Wavelenght-resolved laser-induced fluorescence detection in cappillary electrophoresis: naphtalenesulphonates in river water.

Capillary electrophoresis (CE) is combined with wavelength-resolved laser-induced fluorescence detection for the environmental analysis of naphthalenesulphonates (NS) in river water samples. The method enables the detection and the identification of non- as well as hydroxy- and amino-substituted NS. An approximate 30-fold sample concentration is performed by off-line solid-phase extraction prior to the CE separation. The native-fluorescent NS are excited at 280 nm or 325 nm by an excimer dye laser combination providing tunable UV radiation. Wavelength-resolved fluorescence-emission spectra are recorded on-line by an intensified diode-array detector mounted on a spectrograph. Since the emission spectra are strongly affected by the type and pattern of substitution, they provide much structural information. In combination with migration times identification is possible, if standards are available. The low to sub-μg

Miniaturised pressurised liquid extraction of chloroanilines from soil with subsequent analysis by large-volume injection-gas chromatography-mass spectrometry

A number of chloroanilines were extracted from soil by means of miniaturised pressurised liquid extraction (PLE). The extraction procedure was optimised for both large-volume on-column (LV-OC) and programmed-temperature vaporisation (PTV) injections combined with GC-MS. Hexane was the only extraction solvent suited for LV-OC and hexane/acetone gave the best results when using a PTV. Overall, the hexane/acetone-plus-PTV procedure shows better results than the hexane-plus-LV-OC method in terms of analyte recovery (36-109% versus 5-87%), repeatability (8-13% versus 4-31%) and detection limits. Both approaches allow detection of the chloroanilines in complex soil samples down to the 5-50 ng/g range. However, the PTV-based procedure is superior as regards robustness: over one hundred samples can be analysed without any maintenance being required. © 2004 Elsevier B.V. All rights reserved

Role of the retaining precolumn in large-volume on-column injections of volatiles to gas chromatography

In the present study the retaining precolumn, which is commonly used in a set-up for large-volume on-column injections, or when solid-phase extraction (SPE) or liquid chromatography is coupled to gas chromatography (GC), was removed after varying its length from the standard length of 3 m down to zero. A dramatic increase of the evaporation rate of the injected organic solvent was obtained from a typical value of 100 μl/min up to 300 μl/min. The increased evaporation rate allowed (i) injection of a larger volume in the same retention gap, (ii) faster injection/transfer of the organic solvent and (iii) reduction of the transfer temperature. As volatile compounds under partially concurrent solvent evaporation conditions are easily lost once the organic solvent has been removed via a solvent-vapour exit (SVE), the parameters for large-volume injection, i.e. the evaporation rate and injection speed, were optimised using accurate measurements of the real flow-rate of the carrier gas into the GC system. All these options have been evaluated over the last 4 years. In order to demonstrate that omitting the retaining precolumn had no effect on the application range of the on-column interface, analytes as volatile as benzene were injected into GC-MS using 50-200 μl of n-pentane solutions. Contaminants were extracted from river water and wastewater into n-pentane using in-vial liquid-liquid extraction. The detection limits for benzene, toluene, ethylbenzene and m-xylene were ∼10 ng/l. To obtain optimum results the SVE had to be closed 1 s before the end of evaporation. Several brands of n-pentane were analysed to check for the presence of benzene. Most of them contained interfering compounds and benzene at the low μg/l level and therefore had to be cleaned by means of column chromatography. As another example

Evaluation of modulators and electron-capture detectors for comprehensive two-dimensional GC of halogenated organic compounds

Different cryogenic and a heated GCxGC modulator(s) were evaluated and compared for the analysis of high-boiling halogenated compounds. The cryogenic modulators investigated were: (i) the longitudinally modulated cryogenic system; (ii) the liquid-nitrogen-cooled jet modulator (KT2001); (iii) a dual-jet CO2 modulator (made in-house); (iv) a semi-rotating cryogenic modulator (made in-house) and (v) a CO2 loop modulator (KT2003); the heated modulator was the slotted heater system (sweeper). Each modulator was optimised with respect to analyte peak widths at half height in the second-dimension. n-Alkanes, chlorinated alkanes, polychlorinated biphenyls (PCBs) and fluorinated polycyclic aromatic hydrocarbons (F-PAHs) were used as test analytes. The flow rate of the coolant was found to be an important parameter, i.e. the flow rate of the gaseous nitrogen in the KT2001, and of the liquid CO2 in the other cryogenic modulators. For the slotted heater the stroke velocity and pause time were important parameters. This modulator had a limited application range in terms of temperature due to a necessary 100 °C difference between sweeper and oven temperature. All cryogenic modulators were found to be suitable for the GCxGC analysis of high-boiling compounds, but the CO2 modulators are to be preferred to the KT2001 due to a wider application range and slightly narrower peaks. As regards the performance of three commercially available electron-capture detectors (ECDs), the aim was to obtain narrow peak widths in GCxGC, i.e. to avoid band broadening caused by the cell volume. The most important parameters were the flow rate of the make-up gas and the detector temperature which both should be as high as possible. Comparison of analyte peak widths obtained with ECD mode and flame ionisation detection (FID) showed that all ECDs exhibited band broadening compared to the FID. The narrowest peaks were obtained with the Agilent micro-ECD, which has a cell volume of only 150 ?