pg range [48]... 

The combination of two techniques, simulated moving bed and supercritical fluid chromatography (SFC), leads to an apparatus with unique features. Besides the known advantages of the SMB process, like reduced solvent consumption, and its continuity the use of supercritical carbon dioxide as mobile phase offers an easy product recovery by depressurizing the supercritical fluid. Clavier et al. 

SFC) with supercritical carbon dioxide as mobile phase. 

Alvarez-Zepeda A (1991) Part I. A thermodynamic study of acetonitrile + water mixturesin reversed-phase liquid chromatography. Part n. A gas chromatographic study of the effect of temperature and column pressure on solute retention on a bonded phase using helium and carbon dioxide as mobile phases. Ph.D. thesis, Georgetown University, Washington DC... 

Capillary SFC using carbon dioxide as mobile phase and a FID as detector has been applied to the analysis of several essential oils and seemed to give more reliable quanti cation than GC, especially for oxygenated compounds. However, the separation ef ciency of GC for monoterpene hydrocarbons was, as expected, better than that of SFC. Manninen et al. (1990) published a comparison of a capillary GC versus a chromatogram obtained by capillary SFC from a linalool-methyl chavicol basil oil chemotype exhibiting a fairly good separation by SFC. 

Applications, Analysis of aikylbenzene sulphonates and alkyl sulphonates on a fused silica open tubular column (10 m x 0.53 or 0.25 mm i.d.) coated with 0.1 or 0.2 micron SE54 with carbon dioxide as mobile phase and FID is described in [8]. The anionics were derivatised before analysis. Among the many examples of analysis of nonionic surfactants are the following ... 

The examples described in Sects. 2-4 all use carbon dioxide as the phase to dissolve the substrates and/or products. Under continuous operation, the CO2 phase thus serves as the mobile phase. However, one may also envisage a so-called inverted scenario, where SCCO2 becomes the stationary catalyst phase and a second liquid phase contains substrates and products. This allows the processing of components that are not or only very poorly soluble in SCCO2. Furthermore, as it uses a liquid as continuous phase, energy-demanding compression cycles of the CO2 phase are avoided. A necessary prerequisite is the use of a sufficiently C02-philic catalyst as outlined below. 

For the separation of very-polar phenoHc Mannich bases, Fuchsluefer et al. used the novel fluid ethane with dimethyl ether as the modifier [79]. The normal carbon-dioxide-based mobile phases, even with polar modifiers, could not elute these compounds. They identified the main oligomeric products and several of the byproducts in the manufacture of these compounds, which are used as hardeners and accelerators in epoxy resins. They coupled their SFC outlet to a MS in the atmospheric-pressure chemical ionization mode. 

Figure 6.9 Separation of a poly(styrene) oligomer mixture of 2000 average molecular weight by open tubular column SFC using a linear density program (A) and an asymptotic density progreua in (B) with carbon dioxide as the mobile phase. (Reproduced with permission from ref. 115. Copyright Preston Publication, Inc.)...

The Chirasil-Metal stationary phase can be thermally immobilized on a glass surface156, thus increasing the temperature stability up to 160 °C. The immobilized Chirasil-Metal stationary phase can also be used in the SFC mode using supercritical carbon dioxide as the mobile phase156. 

Separations were performed on either silica- or amino-bonded stationary phase columns, using carbon dioxide with various modifiers as mobile phases. Each column exhibited distinctly different selectivities to the examined sulfonamides, the amino-bonded column being much more sensitive to modifier variations. In a continuation of the sulfonamide study, packed-column SFC was further evaluated for possible application to the analysis of furazolidone, chloramphenicol, and lincomycin residues (82). Separation was effected on an amino-bonded stationary phase using carbon dioxide with methanol modifier as the mobile phase, whereas detection was accomplished by MS. 

Using ternary mixtures of additive/methanol/carbon dioxide as the chromatographic mobile phase, linear plots of log k vs Ej were obtained for... 

We have used carbon dioxide as the supercritical fluid and methanol followed by water as the modifiers or entrainers. In our typical extraction experiments, which are the extraction of sulfonylurea and phenylmethylurea compounds from soil and plant materials, the solid matrix phase is saturated with the entrainers or modifiers and then pressurized in the extraction vessel with the supercritical fluid. For the sample extractions described here, methanol and water were used as matrix saturants, as opposed to mobile phase modifiers. 

Supercritical fluid extraction/chromatography can be used to characterize many of the components of todays high performance automobile coatings. For example, aliphatic isocyanates are highly reactive with protic solvents and are not chromophoric, therefore, their analysis poses a formidable task to the analytical chemist. Using carbon dioxide as the mobile phase in... 

Pure fluids. Carbon dioxide is often the mobile phase of choice for SFC, since it has relatively mild critical parameters, is nontoxic and inexpensive, chemically inert, and is compatible with a wide variety of detectors including the flame ionization detector (FID) used widely in GC and the UV absorbance detector employed frequently in HPLC (7). The usefulness of carbon dioxide as a mobile phase in many instances is somewhat limited, however, because of its nonpolarity (8), and many polar compounds appear to be insoluble in it. For a sample containing polar compounds, pure carbon dioxide may not be the proper mobile phase. The elution of polar compounds is often difficult and the peak shapes for these polar compounds are sometimes poor. This latter difficulty is commonly observed with nonpolar supercritical fluids and may be due to active sites on the stationary phase rather than any inherent deficiency in the fluid itself. 

Berge and Deye studied the effect of column surface area on the retention of polar solutes [18]. They found that there was a linear relationship between retention and the surface area. 4-Hydroxy benzoic acid was used as a model acidic compound, and sulfamethazine, sulfanilamide, sulfi-somidine, and sulfapyridine were used as the model basic compounds. The separations were carried out on a packed Nucleosil Diol column with a methanol-modified carbon dioxide as the mobile phase. The UV detector was used for the analysis. It was observed that 0.1% acetic acid for the acidic solutes and 0.1% isopropylamine for basic solutes was required in the methanol to achieve the separations. The efficiency was found to be similar for 100-, 300-, and 500-A packing materials. 

Perkins et al. reported the packed-column SFC of four veterinary antibiotics (levamisole, furazolidone, chloramphenicol, and lincomycin) using an amino column with methanol-modified carbon dioxide as the mobile phase [22]. A baseline separation of all four analytes was obtained in less than 4 min. The effect of several modifiers such as 2-methoxy-ethanol,... 

Heaton et al. have reported the supercritical fluid chromatography of taxicin I and taxicin II extracted by supercritical fluid extraction of Taxu baccata, the English yew tree [41]. They compared capillary- and packed- column SFC and concluded that packed-column SFC was better than capil4 lary-column SFC for quantitative analysis of these compounds. Capillary SFC was done on either a biphenyl or carbowax column with unmodified carbon dioxide as the mobile phase. The packed-column SFC was performed on a nitrile column with a mobile phase consisting of a methanol gradient with carbon dioxide. 

Gyllenhaal and Vessman have described the packed-column SFC of omeprazole and related compunds using an amino column with triethyla-mine- and methanol-modified carbon dioxide as the mobile phase [42]. Triethylamine (1%) was added to the methanol. The method was compared with an existing HPLC method, and it was concluded that SFC was about... 

O. Gyllenhaal and J. Vessman, Packed-column supercritical fluid chromatography of omeprazole and related compounds selection of column support with triethylamine and methanol-modified carbon dioxide as the mobile phase, J. Chromatogr., 628 215 (1993). 

Veuthey and Haerdi reported the separation of amphetamines using packed-column SFC [26]. The amphetamines were derivatized with 9-fluorenylmethyl chloroformate and chromatographed with a methanol or 2-propanol-modified carbon dioxide as the mobil phase. The separations were compared on bare silica and aminopropyl-bonded silica columns. Both columns gave comparable results and the separation of all five amphetamines (methylamphetamine, amphetamine, phenethylamine, ephed-rine, and norephedrine) was achieved in less than 5 min. Both methanol and 2-propanol-modified carbon dioxide gave comparable results. It was observed that the modifier concentration had more effect on the solvating power than the mobile-phase density. 

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