Trace analysis of triazines and organophosphorus pesticides in water

A method for the determination of trace levels of triazines and organophosphorus pesticides in water is presented. The extraction method is based on a solid-phase extraction on C-18 bound silica SPE cartridges. A precolumn filled with Merck C-18 bound silica and home-made C-18 bound silica have been tested at a flow-rate of 3 ml/min with comparable preconcentration yields. A SIM-MS method using a (15)N labelled internal standard has been developed for the organophosphorus pesticides. Detection limits lower than 1 microg/L have been obtained. Separations have been carried out on a conventional GC column OV 17 (1 m) and a capillary column OV 17 (25 m) with a temperature program from 150 degrees C (2 min) to 300 degrees C (rate of 6 degrees C/min).     

Preparation of octadecyl modified column gels using heat-treated silicas and their retention behaviour in high-performance liquid chromatography

Summary The effect of silanol groups on three types of octadecylmodified column gels using heat-treated silicas by calcination has been studied by high-performance liquid chromatography. After heat-treating at 180°C, 500°C and 950°C, the silicas treated with octadecyldimethylchlorosilane were used for the measurement of physical and chemical analysis. From elemental carbon analysis data, the reactive silanol group concentrations, _OH(s), were determined to be 2.0 in the 180°C treated silica, 2.1 in the 500°C treated silica and 1.6 in the 950°C treated silica, respectively (original silica: mean pore diameter 116 Å, specific surface area 298 m²/g, pore volume 1.22 ml/g, particle size 5.0 m). The separation factors, , of pyridine versus phenol were measured to be 0.79 on 180°C treated silica, 0.91 on 500°C treated silica and 1.98 on 950°C treated silica, using acetonitrile-water mixtures as the eluent. And then, on the basis of the physico-chemical and chromatographic data, the three types of octadecyl modified column gels using heat-treated silicas by calcination have been compared.     

GC-NPD investigation of the recovery of organonitrogen and organophosphorus pesticides from apple samples: The effect of the extraction solvent

Summary A gas chromatographic method employing a capillary column and a selective nitrogen/phosphorus detector (NPD) has been developed for the determination of organophosphorus (OP) and organonitrogen (NP) pesticides in horticultural samples (apples). The separation of sixteen pesticides and the internal standard was performed in thirteen minutes. The analytical characteristics of the method, including linear response ranges, detection limits, and reproducibility, have been studied using a 11 mixture of ethyl acetate and xylene as extraction solvent. The possibility of mutual interference between pesticides has also been studied. A procedure for the quantitative extraction of the sixteen pesticides from apple samples has also been developed; for fifteen of the pesticides recoveries >85% were obtained after 90 minutes extraction. The effect of different solvents both on recovery and on the sensitivity of the subsequent chromatography were also investigated. It was found that the sensitivity required must be considered when the solvent for sample treatment is selected.     

Solid phase microextraction using new sol–gel hybrid polydimethylsiloxane-2-hydroxymethyl-18-crown-6-coated fiber for determination of organophosphorous pesticides

A new sol–gel hybrid coating, polydimethylsiloxane–2-hydroxymethyl-18-crown-6 (PDMS–2OHMe18C6) was prepared in-house for use in solid phase microextraction (SPME). The three compositions produced were assessed for its extraction efficiency towards three selected organophosphorus pesticides (OPPs) based on peak area extracted obtained from gas chromatography with electron capture detection. All three compositions showed superior extraction efficiencies compared to commercial 100 μm PDMS fiber. The composition showing best extraction performance was used to obtain optimized SPME conditions: 75 °C extraction temperature, 10 min extraction time, 120 rpm stirring rate, desorption time 5 min, desorption temperature 250 °C and 1.5% (w/v) of NaCl salt addition. The method detection limits (S/N = 3) of the OPPs with the new sol–gel hybrid material ranged from 4.5 to 4.8 ng g⁻¹, which is well below the maximum residue limit set by Codex Alimentarius Commission and European Commission. Percentage recovery of OPPs from strawberry, green apple and grape samples with the new hybrid sol–gel SPME material ranged from 65 to 125% with good precision of the method (%RSD) ranging from 0.3 to 7.4%.     

基于氧化石墨烯气凝胶固相萃取柱检测有机磷农药北大核心CSCD

以氧化石墨烯气凝胶三维纳米材料作为固相萃取的吸附剂,结合高效液相色谱,对食品中的有机磷农药(辛硫磷、双硫磷、倍硫磷、杀螟硫磷)进行检测分析。首先,利用冷冻干燥的方式制备得到氧化石墨烯气凝胶,通过扫描电镜、红外光谱、比表面积吸附等一系列的实验手段对其形貌及物理特性进行了表征,证明其成功合成。从扫描电镜中可见石墨烯的层状褶皱结构,其表面积为740.51 m^(2)/g。然后,将氧化石墨烯气凝胶直接填充于固相萃取柱中,在未借助任何硅胶等基体的条件下进行萃取研究;通过单因素实验,系统研究了萃取和洗脱条件对有机磷农药萃取回收率的影响。结果显示,在上样体积15 mL、样品溶液pH值4、上样速率1.0 mL/min、洗脱剂1.0 mL乙腈的条件下萃取回收率最高。与商用的萃取材料进行比较,包括碳十八硅胶柱(C18)、阴离子交换柱(SAX)、氨基柱(-NH_(2))和硅酸镁柱(Florisil),氧化石墨烯气凝胶填充的固相萃取柱的萃取回收率有明显提高。实验考察了氧化石墨烯气凝胶直接填充的萃取柱的寿命,结果显示该萃取柱可以重复使用15次,可见解决了分散无基体支撑的石墨烯纳米片容易破碎、堵塞筛板的问题。与液相色谱联用建立分析方法,4种有机磷农药的线性范围较宽,辛硫磷、双硫磷和倍硫磷的线性范围为1~200μg/L,杀螟硫磷的线性范围为2~200μg/L,线性拟合良好(线性相关系数r^(2)≥0.9949),检出限为0.2~0.5μg/L,满足于我国和其他国家限定标准的检测。将该方法应用于实际样品,在苹果皮中未检测到有机磷农药,对其进行加标,回收率为70.5%~93.6%,相对标准偏差≤10.4%。     

Solid-Phase Microextraction Gas Chromatography for Determination of Some Organophosphorus Pesticides

A simple and rapid solid-phase microextraction (SPME) method is presented based on activated charcoal–PVC fiber for determination of some organophosphorus pesticides from aqueous samples in direct mode SPME. After optimization of the experimental variables affecting SPME of the target compounds from aqueous solutions, the proposed method was applied to determine pesticides in fruit juice. The analytes in this procedure were preconcentrated for 15 min on the SPME fiber and subsequently desorbed by heating the fiber at 200 °C for 5 min in the GC injection port. Separation was on a capillary column GC followed by flame ionization detection. Recoveries of the pesticides studied in aqueous samples ranged 42%–63% and repeatability for all analytes was < 9% for a single fiber. Fiber-to-fiber reproducibility was < 18%.     

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 m polyacrylate fiber. For organophosphorus pesticides, a 100 m 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 g/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 (P_ow). For triazines it was shown that there is a linear dependence of the logarithm of the analyte response on the log(P_ow) 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.     

Study of 17β-estradiol-3-benzoate, 17α-methyltestosterone and medroxyprogesterone acetate fixation in bovine hair

The detection of steroid residues in hair is a powerful strategy to demonstrate long-term administration of these growth promoters in meat production animals. A fast and reliable method was developed for monitoring anabolic steroids and their esters in hair. A 100 mg hair sample was converted into powder and extracted at 50 °C with methanol (sebum fraction). The remaining hair was digested with 1 M NaOH for further extraction of bound steroids. The two fractions were separately purified onto an aminopropyle solid-phase extraction column and onto a silica SPE cartridge. Steroids were detected either by gas chromatography-tandem mass spectrometry after silylation using N-methyl-N-(trimethylsilyl)-trifluoroacetamide/trimethyliodosilane/dithiothreitol or liquid chromatography-tandem mass spectrometry. This method was applied to hair samples collected over a three months period after treatment of three cows respectively with 17α-methyltestosterone, medroxyprogesterone acetate and 17β-estradiol-3-benzoate. The fixation kinetic into hair of the three steroids have been deeply examined and discussed; relation in-between concentration and distance from the injection site, influence of hair colour and sample treatment consequences have been discussed.     

Solid phase versus solvent extraction of pesticides from water

The average recovery for 12 pesticides spiked into 100 ml of water at 0.1 ppb was 90% when cartridges containing 100 mg of C-18 bonded porous silica were used for adsorption. Flow rates of up to 200 bed volumes per minute were employed for the adsorption step. Quantitative desorption of the pesticides was accomplished with less than 100l of solvent, thus eliminating the need for a solvent reduction step. The pesticides from samples of surface waters were adsorbed onto C-18 bonded porous silica at the sampling site and the cartridges containing the bonded phase were returned to the laboratory for elution and analysis. The analytical results obtained from use of this procedure agreed with those obtained for duplicate samples of the water that were processed in the laboratory using standard solvent extraction procedures.     

A rapid method for the determination of methoprene in tobacco by high performance liquid chromatography

Summary A rapid sample preparation procedure combined with a short reversed-phase HPLC separation for the quantitation of methoprene residue in tobacco samples is described. A ground tobacco sample of 0.5 g is mixed with 3 mL of 2-propanol. The mixture is extracted for twelve minutes with the aid of sonication at an elevated temperature (45–55°C) and then filtered through a 0.45 m disposable filter prior to injection on HPLC. No sample cleanup or solvent evaporation step is required. Chromatographic analysis is performed on a C-18 column and the analysis time is 12.5 minutes. The detection limit for methoprene in tobacco samples is one part per million (g/g).     

三维石墨烯金属网固相萃取测定有机磷农药残留

以金属网为基体材料,通过化学键合的方式将氧化石墨烯和Au纳米颗粒层层组装到金属网表面,得到一种Au纳米颗粒改性的石墨烯气凝胶修饰的金属网萃取材料,并应用于有机磷农药的富集检测.与商用的萃取材料进行对比,相较于SAX、C18、-NH2、Carb、Florisil等材料,金纳米颗粒改性的三维石墨烯气凝胶金属网对有机磷农药分...     

A direct resistively heated gas chromatography column with heating and sensing on the same nickel element

Nickel clad or nickel wired fused silica column bundles were constructed and evaluated. The nickel sheathing or wire functions not only as the heating element for direct resistive heat, but also as the temperature sensor, since nickel has a large resistive temperature coefficient. With this method the temperature controller is able to apply power and measure the temperature simultaneously on the same nickel element, which can effectively avoid the temperature overshoot caused by any delayed response of the sensor to the heating element. This approach also eliminates the cool spot where a separate sensor touches the column. There are some other advantages to the column bundle structure: (1) the column can be heated quickly because of the direct heating and the column's low mass, shortening analysis time. We demonstrate a maximum heating rate of 13 °C/s (800 °C/min). (2) Cooling time is also short, increasing sample throughput. The column drops from 360 °C to 40 °C is less than 1 min. (3) Power consumption is very low – 1.7 W/m (8.5 W total) for a 5 m column and 0.69 W/m (10.4 W total) for a 15 m column when they are kept at 200 °C isothermally. With temperature programming, the power consumption for a 5 m column is less then 70 W for an 800 °C/min ramp to 350 °C. (4) The column bundle is small, with a diameter of only about 2.25 in. All these advantages make the column bundle ideal for fast GC analysis or portable instruments. Column efficiencies and retention time repeatability have been evaluated and compared with the conventional oven heating method in this study. For isothermal conditions, the column efficiencies are measured by effective theoretical plate number. It was found that the plate number with resistive heat is always less than with oven heat, due to uneven heat in the column bundle. However, the loss is not significant – an average of about 1.5% for the nickel clad column and 4.5% for the nickel wired column. Separation numbers are used for the comparison with temperature programming, with results similar to those observed for isothermal conditions. Retention time repeatability for direct heat were 0.010% RSD for isotheral and 0.037% RSD for temperature programming, which is similar to those obtained by oven heat. Applications have been demonstrated, including diesel and PAH analysis.     

亚微米C18键合硅胶固定相加压毛细管电色谱法同时拆分3种手性三唑类农药

采用改良Stöber法制备420 nm亚微米单分散二氧化硅微球,采用C18硅烷化修饰后装填成毛细管色谱柱。采用该色谱柱,在加压毛细管电色谱平台上成功地实现了3对手性三唑类农药烯效唑、烯唑醇和丙环唑的同时拆分和分离。考察了各因素对手性分离效果的影响,优化后的色谱条件为：流动相为乙腈-20 mmol/L磷酸盐缓冲液（pH=6.8）（45：55,v/v）,其中缓冲液中含20 mmol/L羟丙基-γ-环糊精（HP-γ-CD）;泵流速为0.04 mL/min;施加电压-9.4 kV;检测波长220 nm。在上述条件下,烯效唑、烯唑醇和丙环唑3种对映体同时得到拆分和分离,相邻两峰之间的分离度依次为4.20、12.9、4.41、4.09、1.70,分离时间仅为12 min,柱效最高达到310000 plates/m。该研究为手性三唑类农药的同时分离提供了新的分离分析思路。     

Development of a headspace solid-phase microextraction/gas chromatography-mass spectrometry method for determination of organophosphorus pesticide residues in cow milk

In the past few years, organophosphorus compounds become one of the most widely used classes of pesticides due to their acute toxicity against a wide variety of pests. In this work, a method based on solid-phase microextraction in mode headspace (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) was developed and optimized through multivariate factorial design to determine residues of organophosphorus pesticides in cow's milk. Different parameters of the method were evaluated, such as fiber type, temperature, extraction and desorption times, sample volume, effect of salt addition and stirring velocities. The evaluated pesticides were dichlorvos, sulfotep, demeton-S, dimpylate, disulfoton, parathion, methyl parathion, fenitrothion, chlorpyrifos and ethion. The best results were obtained using polydimethylsiloxane/divinylbenzene fiber and headspace mode at 90 °C for 45 min, along with stirring at 600 rpm and desorption for 5 min at 250 °C. Under the optimized conditions, the proposed methodology was able to determine all of the pesticides with variation coefficients between 6.1% and 29.5%. Detection and quantification limits ranged from 2.16 to 10.85 μg L^− 1 and from 6.5 to 32.9 μg L^− 1, respectively. To evaluate residues of these pesticides in milk, cows were exposed to the pesticides of interest and milk was collected after 24 h. The developed method was able to detect trace amounts of these pesticides in the collected milk samples.     

The rapid quantitative analysis of codeine phosphate drug substance by reversed-phase high-performance liquid chromatography

Summary A rapid procedure for the evaluation of codeine phosphate drug substance derived from poppy straw or opium concentrate is described. The gradient HPLC procedure employs a pH 2.5 phosphate buffer, methanol and acetonitrile mobile phase at 40°C and a Bondapak C-18 column. Eight opium alkaloids, including the four major alkaloids, are separated from each other. The paper describes details of the assay procedure and presents data documenting the linearity, specificity, precision, and sensitivity of the method.     

Determination of trace elements in seawater by electrothermal atomic absorption spectrometry with and without a preconcentration step

The determination of the trace metals Cd, Pb and Cu in seawater by electrothermal atomic absorption spectrometry (ETA-AAS) has been investigated. A combination of the platform with mixed palladium nitrate-magnesium nitrate as matrix modifier and Zeeman background correction allows Cd an Pb to be determined by aqueous standard calibration in appropriately diluted seawater samples. Copper can be determined in undiluted seawater samples without chemical modification using a standard additions method. Detection limits (3) of 2.97,5.27 and 1.1 gl^–1 are obtained for Cd, Pb and Cu respectively. A Kelex-100 impregnated silica C18 material (Kelex 100-C18) has been tried and has proved to be effective as a column packing for extraction/preconcentration of these metals from seawater. Using the column extraction method, the sensitivity of the graphite furnace technique is enhanced 50-fold using a 10 l injection volume. Thus, the determination of the studied three metals in seawater at the ng.l^–1 level could be achieved.     

MWCNTs-solid phase extraction combined with ultra-high performance liquid chromatography-tandem mass spectrometry for the determination of eleven organophosphorus pesticides in river water

A method for simultaneous determination of 11 organophosphorus pesticides residues in river water by MWCNTs-solid phase extraction combined with ultra-high performance liquid chromatography/tandem mass spectrometry was developed. After centrifugation and filtration, the target pesticides were enriched with MWCNTs-SPE cartridge. Then the pesticides adsorbed on MWCNTs were eluted with ethyl acetate and dichloromethane, the eluent was dried-up under nitrogen flow and the residue was dissolved in methanol-water (1:1, v/v) as sample solution. The separation was accomplished on a C18 column with the mobile phase consisting of methanol and 0.1% formic acid at 0.20 mL/min in gradient elution. The pesticides were detected in multiple reaction monitoring mode by a triple quadruple mass spectrometer. Good linearities were obtained within 1–200 ng/L, with the correlation coefficients greater than 0.998. The detection and quantification limits were in the ranges of 0.02–1.00 ng/L and 0.07–3.33 ng/L, respectively. The recoveries and relative standard deviations were in the range of 88.3–124.9% and 0.12–20.5%, respectively. The method has been successfully applied to the detection of 34 urban river water samples from Chengdu, China and 7 organophosphorus pesticides were detected with the concentrations of 0.32–211 ng/L.     

An SPME–GC–MS Method for Determination of Organochlorine Pesticide Residues in Medicinal Plant Infusions

A simple method, direct-immersion sampling by solid-phase microextraction and gas chromatography–mass spectrometry (DI-SPME–GC–MS), has been developed for determination of organochlorine pesticides (OCP) in plant infusions. The optimum conditions for SPME with a 100-m PDMS-coated fiber were established by using a central composite design. The extraction time and sample temperature established were 60 min and 50 °C, respectively. The method was validated and used to determine hexachlorobenzene, lindane, 4,4-DDE, aldrin, dieldrin, endrin, heptachlor, heptachlor epoxide, and 4,4-DDT in infusions of Mikania laevigata and Maytenus ilicifolia. Limits for quantitation for the OCP were between 0.2 and 2.0 ng g^–1 except for lindane, for which the LOQ was higher (12 ng g^–1), because of its low affinity for the PDMS fiber. Recovery was in the range 90 to 108% and the intra-assay precision was below 17%. Transfer of the OCP from the plant to the infusion was in the range 0.34 to 3.4% and was correlated with the solubility of each compound in water.     

Quantitative determination of organochlorine pesticides in sewage sludges using soxtec,soxhlet and pressurized liquid extractions and ion trap mass–mass spectrometric detection

A new analytical method is described for the determination of organochlorine pesticides (OCPs) in sewage sludges using GC-ion trap-MS–MS. In this work, 16 organo-chlorine pesticides (OCPs) listed by the US Environmental Protection Agency (US EPA) as priority pollutants were separated and quantified. Sludge samples from three of Kuwaits wastewater treatment plants (WWTPs) were analyzed for organochlorine pesticides (OCPs). Spiked sludge samples were extracted with a mixture of (1:1 v/v) dichloromethane (DCM)/hexane. The extracts were cleaned on a silica/aluminum oxide column, then transferred to a gel permeation chromatography (GPC) column, before undergoing further silica/aluminum oxide clean-up; the presence of OCPs was then confirmed by GC-ion trap-MS–MS. Three extraction techniques, soxtec, soxhlet, and pressurized liquid extractions were utilized, compared and validated using the spiked sludge samples. The methods were validated in term of accuracy (recovery) and precision (RSD). The method recovery values varyied from 76.1 to 92.9% for the three extraction techniques.     

Solid‐phase extraction using chloropropyl functionalized sol–gel hybrid sorbent for simultaneous determination of organophosphorus pesticides in selected fruit samples

A new sol–gel hybrid methyltrimethoxysilane‐chloropropyltriethoxysilane was prepared as sorbent for solid‐phase extraction. The extraction efficiency of the prepared sol–gel hybrid methyltrimethoxysilane‐chloropropyltriethoxysilane was assessed by using three selected organophosphorus pesticides, namely, chlorpyrifos, profenofos, and malathion. Gas chromatography–mass spectrometry was used for detection of organophosphorus pesticides. Several vital parameters were optimized to identify the best extraction conditions. Under the optimum extraction conditions, solid‐phase extraction‐methyltrimethoxysilane‐chloropropyltriethoxysilane method showed good linearity range (0.05‐1 μg/mL) with coefficient of determination more than 0.995. The limits of detection obtained were in the range of 0.01–0.07 μg/mL and limits of quantification ranging from 0.03 to 0.21 μg/mL. The limits of detection obtained for the developed method were 2.3–6.5× lower than the limits of detection of commercial octadecyl silica sorbent. Real samples analysis was carried out by applying the developed method on red apple and purple grape samples. The developed method exhibited good recoveries (88.33–120.7%) with low relative standard deviations ranging from 1.6 to 3.3% compared to commercial octadecyl silica sorbent, which showed acceptable recoveries (70.3–100.2%) and relative standard deviations (6.3–8.8%). The solid‐phase extraction‐methyltrimethoxysilane‐chloropropyltriethoxysilane method is presented as an alternative extraction method for determination of organophosphorus pesticides.