Superheated water chromatography

Superheated water at 100°-240 °C, with its obvious benefits of low cost and low toxicity, was proposed as a solvent for reversed-phase chromatography.59 Hydrophobic compounds such as parabens, sulfonamides, and barbiturates were separated rapidly on poly(styrene-divinyl benzene) and graphitic phases. Elution of simple aromatic compounds with acetonitrile-water heated at 30°-130 °C was studied on coupled colums of zirconia coated with polybutadiene and carbon.60 The retention order on the polybutadiene phase is essentially uncorrelated to that on the carbon phase, so adjusting the temperature of one of the columns allows the resolution of critical pairs of... 

Miller and Hawthorne [416] have developed a chromatographic method that allows subcritical (hot/liquid) water to be used as a mobile phase for packed-column RPLC with solute detection by FID, UV or F also PHWE-LC-GC-FTD couplings are used. Before LC elution the extract is dried in a solid-phase trap to remove the water. In analogy to SFE-SFC, on-line coupled superheated water extraction-superheated water chromatography (SWE-SWC) has been proposed [417]. On-line sample extraction, clean-up and fractionation increases sensitivity, avoids contamination and minimises sources of error. 

Most recently, a further study has been performed using superheated-water HPLC with NMR and MS to analyse a mixture of sulphonamides [68]. The chromatography was performed as before with D20-phosphate buffer (pD 3.0) as eluent. A temperature gradient from 160 to 200 °C at 2°C min-1 was employed. A mixture of four sulphonamides, i.e. sulacetamide, sulphadiazine, sulfamerazine and sulfamethazine, was separated in this system with UV, NMR and MS detection. It rapidly became clear from a study of the spectroscopic data that while sulfacetamide and sulfadiazine gave the expected NMR and mass spectra, those for sulfamerazine and sulfamethazine did not. These compounds gave spectra that were 3 and 6 mass units higher than expected,... 

These investigations of the use of superheated water with NMR spectroscopy are still at an early stage and have not yet been applied to real problems. Many questions remain to be answered concerning the suitability of this chromatography for thermally labile compounds, and with the current stationary phases available the technique is probably limited to moderately polar compounds. However, the technique is readily implemented and may in time prove to be a useful addition to the armoury of HPLC-NMR methods. 

Smith, R.M. and Burgess, R.J. 1997. Superheated water as an eluent for reversed-phase high-performance liquid chromatography. Journal of Chromatography A, 785 49-55. 

Three main aims have driven these studies the use of temperature as a variable to optimize separations, an interest in improved efficiency, and the potential for green separations methods, such as superheated water chromatography, which can eliminate the organic solvent from the mobile phase. 

TABLE 18-3. Superheated Water Chromatography of Nutraceuticals and Natural Products... 

R. M. Smith and R. J. Burgess, Superheated water—A clean eluent for reversed-phase high performance liquid chromatography, Anal. Commun. 33 (1996), 327-329. 

R. M. Smith, R. J. Burgess, O. Chienthavorn, and J. R. Stuttard, Superheated water a new look at chromatographic eluents for reversed-phase liquid chromatography LC-GC Internal. 12 (1999), 30-36. 

R. Nakajima, T. Yarita, and M. Shibukawa, Analysis of alcohols by superheated water chromatography with flame ionization detection, Bunseki Kagaku 52 (2003), 305-309. 

R.Tajuddin and R. M. Smith, On-line coupled superheated water extraction (SWE) and superheated water chromatography (SWC), Analyst 17 (2002), 883-885. 

O. Chienthavorn, R. M. Smith, S. Saha, I. D. Wilson, B. Wright, S. D. Taylor, and E. M. Lenz, Superheated water chromatography-nuclear magnetic resonance spectroscopy and mass spectrometry of vitamins, J. Pharm. Biomed. Anal. 36 (2004), 477-482. 

A new topic is now included Chapter 20 about quahty assurance. Part of it could be found before in chapter 19 but now the subject is presented much broadly and independent of Analytical HPLC . Two chapters in the appendix were updated and expanded by Bruno E. Lendi, namely the ones about the instrument test (now chapter 25) and troubleshooting (now chapter 26). Some new sections were created 1.7, comparison of HPLC with capillary electrophoresis 2.11, how to obtain peak capacity 8.7, van Deemter curves and other coherences 11.3, hydrophilic interaction chromatography 17.2, method transfer 18.4, comprehensive two-dimensional HPLC 23.3, fast separations at 1000 bar 23.5, HPLC with superheated water. In addition, many details were improved and numerous references added. 

GC is the most commonly used separation method in the analysis of BTEX from environmental samples. Liquid chromatography (LC) analysis with superheated water or water-dimethylsulfoxide (DMSO) mixmres has also been reported. In both cases a reduction in the dielectric constant of the mobile phase for the separation of nonpolar analytes was studied. The results showed how the rise in temperamre required a decrease in DMSO in order to achieve the same retention time. 

Kephart, T. S. and Dagsputa, P. K., Superheated water eluent capillary liquid chromatography, Talanta, 56, 977-987, 2002. 

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