Orapin Chienthavorn

Buffered superheated water as an eluent for reversed-phase high performance liquid chromatography

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 °C, 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.

Selective deuterium exchange during superheated heavy water chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry of sulfonamides.

Superheated deuterium oxide has been investigated as an eluent for reversed-phase HPLC on a polystyrene-divinylbenzene column with UV, 1H NMR and MS detection using a series of sulfonamides as model compounds. In the course of these studies, a selective, specific and efficient deuteration of the methyl groups on a pyrimidine ring was observed during chromatography of certain of the sulfonamides. The potential of this methodology for producing deuterium-labelled compounds from substances bearing suitable substituents is considered. The utility of HPLC-NMR-MS as a means for studying on-column reactions is discussed.

Superheated deuterium oxide reversed-phase chromatography coupled to proton nuclear magnetic resonance spectroscopy

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.

Effective and Reusable Monolith Capillary Trap of Nitrosamine Extraction by Superheated Water from Frankfurter Sausage

A novel, simple, rapid, and inexpensive method of extraction and cleanup of nitrosamines from frankfurter sausage was achieved with a capillary filled with monolith of either polystyrene-co-divinylbenzene (PS-DVB), Polydivinylbenzene (P-DVB), or silica that had been fabricated. The study of capability in trapping nonpolar matrix and monolith capillaries with varied lengths revealed that a silica monolith gave the best result for nitrosamine determination. With an online coupling between superheated water extraction (SWE) and silica monolith capillary connected to a 5% phenyl-methylpolysiloxane column, factors affecting the extraction and determination, namely, sensitivity with and without the monolith, reusability, injection-injection repeatability, capillary-capillary precision, and chromatographic separation, were investigated. This confirmed the feasibility of the method. The optimal length of silica monolith capillary was 30 mm, offering reuse more than 20 times. Separation and quantification of selected volatile nitrosamines were carried out using gas chromatography (GC) coupled with either a flame ionization detector (FID) or mass spectrometer (MS). The overall extraction and determination method determined by GC-MS allowed for a recovery of 75-88% with a <5% relative standard deviation (RSD) and detection limit of 2-5 ng of injected nitrosamine.

Pressurized Liquid and Superheated Water Extraction of Active Constituents from Zingiber cassumunar Roxb. Rhizome

Active compounds, terpinene-4-ol and (E)-1-(3,4-dimethoxyphenyl) butadiene (DMPBD), displaying anti-inflammatory activity, were successfully extracted from the rhizome of Zingiber cassumunar Roxb. by pressurized liquid extraction (PLE) using methanol or ethanol and by superheated water extraction (SWE). Optimum conditions of both techniques were 1 mL/min flow rate and 5 min static time. The extraction temperature and dynamic time of the PLE and the SWE were 100°C 5 min and 140°C 20 min, respectively. Compared with water distillation, solvent sonication, and Soxhlet extraction, the PLE produced the highest amount of DMPBD and terpinene-4-ol, whereas the SWE and water distillation provided similar results.

Superheated Water Extraction of Lime Peel: a Comparison with Conventional Methods

Abstract A comparative study of superheated water extraction (SWE) with several conventional methods was performed on lime (Citrus aurantifolia, Swing) peel. Some superheated water parameters affecting the extraction were studied, such as temperature, dynamic and static time, and flow rate. At 130°C, a static and dynamic time of 5 and 15 min, and a water flow at 1 mL min−1, the main components of aroma compounds were successfully removed and collected in 2 mL hexane. Separation and identification of the components were carried out by using gas chromatography‐flame ionization detection (GC‐FID) and GC‐MS. The extraction technique was compared with steam or water distillation and organic solvent sonication. With the same amount of the extract, the highest oxygenated compound yield was found for SWE, while the less valuable monoterpene yields were maximized when using dichloromethane sonication. The composition of oxygenated components present in the SWE extracts, namely linalool, neral, terpineol, geranial, and geraniol, were 4.94, 19.13, 13.03, 30.00, and 10.48%, respectively. Compared in terms of the equal amount of internal standard, water distillation gave highest efficiency in removal of oxygenated components; however, the method required a long extraction time, making it less attractive. The proposed technique was also modified by adding 10–30% methanol or ethanol into the water. A high percentage of alcohol dramatically increased the extraction efficiency of monoterpene but slightly for the oxygenated components. The modified superheated water extraction, therefore, is considered to be an alternative technique to obtain high extraction efficiencies of low polar organics and possibly at a lower temperature.

Fluorescence detection in packed-column supercritical fluid chromatographic separations

Abstract Propranolol and (9-acridinylamino)propranolol (9-AAP) have been separated by supercritical fluid chromatography with fluorescence detection by employing a simple pressure restrictor to protect the detector flow cell. The separations were carried out using a μBondapak C 18 column with a mobile phase of 1% triethylamine in methanol-modified CO 2 at 40°C. The excitation and emission wavelengths for propranolol were 317 nm and 352 nm and for 9-AAP 245 nm and 413 nm, respectively. The sensitivity for propranolol detected by the fluorescence detector was 5.7 ng, approximately 8 times higher than by UV spectroscopic detection and was similar to the results for HPLC with fluorescence detection. A higher sensitivity (0.4 ng) was found for 9-AAP with fluorescence detection.

Nitrosamines Extraction from Frankfurter Sausages by using Superheated Water

An efficient, rapid, and inexpensive method for extraction and clean-up of some selected volatile nitrosamines from frankfurter sausages was developed by using superheated water coupled with solid-phase extraction. Because a coextraction of lipid caused a serious problem during the extraction, a subsequent clean-up step using fat-selective Florisil adsorbent with 60% diethyl ether-dichloromethane was then necessary. Various factors affecting superheated water extraction, such as flow rate, extraction temperature, dynamic time, and static time were optimized by using a full factorial design with three replicates. The optimal extraction temperature was 140°C with dynamic and static time of 10 and 5 min, respectively, and a flow rate of 1.0 mL/min. Separation and quantification of nitrosamines were carried out using GC-FID and GC-MS in selected ion monitoring mode. Direct application of this method to frankfurter samples allowed overall recoveries of N-nitrosamines in the range of 81-106% with < 10% RSD, and the detection limit of the coupling method ranged between 0.47-1.48 ng nitrosamines injected.

Direct Writing of Channels for Microfluidics in Silica by MeV Ion Beam Lithography

The lithographic exposure characteristic of amorphous silica (SiO2) was investigated for 6.8 MeV 16O3+ ions. A programmable proximity aperture lithography (PPAL) technique was used for the ion beam exposure. After exposure, the exposed pattern was developed by selective etching in 4% v/v HF. Here, we report on the development of SiO2 in term of the etch depth dependence on the ion fluence. This showed an exponential approach towards a constant asymptotic etch depth with increasing ion fluence. An example of microfluidic channels produced by this technique is demonstrated.

Inexpensive simple extraction of trace PAHs from water using PS-DVB monolithic beads

A new simple and sensitive analytical technique based on polystyrene-divinyl benzene (PS-DVB) monolithic bead extraction followed by gas chromatography-mass spectroscopic detection (GC-MS) was developed for the determination of polycyclic aromatic hydrocarbons (PAHs) in water. The PS-DVB monolithic bead was fabricated and used as the adsorbent. The experimental parameters controlling the performance of the bead extraction were optimized. Calibration curves showed excellent linear fits, with r2 > 0.995 for all PAHs in the 2–30 000 ng mL−1 range. The limits of detection (LODs) ranged from 0.01 to 0.47 ng mL−1. Recoveries of the PAHs in environmental water samples spiked at a concentration of 500 ng mL−1 were 72–109%, while they were 69–114% for water spiked at 20 ng mL−1. Both intraday and interday repeatabilities were high, with RSDs for 16 PAHs spiked standard solutions being less than 10%. The present study indicated that the proposed method is well suited for the quantification of PAHs in environmental and drinking water samples.