Polar Organophosphorus Pesticides Research Articles

Superhydrophilic graphene oxide/electrospun cellulose nanofibre for efficient adsorption of organophosphorus pesticides from environmental samples.

Superhydrophilic graphene oxide/electrospun cellulose nanofibre (GO/CNF) was synthesized, characterized and successfully used in a solid-phase membrane tip adsorption (SPMTA) as an adsorbent towards a simultaneous analysis of polar organophosphorus pesticides (OPPs) in several food and water samples. Separation, determination and quantification were achieved prior to ultra-performance liquid chromatography coupled with ultraviolet detector. The influence of several parameters such as sample pH, adsorption time, adsorbent dosage and initial concentration were investigated. SPMTA was linear in the range of 0.05 and 10 mg l−1 under the optimum adsorption conditions (sample pH 12; 5 mg of adsorbent dosage; 15 min of adsorption time) for methyl parathion, ethoprophos, sulfotepp and chlorpyrifos with excellent correlation coefficients of 0.994–0.999. Acceptable precision (RSDs) as achieved for intraday (0.06–5.44%, n = 3) and interday (0.17–7.76%, n = 3) analyses. Low limits of detection (0.01–0.05 mg l−1) and satisfactory consistency in adsorption (71.14–99.95%) were obtained for the spiked OPPs from Sungai Pahang, Tasik Cheras, cabbages and rice samples. The adsorption data were well followed the second-order kinetic model and fits the Freundlich adsorption model. The newly synthesized GO/CNF showed a great adsorbent potential for OPPs analysis.

Magnetite-sporopollenin/graphene oxide as new preconcentration adsorbent for removal of polar organophosphorus pesticides in vegetables.

In this study, a new magnetic adsorbent based on magnetite-sporopollenin/graphene oxide (Fe3O4-SP/GO) was successfully developed. The adsorbent was applied for magnetic solid phase extraction (MSPE) of three selected polar organophosphorus pesticides (OPPs), namely, dimethoate, phenthoate, and phosphamidon, prior to gas chromatography analysis with electron capture detection (GC-μECD). The Fe3O4-SP/GO adsorbent combines the advantages of superior adsorption capability of the modified sporopollenin (SP) with graphene oxide (GO) and magnetite (Fe3O4) for easy isolation from sample solution. Several MSPE parameters were optimized. Under optimized conditions, excellent linearity (R2 ≥ 0.9994) was achieved using matrix match calibration in the range of 0.1 to 500ngmL-1. The limit of detection (LOD) method (S/N = 3) was from 0.02 to 0.05ngmL-1. The developed Fe3O4-SP/GO MSPE method was successfully applied for the determination of these three polar OPPs in cucumber, long beans, bell pepper, and tomato samples. Good recoveries (81.0-120.0%) and good relative standard deviation (RSD) (1.4-7.8%, n = 3) were obtained for the spiked OPPs (1ngmL-1) from real samples. This study is beneficial for adsorptive removal of toxic pesticide compounds from vegetable samples.

Synthesis and application of molecularly imprinted silica for the selective extraction of some polar organophosphorus pesticides from almond oil

The aim of this work was to prepare and evaluate molecularly imprinted polymers obtained by a sol-gel approach for the selective solid-phase extraction (SPE) of organophosphorus pesticides (OPs) from almond oil. The performances of molecularly imprinted silicas (MISs), prepared using different conditions of synthesis, were studied by applying different extraction procedures in order to determine the ability of the MISs to selectively extract ten target OPs. For this, the retention of OPs on MISs in pure media was compared with the retention on a non-imprinted silicas (NISs), used as control sorbent, to prove the presence of specific cavities. The most promising MIS allowed the selective extraction of the 3 most polar OPs among the 10 studied. The capacity was studied and the repeatability of the extraction recovery yield was demonstrated both in pure and real media. This MIS was able to selectively extract fenthion sulfoxide and dimethoate contained in almond oil extract after applying the optimized extraction procedure with recovery yields between 100 and 114%. The estimated limit of quantification (LOQ, S/N = 10), thanks to LC/MS analysis in MRM mode, between 1.2 and 4.6 μg/kg for those OPs in the almond fruits, was more than 10 times lower than the Maximum Residue Levels (MRLs) established by the European Commission. This MIS therefore shows a high potential for the analysis of those two polar OPs at trace levels from almond oils.

Selective and Simultaneous Solid Phase Extraction of Polar and Non–Polar Organophosphorus Pesticides Using Sol–Gel Hybrid Silica–Based Sorbent

A new sol–gel hybrid silica–based sorbent, methyltrimethoxysilane–cyanopropyltriethoxysilane (MTMOS–CNPrTEOS) produced in our laboratory was used for highly selective and simultaneous solid phase extraction (SPE) of two polar organophosphorus pesticides (OPPs) and four non–polar OPPs from water samples. The two polar OPPs used as test analytes are dicrotophos and methamidophos while the four non–polar OPPs are diazinon, malathion, methidathion, and chlorpyrifos. Analysis of OPPs was performed using gas chromatography–mass spectrometry in scan mode. Extraction efficiency (based on peak area response) of the new sol–gel hybrid MTMOS–CNPrTEOS was superior to commercial C18 SPE sorbent. The new sorbent showed higher selectivity towards the polar dicrotophos and methamidophos and it was also able to simultaneously extract the four non–polar OPPs with higher extraction efficiency. The limit of detection at S/N=3 for the new sol–gel hybrid sorbent is 5–9× lower and similar accuracy for the six OPPs compared to commercial C18 SPE sorbent. The new sol–gel hybrid material showed high potential as an alternative sorbent material for solid phase extraction of OPPs of wide polarity. It was successfully applied to the selective and simultaneous extraction the six OPPs from tap water and lake water samples.

A combination of ultrasonic assisted extraction with LC–MS/MS for the determination of organophosphorus pesticides in sludge

A method has been developed for the analysis of a wide polarity range of the currently used organophosphorus pesticides (OPs) and their metabolites in sewage sludge samples. Extraction was carried out using ultrasonic assisted extraction (UAE) with different solvents. The levels of OPs in sludge were determined by liquid chromatography-tandem mass spectrometry (LC–MS/MS) using electrospray ionization (ESI) in positive or negative ion mode. Extraction with acetonitrile containing 1% acetic acid gave the best results with recoveries between 83.2% and 106.4% and RSD ≤ 8.7%. Evaluation of matrix effect showed high ion suppression for OPs of intermediate polarity, which decreased to approximately 50% by matrix dilution to an equivalent of 0.5 g of sludge per millilitre; however, for polar OPs, the matrix effect was negligible at the same concentration. Therefore, matrix-matched standards were used for OPs quantification. The limits of quantification were in the range of 1–14 ng g −1. This method was successfully applied to real sludge samples collected from Madrid Province and chlorpyrifos along with its metabolite TCPY were the OPs found in sludge at the highest levels, 113–344 ng g −1 and 33–307 ng g −1, respectively.

Determination of polar organophosphorus pesticides in water samples by hydrophilic interaction liquid chromatography with tandem mass spectrometry

A method combining hydrophilic interaction liquid chromatography (HILIC) with tandem mass spectrometry (MS/MS) was developed for the determination of polar organophosphorus pesticides (OPPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl, and vamidothion) in water samples. To extract the polar OPPs and minimize matrix effects from the water sample, an activated carbon cartridge was used for pretreatment. After pretreatment of the water sample, the eluate from the activated carbon cartridge was directly injected into the HILIC/MS/MS system. The OPPs were separated on an Atlantis HILIC silica column by isocratic elution with a mixture of acetonitrile, isopropanol, and ammonium formate buffer as a mobile phase, and they were detected by positive electrospray ionization MS/MS in the selected reaction monitoring mode. The method was validated at 0.05, 0.5, and 5 microg/L levels in water samples, and the recoveries of polar OPPs were between 76.4 and 98.6%. The limits of detection were between 0.13 and 1.0 pg on-column, and the limits of quantification were between 0.43 and 3.4 pg on-column. The method can be applied to the determination of trace amounts of OPPs in environmental water samples.

Ion chromatography/inductively coupled plasma mass spectrometry for simultaneous determination of glyphosate, glufosinate, fosamine and ethephon at nanogram levels in water

This paper describes the first approach that simultaneously quantifies four polar, water-soluble organophosphorus herbicides, i.e., glyphosate, glufosinate, fosamine and ethephon, at nanogram levels in environmental waters. The target herbicides were separated completely by ion chromatography (IC) on a polymer anion-exchange column, Dionex IonPac AS16 (4.0 mm x 250 mm), with 30 mM citric acid flowing at 0.70 mL min(-1) as the eluent. On-line inductively coupled plasma mass spectrometry (ICP-MS) using a quadrupole mass spectrometer was employed as a sensitive and selective detector of the effluents. Various parameters affecting the separation and detection were systematically examined and optimized. Detection limits of the herbicides achieved with the proposed IC/ICP-MS method were 1.1-1.4 microg L(-1) (as compound) based on a 500-microL sample injection. Matrix anions, metal ions, phosphate, polyphosphates, non-polar and other polar organophosphorus pesticides showed no interference. The developed method was validated using reservoir water, treated water and NEWater samples spiked at the level of 10-25 microg L(-1) with satisfactory recoveries (95-109%). It is applicable to the simultaneous determination of microg L(-1) concentrations of the herbicides in polluted water.

Extraction of highly polar organophosphorus pesticides from water

Some of the pesticides listed in the European 76/464/EC Directive and in the Directive 2000/60/ EC are very polar and require special analytical methodology with respect to their extraction from water. The extraction of the organophosphorus pesticides methamidophos, omethoate, oxydemeton-methyl, mevinphos and trichlorfon with lg P OW below 1 was investigated using 21 different solid-phase materials. Each material was tested on spiked natural water at 4 different pH values, adjusted prior to extraction. The following range of materials were tested: octadecyl silica, polymers, modified silica, ion exchange and carbon. Extraction of the above compounds from water is possible. A relationship between the octanol-water partition coefficient and recovery rates was obtained not only for octadecyl solid phases but also for some polymeric materials. General conclusions about the use of solid-phase materials and specific conclusions about the extraction of particular compounds were made. An optimized extraction procedure was deduced and confirmed.

Selective solid-phase extraction using molecularly imprinted polymer for the analysis of polar organophosphorus pesticides in water and soil samples

An analytical methodology for the analysis of four polar organophophorus pesticides (monocrotophos, mevinphos, phosphamidon, omethoate) in water and soil samples incorporating a molecularly imprinted solid-phase extraction (MISPE) process using a monocrotophos-imprinted polymer was developed. Binding study demonstrated that the polymer showed excellent affinity and high selectivity to monocrotophos. The MISPE procedure including the clean-up step to remove any interferences was optimized. The accuracy and selectivity of the MISPE process developed were verified using a non-imprinted (blank) polymer and a classical ENVI-18 cartridge as the SPE matrix during control experiments. The use of MISPE improved the accuracy and precision of the GC method and lowered the limit of detection. The recoveries of four polar organophosphorus pesticides (OPPs) extracted from 1 L of river water at a 100 ng/L spike level were in the range of 77.5–99.1%. The recoveries of organophosphorus pesticides extracted from a 5-g soil sample at the 100 μg/kg level were in the range of 79.3–93.5%. The limit of detection varied from 10 to 32 ng/L in water and from 12 to 34 μg/kg in soil samples. The molecularly imprinted polymer (MIP) enabled the selective extraction of four organophosphorus pesticides successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.

Determination of acephate and its degradation product methamidophos in soil and water by solid-phase extraction (SPE) and GC-MS

Acephate and its metabolite, methamidophos, are both highly polar organophosphorus pesticides (OPs) and are therefore highly soluble in water, which leads to difficulties when traditional methods of extraction, such as LLE (liquid–liquid extraction), are used. Solid-phase extraction (SPE) is a relatively new, highly versatile method, which has proven successful in many cases that were considered problematic in the past. In this study, several adsorbents (polymeric and silica based) and parameters are considered and modified to obtain maximum recovery. Maximum recoveries for acephate and methamidophos were found to be 90–95% and 85–90% respectively with Oasis HLB cartridges and methylene chloride as the elution solvent. In order to establish applicability and reliability, the matrix effect of several real water and solid (compost and soil) samples was evaluated. A 20–30% diminution of recovery is noted for some samples with a complex matrix containing a high amount of dissolved organic matter.

Determination of polar organophosphorus pesticides in vegetables and fruits using liquid chromatography with tandem mass spectrometry: selection of extraction solvent

A method based on liquid chromatography (LC)–mass spectrometry (MS)/MS was developed for sensitive determination of a number of less gas chromatography (GC)-amenable organophosphorus pesticides (OPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion) in cabbage and grapes. For extraction, several solvents were evaluated with respect to the possibility of direct injection, matrix-induced suppression or enhancement of response, and extraction efficiency. Overall, ethyl acetate was the most favourable solvent for extraction, although a solvent switch was required. For some pesticide/matrix combinations, reconstitution of the residue after evaporation required special attention. Extracts were analysed on a C18 column with polar endcapping. The pesticides were ionised using atmospheric pressure chemical ionisation on a tandem mass spectrometer in multiple reaction monitoring mode. The final method is straightforward and involves extraction with ethyl acetate and a solvent switch to 0.1% acetic acid/water without further cleanup. The method was validated at the 0.01 and 0.5 mg/kg level, for both cabbage and grapes. Recoveries were between 80 and 101% with R.S.D.<11% ( n=5). The limit of quantification was 0.01 mg/kg and limits of detection were between 0.001 and 0.004 mg/kg.

Performance of programmed temperature vaporizer, pulsed splitless and on-column injection techniques in analysis of pesticide residues in plant matrices

A programmed temperature vaporizer (PTV) injection technique has been recently implemented in our laboratory. In present paper its performance is compared with other GC injection techniques commonly used in trace analysis of organic contaminants. Twenty-six pesticides representing different chemical classes were selected for the study. This group comprised compounds typically subjected to discrimination in the injection port of the gas chromatograph, e.g., polar organophosphorus pesticides and thermolabile carbamates. In the first set of experiments standards in pure solvent were injected into GC systems employing different types of injection, i.e., (i) on-column, (ii) pulsed splitless, (iii) PTV solvent split, (iv) PTV splitless, and the responses of analytes were compared. Discrimination of troublesome compounds was significantly decreased with the application of PTV solvent split injection. In the second set of experiments repetitive injections of purified wheat samples were performed, with aims to evaluate the long-term stability of responses, as well as matrix effects in different stages of system contamination for each injection technique. The tolerance of the GC system to co-injected matrix components was increased in the order: on-column<pulsed splitless<PTV solvent split technique. As regards matrix effects, these were suppressed considerably with the PTV solvent split technique in comparison with pulsed splitless injection. With the latter technique after 66 injections of wheat samples relative responses (apparent recovery) reached as much as 450% for some compounds, while with the application of PTV matrix effects did not exceed 200% under the same conditions.

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.

Deuterated internal standards for gas chromatographic-mass spectrometric analysis of polar organophosphorus pesticides in water samples

It is essential to know whether drinking water contains any pesticides up to concentrations close to the European Union limit of 0.1 μg/l, in order to protect the population. Mass spectrometry (MS) using a suitable internal standard (I.S.) should improve the quantitative analysis of pesticides, the I.S. circumventing loss of compounds during the analytical procedure and correcting the analytical variability. In this study we verified this assumption in GC-MS, synthesising specific internal standards for four organophosphorus pesticides with poor stability, comparing the performances with and without the I.S.

Optimized method for the determination of organophosphorus pesticides in meat and fatty matrices

A method was developed and optimized for determination of residues of organophosphorus pesticides (OPs) in meat and fatty matrices. The method was developed for the national Danish monitoring programme, whereby priority was given to simplify the clean-up, avoid use of toxic and harmful organic solvents and allow quantification at ppb level using GC with nitrogen-phosphorus detection (NPD). Homogenized meat was extracted using ethyl acetate, the co-extracted water being removed using anhydrous Na 2SO 4. The clean-up was done through fat precipitation by cooling the extract flowed by solid-phase extraction on C 18 mini-columns. Pesticide residues were determined by GC-NPD using a DB1701 capillary column. The limit of detection was 1 to 20 ppb and limit of determination was 2 to 33 ppd and the method is feasible for control of fat-soluble OPs according to the maximum residue limits set by the European Communities. The method developed covers a broad polarity range from polar OPs, such as acephate and methamidophos, through medium polar OPs to non-polar pesticides, such as prothiofos.

Automated sample preparation with extraction columns followed by liquid chromatography-ionspray mass spectrometry interferences, determination and degradation of polar organophosphorus pesticides in water samples

The determination of polar and/or thermally labile organophosphorus pesticides trichlorfon, dichlorvos, dimethoate, oxydemeton-methyl, mevinphos ( cis and trans), demeton-S-methyl, fenamiphos, fenitrothion, fenthion and diazinon in water samples was investigated using solid-phase extraction followed by liquid chromatography-ionspray mass spectrometry (LC-ISP-MS). Pesticides were spiked at 0.2 μg/l in ground water samples and 200 ml were preconcentrated by using an ASPEC XL system. To improve the recovery of the most volatile pesticides such as dichlorvos, a further drying step with a Baker Spe 12 G apparatus with the vacuum set at 15 p.s.i. was included. A further evaporation step was applied with a gentle stream of nitrogen. A variety of materials (Amberchrom, LiChrolut EN, cyclohexyl, SDB, C 18 and Isolute ENV) were used for the isolation of the target pesticides. The elution step took place at 1 ml/min, with a 5-min contact time between the eluent and the sorbent. LC-ISP-MS permitted the identification of diethyl and di- n-butyl phthalates present as impurities in the cartridge materials. The presence of transformation products of the pesticides, e.g., fenthion sulfoxide, was also observed. The influence of pH and the water matrix (distilled and ground water) on the extraction efficiency was examined. The use of LC-ISP-MS permitted cis- and trans-mevinphos to be distinguished in the water sample owing to the presence of a specific ion at m z 99 . the limits of detection of the overall method were in the range 0.01–0.20 μg/1 using LC-ISP-MS with selected-ion monitoring.

Influence of pesticide–soil interactions on the recovery of pesticides using supercritical fluid extraction

The role of soil organic matter on the recovery of two classes of pesticides and two classes of herbicides using supercritical carbon dioxide has been investigated. Initial studies from spiked Celite indicated that the more polar herbicides required the addition of 10% methanol modified supercritical carbon dioxide to affect extraction. Whereas the relatively non-polar organochlorine pesticides (OCPs) could be extracted using supercritical carbon dioxide only, the moderately polar organophosphorus pesticides (OPPs) required 5% methanol-modified supercritical carbon dioxide to affect quantitative recovery. When using these supercritical conditions each class of pesticide or herbicide was extracted from a slurry-spiked soil. The effects on the recovery from soils with a range of organic matter were noticeable for both classes of pesticides, particularly when the organic matter was at its highest (35%). The role of the modifier was found to be critical in affecting recovery of the polar OPPs and herbicides. The soil-pesticide interaction from these slurry spiked soils could be negated if excess modifier (10%) was added to the supercritical carbon dioxide. Matrix interactions were most severe when no modifier was added (recoveries of OCPs from soil were approximately 50%).

Automated analysis of polar pesticides in water by on‐line solid phase extraction and gas chromatography using the co‐solvent effect

AbstractIn order to meet the requirements of analyzing very low concentrations of pesticides in water (typically at 0.1 μg/l or less), samples have to be concentrated prior to GC‐analysis. Samplie pre‐concentration by off‐line methods based on solid phase extraction (SPE) or liquid‐liquid extraction are very time consuming and cumbersome. Moreover, the quantitative performance of the analytical method as a whole in terms of accuracy and reliability is seriously hindered by elaborate, manually performed sample pre‐treatment steps. This paper describes an automated method based on solid phase extraction and capillary gas chromatography. The technique was applied for the analysis of 31 polar organophosphorus and organonitrogen pesticides. A commercially available HPLC/GC instrument is modified, using the LC‐part for solid phase extraction. The sample, of which only a few ml's is required to obtain sufficiently low detection limits, is delivered by a robotic large volume autosampler. After solid phase extraction and elution, the eluate is transferred into the GC via a so called “loop type interface”. In this paper the instrumentation and analytical methodology is described, as well as the main validation results. The quantitative performance (i.e. recovery and repeatability) of the most polar solutes like metamitron and dimethoate appears to be better than obtained with off‐line SPE as a result of the more beneficial ratio between the amount of sorbent and the sample volume. As the loop‐type interface causes losses of the most volatile compounds, a co‐solvent is added. This co‐solvent provides sufficient trapping capacity in the capillary pre‐columns to allow quantitative analysis of even the most volatile pesticides. Moreover a better separation of early eluting compounds is also established.

Need for food reference material in Latin America

Even if some Latin American countries still need to extend their capacity for food quality control, many do have good control laboratories and high quality research institutions. That makes the need for reference material in Latin America similar to that of other parts of the world. The region has special problems related to mail and shipment delays, and to the lack of information on available reference material. It is recommended that additional reference material being made available for vitamins in food, for polar and non-polar organophosphorus pesticides in vegetables, for organophosphorus pesticide and veterinary drugs in meat etc. Reference material should simulate real samples as closely as possible; reference samples for water should contain phthalates which in environmental samples interfere with organochlorines and reference material for organophosphates in vegetables should contain metabolites and degradation products. It is also recommended that commercial standards for trace metals should have the production date and the guaranteed stability printed on the label. Information on reference material should be included in the methods published by AOAC, AOCS and similar publications.

Organophosphorus sulphides, sulphoxides and sulphones. Part I. Determination of residues in fruit and vegetables by gas-liquid chromatography.

Conditions have been established for the routine quantitative determination of residues of demephion, demeton-S-methyl, disulfoton, fenamiphos, fensulfothion, fenthion, phorate, terbufos, thiometon and their toxic metabolites following conversion into the sulphones. Packed column gas chromatography-mass spectrometry demonstrated that most of the sulphoxides tended to decompose under the conditions required for gas chromatography, whereas most of the sulphides and sulphones were unaffected by such conditions. Temephos and its metabolites and the metabolites of vamidothion decomposed completely during gas chromatography. Some suggestions are given for assessing and avoiding the column priming and enhancement problems often observed in the gas chromatography of these and other polar organophosphorus pesticides.