Fluid high pressure liquid chromatography

Some particular processes can require very high pressures for special applications (i.e. in explosive welding and plating), but pressures between 100 and 1000 bar can be found easily in different industrial processes. Typical examples are the synthesis of ammonia, the synthesis of methanol and the production of low-density polyethylene, but also analytical techniques as high-pressure liquid chromatography. Other important implications are for the storage and transportation of fluids and enhanced oil recovery. 

If a liquid is used as die mobile phase, the technique used is liquid chromatography (LC). The solid adsorbent is constrained in a tube or column through which the liquid mobile phase flows. Any number of solvents, buffer solutions, or supercritical fluids can be used as liquid mobile phases. High-pressure liquid chromatography (HPLC) is used if pressure is needed to force die liquid phase through the tube. If the liquid phase moves over a thin adsorbent surface propelled by capillary action, die technique used is thin-layer chromatography (TLC). In general, two types of surfaces are used as the solid phase. 

High-pressure liquid chromatography has been utilized for the determination of salicylamide in blood, serum and other biological fluids as well as pharmaceutical formulations. Some of recently reported methods are summarized in Table ll. 

High pressure liquid chromatography is used to isolate THC and its two metabolites from the bulk of the other components of body fluids due to their differences in relative retention. By direct injection of the body fluid and subsequent collection following gradient elution, THC and two of its metabolites are simultaneously extracted and significantly purified in one step. 

In normal high pressure liquid chromatography, typical sample volumes are 20-200 p.L this can become as little as 1 nL in capillary HPLC. Pretreatment of the sample may be necessary in order to protect the stationary phase in the column from deactivation. By employing supercritical fluids such as carbon dioxide, pretreatment can be bypassed in many instances so that whole samples from industrial and environmental matrices can be introduced directly into the column. This is due to the fact that the fluid acts as both extraction solvent and mobile phase. Post-column electrochemistry has been demonstrated. For example, fast-scan cyclic voltammo-grams have been recorded as a function of time after injection of microgram samples of ferrocene and other compounds in dichloromethane solvent and which are eluted with carbon dioxide at pressures of the order of 100 atm and temperatures of 50°C the chromatogram is constructed as a plot of peak current vs. time [18]. 

However, as already mentioned earlier, high pressure liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) has evolved in the last few years as the major bioanalytical technique for the bioanalysis of analytes in biological matrices. This is reflected also in a number of LC-MS/MS assays for the determination of dihydropyridine calcium antagonists in biological fluids (Carvalho et al. 2001, Schug et al. 2002 Kang et al. 2004). 

Quantification. High Pressure Liquid Chromatography. In serum or cerebrospinal fluid sensitivity 20ng/ml, UV detection—I. Nilsson-Ehle et al., J. infect. Dis., 1977,135, 414-422. 

Quantification. High Pressure Liquid Chromatography. Review of methods for the analysis of antibiotics in biological fluids—I. Nilsson-Ehle, J. liq. Chromat., 1983, 6, 251-293. 

High Pressure Liquid Chromatography. In plasma chloramphenicol and chloramphenicol succinate, detection limits 500 ng/ml for chloramphenicol and 1 pg/ml for the succinate, UV detection—R. Velagapudi et al., J. Chromat., 1982, 228, Biomed. AppL, 17, 423-428. In cerebrospinal fluid, plasma or serum sensitivity 100 to 200ng/ml, UV detection—R. H. B. Sample etal., Antimicrob. Ag. Chemother., 1979,15, 491-493. 

High Pressure Liquid Chromatography. In plasma detection limit 20 ng/ml, UV detection—R. W. Bury and P. J. Keary, ibid., 350-353. In plasma, urine, or cerebrospinal fluid detection limit 20 ng/ml, UV detection—J. A, Sinkule and W. E. Evans, J. Chromat., 1983, 274 Biomed. AppL, 25, 87-93. 

High Pressure Liquid Chromatography. In raw material, dosage forms or biological fluids detection limit lOpg using... 

High Pressure Liquid Chromatography. In biological fluids sensitivity, 1 jig/ml for ibuprofen in plasma, 5 pg/ml for ibuprofen or the hydroxy or carboxy metabolites in urine, UV detection—G. F. Lockwood and J. G. Wagner, J. Chromat., 1982,232 Biomed. AppL, 21, 335-343. 

Quantification. High Pressure Liquid Chromatography. In plasma sensitivity < 100 ng/ml, UV detection—K. B. Alton, J. Chromat., 1980, 221 Biomed. Appl., 10, 337-344. In serum, plasma, cerebrospinal fluid, or synovial fluid sensitivity 40 ng/ml, fluorescence detection V. L. Pascucci et al, /. pharm. ScL,1983, 72, 1467-1469. 

Quantification. High Pressure Liquid Chromatography-Radioimmunoassay. In biological fluids sensitivity 1 ng/ml, fluorescence detection—P. W. Twitehett et al., J. Chromat., 1978,150, 73-84. 

One of the above-mentioned examples comprises the investigation of hydrocarbon radicals formed by pyrolysis of fluids, such as indene and phenyl-substituted alkanes at about 843 K (36). As a reaction tube, a silica capillary of 1.4 mm inner and 4.7 mm outer diameter was used, which was connected to high-pressure stainless-steel tubing through Teflon seals. It was equipped with pressure transducers on both ends and tested to withstand a maximum pressure of 28 MPa. The hydrocarbon to be pyrolyzed was cycled between a reservoir and the reaction tube by a high-pressure liquid chromatography (HPLC) pump. The tube was heated by a preheated stream of N2 as described above. 

The use of separation techniques, such as gel permeation and high pressure liquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of silicones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of silicone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is applicable up to 10,000 Da (487). 

Ascalone, V. Assay of trimethoprim, sulfamethoxazole and its N4-acetyl metabolite in biological fluids by high-pressure liquid chromatography. J.High Resolut.Chromatogr.Chromatogr.Commun., 1980,3, 261-264... 

Bicchi C., Rubiolo P., Fresia M., Analysis of Constituents of Iris Rhizomes Part III - Packed Column Supercritical Fluid Chromatography and High Pressure Liquid Chromatography of Iridals from Rhizomes of Iris pallida L., Phytochemical analysis 1996, 7, 37-41. 

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