Superheated chromatography

Superheated water extraction has been coupled to superheated chromatography both on line [97] and offline with an intermediate sorbent concentration step [98]. Mixtures with other solvents have been used at high temperatures, such as dimethyl sulfoxide [99] and methanol [100]. Superheated deuterium chromatography has been used so that it could be coupled to NMR spectroscopy [101]. 

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. 

Boundaries in chromatography and extraction are blurring, as evident from the relation between GC, SFC and HPLC, the use of superheated/subcritical water for extraction and chromatography, and the role of enhanced fluidity solvents and pressurised fluid extractions [2]. Extraction is an extreme form of chromatography. Separation science recognises that there is unity in the... 

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. 

With an increased interest and awareness of the impact of society and industry on the environment, there has been a significant attempt in recent years to reduce or replace the usage of organic solvents. Much early work in this area concentrated on the application of supercritical and subcritical carbon dioxide, but in recent years superheated (or subcritical/pressurized hot) water (SHW) has become of interest for both chromatography and extraction [43,54], The earliest work was reported by GuUlemin et al. [55], who used the term thermal aqueous liquid chromatography. As well as using SHW for the separation of... 

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. M. Smith, O. Chienthavorn, I. D. Wilson, and B. Wright, Superheated deuterium oxide reversed-phase chromatography coupled to proton nuclear magnetic resonance spectroscopy, Anal. Commun. 35 (1998), 261-263. 

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

S. Saha, R. M. Smith, E. Lenz, and I. D. Wilson, Analysis of a ginger extract by high-performance liquid chromatography coupled to nuclear magnetic resonance spectroscopy using superheated deuterium oxide as the mobile phase, J. Chromatogr. A 991 (2003), 143-150. 

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