Combining solid-phase microextraction and on-line preconcentration-capillary electrophoresis for sensitive analysis of pesticides in foods

The combined use of solid-phase microextraction (SPME) and different on-line preconcentration strategies for ultrasensitive capillary electrophoresis-ultraviolet (CE-UV) analysis of five pesticides in a single run is investigated. Normal stacking mode (NSM), field-enhanced sample injection (FESI), and stacking with matrix removal (SWMR) are explored to increase the sensitivity of the CE-UV analysis of a selected group of pesticides (cyprodinil, cyromazine, pyrifenox, pirimicarb, and pyrimethanil). It could be observed that reverse polarity-stacking with matrix removal (RP-SWMR) provided the best results in terms of sensitivity (enhancement was up to 272-fold compared with normal injection). The separation buffer consisted of 0.4 mM cetyltrimethylammonium chloride (CTAC), 0.4 M acetic acid at pH 4 containing 5% v / v 2-propanol. This approach was then combined with SPME to determine the pesticides in water, apple, and orange juice. The combination of both preconcentration procedures allowed the determination of these pesticides at concentrations down to 2.5 microg / L in water and 3.1 microg / L in juices (i.e., levels well below the maximum residue limits allowed for these compounds). To our knowledge, this is the first report showing the great possibilities of the combined use of SPME, on-line sample preconcentration, and CE for pesticide analysis.     

Determination of pesticides in wine using micellar electrokinetic chromatography with UV detection and sample stacking

In this work, the analysis of a group of four fungicides (pyrimethanil, nuarimol, procymidone and cyprodinil) and one insecticide (pirimicarb) by micellar electrokinetic chromatography (MEKC) with UV detection using the on-line preconcentration strategy called reversed electrode polarity stacking mode (REPSM) is proposed. After optimisation, an adequate separation electrolyte for the separation and stacking of these pesticides was obtained which consisted of 100 mM borate, 60 mM sodium dodecyl sulphate (SDS), at pH 9.0 and 2% 2-propanol. The use of this running buffer together with the REPSM preconcentration method provided limits of detection (LODs) between 38.3 and 241 microg/L. In order to apply the developed methodology for the analysis of these pesticides in wine samples, several off-line preconcentration strategies (mainly, solid-phase extraction, SPE, and solid-phase microextraction, SPME) were tested. Although the use of a SPE procedure, optimized in this work for water samples, using Oasis HLB cartridges, provided mean recovery values between 79 and 100% for spiked water samples, it could not be applied to the extraction of these pesticides from wine samples due to high interference from the sample matrix. However, the use of a SPME procedure using polydimethylsiloxane/divynilbenzene (PDMS/DVB) fibers allowed the selective extraction of four of the five pesticides which could be perfectly determined. The final combination of the off-line SPME and on-line REPSM preconcentration strategies allowed obtaining LODs between 17.6 and 32.3 microg/L.     

Analysis of triazolopyrimidine herbicides in soils using field-enhanced sample injection-coelectroosmotic capillary electrophoresis combined with solid-phase extraction

In this work, a combined methodology using off-line solid-phase extraction (SPE), on-line field-enhanced sample injection (FESI) and coelectroosmotic capillary electrophoresis with UV detection (CE-UV) is developed for the trace analysis of five triazolopyrimidine sulfonanilide pesticides (i.e., flumetsulam, florasulam, cloransulam-methyl, diclosulam and metosulam). An adequate background electrolyte (BGE) was obtained for the separation of these pesticides using hexadimethrine bromide (HDB) as electroosmotic flow (EOF) modifier. This BGE consisted of 0.00042% HDB, 11 mM formic acid, 16 mM ammonium carbonate and 2.5 mM alpha-CD solution at pH 7.6. The use of this running buffer together with the FESI preconcentration method provided limits of detection (LODs) in the low microg/L range (i.e., between 13.0 and 31.5 microg/L). The optimized FESI-CE-UV method was combined with off-line SPE using C(18) cartridges and applied to the determination of the selected group of pesticides in soil samples. Recovery percentages ranged between 50 and 84% in these samples with LODs between 18 and 34 microg/kg. This work shows the great possibilities of the combined use of SPE-FESI-CE-UV to improve CE sensitivity allowing the achievement of LODs similar to other analytical techniques as GC or HPLC.     

MEKC combined with SPE and sample stacking for multiple analysis of pesticides in water samples at the ng/L level

In this work, a new multiresidue analytical method based on MEKC with UV detection combined with SPE as off-line preconcentration strategy, and reversed-electrode polarity stacking mode (REPSM) as on-line stacking procedure, has been developed for the monitoring of 12 pesticides (carbendazim, pirimicarb, metalaxyl, pyrimethanil, procymidone, nuarimol, azoxystrobin, tebufenozide, fenarimol, benalaxyl, penconazole, and tetradifon) that are currently being used in the Canary Islands (Spain). The optimized MEKC buffer, consisting of 100 mM sodium tetraborate and 30 mM SDS at pH 8.5 with 6% v/v 1-propanol, provided baseline resolution of the 12 pesticides in less than 20 min. The developed method was applied to the analysis of mineral, stagnant, and tap water samples. The proposed SPE-REPSM-MEKC-UV method showed high extraction efficiencies with detection limits (LODs) at the low ng/L level providing LOD values down to 64 ng/L for these real samples.     

Determination of pesticides in drinking water by micellar electrokinetic capillary chromatography

A new analytical procedure using a two-step sample preconcentration (solid-phase extraction (SPE) and field-amplified sample stacking) prior to separation by micellar electrokinetic capillary chromatography was developed for the determination of 14 pesticides such as aldicarb, carbofuran, isoproturon, chlorotoluron, metolachlor, mecoprop, dichlorprop, MCPA, 2,4-D, methoxychlor, TDE, DDT, dieldrin, and DDE in drinking water. Good recoveries of pesticides were obtained using SPE with sample pH adjusted to 2-3. Field-amplified sample stacking was found to give enrichment factors up to 30-fold preconcentration of various pesticides under reversed polarity at -2 kV for 50 s. The optimized background electrolyte (BGE) consisted of 50 mM sodium dodecyl sulfate (SDS), 10 mM borate buffer, 15 mM beta-cyclodextrin (beta-CD), and 22% acetonitrile at pH 9.6, running was under 25 kV and detection at 202 nm. Good linearity was obtained for all pesticides with detection limits down to 0.04-0.46 ng/mL and a working range of 0.1-40 ng/mL. The repeatabilities of migration time and peak area were satisfactory with relative standard deviations (RSDs) between 0.66 and 13.6% and 4.1 and 28%, respectively. All pesticides except dieldrin were found to be detected at concentrations at least tenfold lower than the World Health Organization (WHO) guideline values. The analytical procedure developed offers an economic method for fast screening of multiple pesticide residues in drinking water for health protection. It had been applied to determine carbofuran and MCPA in agricultural run-off water samples, giving satisfactory repeatabilities of 10 and 12%, respectively, with n=5 for the determination of pesticides in contaminated water samples.     

Simultaneous determination of selected endocrine disrupters (pesticides,phenols and phthalates) in water by in-field solid-phase extraction (SPE) using the prototype PROFEXS followed by on-line SPE (PROSPEKT) and analysis by liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry

In this study, a new procedure, based on on-line solid-phase extraction (SPE) and analysis by liquid-chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS), has been developed for the simultaneous, multianalyte determination of 21 selected pesticides, phenols and phthalates in water. SPE was carried out on polymeric PLRP-s cartridges by percolating 20 mL-samples. For sample preconcentration, the performance of a prototype programmable field extraction system (PROFEXS) was evaluated against the commercial laboratory bench Prospekt system used for method development. The Profexs is designed for the automated on-site sampling, SPE preconcentration, and storage of up to 16 samples in SPE cartridges. These cartridges are further eluted and on-line analyzed with the Prospekt coupled to the chromatographic system. In the optimized method, where completely on-line SPE-LC-MS analysis of the samples is carried out with the Prospekt in the laboratory, detection limits lower than 100 ng/L, and satisfactory precision (relative standard deviations <25%) and accuracies (recovery percentages >75%) were obtained for most investigated compounds from the analysis of spiked Milli-Q water. The extraction efficiency achieved with the Profexs was comparable to that of the Prospekt for most compounds and somewhat lower for the most apolar analytes, probably due to adsorption on the pump filters. The completely on-line optimized method was applied to the analysis of surface water, ground water and drinking water from a waterworks in Barcelona. Some pesticides and phenols were found in both surface water and groundwater at ng/L or µg/L levels, but not in the final drinking water. Di(2-ethylhexyl)phthalate (DEHP) was present in all samples investigated, including blanks. To the author's knowledge, this is the first work describing the application of a fully automated on-line SPE-LC-MS method for the simultaneous analysis of pesticides, phenols, and phthalates in water, and the second one that examines the possibilities of the prototype Profexs for automated on-site SPE preconcentration of organic pollutants from water samples.     

Analysis of cytokinin nucleotides in coconut (Cocos nucifera L.) water using capillary zone electrophoresis-tandem mass spectrometry after solid-phase extraction

A method based on solid-phase extraction (SPE) and capillary zone electrophoresis-tandem mass spectrometry (CZE-MS/MS) is described for the separation and determination of six cytokinin nucleotides in coconut water. The best CZE separation for the six cytokinin nucleotide standards was achieved using a 25 mM ammonium formate/formic acid buffer (pH 3.8) and 2% (v/v) methanol with an applied gradient separation voltage (25 kV for 32 min, and then a linear gradient to 30 kV in 5 min, finally 30 kV to the end of separation) in less than 60 min. MS/MS with multiple reaction monitoring (MRM) detection was carried out to obtain sufficient selectivity and sensitivity for the cytokinin nucleotides. The combined use of on-line sample stacking and CZE-MS/MS achieved limits of detection (LODs) in the range of 0.06-0.19 microM for the six cytokinin nucleotides at a signal-to-noise ratio of 3. Furthermore, a novel dual-step SPE procedure was developed for the pre-concentration and purification of cytokinin nucleotides using Oasis HLB and Oasis MAX cartridges. The recoveries of the cytokinin nucleotides after the dual-step SPE were in the range of 44-71%. The combination of off-line SPE, on-line sample stacking and CZE-MS/MS approach was successfully applied to screen for endogenous cytokinin nucleotides present in coconut water sample. trans-Zeatin riboside-5'-monophosphate (ZMP) was detected and quantified in coconut water by CZE-MS/MS after SPE and on-line sample stacking.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Application of capillary zone electrophoresis with large-volume sample stacking to the sensitive determination of sulfonamides in meat and ground water

A CZE method with UV-Vis detection has been established and validated for the determination of nine sulfonamides: sulfapyridine, sulfamethazine, sulfamerazine, sulfamether, sulfadiazine, sulfadimethoxine, sulfamethoxazole, sulfachlorpyridazine, and sulfamethizole. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 45 mM sodium phosphate and 10% methanol at pH 7.3, with temperature and voltage of 27 degrees C and 25 kV, respectively. p-Aminobenzoic acid was used as an internal standard . Taking into account the lack of sensitivity of the UV-Vis detection, the application of an on-line preconcentration methodology, such as large-volume sample stacking with polarity switching has been proposed. This procedure combined with a solvent extraction/SPE method applied for off-line preconcentration and cleanup provides a significant improvement in the LODs, ranging from 2.59 to 22.95 mug/L for the studied compounds; the quantification of these residues being possible below the levels established by EU legislation in animal food products, such as meat. Satisfactory recoveries were also obtained in the analysis of these compounds in ground water.     

Different strategies for the preconcentration and separation of parabens by capillary electrophoresis

Several strategies, namely, large volume sample stacking (LVSS), field‐amplified sample injection (FASI), sweeping, and in‐line SPE‐CE, were investigated for the simultaneous separation and preconcentration of a group of parabens. A BGE consisting of 20 mM sodium dihydrogenphosphate (pH 2.28) and 150 mM SDS with 15% ACN was used for the separation and preconcentration of the compounds by sweeping, and a BGE consisting of 30 mM sodium borate (pH 9.5) was used for the separation and preconcentration of the compounds by LVSS, FASI, and in‐line SPE‐CE. Several factors affecting the preconcentration process were investigated in order to obtain the maximum enhancement of sensitivity. The LODs obtained for parabens were in the range of 18–27, 3–4, 2, and 0.01–0.02 ng/mL, and the sensitivity evaluated in terms of LODs was improved up to 29‐, 77‐, 120‐, and 18 400‐fold for sweeping, LVSS, FASI, and in‐line SPE‐CE, respectively. These preconcentration techniques showed potential as good strategies for focusing parabens. The four methods were validated with standard samples to show the potential of these techniques for future applications in real samples, such as biological and environmental samples.     

Investigation of in-line solid-phase extraction capillary electrophoresis for the analysis of drugs of abuse and their metabolites in water samples

In this study, in‐line solid‐phase extraction (SPE) was used as an enrichment technique in combination with CE for the preconcentration and separation of 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP), cocaine (COC), codeine (COD) and 6‐acetylmorphine (6AM). The separation buffer (BGE) used was 80 mM disodium phosphate anhydrous and 6 mM of HCl (final BGE pH of 3). The SPE extractor consists of a small segment of capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoretic capillary. Different parameters affecting preconcentration were evaluated, such as sample pH, the volume of the elution plug and sample injection time. The detection limits (LODs) reached for standard samples by in‐line SPE‐CE‐UV ranged between 50 and 200 ng/L, with sensitivity enhancement factors ranging from 2300 to 5300. Reproducibility values (expressed in terms of relative standard deviation) were below 7.6% for standard samples. This is a simple and an effective method for the determination of the studied drugs of abuse and their metabolites. The applicability of the developed method was demonstrated in tap and river water samples which were directly analyzed without any off‐line pretreatment. Analytical parameters were evaluated and LODs were between 70 and 270 ng/L with relative recoveries between 85 and 97%.     

Different sample stacking strategies to analyse some nonsteroidal anti-inflammatory drugs by micellar electrokinetic capillary chromatography in mineral waters

Three on-column preconcentration techniques were compared to analyse a group of nonsteroidal anti-inflammatory drugs (NSAIDs) using micellar electrokinetic capillary chromatography (MEKC) under pH-suppressed electroosmotic flow (EOF) in water samples. The analysed drugs were ibuprofen, fenoprofen, naproxen, ketoprofen, and diclofenac sodium. The micellar background electrolyte (BGE) solution was formed by 75 mM sodium dodecyl sulfate (SDS), 40% (v/v) acetonitrile, and 25 mM sodium phosphate at pH 2.5. When this BGE solution was used the applied voltage was reversed, -10 kV, and the drugs were separated within 20 min. The on-column preconcentration modes, characterised all of them for the sample matrix removal out of the capillary by itself under a reverse potential at the same time as the EOF was reduced, were stacking with reverse migrating micelles (SRMM), stacking with reverse migrating micelles-anion selective exhaustive injection (SRMM-ASEI), and field-enhanced sample injection with reverse migrating micelles (FESI-RMM). The sensitivity was improved up to 154-, 263-, and 63-fold, respectively when it was calculated through the peaks height. The optimised methods were validated with spiked mineral water by combining off-line solid-phase extraction (SPE) and the proposed on-line sample stacking strategies. The detection limits (LODs) of NSAIDs in mineral water were at ng/L levels.     

Large-volume sample stacking for the analysis of seven beta-lactam antibiotics in milk samples of different origins by CZE

A method for the simultaneous determination of eight beta-lactam antibiotics (nafcillin, cloxacillin, oxacillin, dicloxacillin, ampicillin, amoxicillin, and penicillin G) in fortified milk samples of different origins has been proposed by using CZE with diode-array detection (CZE-DAD). Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using 175 mM Tris buffer with 20% ethanol at pH 8.0. Methylparaben has been used as an internal standard (IS). Taking into account the lack of sensitivity of the UV-Vis detection, a solvent extraction/SPE method was applied for off-line preconcentration and sample cleanup, and also an on-line preconcentration methodology, such as large-volume sample stacking (LVSS) with polarity switching, was developed, providing LODs ranging from 2 to 10 microg/L. The method permits the quantification of these residues below the levels established in milk by the EU Regulation. Satisfactory recoveries ranging from 86 to 93% were also obtained in milk samples of different origins.     

On-line preconcentration strategies for analyzing pesticides in fruits and vegetables by micellar electrokinetic chromatography

Five pesticides (fludioxonil, procymidone, pyriproxyfen, dinoseb and carbendazim) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 20 mmol l(-1) phosphate buffer at pH 2.3, containing 25 mmol l(-1) sodium dodecylsulfate and 10% methanol. Three on-line concentration strategies, sweeping (SW), normal stacking with reversed migration and a water plug (SRW) and stacking with reverse migration and removal of sample matrix using polarity switching (SRMM), were compared. About 10-, 30- and 50-fold increases in detection sensitivity, compared with standard hydrodynamic injection (5 s at 0.5 psi), were observed with SW, SRW and SRMM, respectively. Limits of detection (LODs) ranged from 0.002 to 0.03 microg ml(-1) using only the on-line preconcentration procedures without any off-line concentration of the extract. A solid-phase extraction (SPE) procedure, for previous isolation and concentration of the analytes, was used in combination with any of the proposed on-line preconcentration strategies, which achieves the determination of pesticides at limits of quantification (LOQs) lower than 0.01 mg kg(-1). The recoveries obtained by SPE in samples spiked at 0.01 mg kg(-1) were between 70 and 100%, with RSDs between 10 and 18% using SRMM. Samples of fruits and vegetables were taken from the market, extracted by the proposed procedure and analyzed with RM-MEKC with the on-line strategies.     

Improving sensitivity by large-volume sample stacking combined with sweeping without polarity switching by capillary electrophoresis coupled to photodiode array ultraviolet detection

An easy, simple, and highly efficient on-line preconcentration method for polyphenolic compounds in CE was developed. It combined two on-line concentration techniques, large-volume sample stacking (LVSS) and sweeping. The analytes preconcentration technique was carried out by pressure injection of large-volume sample followed by the EOF as a pump pushing the bulk of low-conductivity sample matrix out of the outlet of the capillary without the electrode polarity switching technique using five polyphenols as the model analytes. Identification and quantification of the analytes were performed by photodiode array UV (PDA) detection. The optimal BGE used for separation and preconcentration was a solution composed of 10 mM borate-90 mM sodium cholate (SC)-40% v/v ethylene glycol, without pH adjustment, the applied voltage was 27.5 kV. Under optimal preconcentration conditions (sample injection 99 s at 0.5 psi), the enhancement in the detection sensitivities of the peak height and peak area of the analytes using the on-line concentration technique was in the range of 18-26- and 23-44-fold comparing with the conventional injection mode (3 s). The detection limits for (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (+)-catechin (C), (-)-epigallocatechin gallate (EGCG), and (-)-epicatechin gallate (ECG) were 4.3, 2.4, 2.2, 2.0, and 1.6 ng/mL, respectively. The five analytes were baseline-separated under the optimum conditions and the experimental results showed that preconcentration was well achieved.     

Trace determination of sulfonylurea herbicides in water and grape samples by capillary zone electrophoresis using large volume sample stacking

A sensitive and reliable method using capillary zone electrophoresis with UV-diode array detection has been developed and validated for trace determination of residues of sulfonylurea herbicides in environmental water samples and grapes from different origins. The analytes included are triasulfuron, rimsulfuron, flazasulfuron, metsulfuron-methyl, and chlorsulfuron. Optimum separation has been achieved on a 48.5-cm × 50-μm (effective length 40 cm) bubble cell capillary using 90 mM ammonium acetate buffer, pH 4.8, by applying a voltage of 20 kV at 25 °C and using p-aminobenzoic acid as the internal standard. In order to increase sensitivity, large volume sample stacking with polarity switching has been applied as on-line preconcentration methodology. For water samples, a solid-phase extraction (SPE) procedure based on the use of Oasis HLB cartridges was applied for off-line preconcentration and cleanup. For grape samples, the SPE procedure was achieved with C₁₈ sorbent, after extraction of the compounds with MeOH:H₂O (1:1) by sonication. The limits of detection for the studied compounds were between 0.04 and 0.12 μg/L for water samples and 0.97 and 8.30 μg/kg in the case of grape samples, lower in all cases than the maximum residue limits permitted by the EU for this kind of food. The developed methodology has demonstrated its suitability for the monitoring of these residues in environmental water and grape samples with high sensitivity, precision, and satisfactory recoveries.     

Strategies for the on-line preconcentration and separation of hypolipidaemic drugs using micellar electrokinetic chromatography

Three strategies were investigated for the simultaneous separation and on-line preconcentration of charged and neutral hypolipidaemic drugs in micellar electrokinetic chromatography (MEKC). A background electrolyte (BGE) consisting of 20 mM ammonium bicarbonate buffer (pH 8.50) and 50 mM sodium dodecyl sulfate (SDS) was used for the separation and on-line preconcentration of the drugs. The efficiencies of sweeping, analyte focusing by micelle collapse (AFMC), and simultaneous field-amplified sample stacking (FASS) and sweeping, were compared for the preconcentration of eight hypolipidaemic drugs in different conductivity sample matrices. When compared with a hydrodynamic injection (5 s at 50 mbar, 0.51% of capillary volume to detection window) of drug mixture prepared in the separation BGE, improvements of detection sensitivity of 60-, 83-, and 80-fold were obtained with sweeping, AFMC and simultaneous FASS and sweeping, respectively, giving limits of detection (LODs) of 50, 36, and 38 μg/L, respectively. The studied techniques showed suitability for focusing different types of analytes having different values of retention factor (k). This is the first report for the separation of different types of hypolipidaemic drugs by capillary electrophoresis (CE). The three methods were validated then applied for the analysis of target analytes in wastewater samples from Hobart city.     

Graphene‐based solid‐phase extraction disk for fast separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples

Graphene has great potentials for the use in sample preparation due to its ultra high specific surface area, superior chemical stability, and excellent thermal stability. In our work, a novel graphene‐based SPE disk was developed for separation and preconcentration of trace polycyclic aromatic hydrocarbons from environmental water samples. Based on the strong π–π stacking interaction between the analytes and graphene, the analytes extracted by graphene were eluted by cyclohexane and then determined by GC‐MS. Under the optimized conditions, high flow rate (30 mL/min) and sensitivity (0.84–13 ng/L) were achieved. The proposed method was successfully applied to the analysis of real environmental water samples with recoveries ranging from 72.8 to 106.2%. Furthermore, the property of anticlogging and reusability was also improved. This work reveals great potentials of graphene‐based SPE disk in environmental analytical.     

Determination of sulfophenyl carboxylic acids in agricultural groundwater samples by CE with ultraviolet absorption detection

An analytical method for the determination of six sulfophenyl carboxylic acids, namely (p-sulfophenyl)acetic, 2-(p-sulfophenyl)propionic, 2-(p-sulfophenyl)butyric, 3-(p-sulfophenyl)butyric, 4-(p-sulfophenyl)butyric, and 5-(p-sulfophenyl)valerianic acid, in agricultural irrigation water samples was developed. It involves an SPE procedure, an on-line preconcentration normal stacking mode and subsequent separation and determination using CE with UV detection (CE-UV). p-Sulfobenzoic acid was used as internal standard. The compounds were separated with an uncoated capillary and a 25 mM ammonium acetate/acetic acid buffer solution (pH 5.5) with 2-propanol (30% v/v) and 0.75 mM CTAB. Analyses were run at -25 kV, 25 degrees C, and 100 s of hydrodynamic injection with UV detection at 225 nm. Quantification limits found ranged between 4 and 6 ng/mL. The proposed method was validated using a recovery assay. It was satisfactorily used for the determination of these compounds in groundwater samples to track down the biodegradation of linear alkylbenzene sulfonates in an agricultural soil from the fertile plain of Granada (Spain).     

固相萃取-气相色谱-质谱联用同时测定河水和海水中87种农药

采用固相萃取-气相色谱-质谱联用技术,建立了河水和海水中87种农药(24种有机磷、15种有机氯、12种唑类、9种拟除虫菊酯类、5种氨基甲酸酯类、7种酰胺类及15种其他新型农药)的多残留同时分析方法。优化了影响分离效果和灵敏度的仪器参数,考察了固相萃取柱柱型及水样体积、pH、盐度的影响,采用NH2柱优化了净化效果,内标法和替代物法用于数据的质量控制。结果表明: 在最佳条件下,各目标农药的方法检出限为0.1～6.6 ng/L;以实际河水和海水为基底,在5 ng/L和20 ng/L的加标水平下,绝大多数目标农药的回收率为60%～120%,相对标准偏差(n=4)为0.01%～9.7%。该法灵敏、准确,已成功地应用于福建九龙江河口区表层水样中多种类农药的复合污染监测,检出包括5种有机磷类、3种酰胺类、4种唑类、3种氨基甲酸酯类、2种拟除虫菊酯类等农药20种。