Matrix-induced effects: a critical point in the gas chromatographic analysis of pesticide residues

The influence of several experimental factors related to the enhanced gas chromatographic responses yielding apparent recoveries of pesticide residues greater than 100% was investigated. Optimisation of a gel permeation chromatographic clean-up step with respect to the trueness and precision of generated data was performed. An increase of relative detector response (100%=response of analyte in pure solvent solution) was evidenced to be dependent both on the concentration of the analyte and the character of the matrix: pronounced matrix-induced effects were observed particularly in orange and wheat extracts at low concentration levels of analytes (especially for GC–electron-capture detection analysis of certain pesticides). As soon as the splitless injector became contaminated after injection of large series of matrix-containing samples, a decrease of relative responses of pesticides, largely below 100%, was experienced. Although troublesome compounds tending to give matrix-induced effects can be identified, and increased recoveries may be tentatively predicted, poor accuracy of generated data can be presumed as long as quantitation is not based on a standard prepared in blank matrix extract to compensate for matrix-induced effects.     

A new conceptual approach to assigning biomass combustion-derived methoxyphenol structures by using a gas chromatographic retention index model

A new conceptual approach towards iteratively constructing chromatographic retention time/index models is presented. The approach is applicable where there is potential structural uncertainty in a number of members of the dataset used in constructing the model, and where limited spectroscopic information is available to guide the process. The model is demonstrated on a suite of biomass combustion-derived methoxyphenols for which gas chromatographic polydimethylsiloxane retention index data was available in the literature, but where there was ambiguity regarding the identity of several members of the dataset. The retention property model is populated by sequentially screening a series of candidate structures that meet basic mass spectrometric requirements by using a multiple linear regression model containing molecular and physicochemical properties that have been previously shown to yield reliable predictions of chromatographic behaviour within a compound class. The criteria for deciding on the likely structure(s) out of a suite of candidate structures is based upon the improved quality of fit the most probable structure gives the regression model relative to other candidate structures. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Qualitative and quantitative analysis of organophosphorus pesticide residues using temperature modulated SnO(2) gas sensor

Qualitative and quantitative analysis of organophosphorus pesticide residues (acephate and trichlorphon) using temperature modulated SnO₂ gas sensor were studied. The testing method employed only a single SnO₂-based gas sensor in a rectangular temperature mode to perform the qualitative analysis of pure pesticide vapor and a binary vapor mixture in the air. Experimental results showed that in the range 250-300 °C and at the modulating frequency of 20 mHz the high selectivity of the sensor could be achieved. The quantitative analysis of the pure pesticide vapor and their mixture were performed by fast Fourier transformation (FFT). The higher harmonics of the FFT characterized the non-linear properties of the response at the sensor surface. The amplitudes of the higher harmonics exhibited characteristic variations that depend on the concentration and the kinetics of pesticide species on the sensor surface.     

Reduction of analysis time in gas chromatography. Application of low-pressure gas chromatography-tandem mass spectrometry to the determination of pesticide residues in vegetables

An alternative to conventional capillary gas chromatography (GC) is evaluated as a new approach to determine pesticide residues in vegetables. Low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS-MS) is proposed after a fast and simple extraction of the vegetable samples with dichloromethane and without clean up. The use of the above-mentioned GC technique reduced the total time required to determine 72 pesticides to less than half the present time (31 min), increasing the capability of a monitoring routine laboratory. The use of guard column and plug of carbofrit into the glass liner in combination with LP-GC was evaluated. The method was validated with limits of quantitation low enough to determine the pesticide residues at concentrations below the maximum residue levels stated by legislation. In order to assess its applicability to the analysis of real samples, 25 vegetable samples previously determined using conventional-capillary GC-MS-MS were analysed by LP-GC-MS-MS. The results obtained with the compared techniques showed differences lower than 0.01 mg kg(-1).     

气相色谱-质谱法分析烟草中有机磷农药残留量及其烟支转移率研究

建立了一种用加速溶剂萃取,自动固相萃取净化,气相色谱/质谱联用检测烟草中29种有机磷农药残留量的方法.考察了加速溶剂萃取仪的萃取温度、溶剂、加热时间和循环次数对回收率的影响,对固相萃取的洗脱溶液及其体积和流速进行了优化,利用保留时间和定性离子定性,以灭蚁灵为内标进行定量,29种有机磷农药的平均回收率在61.4%～128%之间,相对标准偏差在12%以下,符合烟草中农药多残留检测的要求.通过对烟支进行加标,探讨了有机磷农药向主流烟气和烟蒂的转移情况,其向主流烟气的平均转移率为小于6.3%,相对标准偏差为8.0%～18.5%,而烟蒂平均截留率为0.3%～15.0%,相对标准偏差为6.5%～21.3%,表明有机磷农药有较小的转移,为卷烟安全性评价提供了可靠的数据.     

Automated glass capillary gas chromatographic analysis of PCB and organochlorine pesticide residues in agricultural products

Complicated PCB mixtures can be separated in individual compounds using glass capillary gas chromatography, (GC)². Depending on extraction and clean-up procedure it is also possible to separate and determine organochlorine pesticides at the same time. This (GC)² technique can be used to determine the contents of individual chlorinated biphenyls in milk products and animal feedstuffs and in the analysis of complicated extracts of soil and vegetable material. Practical aspects concerning connection of the capillary, automatic splitless injection, repeatability of the retention time, quality of the column with respect to separation and adsorption and degradation of DDT are discussed. The detection of individual chlorinated biphenyls is possible at the ppb level in fats and vegetable materials, using an extraction and clean-up procedure, based on saponification of the sample. Preliminary results for milk, obtained from several areas, are shown.     

气相色谱-三重四极杆串联质谱结合QuEChERS测定三七中有机磷农药残留

建立了改良的QuEChERS样品前处理法,结合气相色谱-三重四极杆串联质谱(GC-MS/MS)同时测定三七中18种有机磷农药残留的方法。样品经1%乙酸-乙腈提取,改良QuEChERS技术净化,利用GC-MS/MS采取多反应离子监测模式测定,基质匹配校准曲线外标法定量。18种有机磷农药残留在2.5~120.0μg/kg范围内线性良好,相关系数(R2)大于0.99;检出限为0.4~1.5μg/kg,定量限为0.8~2.5μg/kg。在3个加标水平(2.5,8.0,60.0μg/kg)下平均回收率为70.5%~118.9%,相对标准偏差为1.0%~9.8%。     

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.     

气相色谱-质谱法同时检测中草药保健食品中41种有机磷和氨基甲酸酯类农药残留

建立了乙腈:丙酮(3∶7,V/V)混合溶液提取,CARB/NH2固相萃取柱净化,气相色谱-质谱(GC-MS)同时测定中草药保健食品中41种有机磷和氨基甲酸酯类农药残留,外标法定量.方法的检出限为0.01～0.05 mg/kg,回收率为62.2％～114.9％,相对标准偏差为4.5％～15％.方法适用于多种农药残留的同时...     

A high-throughput approach for the determination of pesticide residues in cucumber samples using solid-phase microextraction on 96-well plate

A high-throughput solid-phase microextraction (SPME) on 96-well plate together with gas chromatography–mass spectrometry (GC–MS) was developed for the determination of some selected pesticides in cucumber samples. Pieces with the length of 1.0 cm of silicon tubing were precisely prepared and then coated on the end part of stainless steel wires. The prepared fibers were positioned in a home-made polytetrafluoroethylene (PTFE)-based constructed ninety-six holes block to have the possibility of simultaneous immersion of the SPME fibers into the center of individual wells. Pesticides such as diazinon, penconazol, tebuconazol, bitertanol, malathion, phosalone and chlorpyrifos-methyl were selected for their highly application in cucumber field. The performances of the SPME fibers, such as intra and inter-fibers reproducibility, were evaluated and the results showed a good similarity in extraction yields. A volume of 1 mL of the aquatic supernatant of the cucumber samples was transferred into the 96-well plate and the array of SPME fibers was applied for the extraction of the selected pesticides. The important parameters influencing the whole extraction process including, organic solvent percent, salt addition, dilution factor, stirring rate and extraction time were optimized. The inter- and intra-day RSD% were found to be less than 15.4%. Limits of detection (LOD) and limits of quantification (LOQ) were below 60 and 180 μg kg⁻¹, respectively. The coefficient of determination was satisfactory (r² > 0.99) for all the studied analytes. The developed method was successfully applied to the monitoring of several samples gathered from local markets.     

Determination of 195 pesticide residues in Chinese herbs by gas chromatography-mass spectrometry using analyte protectants

The phenomenon known as "matrix-induced enhancement effect" is not only observed in the analysis of pesticides in food, but also in Chinese herbs. Several approaches have been proposed to overcome the matrix-induced effect, but each method has serious limitations. Compared with standard calibration methods, the procedure with adding analyte protectants offers a more convenient and effective route to solve the problem. In the current study, we have analyzed 195 types of pesticides in Chinese herbs by gas chromatography-mass spectrometry (GC-MS), and the compounds that are susceptible to matrix effect were picked up and confirmed. In addition, several analyte protectants were evaluated and the most effective combination was determined. D-ribonic acid-γ-lactone (2 mg/ml) and D-sorbitol (1 mg/ml) were shown to be the best analyte protectants for the analysis of most pesticides.     

Toward automated chromatographic fingerprinting: A non-alignment approach to gas chromatography mass spectrometry data

In contrast to targeted analysis of volatile compounds, non-targeted approaches take information of known and unknown compounds into account, are inherently more comprehensive and give a more holistic representation of the sample composition. Although several non-targeted approaches have been developed, there's still a demand for automated data processing tools, especially for complex multi-way data such as chromatographic data obtained from multichannel detectors. This work was therefore aimed at developing a data processing procedure for gas chromatography mass spectrometry (GC–MS) data obtained from non-targeted analysis of volatile compounds. The developed approach uses basic matrix manipulation of segmented GC–MS chromatograms and PARAFAC multi-way modelling. The approach takes retention time shifts and peak shape deformations between samples into account and can be done with the freely available N-way toolbox for MATLAB. A demonstration of the new fingerprinting approach is presented using an artificial GC–MS data set and an experimental full-scan GC–MS data set obtained for a set of experimental wines.     

A SPME-GC-MS approach for antivarroa and pesticide residues analysis in honey

Summary Results are presented that were obtained independently by two laboratories employing solid-phase micro extraction (SPME) for the analysis of pesticide residues in honey. The compounds Amitraz, Coumaphos, Cymiazole, Bromopropylate and Fluvalinate, used for chemitherapic treatment of beehives and other widely used agricultural insecticides, were extracted using a polydimethylsiloxane fiber of 100 μm thickness. The precision, accuracy, intervals of linearity and detection limits of the methodare discussed. Considering the rapidity and simplicity of this technique and, on the other hand, the difficulties arising from its application to a very complex matrix, SPME can certainly be considered a useful tool for the rapid screening of residues in honey.     

固相萃取净化-气相色谱/串联质谱法测定茶叶中54种农药残留量

建立了固相萃取净化-气相色谱/串联质谱(SPE-GC-MS/MS)分析茶叶中54种农药残留的方法。样品用乙睛提取,提取液经石墨化炭黑/氨基固相萃取柱净化后,采用气相色谱-串联质谱方法在分时段选择反应监测模式下进行测定,外标法定量。当54种农药加标水平为10、50、100μg/kg时,回收率为60%～150%,方法的相对标准偏差小于16%;定量限(LOQ)均小于10μg/kg;在20～320μg/L范围内线性关系良好。方法已用于同时检测茶叶中农药多残留。     

Determination of organophosphorus pesticide residues in fruits by gas chromatography with ITD and NPD detection

Summary Several widely used organophosphorus insecticides, diazinon, methyl-parathion, fenitrothion, malathion, fenthion and methidathion were selected for inclusion in this work. A comparative study of the multiresidue determination of these compounds in citrus fruit and grapes has been carried out by gas chromatography with nitrogen-phosphorus and ion trap detection. Samples were spiked with 0.1, 0.5 and 1 mg kg^–1 of each pesticide and blended in a Sorvall homogeniser with ethyl acetate. Column clean-up on Florisil was necessary for citrus peel extracts. The average recoveries varied from 81 to 107% with a relative standard deviation between 0.3 and 9.5% for GC-ITD and from 86 to 104% with a relative standard deviation ranging from 1.4 to 8.0% for GC-NPD. The detection limit of the method was 10 ng g^–1 or less for each organophosphorus insecticide, with both detectors. This method was applied to the analysis of treated lemons and 0.25 mg kg^–1 of fenitrothion in fruit was detected a week after treatment and identified by its mass spectrum. The results obtained showed that the proposed methods are reproducible and sensitive enough for the simultaneous determination of these insecticides in fruits at residue level.     

A priori method of evaluating uncertainties in qualitative chromatographic analysis: probabilistic approach

Probabilistic algorithms to evaluate result reliability in qualitative chromatographic analysis are discussed in the paper. The elementary uncertainty (P₀), concerned with a single test (comparison of sample and reference peak positions), is treated as the sum of misidentification and omission probabilities. Both constituents are calculated separately using the simplified model and Laplace functions. In the model, the main reasons for elementary uncertainties are random normally distributed deviations during retention characteristic measurement. Algorithms to calculate both constituents of P₀ have to take into account real measurement precision, supposed composition of the sample, content of the database, chosen coincidence criterion and other factors. At a high selectivity of retention, the 3 value is recommended as the most convenient coincidence criterion. It leads to more reliable and unambiguous attribution of peaks in the chromatogram. For cases that are more complicated, the probabilistic algorithms based upon Bernoulli theorem are proposed to calculate the summary uncertainty of identification, concerned with the multiple test. They take into account P₀ value, the number of repeated single tests (n) in the similar or different conditions, and chosen identification criterion K (minimal number of coincidences). The above-mentioned algorithms lead to a priori optimisation of the mode of operation of any identification software system associated with the chromatograph. They can be useful during a metrological validation of corresponding qualitative analysis methods.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, November 4–6, 2003, Eilat, Israel.The opinions reflected in this paper are those of the author only. AQUAL does not necessarily endorse them.     

Rapid analysis of multiple pesticide residues in fruit-based baby food using programmed temperature vaporiser injection-low-pressure gas chromatography-high-resolution time-of-flight mass spectrometry

A rapid method using programmed temperature vaporiser injection-low-pressure gas chromatography-high-resolution time-of-flight mass spectrometry (PTV-LP-GC-HR-TOF-MS) for the analysis of multiple pesticide residues in fruit-based baby food was developed. The fast and inexpensive buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and "conventional" approach that employs ethyl acetate extraction followed by gel permeation chromatography (GPC) cleanup were employed for sample preparation. A PTV injector in solvent venting mode was used to reduce volume of acetonitrile and acetic acid (from the buffered QuEChERS extracts) that caused higher column bleed without their elimination. Otherwise, the time-to-digital converter would become saturated in HR-TOF-MS. For fast GC separation allowing analysis of 100 analytes within a 7 min runtime, both a high temperature programming rate and vacuum conditions in a megabore GC column were employed. The use of HR-TOF-MS allowed the unbiased identification and reliable quantification of target analytes through the application of a narrow mass window (0.02 Da) for extracting analyte ions and the availability of full spectral information even at very low levels. With only a few exceptions, the lowest calibration levels for the pesticides tested were 相似文献   

Analytical methods for estimation of organophosphorus pesticide residues in fruits and vegetables: A review

Use of pesticides has turned out to be an obligatory input to agriculture and public health. Versatile use of pesticides had resulted in contamination of all basic necessities of life, i.e. air, water and food. Among various pesticides, organophosphorus pesticides (OPPs), derivative of phosphoric acid, are the most extensively used insecticides or acaricides in many crops. Due to low persistency and high killing efficiency of OPPs, many agriculturalists regularly use this group of pesticides for various vegetables and fruits crops. The continuous use of pesticides has caused the deleterious effects to ecosystem. In response to this, a number of methods have been developed by several regulatory agencies and private laboratories and are applied routinely for the quantification and monitoring of multi pesticide residues in vegetables and crops. The present review pertains to various extraction and quantification procedures used world wide to analyze OPPs residues in various vegetables and fruits.     

Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography-mass spectrometry (LP-GC-MS). No special techniques for injection or detection with a common quadrupole GC-MS instrument were required to use this approach. The LP-GC-MS approach used an analytical column of 10 m x 0.53 mm I.D., 1 microm film thickness coupled with a 3 m x 0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC-MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC-MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC-MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC-MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC-MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.     

Application of a system suitability test for quality assurance and performance optimisation of a gas chromatographic system for pesticide residue analysis

In pesticide residue analysis, screening for over 150 compounds has to be performed on a daily basis. As part of the quality control measures it is crucial to verify that the chromatographic system fits the purpose, or if any deterioration occurred during its previous use. The operation conditions of the chromatographic system can be best monitored with properly selected system suitability test (SST) mixtures, which provide information with one injection on the characteristic performance parameters of the whole system from the injector to the detectors. We developed SST mixtures that are also suitable for use with electron-capture, nitrogen-phosphorus and pulse flame photometric detectors. These SST mixtures were applied over 3 years to monitor the system performance parameters, such as the number of effective theoretical plates, resolution, asymmetry, detection limit and selectivity. The applicability and advantages of these tests are illustrated and discussed.