Lobna A. Hussein

Simultaneous determination of eight neonicotinoid insecticide residues and two primary metabolites in cucumbers and soil by liquid chromatography–tandem mass spectrometry coupled with QuEChERS

A new, rapid, sensitive, precise and validated high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) method was developed for the simultaneous determination of eight neonicotinoid insecticides with their two primary metabolites in cucumbers and soil based on QuEChERS as a pretreatment procedure. In QuEChERS procedure, cucumber samples were extracted with acetonitrile and cleaned using (C18 sorbent material), while soil samples were extracted with a mixture of acetonitrile:dichloromethane (8.3:16.7v:v). The LC-MS/MS conditions were optimized to provide good selectivity and specificity of the developed method where neonicotinoids were separated using gradient elution of water and acetonitrile both containing 0.1% formic acid with Gemini C18 column where the last compound was eluted at 9.5min. Average recoveries of the eight neonicotinoids and their metabolites ranged between 81.6% and 95.7% in fortified cucumber samples with relative standard deviations (RSDs) lower than 13.18% and between 80.3% and 104% in fortified soil samples with relative standard deviations (RSDs) lower than 8.44%. The limits of detection (LODs) and quantification (LOQs) for the ten compounds were in the ranges of (0.08-6.06ng/g) and (0.26-20ng/g), respectively. The method was applied successfully to determine residues and rate of disappearance of the eight neonicotinoids from cucumber and soil and their half-lives where a safety pre-harvest interval of 5days for acetampirid, 12days for imidacloprid, 15days for nitenpyram, 12days for thiamethoxam, 5days for flonicamid, 8days for clothianidin, 2days for Dinotefuran, and 1day for thiacloprid were suggested.

Simultaneous determination of three neonicotinoid insecticide residues and their metabolite in cucumbers and soil by QuEChERS clean up and liquid chromatography with diode-array detection

A new sensitive, selective and validated HPLC-DAD method was developed for the simultaneous determination of three neonicotinoid insecticides named dinotefuran, thiamethoxam and Clothianidin with their metabolite 1-methyl-3-nitroguanidine in cucumbers and soil based on QuEChERS as a pretreatment procedure. In the QuEChERS procedure, cucumber samples were extracted with acetonitrile and cleaned using C18, while soil samples were extracted with a mixture of acetonitrile : dichloromethane (1 : 2). The HPLC conditions were optimized where the neonicotinoids were separated using a gradient elution of water : acetonitrile and a Synergy Hydro RP C18 column. Matrix matched calibration standards were prepared in cucumbers and soil to eliminate the interference of the matrix. Relative standard deviations (RSDs) were less than 2.08% for all of the recovery tests. The limits of detection (LODs) and quantification (LOQs) for the neonicotinoids were in the ranges of 0.01–0.08 μg g−1 and 0.03–0.24 μg g−1, respectively. The method was applied successfully to determine residues and rates of disappearance of the three neonicotinoids from cucumbers and soil and their half lives.

Sensitive spectrofluorimetric methods for determination of ethopabate and amprolium hydrochloride in chicken plasma and their residues in food samples

Two sensitive and selective spectrofluorimetric methods are proposed to determine ethopabate (ETH) and amprolium hydrochloride (AMP). First derivative synchronous spectrofluorimetry determines the natively fluorescent ethopabate at 288 nm in presence of amprolium hydrochloride which is a non fluorescent quaternary compound with average recovery 100.54±0.721 over a concentration range of 0.01-0.8 μg/mL. Limits of detection (LOD) and quantification (LOQ) are 0.002 and 0.007 μg/mL, respectively. The second method is direct synchronous spectrofluorimetry for determining amprolium hydrochloride at 362 nm after a reaction with 5% NaOH and 0.08% potassium ferricyanide that is optimized by a two-level factorial design. This method is linear over a concentration range of 0.01-0.65 μg/mL with average recovery 99.4±1.28. Limits of detection (LOD) and quantification (LOQ) are 0.002 and 0.006 μg/mL, respectively. The proposed methods are found to be valid and applicable for the analysis of ETH and AMP in their veterinary formulation. They are successfully applied to determine the studied drugs in chicken plasma and their residues in chicken muscle, liver, egg and chicken-based baby food product with recoveries in the ranges of 95.71-108.73% and 97.36-111.89% and for ETH and AMP, respectively.

Investigation of different spectrophotometric and chemometric methods for determination of entacapone, levodopa and carbidopa in ternary mixture

New, simple, accurate and sensitive UV spectrophotometric and chemometric methods have been developed and validated for determination of Entacapone (ENT), Levodopa (LD) and Carbidopa (CD) in ternary mixture. Method A is a derivative ratio spectra zero-crossing spectrophotometric method which allows the determination of ENT in the presence of both LD and CD by measuring the peak amplitude at 249.9nm in the range of 1-20μgmL-1. Method B is a double divisor-first derivative of ratio spectra method, used for determination of ENT, LD and CD at 245, 239 and 293nm, respectively. Method C is a mean centering of ratio spectra which allows their determination at 241, 241.6 and 257.1nm, respectively. Methods B and C could successfully determine the studied drugs in concentration ranges of 1-20μgmL-1 for ENT and 10-90μgmL-1 for both LD and CD. Methods D and E are principal component regression and partial least-squares, respectively, used for the simultaneous determination of the studied drugs by using seventeen mixtures as calibration set and eight mixtures as validation set. The developed methods have the advantage of simultaneous determination of the cited components without any pre-treatment. All the results were statistically compared with the reported methods, where no significant difference was observed. The developed methods were satisfactorily applied to the analysis of the investigated drugs in their pure form and in pharmaceutical dosage forms.

Five different spectrophotometric methods for determination of Amprolium hydrochloride and Ethopabate binary mixture.

Five simple, specific, accurate and precise UV-spectrophotometric methods are adopted for the simultaneous determination of Amprolium hydrochloride (AMP) and Ethopabate (ETH), a binary mixture with overlapping spectra, without preliminary separation. The first method is first derivative of the ratio spectra ((1)DD) for determination of AMP and ETH at 234.7nm and 306.8nm respectively with mean percentage recoveries 99.76±0.907 and 100.29±0.842 respectively. The second method is the mean centering of the ratio spectra for determination of AMP and ETH at 238.8nm and 313nm respectively with mean percentage recoveries 100.26±1.018 and 99.94±1.286 respectively. The third method is based on dual wavelength selection for determination of AMP and ETH at 235.3nm & 308nm and 244nm & 268.4nm respectively with mean percentage recoveries 99.30±1.097 and 100.03±1.065 respectively. The fourth method is ratio difference method for determination of AMP and ETH at 239nm & 310nm and 239nm & 313nm respectively with mean percentage recoveries 99.27±0.892 and 100.40±1.814 respectively. The fifth one is area under the curve (AUC) method where the areas between 235.6-243nm and 268.3-275nm are selected for determination of AMP and ETH with mean percentage recoveries 100.35±1.031 and 100.39±0.956 respectively. These methods are tested by analyzing synthetic mixtures of the two drugs and they are applied to their pharmaceutical veterinary preparation. Methods are validated according to the ICH guidelines and accuracy, precision and repeatability are found to be within the acceptable limit.

Simultaneous spectrophotometric determination of indacaterol and glycopyrronium in a newly approved pharmaceutical formulation using different signal processing techniques of ratio spectra.

Three spectrophotometric methods have been developed and validated for determination of indacaterol (IND) and glycopyrronium (GLY) in their binary mixtures and novel pharmaceutical dosage form. The proposed methods are considered to be the first methods to determine the investigated drugs simultaneously. The developed methods are based on different signal processing techniques of ratio spectra namely; Numerical Differentiation (ND), Savitsky-Golay (SG) and Fourier Transform (FT). The developed methods showed linearity over concentration range 1-30 and 10-35 (μg/mL) for IND and GLY, respectively. The accuracy calculated as percentage recoveries were in the range of 99.00%-100.49% with low value of RSD% (<1.5%) demonstrating an excellent accuracy of the proposed methods. The developed methods were proved to be specific, sensitive and precise for quality control of the investigated drugs in their pharmaceutical dosage form without the need for any separation process.

Development of Microwave-Assisted Extraction of Trigonelline Biomarker from Trigonella foenum-graecum Seeds Followed by High-Performance Thin-Layer Chromatographic and High-Performance Liquid Chromatographic Analyses

An efficient and fast microwave-assisted extraction (MAE) technique was developed for extracting trigonelline as an indicative biomarker for the quality control of Trigonella foenum-graecum seeds. The MAE procedure was optimized and compared with other conventional extraction techniques. The optimal conditions of MAE were 50% methanol as solvent, solid—liquid ratio 1:20 g mL−1, irradiation power 40%, and two extraction cycles, 3 min each. The proposed extraction technique produced a maximum yield of 7.89 mg g−1 trigonelline in 6 min which was 1.28 and 2.20 times more efficient than 3 h of heat reflux and 15 h of maceration extraction, respectively. Furthermore, rapid high-performance thin-layer chromatographic and high-performance liquid chromatographic methods for the quantification of trigonelline were established and validated. The methods were found to be simple, sensitive, precise, accurate, and specific for the estimation of trigonelline in T. foenum-graecum seeds extract and overcame disadvantages of previously published methods.

Different techniques for determination of imidacloprid insecticide residues

Three sensitive, selective and precise methods for determination of imidacloprid insecticide residues in tomatoes have been developed. The first method is TLC-Densitometry where imidacloprid was extracted with acetonitrile without the need for a clean up step then the extract was applied to TLC plates using toluene: acetonitrile (7:3) as a solvent system. The recoveries ranged from 92.57 to 96.31% in tomato samples. The limit of detection of the method was 1.39 mg/kg. The second method depends on indirect fluorimetric determination of imidacloprid by quenching anthracene synchronous fluorescence. The recoveries ranged from 96.16 to 99.83% in tomato samples. The limit of detection of the method was 0.32 mg/kg. The third method is high-performance liquid chromatography with UV detection where imidacloprid was extracted with acetonitrile followed by clean up using column chromatography. The recovery of imidacloprid in tomato samples ranged from 85.20 to 93.15%. The limit of detection of the method was 0.12 mg/kg. The three methods were used to study the kinetic disappearance of imidacloprid from tomatoes. It was found to follow a first order reaction with t1/2 = 5.31 ± 0.3 days, whereas K (reaction rate constant) was found to be 0.13 ± 0.008 day−1.

Novel potentiometric sensors for the determination of the dinotefuran insecticide residue levels in cucumber and soil samples

Five new potentiometric membrane sensors for the determination of the dinotefuran levels in cucumber and soil samples have been developed. Four of these sensors were based on a newly designed molecularly imprinted polymer (MIP) material consisting of acrylamide or methacrylic acid as a functional monomer in a plasticized PVC (polyvinyl chloride) membrane before and after elution of the template. A fifth sensor, a carboxylated PVC-based sensor plasticized with dioctyl phthalate, was also prepared and tested. Sensor 1 (acrylamide washed) and sensor 3 (methacrylic acid washed) exhibited significantly enhanced responses towards dinotefuran over the concentration range of 10-7-10-2molL-1. The limit of detection (LOD) for both sensors was 0.35µgL-1. The response was near-Nernstian, with average slopes of 66.3 and 50.8mV/decade for sensors 1 and 3 respectively. Sensors 2 (acrylamide non-washed), 4 (methacrylic acid non-washed) and 5 (carboxylated-PVC) exhibited non-Nernstian responses over the concentration range of 10-7-10-3molL-1, with LODs of 10.07, 6.90, and 4.30µgL-1, respectively, as well as average slopes of 39.1, 27.2 and 33mV/decade, respectively. The application of the proposed sensors to the determination of the dinotefuran levels in spiked soil and cucumber samples was demonstrated. The average recoveries from the cucumber samples were from 7.93% to 106.43%, with a standard deviation of less than 13.73%, and recoveries from soil samples were from 97.46% to 108.71%, with a standard deviation of less than 10.66%. The sensors were applied successfully to the determination of the dinotefuran residue, its rate of disappearance and its half-life in cucumbers in soil in which a safety pre-harvest interval for dinotefuran was suggested.

Micelle enhanced and native spectrofluorimetric methods for determination of sertindole using sodium dodecyl sulfate as sensitizing agent.

Two stability indicating spectrofluorimetric methods were developed and validated for the determination of sertindole (SER) in the presence of its acid and oxidative degradates at λ(ex) 257 nm and λ(em) 335 nm. Method A was based on measuring the native fluorescence of SER using isopropanol as solvent. Method B was based on the enhancement of native fluorescence of SER quenched in aqueous media by using micellar microenvironment created by sodium dodecyl sulfate (SDS) anionic micelles using Britton Robinson Buffer (BRB) pH3.29 as solvent. Different factors affecting fluorescence intensity; both native and enhanced, were carefully studied to reach the optimum conditions of measurements. The proposed spectrofluorimetric methods were validated in accordance with ICH guidelines and were successfully applied for the determination of SER in bulk powder and pharmaceutical preparation with high sensitivity and stability indicating power. They were also statistically compared to the manufacturer methods with no significant difference in performance.