Superheated heavy water can be used as the eluent for reversed-phase chromatography with on-line HPLC-NMR and HPLC-NMR-MS detection. The method has been demonstrated for the separation of model drugs (analgesics and caffeine) on a poly(styrene-divinylbenzene) stationary phase in isothermal and temperature-programmed modes. One-and two-dimensional spectra could be obtained with less interference from the mobile phase than with conventional HPLC-NMR eluents. Unlike supercritical fluid chromatography-NMR, the spectra could be measured at room temperature and atmospheric pressure. The combination of superheated water HPLC-NMR-MS chromatography enables both NMR and MS spectra to be obtained simultaneously for the same sample.
The on-line coupling of superheated deuterium oxide reversed-phase liquid chromatography and NMR spectroscopy overcomes many of the problems faced by conventional HPLC-NMR systems and provides a new method for the examination of moderately polar organic compounds. Samples of salicylamide and barbiturates were separated on a polystyrene-divinylbenzene (PS-DVB) column and transferred to a NMR spectrometer for on-line or stop-flow detection. This approach enables isothermal and temperature gradient reversed-phase HPLC-NMR spectroscopy to be readily carried out without the use of deuterated organic solvents. Unlike supercritical fluid chromatography-NMR spectroscopy, the method can be carried out with a low pressure HPLC-NMR probe.
SummaryInorganic buffers have been used to control the pH of a superheated water eluent for reversed-phase liquid chromatography. Using a temperature gradient from 70-190 ~ the relative order of elution of a series of sulfonamides on a polystyrene-divinyl benzene column was determined at pH 3, 7 and 11. The separations were compared with conventional reversed-phase separations on polymer and ODS-bonded silica columns. The apparent pKa values of selected sulfonamides at elevated temperatures were determined from their retention factors across in a range of superheated buffers and the values were compared to those reported at room temperature.
In this study a laboratory-made superheated water system was applied in order to extract some pesticides from sand, sediment and soil samples. Extraction efficiencies were investigated at different time intervals with regard to temperature, type and amount of organic modifier. Pesticides were removed from the aqueous extract using dichloromethane as a trapping solvent. The optimal extraction temperature from sand specimens for malathion, heptachlor, aldrin, dieldrin, butachlor, metalaxyl and propiconazole was found to be 160 degrees C, while those for chlordane and thiobencarb were 120 degrees C and 180 degrees C, respectively. The static extraction time for heptachlor, aldrin, dieldrin, butachlor and metalaxyl was found to be 15 min, whereas for malathion and thiobencarb it was 5 min, and for chlordane and propiconazole it was 10 and 20 min, respectively. Recoveries for the extractions of the pesticides from sand under optimized extraction conditions ranged between 96 and 101%. Those obtained from sediment under such conditions were unsatisfactory, and were consequently improved by adding an organic modifier to the superheated water, and sodium chloride to the extract during liquid-liquid extraction. These procedures were optimized further for the parameters described and recoveries exceeded 91%, with the exception of butachlor. The extraction technique was also applied to soil samples at a reduced water flow rate of 0.5 mL min(-1), yielding recoveries of 82-105%, and 76% for dieldrin. The reproducibilities, expressed as relative standard deviations (RSDs), ranged between 2 and 13%.
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