Pesticides In Aqueous Samples Research Articles

Application of Solid-Phase Microextraction for the Determination of Organonitrogen Pesticides in Aqueous Samples by Gas Chromatography with Nitrogen-Phosphorus Detector

A method based on solid-phase microextraction and gas chromatography nitrogen-phosphorus detector for the determination of common organonitrogen pesticides (ONPs) in aqueous samples was described. Three kinds of commercially available coated fused-silica fibres were compared: 100 µm PDMS, 85 µm PA, and 65 µm CW-DVB; 65 µm CW-DVB was the most sensitive fibre coating for the analytes' determination. The extraction time, the stirring, the content of salt, and the content of organic solvents were found to have a significant influence on extraction efficiency. The optimised conditions were 65 µm CW-DVB fibre, 40 min extraction time, with rapid stirring and concentration of NaCl was fixed at 0.25 g/mL. The linear range was 0.1-100 µg/L for most of the compounds. The limits of detection (LODs) ranged from 0.02 mg/L (for trifluralin, simazine, terbuthylazine, cyanazine, and pendimethalin) to 0.08 µg/L (for terbutryn) and RSD % of repeatability were for most of the compounds below 10%. Thus the maximum level set by the European Union for pesticides and drinking waters can be verified. The recovery of spiked water samples was compared and validated with the liquid-liquid extraction one. Environmental water samples were analysed and trifluraline was detected.

Analysis of Organochlorine Pesticides by Solid-Phase Microextraction followed by Gas Chromatography-Mass Spectrometry

Solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) was optimized for the analysis of hexachlorocyclohexanes, DDD, DDE, DDT and other organochlorine pesticides in aqueous samples. Higher extraction efficiency was observed with the SPME fibre coated with 100 µm polydimethylsiloxane than with the fibres coated with 85 µm polyacrylate or 65 µm polydimethylsiloxane/divinylbenzene. Equilibration times were longer than 60 min, except for the hexachlorocyclohexanes, in spite of rapid stirring of the sample. However, precise quantitative analysis could be performed also under non-equilibrium conditions: i.e. repeatability standard deviations below 20%. Salt addition had a positive effect on the response for the hexachlorocyclohexanes, whereas the extraction of the other analytes was affected negatively. The pH of the sample solution did not influence the extraction efficiency. The desorption was performed for 5 min at 275°C directly in the GC injector. At shorter desorption times or lower temperatures a significant carry-over was observed for the heavier analytes. Generally, detection limits in the ng/L range were obtainable.

Application of solid-phase microextraction for the determination of organophosphorous pesticides in aqueous samples by gas chromatography with flame photometric detector

A method based on solid-phase microextraction and gas chromatography flame photometric detector for the determination of organophosphorous pesticides (OPPs) in aqueous samples was described. Five kinds of commercially available fibers—7, 30 and 100 μm PDMS, 85 μm PA and 65 μm PDMS-DVB—were compared and 100 μm PDMS and 85 μm PA were the most sensitive fiber coatings for the analytes. The extraction time, extraction temperature, pH and content of NaCl were found to have significant influence on extraction efficiency. The optimized conditions were 100 μm PDMS fiber, 30 min extraction time at 40 °C, with 3% NaCl content and no pH adjustment. The linear range was 0.5–100 μg l −1 for most of the analytes. The limits of detection (LODs) ranged from 0.049 μg l −1 (for parathion) to 0.301 μg l −1 (for carbophenothion) and RSD% of repeatability at the 10 μg l −1 level were all below 8%. Environmental water samples were analyzed, but none of the analytes was detected. The recovery of spiked water samples was from 75.3 to 102.6%.

Determination of polar organophosphorus pesticides in aqueous samples by direct injection using liquid chromatography–tandem mass spectrometry

It was demonstrated that four out of six of the very polar organophosphorus pesticides (OPs), i.e. acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion, could not be extracted from water using commonly available SPE cartridges. In addition, GC analysis on all six compounds was found to be troublesome due to their polar and thermolabile character. This initiated the development of an alternative highly sensitive and selective method for the determination of the above mentioned very polar OPs in water, based on LC–MS. Large volume (1 ml) water samples were directly injected onto an RP18 HPLC column with a polar endcapping. The latter was essential for obtaining retention and maintaining column performance under 100% aqueous conditions during the sampling. The compounds were ionized using atmospheric pressure chemical ionization and detected on a tandem mass spectrometer operated in multiple reaction-monitoring mode. The detection limits were in the range of 0.01–0.03 μg/l. Compared to conventional GC methods, the developed LC–MS procedure is very straightforward, fast and more reliable. This application demonstrates the applicability of LC–MS for analysis of polar OPs in surface, ground and drinking water, as a more favourable alternative to GC.

Comparison of gas chromatography with NPD, MS, and tandem MS-MS in the multiresidue analysis of pesticides in environmental waters

Gas chromatography (GC) with nitrogen-phosphorus detection (NPD) and mass spectrometry (MS), in full scan and tandem (MS-MS) modes have been used to determine eleven pesticides in aqueous samples. Preconcentration of 500 mL water with C18 cartridges enabled the determination of pesticides at ng L−1 levels. The best precision and sensitivity were obtained from GC-NPD and GC-MS-MS. The limits of detection were between 4 and 44 ng L−1 for NPD and 1 and 40 ng L−1 for MS-MS. The application of this methodology to the determination of pesticides in real samples was tested by analyzing wetland samples from province of Almeria (Spain). The results obtained were compared and the advantage of MS-MS over NPD for highly selective quantitative determination of pesticides in complex matrices is discussed.

On-line coupling of solid-phase extraction to gas chromatography with fast solvent vaporization and concentration in an open injector liner: Analysis of pesticides in aqueous samples

The purpose of this study is to combine solid-phase extraction (SPE) with gas chromatography (GC) for the fully automated determination of pesticides and herbicides in aqueous samples. The interface technique employed for connecting SPE with GC was fast solvent vaporization and concentration in an open injector liner. The interface device consisted of the programmed-temperature vaporizing injector without using the packing material in the liner and the target compounds were concentrated around the inlet of the GC capillary column. This avoided the degradation of target compounds, and no precise control of the injecting speed was required, when an automatic SPE system was connected to GC–MS. The aqueous samples used in this system were prepared by spiking 29 kinds of pesticide and herbicide compounds, which are regulated by the Ministry of Health and Welfare of the Japanese National government, in purified water and river water, to a resulting concentration of 1 μg/l. Employing this system, the recoveries and RSDs ( n=6) of most compounds were greater than 75% and within 10%, respectively. From the results of this study, we found that on-line automatic SPE and capillary GC–MS equipped with the fast solvent vaporizing and concentrating method in an open injector liner could be connected in order to obtain good results for the determination of pesticides in water samples.

Solid-phase microextraction and gas chromatography with mass spectrometric detection for the determination of pesticides in aqueous samples

Solid-phase microextraction (SPME) is a fast, alternative method for extracting organochlorine, triazine and thiocarbamate pesticides. An 85-μm polyacrylate fiber was used to extract the analytes directly from aqueous samples and then thermal desorption was carried out in the hot injector of a gas chromatograph–mass spectrometer. To enhance the sensitivity of SPME, the temperature and the length of the extraction and desorption steps and the pH and salt concentration of the sample were optimized. The linearity of most of pesticides for real samples was found to be between 0.07 and 30 μg l−1 when GC–MS under full-scan acquisition was used and between 0.005 and 10 μg l−1 when selected-ion monitoring (SIM) acquisition was used. Limits of detection at the sub μg l−1 level were achieved with GC and MS under the full-scan acquisition mode and at the ng l−1 level for MS under SIM acquisition. The repeatability of the method for tap water spiked at a level of 0.5 μg l−1 (n=5) was below 25% (R.S.D.).

Determination of acidic chlorinated pesticides in water: Comparison of official EPA method 515.1 and liquid-solid extraction HPLC/UV and HPLC/PBMS analyses

A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.

On-line sample handling strategies for the trace-level determination of pesticides and their degradation products in environmental waters

An overview of the use of on-line techniques is presented. First, it includes the on-line coupling of solid-phase extraction and liquid chromatography, which is certainly the most commonly used automated technique really well adapted to the multiresidue analysis of pesticides in aqueous samples. The different parameters which govern the method (dimension of the pre-columns, type of sorbents, pre-columns in series, quantitative analysis) are discussed and applications to various waters are presented. Emphasis is given to the limits of detection obtained using UV diode array, fluorescence or electrochemical detection modes. The on-line post-column reaction detection coupled to liquid chromatography are also reviewed with emphasis on the determination of N-methylcarbamates. The performances of the on-line mass spectrometric detection coupled to solid-phase extraction and liquid chromatography are presented using thermospray, particle beam or electrospray. The main characteristics of the on-line coupling of solid-phase extraction and gas chromatography are also given, with various applications and corresponding detection limits. The recent results obtained with the on-line coupling of gas chromatography with solid-phase micro-extraction are outlined. Supercritical fluid extraction is also mentioned as a new sample handling technique which can be easily on-line coupled to the Chromatographic separation.

Determination of pesticides in aqueous samples by solid-phase microextraction in-line coupled to gas chromatography—mass spectrometry

A multiresidue method was developed for the determination of nitrogen- and phosphorous-containing pesticides (amines, anilides, phosphorothioates, and triazines) by solid-phase microextraction (SPME) in-line coupled to gas chromatography-mass spectrometry (GC/MS). The 85-µm polyacrylate fiber was first dipped into the aqueous sample for a given time and then directly introduced into the heated injector of the gas chromatography-mass spectrometer, where the analytes are thermally desorbed. The method was evaluated with respect to the limit of detection, linearity, and precision. The limit of detection [selected ion monitoring (SIM) mode] depends on the compound and varies from 5 to 90 ng/L. The method is linear over at least 3 orders of magnitude with coefficients of correlation usually ≥0.996. In general, the coefficient of variation (precision) is <10%. The partitioning of the analyte between the aqueous phase and the polymeric phase depends on the hydrophobicity of the compound as expressed by the octanol-water partitioning coefficient P ow. The addition of sodium chloride has a strong effect on the extraction efficiency. This effect increases with decreasing hydrophobicity (increasing polarity) of the compound.The triazines atrazine, simazine, and terbuthylazine were first identified and quantified in water samples from the effluent of sewage plants by SPME-gas chromatography-nitrogen-phosphorus detection (GC/NPD). For such a complex matrix GC/NPD is not sufficiently selective for an unambiguous identification at low levels (<1 ppb) of pesticides. Selectivity may be enhanced by using SMPE-GC/MS in the SIM mode with three characteristic ions for each pesticide. This method allows an unequivocal identification and quantification at low levels of pesticides in environmental samples.At a target limit of detection below 100 ng/L, SPME-GC/MS represents a very simple, fast, selective, and solvent-free multimethod for the extraction and determination of these nitrogen- and phosphorous-containing pesticides from aqueous samples.

Determination of organophosphorus, triazine and 2,6-dinitroaniline pesticides in aqueous samples via solid-phase microextraction (SPME) and gas chromatography with nitrogen-phosphorus detection

Solid-phase microextraction (SPME) represents a very simple and rapid method for the extraction of organophosphorus, triazine and 2,6-dinitroaniline pesticides from aqueous samples without making use of any solvents. The same fiber can be used repeatedly. Moreover, a sample volume as small as 3 mL can be employed with no loss in sensitivity. 34 compounds have been extracted from aqueous samples by SPME using a 85 μm polyacrylate fiber. For organophosphorus pesticides, a 100 μm polydimethylsiloxane fiber has been used additionally for comparison. The fibers were directly introduced into the heated split/splitless injector of the gas chromatograph and determined using a nitrogen-phosphorus detector. The method was evaluated with respect to the limit of detection (LOD), linearity and precision. The limit of detection (LOD) depends on the compound and varies from 0.005–0.09 μg/L. The method is linear over at least three orders of magnitude with coefficients of correlation usually >0.999. For triazines and 2,6-dinitroanilines the coefficient of variation (precision) is <8% while for organophosphorus compounds it may reach values up to 18% (however, if the latter compounds are extracted using the polydimethylsiloxane phase considerably higher precision is achieved). The partitioning of the analyte between the aqueous phase and the polymeric phase depends on the hydrophobicity of the compound as expressed by the octanol/water partitioning coefficient (Pow). For triazines it was shown that there is a linear dependence of the logarithm of the analyte response on the log(Pow) i.e. the higher the hydrophobicity, the higher the affinity of the analytes to the polymeric phase of the fiber and the higher the response. Salt addition has a strong effect on the extraction efficiency. This effect increases with decreasing hydrophobicity (increasing polarity) of the compound. The triazines ametryn, atrazine, propazine, simazine and simetryn have been identified in a ground water well sample by SPMEGC/NPD.

Mass spectrometric analysis of nitrogen- and phosphorus-containing pesticides by liquid chromatography—mass spectrometry

A series of nitrogen- and phosphorus-containing pesticides (amines, anilides, carbamates, phosphonates, phenylureas, sulfonylureas, and triazines) was examined by thermospray (TSP) ionization. A method is described that employs off-line and on-line solid-phase extraction and TSP liquid chromatography—mass spectrometry (LC-MS) with time-scheduled selected ion monitoring (SIM) for environmental monitoring of these pesticides in aqueous samples. SIM detection limits for the pesticides analyzed in conjunction with reversed-phase high-performance liquid chromatography range from 40 to 600 pg. In addition, methods for inducing fragmentation in thermospray LC-MS are presented. The structural information gained therefrom can be used to confirm a tentative identification. Therefore, fragmentation pathways under certain experimental conditions were investigated. Atmospheric pressure chemical ionization, electrospray, fast-atom bombardment, 252Cf plasma desorption, and collision-activated dissociation spectra are presented for several pesticides to confirm the proposed pathways and to gain additional and complementary information. Further confirmation may be achieved by postcolumn addition of different alkylated amines to the carrier stream in TSP operation to induce postcolumn on-line derivatization (POD) reactions in the condensed phase of the vaporizer probe with selected pesticides. Additional clustering reactions in combination with solvent-mediated chemical ionization are observed by the POD technique. Both processes can be used to enhance the structural information from TSP spectra and thus the specificity of the method.

Graphitized carbon black extraction cartridges for monitoring polar pesticides in water

Our previously reported procedure for analyzing pesticides in aqueous samples involving liquid-solid extraction by graphitzed carbon black (GCB) followed by liquid chromatography was appropriately modified for extending the analysis to very polar pesticides and pesticide metabolites. For this purpose, a 1-g GCB reversible extraction cartridge was adopted. Pesticide reextraction was performed by back-flushing the cartridge with a suitable eluant phase. The advantages of back-flush over forward flush desorption are illustrated

Determination of organophosphorus pesticides in aqueous samples by on-line membrane disk extraction and capillary gas chromatography

A fast and simple procedure for the analysis of aqueous samples by on-line membrane disk extraction and capillary gas chromatography (GC) is presented. As an example, organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.2 mm diameter extraction disks. The layers are dried by a stream of nitrogen (10–15 min; ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapour exit. The final analysis is carried out by GC with thermionic detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from two European rivers. With a sample volume of only 2.5 ml, detection limits of 10–30 ppt are achieved in tap water and of 50–100 ppt in river water.

Concentration and determination of trace amounts of chlorinated pesticides in aqueous samples

A method for the quantitative analysis of the organochloro-pesticides heptachlor, dieldrin, DDT and aldrin in water, using the HPLC technique of on-line trace enrichment, has been developed. A standard HPLC isocratic analytical system was employed the principle modification being the incorporation of a short pre-column across the sample loop connections of a Rheodyne 7125 valve to serve as the trace enrichment column. Pesticide recoveries of >95% were achieved at sample flow rate of 5–15 ml/min by employing stainless steel fittings throughout the system and with 5% methanol included in the pesticide sample reservoir. The pesticides were concentrated onto a 50 mm, 10 μm Spherisorb ODS column; analysis was performed on a 25 cm, 5 μm Spherisorb ODS column with methanol-water (75∶25) elution; detection was by UV absorption measurement at 220 mm and 0.64 AUFS.