On-line solid-phase extraction coupled to supercritical fluid chromatography to determine phenol and nitrophenols in water.

Determining of phenol and nitrophenols using solid-phase extraction on-line coupled to supercritical fluid chromatography (SFC) is studied. SFC quickly separated the compounds studied, in less than 6 min, and solid-phase extraction was used to decrease the limits of detection. C18, PLRP-S and a highly cross-linked styrene-divinylbenzene copolymer in a 10 x 3 mm I.D. laboratory-packed precolumn were tested comparatively as sorbents in the preconcentration step. Tetrabutylammonium bromide was used as ion-pair reagent in the extraction process to increase breakthrough volumes, mainly for phenol. Performance of the method was checked with tap and river waters.

Packed-column supercritical fluid chromatography coupled with solid-phase extraction for the determination of organic microcontaminants in water.

A multiresidue method for the analysis of 35 common contaminants (including pesticides, polycyclic aromatic hydrocarbons and phenols) in lough and river waters from Castilla y León Spanish region, by using supercritical fluid chromatography (SFC) with five silica packed columns, is described. In order to decrease the detection limits, a preconcentration step by coupling solid-phase extraction to the SFC system was used. The different variables affecting the extraction procedure were studied and optimized, selecting the Isolute Env+ as the best sorbent. The detection limits achieved ranged from 0.4 to 2.6 micrograms l-1.

Determination of polycyclic aromatic hydrocarbons in waters by use of supercritical fluid chromatography coupled on-line to solid-phase extraction with disks.

The potential of supercritical fluid chromatography (SFC) coupled on-line to solid-phase extraction (SPE) with disks for determining sixteen different polycyclic aromatic hydrocarbons (PAHs) was assessed. A preliminary study of the chromatographic separation was conducted that led to the use of SPE coupled to SFC for improved detection limits. Disks of two different materials, i.e., C18 and polystyrene-divinylbenzene, were assayed in terms of the variables influencing the extraction step. C18 disks provided the best results, with detection limits ranging from 0.1 to 1.5 micrograms l-1. The ensuing method was applied to river and tap water with good repeatability and reproducibility, and no interference from the sample matrix.

Determination of the 2-bromomethyl-2-(2,4-dichlorophenyl)-1, 3-dioxolan-4-yl)methyl benzoate diastereoisomers by supercritical fluid chromatography.

The study of the separation and determination of the two 2-bromomethyl-2-(2,4-dichlorophenyl)-1,3-dioxolan-4-yl-methyl benzoate diastereoisomers is presented in this work. The separation was achieved using packed column supercritical fluid chromatography. Three stationary phases were checked, the C(18) packing providing the best results. The influence of several parameters (nature and percentage of modifier, temperature and pressure) on the separation were also evaluated. The baseline separation (R(s)=1.78) of the compounds was obtained in only 2 min, using a C(18) column, a pressure of 100 bar, a temperature of 35 degrees C, a flow-rate of 2. 5 ml/min and 5% of 2-propanol as organic modifier. Under these conditions the unwanted diastereoisomer (trans) was eluted before the main compound (cis), so the determination of the purity was more accurate.

Use of light and scanning electron microscopy to examine colonisation of barley rhizosphere by the nematophagous fungus Verticillium chlamydosporium.

Barley roots were readily colonised by the nematophagous fungus Verticillium chlamydosporium. Light microscopy (LM) but also low temperature scanning electron microscopy (LTSEM) revealed details of the colonisation process. Hyphae were found on the rhizoplane often with dictyochlamydospores. Hyphae of V. chlamydosporium penetrated epidermal cells, often by means of appressoria. A hyphal network was formed in epidermal and cortical cells. Likewise, hyphal coils were found within root cells next to transverse cell walls. Cortical cells were the limits of fungal colonisation, since no hyphae were seen in the vascular cylinder. Modifications of root cell contents (phenolic droplets and callose appositions) were common three weeks after inoculation with V. chlamydosporium. These features may indicate induction of plant defence reactions in late stages of root colonisation by the fungus. Both LTSEM and LM have proved extremely useful to describe root colonisation by the fungus. The results found may have implications in the mode action of nematophagous fungi against plant parasitic nematodes.