Determination of Maleic Hydrazide in Potato Samples Using Capillary Electrophoresis with Dual Detection (UV‐Electrochemical)

A new method for the separation of a mixture of different herbicides (propham, chlorpropham, asulam, metamitron, linuron, and maleic hydrazide) using MEKC is proposed. A base‐line separation for the mixture of herbicides is achieved in less than six minutes. The detection limits obtained for all the herbicides were lower than 1.0 μM using UV detection. This separation method was used for the determination of maleic hydrazide in potato samples. If a dual (UV‐electrochemical) detection system is employed, chlorpropham can be also detected. The results obtained showed that electrochemical detection was ten folds more sensitive than UV detection for maleic hydrazide. The detection limit of the proposed method for maleic hydrazide employing electrochemical detection was 1.3 μg g^?1, this value is lower than 50 μg g^?1, which is the maximum residue level permitted for this plant growth regulator in potato samples. The results obtained in the work clearly demonstrate the advantage of using electrochemical detection coupled to capillary electrophoresis, using this detection the concentration limits are not compromised by miniaturization and the components required are simple and inexpensive.     

Determination of imidacloprid, metalaxyl, myclobutanil, propham, and thiabendazole in fruits and vegetables by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry

Imidacloprid, metalaxyl, myclobutanil, propham, and thiabendazole have been simultaneously determined in strawberries, oranges, potatoes, pears, and melons by matrix solid-phase dispersion (MSPD) followed by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) in positive-ion mode. The samples were homogenized with C8 bonded silica as MSPD sorbent, placed in a glass column, and eluted with dichloromethane. Chromatographic separation of the compounds was achieved on a reversed-phase LC column using a methanol-ammonium formate (50 mmol L(-1)) gradient as a mobile phase. Samples were screened by monitoring the protonated molecular ion at m/z 256 for imidacloprid, 280 for metalaxyl, 289 for myclobutanil, and 202 for thiabendazole, and the main fragment at m/z 138 for propham. Positive samples were confirmed by multiple-ion monitoring. The repeatability (<20%) and recovery (>57%) of the method were good, and limits of detection (<0.05 mg kg(-1)) were adequate.     

Application of matrix solid-phase dispersion to the determination of amitrole and urazole residues in apples by capillary electrophoresis with electrochemical detection

A new method based on matrix solid-phase dispersion (MSPD) extraction was studied for the extraction of amitrole (3-amino-1,2,4-triazole), and its metabolite urazole (3,5-dihydroxy-1,2,4-triazole), in apple samples. The influence of experimental conditions on the yield of the extraction process and on the efficiency of the cleanup step was evaluated. Determination was carried out by capillary electrophoresis (CE) with electrochemical detection, demonstrating the compatibility between MSPD and CE techniques. The method has been successfully applied to different apple varieties. Recoveries in samples spiked at 1.6 and 1.7 μg g⁻¹ for amitrole and urazole were 88 and 82%, respectively. The limits of detection were 0.4 μg g⁻¹ for both compounds using electrochemical detection.     

烤鳗中6种农药残留量的液相色谱-质谱/质谱法同时测定

建立了烤鳗中苯胺灵、嘧菌酯、氨苯乙酯、氟酮唑草、丙蝇驱、唑螨酯6种农药残留的同时检测方法.烤鳗样品采用乙腈、中性氧化铝超声基体分散吸附、涡旋混合提取,Florisil固相萃取小柱净化、浓缩,以乙腈-乙酸铵缓冲液为流动相进行色谱分离,串联质谱检测.结果表明,6种化合物在0.5 ～1 000 μg/L范围内线性关系良好,方法的检出限为0.03 ～2.3 μg/kg,定量下限为0.09 ～7.7 μg/kg,平均加标回收率为75% ～104%,相对标准偏差(RSD)为1.6% ～15%,满足当前进出口残留控制要求.     

Use of autoclave extraction and liquid chromatography with tandem mass spectrometry for determination of maleic hydrazide residues in tobacco

Maleic hydrazide has been extensively used as an effective growth regulator in tobacco sucker control. After application, maleic hydrazide distributes itself throughout the tobacco plant where it can exist as free, or forms glucoside conjugates with glucose, or becomes bound with lignin. Among them, free maleic hydrazide and its glucoside conjugates are extractable under conventional solvent extraction, while lignin bound maleic hydrazide is claimed to be non‐extractable. Herein, an autoclave extraction method has been developed to extract maleic hydrazide effectively, in which tobacco samples are extracted in an autoclave at 130°C for 1 h using 4 M hydrochloric acid. Under such pressurized hot acidic water conditions, lignin bound maleic hydrazide can be released. Meanwhile, glucoside conjugates are hydrolyzed. Total maleic hydrazide is detected by liquid chromatography coupled with tandem mass spectrometry, and the quantitative results coincide well with that obtained from the international standard method. The proposed autoclave extraction with liquid chromatography and tandem mass spectrometry method exhibits excellent linearity in the range of 5–200 mg/kg (R² = 0.9998), the matrix matched limit of detection and limit of quantification is 0.68 and 2.27 mg/kg, respectively. This method is simple and improves sample capacity, providing an effective approach to monitoring maleic hydrazide residues in tobacco.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

Determination of Phenylureas Herbicides in Foodstuffs Based on Matrix Solid-Phase Dispersion Extraction and RP-LC with UV Detection

A new method for simultaneous determination of seven kinds of phenylurea herbicides (PUHs) in solid foodstuffs was established based on matrix solid phase dispersion (MSPD)–RP-LC. The procedure of MSPD is simple and not time-consuming. C₁₈-bonded silica and anhydrous alumina were, respectively, used as dispersion sorbent and purificant, and dichloromethane as extraction reagent. Under the optimum conditions, seven kinds of herbicides were separated completely within 30 min, response was a linear function of concentration over the range 2.5–500 μg L^?1 with good correlation coefficients (>0.99) and lower detection limits (0.25 and 0.5 μg L^?1). Intra-day and inter-day precision of the peak areas for seven PUHs were less than 3.7 and 5.3%. The new method was used to detect seven PUHs in four kinds of solid foodstuffs with average recoveries range from 73.1 to 101%.     

Improved extraction and clean-up of imidazolinone herbicides from soil solutions using different solid-phase sorbents

Extraction and quantification of herbicide residues from soil are important in understanding the behaviour of persistent herbicides. This research investigated extraction and clean-up methods for imidazolinone herbicides from soil and soil amended with organic material. A series of solvent mixes, pH conditions and sorbents was tested. Across three imidazolinone herbicides: imazapyr, imazethapyr and imazaquin, 0.5 M NaOH extraction gave greater than 90% recovery from soil samples; however, 0.5 M NaOH:MeOH (80:20) resulted in higher recovery for imazaquin, but not for the other two herbicides. Of the sorbents tested, the use of chromatographic mode sequencing using C₁₈ and SCX sorbents provided consistent high (>85%) recovery of all three herbicides from soil and separation of the herbicides from other soil components by high performance liquid chromatography (HPLC). These two methods will allow high recovery of these imidazolinone herbicides from soil and have the ability to detect these herbicides without interference from other soil components.     

Matrix solid-phase dispersion

Matrix solid-phase dispersion (MSPD) is a patented process, first reported in 1989, for conducting simultaneous disruption and extraction of solid and semi-solid samples. MSPD permits complete fractionation of the sample matrix components as well as the ability to selectively elute a single compound or several classes of compounds from the same sample. The method has been applied to the isolation of drugs in food animal tissues but has also found wide application in the analysis of herbicides, pesticides and pollutants from animal tissues, fruits, vegetables and other matrices. The present article provides a review of MSPD applications in these and related fields and discusses the factors known to affect MSPD methods. Both the practical and theoretical aspects of MSPD are also presented.     

Determination of acetanilide herbicides in cereal crops using accelerated solvent extraction, solid-phase extraction and gas chromatography-electron capture detector

A method was developed to determine eight acetanilide herbicides from cereal crops based on accelerated solvent extraction (ASE) and solid-phase extraction (SPE) followed by gas chromatography-electron capture detector (GC-ECD) analysis. During the ASE process, the effect of four parameters (temperature, static time, static cycles and solvent) on the extraction efficiency was considered and compared with shake-flask extraction method. After extraction with ASE, four SPE tubes (graphitic carbon black/primary secondary amine (GCB/PSA), GCB, Florisil and alumina-N) were assayed for comparison to obtain the best clean-up efficiency. The results show that GCB/PSA cartridge gave the best recoveries and cleanest chromatograms. The analytical process was validated by the analysis of spiked blank samples. Performance characteristics such as linearity, limit of detection (LOD), limit of quantitation (LOQ), precision and recovery were studied. At 0.05 mg/kg spiked level, recoveries and precision values for rice, wheat and maize were 82.3-115.8 and 1.1-13.6%, respectively. For all the herbicides, LOD and LOQ ranged from 0.8 to 1.7 μg/kg and from 2.4 to 5.3 μg/kg, respectively. The proposed analytical methodology was applied for the analysis of the targets in samples; only three herbicides, propyzamid, metolachlor and diflufenican, were detected in two samples.     

Determination of maleic hydrazide residues in cured tobacco by gas chromatography.

A rapid and sensitive method for measuring maleic hydrazide (6-hydroxy-2H-pyridazin-3-one) residues in cured tobacco is described. A mixture of free and bound maleic hydrazide is extracted with hydrochloric acid in which maleic hydrazide glycoside is simultaneously hydrolysed. The free maleic hydrazide obtained is methylated using dimethyl sulphate and the derivative is partitioned into chloroform and determined by capillary gas chromatography using a nitrogen-phosphorus detector. The limit of detection of maleic hydrazide is 5 ppm.     

Extraction of maleic hydrazide residues from potato crisps and their determination using high-performance liquid chromatography with UV and atmospheric pressure chemical ionisation mass spectrometric detection

A method was required for the determination of maleic hydrazide residues in potato crisps. A published method for the extraction of the analyte from onions and potatoes was evaluated and found to be inappropriate due to the inability of the extracting solvent to penetrate the oily matrix. A method was developed to overcome this problem; the resulting recovery data (mean=92.9%. R.S.D.=8.3%, N=16) confirmed its efficiency, and was used to analyse 48 retail potato crisp samples. To confirm possible residues identified by screening with HPLC-UV, and HPLC-atmospheric pressure chemical ionization MS method was developed. There was good agreement between the data obtained from the detection techniques (R²=0.978, slope=1.11).     

Evaluation of two sample treatment methodologies for large-scale pesticide residue analysis in olive oil by fast liquid chromatography–electrospray mass spectrometry

In this study, a comprehensive evaluation of two simple sample treatment methodologies has been carried out for the development of large-scale multi-residue methods for pesticide testing in olive oil. The proposed methodologies are based on (a) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using graphitized carbon black, primary-secondary amine and C₁₈ sorbents; (b) liquid partitioning with acetonitrile saturated with petroleum ether followed by matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a Florisil cartridge for final clean-up in the elution step. To evaluate the proposed sample treatment methodologies, 105 representative multi-class pesticides were studied using fast liquid chromatography–electrospray time-of-flight mass spectrometry (LC–TOFMS). For validation purposes, recoveries studies were carried out at 10 and 100 μg kg⁻¹ levels, yielding recovery rates in the range 70–130% for 72% of analytes using liquid–liquid procedure and for 57% analytes using MSPD procedure. The LC–MS method provided good linearity, precision and accuracy. The limits of detection obtained were lower than 10 μg kg⁻¹ for more than 85% analytes using both sample treatment methodologies. In addition, minor matrix effects (i.e. signal suppression or enhancement ≤20%) were observed in ca. 70% of the studied compounds. Data obtained shows that both sample treatment methodologies proposed can be successfully applied for large-scale pesticide testing in olive oil samples, showing the ability to quickly detect trace amount of over one hundred target species with different physicochemical properties, without requiring expensive instrumentation for sample treatment step and involving relatively low amounts of solvent consumption and waste generation.     

Study of the voltammetric behaviour of maleic hydrazide and its determination at a hanging mercury drop electrode

Voltammetric behaviour of maleic hydrazide pesticide dissolved in a Britton-Robertson buffer was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the process at the Hg electrode was diffusion controlled; the reaction was irreversible and involved a change of one proton and a transfer of one electron. A quantitative differential pulse voltammetric method for determination of maleic hydrazide was developed on the basis of these studies involving the reduction of the compound at a hanging mercury drop electrode. A linear calibration was obtained in the range of 0.5-5.5 mg l⁻¹, and the developed DPV methodology was then applied for the determination of maleic hydrazide in spiked vegetable samples by the standard addition method. Satisfactory percentage R.S.D. (∼2%), percentage recovery values (∼85%) and LOD (0.215 mg l⁻¹) were obtained. These compared well with the results from the alternative spectrophotometric method.     

Comparison of various liquid chromatographic methods for the analysis of avermectin residues in citrus fruits

Various liquid chromatographic (LC) techniques for analyzing avermectin (Abamectin) were compared after extraction of residues from citrus fruit samples by matrix solid-phase dispersion (MSPD). LC with UV and fluorescence detection were used as also was LC coupled to the mass spectrometer by an electrospray interface. The results obtained by the three methods were compared in terms of sensitivity and selectivity. The combination of MSPD extraction and LC with fluorescence detection have made it possible to quantify 0.5 microg kg(-1) of Abamectin in 0.5 g of orange sample, with an overall average recovery of 94%. The procedure provides a simple and sensitive method for monitoring Abamectin residues in citrus fruit at the levels required by legislation.     

Simultaneous HPLC determination of phenylurea herbicides and their corresponding anilines in water after on-line preconcentration

On-line preconcentration on a short C₁₈ column, prior to HPLC with UV and electrochemical detection, has been used for determination of some phenylurea herbicides and their possible degradation products, substituted anilines, in water samples. With electrochemical detection the detection limit at a signal-to-noise ratio of 3 was 5 ppt for 4-chloroaniline and 4-bromoaniline and 7 ppt for 3,4-dichloroaniline; with UV detection the detection limit was ca 300 ppt for all analytes.     

Fast and selective extraction of chloramphenicol from soil by matrix solid‐phase dispersion using molecularly imprinted polymer as dispersant

The molecularly imprinted polymer (MIP) was synthesized and used as dispersant of matrix solid‐phase dispersion (MSPD) for the extraction of chloramphenicol (CAP) in soil samples. The satisfactory recovery of CAP was obtained by the optimized extraction conditions: 1:2 as the ratio of sample to MIPs; 5 min as the dispersion time; 30% aqueous methanol as washing solvent and methanol as elution solvent. The CAP extracted from soil was determined by LC‐MS/MS. The slight ion suppression phenomenon was observed for the CAP when the sample was cleaned up by MSPD with MIP as dispersant, when compared with C18 as MSPD dispersant, which caused significant ion suppression. LOD of CAP is 4.1 ng/g. RSDs of intra‐ and inter‐day tests ranging from 3.1 to 6.2% and from 3.9 to 8.3% are obtained. At all three fortified levels (20, 100 and 500 ng/g), recoveries of CAP are in the range of 86.9–92.6%. The effect of ageing time of spiked soil sample on the CAP recovery was examined. The CAP recovery decreased from 91.0 to 36.9% when the ageing time changed from 1 day to 4 wk.     

Comparison of extraction techniques for quantitative analysis of pendimethalin from soil and rice grain

The paper exploits the development, optimization, and comparison of fast, efficient, quantitative analytical extraction techniques such as ultrasonic-assisted extraction (UAE) and matrix solid-phase dispersion (MSPD) for proficient extraction of pendimethalin from soil and rice samples. Residues of pendimethalin were quantified using high-performance liquid chromatography. Impact of several experimental parameters of UAE and MSPD techniques on extraction of pendimethalin from soil and rice samples was also evaluated. Under the optimized conditions, the mean percent recoveries obtained from both methods were in the range of 80.3–101.3 and 81.7–103.1, respectively, with relative standard deviation <10. Linearity was in the range of 0.003–5.0?µg?mL^?1 with limit of detection and limit of quantification as 0.001 and 0.003?µg?g^?1, respectively. MSPD method was found superior in terms of low solvent consumption, small sample size, and reduced matrix coextracts due to simultaneous extraction and cleanup steps. Both extraction methodologies were successfully applied in monitoring routine soil and rice samples, in which pendimethalin residues (0.003–0.007?µg?g^?1) were detected in few rice samples while residues in soil samples were below the quantification limit.     

Determination of neonicotinoid insecticides in environmental samples by micellar electrokinetic chromatography using solid‐phase treatments

A sensitive and reliable method based on MEKC has been developed and validated for trace determination of neonicotinoid insecticides (thiamethoxam, acetamiprid, and imidacloprid) and the metabolite 6‐chloronicotinic acid in water and soil matrices. Optimum separation of the neonicotinoid insecticides was obtained on a 58 cm long capillary (75 μm id) using as the running electrolyte 40 mM SDS, 5 mM borate (pH 10.4), and 5% (v/v) methanol at a temperature of 25°C, a voltage of 25 kV and with hydrodynamic injection (10 s). The analysis time was less than 7 min. Prior to MEKC determination, the samples were purified and enriched by carrying out extraction‐preconcentration steps. For aqueous samples, off‐line SPE with a sorptive material such as Strata‐X (polymeric hydrophobic sorbent) and octadecylsilane (C₁₈) was carried out to clean up and preconcentrate the insecticides. However, for soil samples, matrix solid‐phase dispersion (MSPD) was applied with C₁₈ used as the dispersant. Good linearity, accuracy, and precision were obtained and the detection limits were in the range between 0.01 and 0.07 μg mL^?1 for river water and 0.17 and 0.37 μg g^?1 for soil samples. Recovery levels reached greater than 92% for all of the assayed neonicotinoids in river water samples with Strata‐X. In soil matrices, the best recoveries (63–99%) were obtained with MSPD.     

Determination of sulfonylurea herbicides in soil extracts by solid-phase extraction and capillary zone electrophoresis

Summary Sulfonylurea herbicides in soil extracts were concentrated using off-line solid-phase extraction (SPE), and determined by capillary zone electrophoresis (CZE) and UV detection. The method involves extraction of soils with 0.1 M NaHCO₃ solution and subsequent preconcentration by using C₁₈ cartridges prior to separation of the pesticide using CZE. The results show that a C₁₈ cartridge is suitable for the purification of sulfonylurea herbicides in soil extracts with the recoveries ranging from 65–103%. The separation conditions affecting the resolution and detection sensitivity was systematically investigated. The sulfonylureas were resolved well using 30 mM sodium acetate (NaAc)/acetic acid (HAc)+10% acetonitrile (ACN) buffer at pH 4.80. The calibration plots for the test solutes in the concentration of 0.2–50 mg L⁻¹ were linear with detection limits in the range of 0.05–0.10 mgL⁻¹. The proposed method has been successfully demonstrated for the determination of sulfonylurea herbicides in soil samples.