Selective supercritical fluid extraction of organochlorine pesticides and herbicides from aqueous samples

Supercritical fluid extraction (SFE) of organochlorine pesticides and two classes of herbicides is achieved from a water matrix using solid-phase extraction prior to SFE. This technique allows for the removal of water prior to supercritical elution with carbon dioxide. Selectivity of extraction between these two groups of compounds is demonstrated by adding 10% methanol modifier to the CO2 after an initial extraction with CO2 only. The first extraction (CO2 only) is used to preferentially remove organochlorine pesticides (approximately 90%) with minimal extraction of the herbicides (less than 5%). Modified CO2 is then used to extract the herbicides, and approximately 90% is recovered. The extracts are analyzed by either gas chromatography with mass selective detection for organochlorine pesticides or reversed-phase high-performance liquid chromatography for the herbicides. This SFE selective extraction may prove useful in segregating pesticides from herbicides prior to analysis. In addition, chromatographic selectivity is also achieved because organochlorine pesticides cannot be determined using reversed-phase high-performance liquid chromatography, and the herbicides are not directly amenable to gas chromatographic separation

Selective extraction of organochlorine and organophosphorus pesticides using a combined solid phase extraction-supercritical fluid extraction approach

Supercritical fluid extraction (SFE) of pesticides has been investigated for the possibility of selective extraction between organochlorine (OCPs) and organophosphorus (OPPs) compounds. Three OCPs and OPPs were trapped onto a C18 Empore® extraction disk prior to SFE with CO2 only and methanol-modified CO2 at various pressures and constant temperature. The results indicate that OCPs can be quantitatively extracted using CO2 only whereas OPPs require a modifier for extraction

Supercritical fluid extraction of organochlorine pesticides from an aqueous matrix

Supercritical fluid extraction (SFE) conditions were optimised for the removal of organochlorine pesticides (OCPs) from water. OCPs were collected and extracted from solid-phase extraction disks (Empore) and also directly from a water sample using a modified extraction cell. High recoveries (>90%) were obtained for two of the three OCPs with Empore disks. Despite the good solubility of OCPs in pure CO2, the analyte recoveries decreased when they were extracted directly from water. Three different flow-rates were used in the direct SFE with no apparent change in recovery, indicating that extraction was diffusion-controlled. The effect of increasing the ionic strength of the aqueous sample on analyte recovery was investigated

Predicting solubility in supercritical fluid extraction using a neural network

A neural network has been constructed for prediction of the solubility of analytes in supercritical carbon dioxide. Preliminary studies for the input of molecular structure into the network indicates that connectivity indices are adequate to provide structural information in a condensed form. This allows neural networks, which would otherwise be very extensive, to have reduced training times; it also reduces the possibility of memorization of the training data and over-training of the network

Experimental design approach for supercritical fluid extraction

Experimental design with multilinear regression has been used to examine the relative contribution of the main experimental variables during supercritical fluid extraction. Six steroidal compounds of various solubilities in supercritical CO2 were considered. The results indicate that the density of the supercritical fluid has the greatest effect on the solubilisation and transfer of steroid from extraction cell to collection device. The minimum number of cell volumes of supercritical CO2 required for effective extraction was experimentally determined

Extraction of surfactants from aqueous media by supercritical fluid extraction

Two methods for the supercritical fluid extraction (SFE) of analytes from aqueous media were evaluated: direct extraction and solid-phase extraction (SPE) discs. SPE discs were used to isolate an alcohol phenol ethoxylate (APE) non-ionic surfactant from an aqueous matrix prior to extraction using supercritical CO2. This method was compared with the direct SFE of surfactant from the aqueous matrix. The second method allowed the continuous extraction of analyte from water using a modified extraction cell. The extraction cell was designed to maximize the exposure of the analyte to supercritical CO2 interactions and thereby allow the continuous extraction of the analyte from an aqueous sample. The results suggest that there is a difference in the effects of diffusion and equilibrium on the extraction process for the two methods of extraction studied

Determination of octanol-water partition coefficients using gradient liquid chromatography

The use of liquid chromatography to estimate octanol-water partition coefficients, log k(ow), has been demonstrated. The capacity factor with a mobile phase of 100% water, k(w), has been found to be a useful chromatographic parameter. Values of k(w) were derived from a computer software package (Hipac-G), designed for optimization and simulation of gradient LC systems. The chromatographic parameter, k(w) correlates well with both literature and isocratic LC-generated log k(ow) values. The gradient LC method could be extended to a wider range of test compounds

Quantitative structure-extraction relationships: A model for supercritical fluid extraction

A rapid method for predicting the solubility of an analyte in supercritical carbon dioxide is reported. The method is based on determining the hydrophobic interaction and the solubility parameter from easily obtained constants. The simplicity of the method is demonstrated with respect to a group of substituted benzophenones. Hydrophobicity is derived from log P values as determined by the Hansch-Leo method, whereas the solubility parameter is determined by the method of Fedors. Multilinear regression has indicated a direct correlation between the amount of analyte extracted, expressed as the mole fraction, and the log Pl solubility parameters

Determination of antifungals in rodent diet by supercritical fluid extraction followed by packed column supercritical fluid chromatography with ultraviolet detection

Supercritical fluid extraction (SFE) followed by packed column supercritical fluid chromatography with ultraviolet detection was evaluated as a quantitative method for determining 4 antifungals (fluconazole, tioconazole, hexaconazole, and UK-47,265) in rodent diet. Chromatography was achieved with a cyano-bonded silica column, UV detection at 210 nm, and methanol-modified supercritical carbon dioxide as mobile phase. The effects of modifier concentration, temperature, and column pressure on antifungal retention time was studied. Off-line SFE was optimized at 2 spike levels, ranging from 0.5 to 10 g/kg, for each of the 4 antifungals. Average recoveries ranged from 79.0% for UK-47,265 to 96.5% for hexaconazole. Overall, the procedure provides a suitable method for analyzing antifungals in spiked rodent diet

Z-band alternatively spliced PDZ motif protein (ZASP) is the major o-linked β-N-acetylglucosamine-substituted protein in human heart myofibrils

We studied O-linked β-N-acetylglucosamine (O-GlcNAc) modification of contractile proteins in human heart using SDS-PAGE and three detection methods: specific enzymatic conjugation of O-GlcNAc with UDP-N-azidoacetylgalactosamine (UDP-GalNAz) that is then linked to a tetramethylrhodamine fluorescent tag and CTD110.6 and RL2 monoclonal antibodies to O-GlcNAc. All three methods showed that O-GlcNAc modification was predominantly in a group of bands ∼90 kDa that did not correspond to any of the major myofibrillar proteins. MALDI-MS/MS identified the 90-kDa band as the protein ZASP (Z-band alternatively spliced PDZ motif protein), a minor component of the Z-disc (about 1 per 400 α-actinin) important for myofibrillar development and mechanotransduction. This was confirmed by the co-localization of O-GlcNAc and ZASP in Western blotting and by immunofluorescence microscopy. O-GlcNAcylation of ZASP increased in diseased heart, being 49 ± 5% of all O-GlcNAc in donor, 68 ± 9% in end-stage failing heart, and 76 ± 6% in myectomy muscle samples (donor versus myectomy p < 0.05). ZASP is only 22% of all O-GlcNAcylated proteins in mouse heart myofibrils