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V Pichon

Publications and source records attributed to V Pichon.

11 recordsLinked to original sources
PubMed2006

An interlaboratory study to evaluate potential matrix reference materials for herbicides in water.

Matrix reference materials (MRM) are essential tools for the validation of analytical protocols. Nowadays, there are no such materials for the determination of herbicides in water. Pesticides stored in acetonitrile and stored on solid phase extraction (SPE) cartridges previously percolated with a water sample spiked with triazines and phenylureas have proven to be good candidates for reference materials because of their satisfactory stability under appropriate temperature conditions. To evaluate the behaviors of these materials containing pesticides and to be analyzed by liquid chromatography, a collaborative study including 15 laboratories has been organized. Observed reproducibility on candidate materials after the removal of extreme results was 16.1% for the vials with pesticides in acetonitrile (at around 0.125 mg/L) directly analyzed, 29.2% for a water sample spiked with the pesticides (at around 0.5 microg/L) analyzed after preconcentration on a cartridge and 26.7% for the cartridges previously percolated with a water containing the pesticides (250 mL at around 0.5 microg/L for each pesticide) analyzed after elution. Such dispersion values are quite compatible with the requirement of a further certification for such materials.

Acetonitriles↗
PubMed2004

Retention mechanism of analytes in the solid-phase extraction process using molecularly imprinted polymers. Application to the extraction of triazines from complex matrices.

Two molecularly imprinted polymers (MIPs), prepared in dichloromethane with terbutylazine and ametryn as template molecules, were evaluated for the selective extraction of triazines from complex matrices. Various parameters affecting extraction recoveries on MIPs were studied in order to obtain an optimized extraction procedure allowing to reduce non-specific interactions. In order to test the selectivity of the MIPs, the same procedure was applied to the extraction of compounds possessing the same polarity and size as the triazines. By means of molecular modeling, the effects of the electric charge distribution and of the size of the molecules on the retention mechanism were studied. The value of capacity for terbutylazine MIP was also measured. At last, the high selectivity resulting from the use of MIPs was clearly demonstrated by their applications to the clean-up of grape juice and soil extracts spiked with triazines. In addition, the soil extract was cleaned-up by immunoextraction allowing the comparison of both approaches in terms of selectivity.

Models, Molecular↗
PubMed2003

Optimization of the class-selective extraction of triazines from aqueous samples using a molecularly imprinted polymer by a comprehensive approach of the retention mechanism.

Direct, selective solid-phase extraction of triazines from aqueous samples is presented using a molecularly imprinted polymer (MIP) made with terbutylazine as template molecule. After optimization of the steps of the procedure, 14 triazines including degradation products were studied and satisfactory extraction recoveries were obtained except for thiotriazines. By comparing results obtained with the terbutylazine MIP and a similar non-imprinted polymer, it was determined that retention was achieved via specific interactions except for hydroxyterbutylazine. Selectivity of the extraction procedure was also verified by applying the MIP for the extraction of phenylureas that were not retained on it. The effects of the charge distribution and of molecular volume of the triazines (obtained by molecular modeling) on the selectivity of interactions between the analytes and the MIP were studied. However, when the optimized procedure was applied to real samples, low extraction recoveries were obtained due to strong matrix effects: ion-exchange occurs between the carboxylate groups of the MIP and the ionic species of the sample, that prevents subsequent specific interactions. By introducing an acid wash step, the procedure was successfully applied for the class-selective extraction of triazines from industrial effluent and surface water samples. Finally, increased extraction recoveries were achieved for the polar degradation products of triazines by using a mixed-phase composed of a polymeric sorbent and the MIP.

Chromatography, High Pressure Liquid↗
PubMed2000

Immunoaffinity solid-phase extraction for the trace-analysis of low-molecular-mass analytes in complex sample matrices.

Immunoaffinity solid-phase extraction (SPE) sorbents, so-called immunosorbents (ISs), are based upon molecular recognition using antibodies. Thanks to the high affinity and high selectivity of the antigen-antibody interaction, they allow a high degree of molecular selectivity and have shown to be a unique tool in the sample preparation area these last few years. Extraction and clean-up of complex biological and environmental aqueous samples are achieved in the same step and from large volumes when required. Their application to extracts from solid matrixes is solvent-free and more simple than any other clean-up procedure. Single analytes can be targeted, but since an antibody can also bind one or more analytes having structure similar to the one used for its preparation, ISs have been developed for targeting a single analyte and its metabolites. The cross-reactivity was also exploited for developing ISs that could selectively extract a whole class of structurally related compounds. This review describes the current technology used for the synthesis of the ISs, their properties and their field of application. The different parameters governing the antigen-antibody interactions and the solid-phase extraction process are discussed. Emphasis is given to the optimisation of the SPE sequence, especially to the desorption and regeneration steps. The importance of the capacity and its relationship with the analytes recovery and breakthrough volumes is highlighted for class-specific ISs. Multi-class-selective ISs are also presented. Validation studies are reviewed using various certified reference materials. Relevant examples, involving combination with chromatography in both off-line and on-line mode, illustrate the high selectivity provided in various complex matrixes. Miniaturisation is also described, since it allows high throughput of samples.

Animals↗
PubMed2000

Solid-phase extraction for multiresidue analysis of organic contaminants in water.

To overcome the limitations of the detection systems associated with gas or liquid chromatography, a sample pretreatment is required with the objective to provide a sample fraction enriched with all the target analytes and as free as possible from other matrix components. There is now no doubt that solid-phase extraction (SPE) has now become the method of choice for carrying out simultaneously the extraction and concentration of many compounds in aqueous samples. Many recent applications of SPE to multiresidue analysis are reviewed with an emphasis on the importance of the choice of the sorbent and of the sample volume. SPE is particularly well adapted to multiresidue analysis including compounds from a wide range of polarity or characterized by various physico-chemical properties. However, SPE is not completely free from practical problems inherent to the nature of the compounds or to the coupling to the chromatographic systems. Many examples are reported to illustrate these problems which can in most cases be circumvented. New developments in SPE are also reviewed.

Chromatography, Liquid↗
PubMed2000

Okadaic acid production from the marine benthic dinoflagellate Prorocentrum arenarium Faust (Dinophyceae) isolated from Europa Island coral reef ecosystem (SW Indian Ocean).

Okadaic acid was isolated from a strain of Prorocentrum arenarium Faust (Prorocentrales, Dinophyceae) collected from Europa Island (40 degrees 22'E, 22 degrees 20'S, SW Indian Ocean). The presence of okadaic acid in the algal extract was suspected after cytotoxicity and phosphatase 2A inhibition testing. It was confirmed by ADAM derivatization, immunoaffinity extraction and liquid chromatography with fluorimetric detection analysis as well as by liquid microchromatography with mass spectrometric detection. Results indicate that the P. arenarium strain was toxinogenic and could be potentially involved in the toxin production associated with the human diseases, diarrhetic shellfish poisoning and possibly ciguatera fish poisoning in the SW Indian Ocean area.

Animals↗
PubMed1999

Selective immunoclean-up followed by liquid or gas chromatography for the monitoring of polycyclic aromatic hydrocarbons in urban waste water and sewage sludges used for soil amendment.

A selective clean-up procedure using immunoaffinity solid-phase extraction was applied for the trace-level determination of polycyclic aromatic hydrocarbons (PAHs) in urban waste water and sewage sludges used for soil amendment. Anti-pyrene antibodies have been immobilized on a silica-based sorbent and the cross-reactivity of the antibodies towards structurally related compounds were allowed to extract the whole class of priority PAHs. The selectivity of the antibodies provided clean extracts from sludges and, therefore, the identification and quantification were shown to be easier using either liquid chromatography (LC) with UV diode array and fluorescence detection in series or gas chromatography-mass spectrometry (GC-MS), although some loss of up to 50% was observed for the clean-up. The identification of the PAHs by matching of UV and MS spectra was greatly improved. The procedure, including immunoclean-up and LC coupled to diode array and fluorescence detection, was validated using certified reference materials with native PAHs of concentrations in the range of 0.57-2.16 mg/kg (dry sludges).

Chromatography, Gas↗
PubMed1999

Selective on-line immunoextraction coupled to liquid chromatography for the trace determination of benzidine, congeners and related azo dyes in surface water and industrial effluents.

A new extraction immunosorbent involving antigen-antibody interactions was coupled on-line to liquid chromatography for the selective extraction in aqueous samples of benzidine and congeners, widely used as intermediate compounds in the manufacturing of dyes and pigments. Due to the cross-reactivity of the antibodies for analytes with chemical structures closely related to that of the analyte used for immunization, the immunoextraction sorbent was shown to be able to extract aminoazobenzene and related azo dyes with good recoveries. The on-line coupling was optimized for the trace determination of benzidine, dichlorobenzidine, aminoazobenzene and some azo dyes with detection limits in the range 0.1 to 1 microgram/l. The high selectivity of the immunoextraction was shown by comparing the analysis of an industrial textile effluent obtained using precolumns packed either with a non-selective polymeric sorbent or with the anti-benzidine immunosorbent. In such complex samples, extraction and clean-up are achieved in the same step.

Azo Compounds↗
PubMed1998

Multiresidue analysis of pesticides using new laminar extraction disks and liquid chromatography and application to the French priority list.

The national French lists of priority pesticides to be monitored in drinking and/or surface water contain various pesticides with a wide range of physico-chemical properties and can be modified on a regional scale with the addition of other pesticides, depending on local agricultural usage. A multiresidue extraction method is presented using new disk formats engineered for high throughput that are particularly well adapted to the extraction of compounds from high volumes of dirty samples. However, because of the occurrence of very polar and very apolar compounds in the lists, two procedures are required for the extraction step. Divinylbenzene disks were used to extract the more polar compounds, as well as the moderately polar or acidic ones. For apolar pesticides, a C18 silica disk was used, and 10% methanol was added to the water sample before percolation in order to avoid adsorption on the flasks and connecting tubes. Since 1 l of surface water is extracted in less than 5 min without previous filtration using these new laminar disks, the percolation time is no longer a limiting factor in the analysis scheme of surface water samples containing suspended matter. The sample volume can be easily increased in order to reach lower detection limits, provided that the extraction conditions have been optimized in order to minimize the amount of co-extracted and interfering substances. A considerable decrease in the effect of the humic and fulvic substances was achieved using divinylbenzene disks, which allows the samples to be handled at pH 6, for the polar pesticides. Moreover, the necessary addition of 10% methanol in the samples for the extraction of the apolar ones also considerably decreases the amount of co-extracted analytes. The time of the whole sample preparation sequence, i.e., conditioning of the disks, sample extraction, sample clean-up and desorption, is achieved within 10 min for six simultaneous samples. Detection limits in the range 0.01-0.05 microgram l-1 are easily obtained for most pesticides contained in the national lists from 1 l of real surface water samples. The two procedures described in this work allow the handling of any compounds having a water-octanol constant, log Kow, in the range 1-6.

Chromatography, Liquid↗