Md. Musfiqur Rahman

Development of a simple extraction and oxidation procedure for the residue analysis of imidacloprid and its metabolites in lettuce using gas chromatography

Simple extraction and optimised oxidation procedures were developed for the determination of the total residues of imidacloprid and its metabolites (containing the 6-chloropicolyl moiety) in lettuce using a gas chromatography-micro electron capture detector (GC-μECD). Samples were extracted with acetonitrile, and the extract was then evaporated. The remaining residues were dissolved in water and oxidised with potassium permanganate to yield 6-chloronicotinic acid (6-CAN). The acid residues were further dissolved in n-hexane:acetone (8:2, v/v) and then silylated with MSTFA (N-methyl-N-(trimethylsilyl)trifluoroacetamide) to 6-chloronicotinic acid trimethylsilyl ester. Calibration curves were linear over the concentration ranges (0.025-5 μg mL(-1)) with a determination coefficient (r(2)) of 0.991. The limits of detection and quantification were 0.015 and 0.05 mg kg(-1), respectively. Recoveries at two fortification levels ranged between 72.8% and 108.3% with relative standard deviation (RSD) lower than 8%. The method was effective, and sensitive enough to determine the total residues of imidacloprid and its metabolites in field-incurred lettuce samples. The identity of the analyte was confirmed using gas chromatography-tandem mass spectrometry (GC-MS/MS).

Matrix enhancement effect: A blessing or a curse for gas chromatography?—A review

The matrix enhancement effect in gas chromatography (GC) has been a problem for the last decade and results in unexpected high recovery. Most efforts, including the use of different types of injectors/matrix simplification procedures, and further clean-up associated with removing this effect has focused on equalizing the response of the standard in the solvent and matrix. However, after eliminating the matrix enhancement effect, the sensitivity of GC remained unchanged. But, GC sensitivity can be increased by utilizing this matrix effect originating from a matrix-matched standard. Very few studies have highlighted utilizing the matrix effect but have rather advocated eliminating it. Analyte protectants (3-ethoxy-1,2-propanediol, gulonolactone and sorbitol) have been introduced as an alternative for GC-mass spectroscopy (GC-MS) (not examined for other GC detectors), as they equalize the response without removing the matrix effect, and, hence, increase sensitivity. Versatile applications of analyte protectants are not observed in practice. The European guidelines recommend the use of matrix-matched standard calibration for residue measurements. As a result, numerous applications are available for matrix-matched standards that compensate for the matrix effect. Moreover, the matrices (among them pepper leaf matrix) act as a protectant for thermolabile analytes in some cases. A lower detection limit should be achieved to comply with the maximum residue limits. Therefore, the matrix enhancement effect, which is considered a problem, can play an important role in lowering the detection limit by increasing the transfer of analyte from the injection port to the detector.

Residues and contaminants in tea and tea infusions: a review

Consumers are very aware of contaminants that could pose potential health hazards. Most people drink tea as an infusion (adding hot water); however, in some countries, including India, China and Egypt, tea is drunk as a decoction (tea and water are boiled together). An infusion usually brings the soluble ingredients into solution, whereas a decoction brings all soluble and non-soluble constituents together. Therefore, a cup of tea may contain various kinds of contaminants. This review focuses on green and black tea because they are most commonly consumed. The target was to examine the transfer rate of contaminants – pesticides, environmental pollutants, mycotoxins, microorganisms, toxic heavy metals, radioactive isotopes (radionuclides) and plant growth regulators – from tea to infusion/brewing, factors contributing to the transfer potential and contaminants degradation, and residues in or on the spent leaves. It is concluded that most contaminants leaching into tea infusion are not detected or are detected at a level lower than the regulatory limits. However, the traditional practice of over-boiling tea leaves should be discouraged as there may be a chance for more transfer of contaminants from the tea to the brew.

Dynamic behaviour and residual pattern of thiamethoxam and its metabolite clothianidin in Swiss chard using liquid chromatography-tandem mass spectrometry.

A simultaneous method was developed to analyse thiamethoxam and its metabolite clothianidin in Swiss chard using tandem mass spectrometry (in the positive electrospray ionisation mode using multiple reaction monitoring mode) to estimate the dissipation pattern and the pre-harvest residue limit (PHRL). Thiamethoxam (10%, WG) was sprayed on Swiss chard grown in two different areas under greenhouse conditions at the recommended dose rate of 10 g/20 L water. Samples were collected randomly up to 14 days post-application, extracted using quick, easy, cheap, effective, rugged, safe (QuEChERS) acetate-buffered method and purified via a dispersive solid phase extraction (d-SPE) procedure. Matrix matched calibration showed good linearity with determination coefficients (R(2)) ⩾ 0.998. The limits of detection (LOD) and quantification (LOQ) were 0.007 and 0.02 mg/kg. The method was validated in triplicate at two different spiked concentration levels. Good recoveries (n=3) of 87.48-105.61% with relative standard deviations (RSDs) < 10 were obtained for both analytes. The rate of disappearance of total thiamethoxam residues in/on Swiss chard was best described by first-order kinetics with half-lives of 6.3 and 4.2 days. We predicted from the PHRL curves that if the residues were <19.21 or 26.98 mg/kg at 10 days before harvest, then total thiamethoxam concentrations would be below the maximum residue limits during harvest.

Consequences of the matrix effect on recovery of dinotefuran and its metabolites in green tea during tandem mass spectrometry analysis

Determining the residues of dinotefuran and its metabolites (MNG, UF, and DN) is highly problematic because of their polar characteristics. Additionally, tea contains many compounds that can interfere with residue analysis. Thus, the aim of the present study was to refine the extraction method that assures good recoveries for dinotefuran and its metabolites and removes most of the matrix components in green tea using liquid chromatography-tandem mass spectrometry (LC/MS/MS). We attempted to increase the extraction efficiency of the QuEChERS method by selecting the appropriate solvents among ethyl acetate, acetone, isopropanol, 25% methanol in acetonitrile, and methanol. We found that methanol was the best extraction solvent for dinotefuran and its polar metabolites in dry green tea samples; however, due to a limitation of an appropriate partitioning salt, acetonitrile was used as the extraction solvent. Matrix enhancement and suppression effects were observed for all analytes, which made the recovery rates variable. DN recovery was <70% when compared with matrix-matched calibration, whereas it was within the acceptable range (70-120%) when compared with solvent calibration. The opposite was observed for MNG and dinotefuran due to a matrix suppression effect. UF recovery was consistent in both matrix-matched and solvent calibrations despite having little suppressive effect. The method was successfully applied and dinotefuran and its metabolite residues were found in field-incurred green tea samples. The current findings suggest that using methanol as an appropriate QuEChERS solvent for problematic polar pesticides and investigating a suitable partitioning salt would considerably strengthen the practical impact of such data.

Simultaneous multi-determination and transfer of eight pesticide residues from green tea leaves to infusion using gas chromatography

A method for determining eight pesticide (cyhalothrin, flufenoxuron, fenitrothion, EPN, bifenthrin, difenoconazole, triflumizole, and azoxystrobin) residues in made green tea as well as a tea infusion (under various brewing water temperatures; 60, 80, and 100°C) using gas chromatography (GC) micro-electron capture detector (μECD) was developed and validated. The extraction method adopted the relatively commonly used approach of solid sample hydration, with the green tea hydrated before being extracted through salting out with acetonitrile followed by a cleanup procedure. The analytes were confirmed using GC-coupled to tandem mass spectrometry (GC/MS/MS) with a triple quadrupole. The linearity of the calibration curves yielded determination coefficients (R(2)) >0.995. Recoveries were carried out using blank samples spiked with all analytes at two levels. The results demonstrated that all pesticides were recovered within the range of 77-116% with a relative standard deviation (RSD) ⩽14%. The quantification limits of 0.015-0.03 mg/kg were lower than the maximum residue limits (MRLs) set by the Korea Food and Drug Administration (KFDA) for all analytes (0.05-10mg/kg). The infusion study indicated that cyhalothrin, flufenoxuron, and bifenthrin did not infuse into the tea brew from the made tea. Increases in brewing time resulted in increased transfer of azoxystrobin, fenitrothion, and difenoconazole from the made tea to the brew; however, this was not the case with triflumizole or EPN. We conclude that transfer of pesticides appeared to be dependent on their water solubilities and drinking a cup of tea is recommended to be at a water temperature of 60°C.

Feasibility and application of an HPLC/UVD to determine dinotefuran and its shorter wavelength metabolites residues in melon with tandem mass confirmation

A new analytical method was developed for dinotefuran and its metabolites, MNG, UF, and DN, in melon using high-performance liquid chromatography (HPLC) coupled with an ultraviolet detector (UVD). Due to shorter wavelength, lower sensitivity to UV detection, and high water miscibility of some metabolites, QuEChERs acetate-buffered version was modified for extraction and purification. Mobile phases with different ion pairing or ionisation agents were tested in different reverse phase columns, and ammonium bicarbonate buffer was found as the best choice to increase the sensitivity of target analytes to the UV detector. After failure of dispersive SPE clean-up with primary secondary amine, different solid phase extraction cartridges (SPE) were used to check the protecting capability of analytes against matrix interference. Finally, samples were extracted with a simple and rapid method using acetonitrile and salts, and purified through C(18)SPE. The method was validated at two spiking levels (three replicates for each) in the matrix. Good recoveries were observed for all of the analytes and ranged between 70.6% and 93.5%, with relative standard deviations of less than 10%. Calibration curves were linear over the calibration ranges for all the analytes with r(2)≥ 0.998. Limits of detection ranged from 0.02 to 0.05 mg kg(-1), whereas limits of quantitation ranged from 0.06 to 0.16 mg kg(-1) for dinotefuran and its metabolites. The method was successfully applied to real samples, where dinotefuran and UF residues were found in the field-incurred melon samples. Residues were confirmed via LC-tandem mass spectrometry (LC-MS/MS) in positive-ion electrospray ionisation (ESI(+)) mode.

A modified QuEChERS method for simultaneous determination of flonicamid and its metabolites in paprika using tandem mass spectrometry.

A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) acetate-buffered sample preparation method was developed to improve extraction recovery of flonicamid and its two metabolites (4-trifluoromethylnicotinic acid and N-(4-trifluoromethylnicotinoyl)glycine) in paprika followed by analysis using tandem mass spectrometry. Acidified acetonitrile (containing 5% acetic acid) was used as an extraction solvent and partitioning was carried out using sodium chloride. The extract was then cleaned up using C18. The linearity over a concentration range of 0.005-1 μg/mL was good with a determination coefficient (R(2))>0.9997. Recovery at three different fortification levels was 82.2-101.7% with a relative standard deviation <10 for all analytes. The limit of quantitation of 0.01 mg/kg was quite lower than the maximum residue level set by the Korea Food and Drug Administration (2mg/kg). The method was successfully applied to determine flonicamid and its metabolites from field incurred samples. The undulating residue pattern observed for the parent analyte together with its metabolites could explain the movement behavior of systemic pesticides into plants over time.

Quick, easy, cheap, effective, rugged, and safe sample preparation approach for pesticide residue analysis using traditional detectors in chromatography- A review

In pesticide residue analysis, relatively low-sensitivity traditional detectors, such as UV, diode array, electron-capture, flame photometric, and nitrogen-phosphorus detectors, have been used following classical sample preparation (liquid-liquid extraction and open glass column cleanup); however, the extraction method is laborious, time-consuming, and requires large volumes of toxic organic solvents. A quick, easy, cheap, effective, rugged, and safe method was introduced in 2003 and coupled with selective and sensitive mass detectors to overcome the aforementioned drawbacks. Compared to traditional detectors, mass spectrometers are still far more expensive and not available in most modestly equipped laboratories, owing to maintenance and cost-related issues. Even available, traditional detectors are still being used for analysis of residues in agricultural commodities. It is widely known that the quick, easy, cheap, effective, rugged, and safe method is incompatible with conventional detectors owing to matrix complexity and low sensitivity. Therefore, modifications using column/cartridge-based solid-phase extraction instead of dispersive solid-phase extraction for cleanup have been applied in most cases to compensate and enable the adaptation of the extraction method to conventional detectors. In gas chromatography, the matrix enhancement effect of some analytes has been observed, which lowers the limit of detection and, therefore, enables gas chromatography to be compatible with the quick, easy, cheap, effective, rugged, and safe extraction method. For liquid chromatography with a UV detector, a combination of column/cartridge-based solid-phase extraction and dispersive solid-phase extraction was found to reduce the matrix interference and increase the sensitivity. A suitable double-layer column/cartridge-based solid-phase extraction might be the perfect solution, instead of a time-consuming combination of column/cartridge-based solid-phase extraction and dispersive solid-phase extraction. Therefore, replacing dispersive solid-phase extraction with column/cartridge-based solid-phase extraction in the cleanup step can make the quick, easy, cheap, effective, rugged, and safe extraction method compatible with traditional detectors for more sensitive, effective, and green analysis.

Pepper leaf matrix as a promising analyte protectant prior to the analysis of thermolabile terbufos and its metabolites in pepper using GC–FPD

During gas chromatography (GC), the matrix can deactivate the active site during the transport of the compound from the injector to the detector. This deactivation capacity varies among matrices, as it is dependant on the concentrations of the different constituent compounds of each matrix. During the analysis of terbufos and its metabolites, two of its metabolites were highly thermolabile, and were readily decomposed inside the GC system. As the matrix can mask the active site, we carried out a matrix-matched calibration in an effort to protect the analyte against decomposition. As a component of our analysis, the pepper matrix was the first to be matched; however, it failed to completely protect the metabolites. Subsequently, a variety of different compounds, including 3-ethoxy-1,2-propanediol, gulonolactone, and sorbitol at 10, 1, and 1mg/mL were tested; however, none of these generated the desired effect. We surmised that some of the compounds may have decomposed inside the injection port, so we introduced a carbofrit inlet liner, which is highly inert. But, this step did not improve the protective qualities of the matrices. Finally, pepper leaf matrix was added to the pepper matrix, and we observed a profound protective effect for almost all of the analytes tested. A selective detector (flame photometric detector with phosphorus filter) was used to facilitate a high matrix concentration without interaction with the analyte. After resolving the problem of these two metabolites, terbufos and its five toxic metabolites were analyzed in pepper and pepper leaf samples. The recovery rates for terbufos and its metabolites were 73-114.5% with a relative standard deviation of <12%. This method was successfully applied to field samples, and terbufos sulfone, terbufos sulfoxide, and terbufoxon sulfoxide were found as residues in the suspected pepper and pepper leaf samples.