Stable isotope dilution assay for the accurate determination of tricaine in fish samples by HPLC–MS–MS

Tricaine methanesulfonate is one of most commonly used anesthetics in fish during blood sampling, artificial propagation and long‐distance transportation. In this study, an accurate method for the quantitative determination of tricaine in fish samples by a stable isotope dilution assay coupled with high‐performance liquid chromatography–triple quadrupole mass spectrometry was developed. Tricaine‐D₅ was synthesized and used as an isotopically labeled internal standard for the determination of tricaine. The analytical performance of the method was validated for tricaine determination in marine fish and freshwater fish. The determination of tricaine was linear in the range of 2.0–200.0 μg L^?1. The limit of detection and limit of quantitation for fish muscle tissues were 1.0 and 4.0 μg kg^?1, respectively. Good recoveries were obtained in the range of 92.08–97.50%. The inter‐ and intra‐assay relative standard deviations (RSD values) were investigated, and the values were 0.39–3.01 and 0.85–2.77%, respectively. The values of CCα and CCβ were 10.21–10.43 and 10.42–10.87 μg kg^?1, respectively. The clearance of MS‐222 from grass carp was further studied using our method. The results demonstrate that MS‐222 could be well absorbed and rapidly eliminated after bath administration.     

Simultaneous determination of sulfoxaflor in 14 daily foods using LC-MS/MS

Sulfoxa?or residues in 14 daily foods, including rice, sorghum, chilli, cucumber, white pear, apple, egg, beef brisket, chicken breast, fish, pork liver, milk, pine nut and honey, were simultaneously determined using a modified QuEChERS and LC–MS/MS method. These foods were classified into three categories to be purified. A combination of 25 mg of octadecylsilane (C18) + 25 mg of primary and secondary amine (PSA) + 50 mg of graphitised carbon black (GCB) + 150 mg of MgSO₄ was used to purify the rice, sorghum, honey, apple and white pear. A combination of 25 mg of C18 + 50 mg of PSA + 50 mg of GCB + 150 mg of MgSO₄ was used to purify the chilli and cucumber. A combination of 50 mg of C18 + 25 mg of PSA + 50 mg of GCB + 150 mg of MgSO₄ was used to purify the pine nuts, egg, beef brisket, chicken breast, fish, pork liver and milk. The linearity coefficient values were greater than 0.9975. The limit of detection and limit of quantification were in the ranges of 0.7?1.8 and 2.0?5.0 μg kg^?1, respectively. Average recoveries of the sulfoxa?or at the 14 food matrices at spiking levels of 5.0, 10 and 50 μg kg^?1 ranged from 74.0% to 100.8%, and the relative standard deviation ranged from 2.2% to 11.2%. This is a simple and rapid method for the determination of sulfoxa?or residues in various kinds of daily foods.     

An LC–MS/MS method for the quantification of diclofenac sodium in dairy cow plasma and its application in pharmacokinetics studies

An LC–MS/MS method with internal standard tolfenamic acid for determining diclofenac sodium (DCF) in dairy cow plasma was developed and validated. Samples were processed with protein precipitation by cold formic acid–acetonitrile. Determination of DCF was performed using LC–ESI⁺–MS/MS with the matrix‐matched calibration curve. The results showed that the method was sensitive (LOD 2 ng mL^?1, LOQ 5 ng mL^?1), accurate (97.60 ± 5.64%), precise (<10%) and linear in the range of 5–10,000 ng mL^?1. A single intravenous (i.v.) or intramuscular (i.m.) administration of 5% diclofenac sodium injection at a dose of 2.2 mg kg^?1 was performed in six healthy dairy cows according to a two‐period crossover design. The main pharmacokinetic (PK) parameters after a single i.v. administration were as follows: t_1/2β, 4.52 ± 1.71 h; AUC, 77.79 ± 16.76 h μg mL^?1; mean residence time, 5.16 ± 1.11 h. The main PK parameters after a single i.m. administration were as follows: T_max, 2.38 ± 1.19 h; C_max, 7.46 ± 1.85 μg mL^?1; t_1/2β, 9.46 ± 2.86 h; AUC 67.57 ± 13.07 h μg mL^?1. The absolute bioavailability was 87.37 ± 5.96%. The results showed that the diclofenac sodium injection had PK characteristics of rapid absorption and slow elimination, and high peak concentration and bioavailability in dairy cows, and that the recommended clinical dosage of diclofenac sodium injection is 2.2 mg kg^?1.     

A simple LC–MS/MS method facilitated by salting‐out assisted liquid–liquid extraction to simultaneously determine trans‐resveratrol and its glucuronide and sulfate conjugates in rat plasma and its application to pharmacokinetic assay

A simple LC–MS/MS method facilitated by salting‐out assisted liquid–liquid extraction (SALLE) was applied to simultaneously investigate the pharmacokinetics of trans‐ resveratrol (Res) and its major glucuronide and sulfate conjugates in rat plasma. Acetonitrile–methanol (80:20, v /v) and ammonium acetate (10 mol L⁻¹) were used as extractant and salting‐out reagent to locate the target analytes in the supernatant after the aqueous and organic phase stratification, then the analytes were determined via gradient elution by LC–MS/MS in negative mode in a single run. The analytical method was validated with good selectivity, acceptable accuracy (>85%) and low variation of precision (<15%). SALLE showed better extraction efficiency of target glucuronide and sulfate conjugates (>80%). The method was successfully applied to determine Res and its four conjugated metabolites in rat after Res administration (intragastric, 50 mg kg⁻¹; intravenous, 10 mg kg⁻¹). The systemic exposures to Res conjugates were much higher than those to Res (AUC_0–t , i.v., 7.43 μm h; p.o., 8.31 μm h); Res‐3‐O‐β ‐d ‐glucuronide was the major metabolite (AUC_0–t , i.v., 66.1 μm h; p.o., 333.4 μm h). The bioavailability of Res was estimated to be ~22.4%. The reproducible SALLE method simplified the sample preparation, drastically improved the accuracy of the concomitant assay and gave full consideration of extraction recovery to each target analyte in bio‐samples.     

Simultaneous stereoselective detection of chiral fungicides in soil by LC–MS/MS with fast sample preparation

An enantioselective method was developed for the simultaneous detection of five chiral fungicides in soil, including fenbuconazole ( 1 ), tetraconazole ( 2 ), nuarimol ( 3 ), triticonazole ( 4 ), and simeconazole ( 5 ) by LC–MS/MS on a chiral stationary phase of cellulose tris‐(3‐chloro‐4‐methylphenylcarbamate) with a gradient elution. A new multifunctional filter was designed to simplify the QuEChERS (where QuEChERS is quick, easy, cheap, effective, rugged, and safe) method by simultaneous cleanup and filtration when the sample extracts were directly passed through it. Good linearities (R² > 0.9980) were obtained in the range 0.005–2.5 mg/L, and the recovery rates were 77.4–103.6% with RSDs of 0.7–12.2% for intraday precision and 1.2–11.0% for interday precision. The LODs and LOQs for all enantiomers were in the range 0.1–0.2 and 0.25–0.5 μg/kg, respectively. The analysis of the incubated soil suggests that this method is reliable and practical for the stereoselective detection of chiral fungicides.     

Simultaneous determination of thiamethoxam and its metabolite clothianidin by LC-MS/MS in goji berry and soil

In this study, an effective analytical method for simultaneous determination of thiamethoxam and its metabolite clothianidin in goji berry and soil was developed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The recoveries of the compounds in goji berry and soil at the levels of 0.005, 0.02, and 0.1 μg kg^?1 were 84.7–98.9% and the relative standard deviations (RSDs) were 0.9–3.2%. The limits of detection (LOD) for both compounds in goji berry and soil matrices were 0.001 mg kg^?1; the limits of quantification (LOQ) were 0.005 mg kg^?1 for both compounds in two matrices. The dissipation and final residual experiments in 2016 with the commercial formulation of dinotefuran ? thiamethoxam 30% suspension concentrate (SC) was conducted in goji berries in northwest China (Qinghai, Gansu, Inner Mongolia, and Ningxia). Thiamethoxam was dissipated fast in goji plant ecosystem with half-lives were 1.08–1.01 and 2.04–4.25 days in goji berry and soil. The final residues of thiamethoxam were <0.005–0.382 and <0.005–1.120 mg kg^?1 in goji berry and soil, respectively.     

Simultaneous determination of pinoxaden,cloquintocet-mexyl,clodinafop-propargyl ester and its major metabolite in barley products and soil using QuEChERS modified with multi-walled carbon nanotubes coupled with LC–MS/MS

Herein, a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method with multi-walled carbon nanotube (MWCNT) as a dispersive solid-phase extraction was developed for simultaneous determination of pinoxaden (PXD), cloquintocet-mexyl (CLM), clodinafop-propargyl ester (CPE) and its major metabolite (clodinafop, CP) in barley grass powder, barley grain, and soil using liquid chromatography–tandem mass spectrometry (LC–MS/MS). We found that MWCNT as an absorbent could improve the recoveries of the tested analytes, particularly CP, in complex matrices. Under the optimum conditions, the established MWCNT-modified QuEChERS coupled with LC–MS/MS method exhibited excellent linearity (R²) of ≥0.9912, low limits of detection (LODs) and quantification (LOQs) of 0.02–0.07 and 0.29–1.26 μg kg⁻¹, and acceptable recoveries of 80–130% with intra- and inter-day relative standard deviations (RSDs) < 10.5%. No strong matrix effect (ME) has been observed on the respective samples. The method was successfully applied to monitor the tested analytes in the representative field incurred samples. Conclusively, the proposed method is sensitive and reliable and could be used to monitor the residues of PDX, CLM, CPE, and CP in complicated agro-products and soil matrices.     

Dissipation,residues and risk assessment of spirotetramat and its four metabolites in citrus and soil under field conditions by LC‐MS/MS

A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method for the simultaneous determination of spirotetramat and its four metabolite residues in citrus, peel, pulp and soil was developed and validated by liquid chromatography with tandem mass spectrometry (LC‐MS/MS). The samples were extracted with acetonitrile (1%, glacial acetic acid, v/v) and purified using primary secondary amine and octadecylsilane. The limit of detection was 0.01–0.13 mg/kg, whereas that of quantification was 0.02–0.40 mg/kg for spirotetramat and its metabolites. The average recoveries of spirotetramat, spirotetramat‐enol, spirotetramat‐mono‐hydroxy, spirotetramat‐enol‐glucoside and spirotetramat‐ketohydroxy in all matrices were 73.33–107.91%, 75.93–114.85%, 76.44–100.78%, 71.46–103.19% and 73.08–105.27%, respectively, with relative standard deviations < 12.32%. The dissipation dynamics of spirotetramat in citrus and soil followed first‐order kinetics, with half‐lives of 2.3–8.5 days in the three sampling locations. The terminal residues of spirotetramat in four matrices at the three locations were measured below the 1.0 mg/kg maximum residue limit set by China, and residues were found to be concentrated on the peel. The risk assessment of citrus was evaluated using risk quotients. The risk quotient values were found to be significantly <1, suggesting that the risk to human health was negligible when using the recommended doses of spirotetramat in citrus. These results could provide guidance for the safe and proper application of spirotetramat in citrus in China.     

A comparative study of biochar,multiwalled carbon nanotubes and graphitized carbon black as QuEChERS absorbents for the rapid determination of six triazole fungicides by UPLC-MS/MS

A rapid, effective and sensitive method to quantitatively determine six fungicide residue was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). The target compounds were extracted by using acetonitrile and the sorbent used for clean-up in this modified QuEChERS analytical method were biochar, multiwalled carbon nanotubes (MWCNT) and graphitized carbon black (GCB). Results indicated that the MWCNT (10 mg) was the most effective sorbent in removing pigment. This method was validated on spinach, tomato, cucumber, celery, lettuce, rape, pakchoi, romaine lettuce and eggplant matrices spiked at three concentration levels of 0.01, 0.1 and 1 mg kg^?1. It exhibited recoveries between 73.1% and 118.2% with RSD values below 20%. Matrix-matched calibrations were performed with the coefficients of determination >0.9901 between concentration levels of 0.01–1 mg kg^?1. The limit of quantity (LOQ) for six pesticides ranged from 0.0036 to 0.011 mg kg^?1. The developed method was satisfactorily applied to determine pesticide residues in market vegetable samples.     

LC and LC–MS Study of the Bioavailability and Metabolites of TM208 after Oral and Intravenous Administration to Rat

4-Methylpiperazine-1-carbodithioic acid 3-cyano-3,3-diphenylpropyl ester hydrochloride (TM208) is a new compound expected to become a new drug because of excellent in vivo and in vitro anticancer activity and low toxicity. A new, specific and sensitive LC method was set up for detecting the bioavailability of TM208 after oral administration. Samples were extracted with ethyl acetate after oral and intravenous administration. The retention times of TM208 and plunarizine (I.S.) were 5.5 and 9.9 min, respectively. The linear range was 0.125–50 μg mL^?1. The accuracy (error, %) for three concentrations was 2.7–16.6%. Intra-day precision (as RSD) was 1.6–6.9% and inter-day precision was 7.6–11.5%. Extraction recovery of TM208 was 84.15–89.51% and that of the I.S. was 83.3%. Results from stability testing indicated that samples should be analyzed within 24 h or frozen immediately for later analysis. The bioavailable fraction (F) calculated by use of a non-compartment model was 63.3%. Pharmacokinetic data for TM208 were: mean residence time 24.3 and 5.1 h, V _d 186.2 and 35.5 L kg^?1, and Cl 6.9 and 4.2 L h^?1 kg^?1 after oral and intravenous administration, respectively. LC–MS comparison of the metabolites after the two methods of administration showed the kind and content of metabolites of TM208 in rat urine after intravenous administration were more than after oral administration. The experimental results show that the low anticancer activity of TM208 after intravenous administration is related to rapid elimination of the drug, and that the kind and content of metabolites do not affect the bioactivity of TM208.     

Rapid simultaneous determination of codeine and morphine in plasma using LC‐ESI‐MS/MS: Application to a clinical pharmacokinetic study

A rapid and sensitive high‐performance LC‐MS/MS method was developed and validated for the simultaneous quantification of codeine and its metabolite morphine in human plasma using donepezil as an internal standard (IS). Following a single liquid‐liquid extraction with ethyl acetate, the analytes were separated using an isocratic mobile phase on a C₁₈ column and analyzed by MS/MS in the selected reaction monitoring mode using the respective [M+H]⁺ ions, mass‐to‐charge ratio (m/z) 300/165 for codeine, m/z 286/165 for morphine and m/z 380/91 for IS. The method exhibited a linear dynamic range of 0.2–100/0.5–250 ng/mL for codeine/morphine in human plasma, respectively. The lower LOQs were 0.2 and 0.5 ng/mL for codeine and its metabolite morphine using 0.5 mL of human plasma. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated LC‐MS/MS method was applied to a pharmacokinetic study in which healthy Chinese volunteers each received a single oral dose of 30 mg codeine phosphate.     

Evaluation of the influence of mirabilite on the absorption and pharmacokinetics of the ingredients in Dahuang‐mudan decoction by a validated UPLC/QTOF–MS/MS method

Dahuang‐mudan decoction (DMD) has been widely used for disease treatment in China for 1700 years. The formula consists of Rhubarb, moutan bark, Prunus persica, wax gourd kernel and mirabilite, which have been well studied by multidisciplinary approaches. However, the role of the mineral mirabilite in DMD is unclear. The objective of this study was to investigate the effects of mirabilite on the absorption and pharmacokinetics of the ingredients in DMD. The constituents were identified in DMD extract and the plasma of mirabilite–DMD (MDMD, 50 g kg^?1) treated rats and nonmirabilite–DMD (NMDMD, 50 g kg^?1) treated rats. The plasma was also used to investigate the effects of mirabilite on the pharmacokinetics of active ingredients in DMD using a new validated UPLC–MS/MS method. The results showed that 63 compounds were identified in the extract of DMD, 27 and 22 of which were found in the plasmas of MDMD‐ and NMDMD‐treated rats, respectively. Furthermore, the results of a pharmacokinetic study suggested that mirabilite influenced the absorption of the five constituents by decreasing the absorption of emodin and rhein while increasing the absorption of aloe‐emodin, paeoniflorin and amygdalin; the pharmacokinetic parameters, including the T_max, C_max, AUC_0–t, MRT_0–t, CLz and t_1/2 of five constituents, significantly changed in MDMD‐treated rats compared with the NMDMD. The method validation for selectivity, precision, accuracy, matrix effect, recovery and stability met the acceptance criteria. These findings uncover the roles of mirabilite in DMD and demonstrate the application of scientific principles to the study of DMD in human health care.     

Simultaneous determination of idelalisib and its metabolite GS‐563117 in dog plasma by LC–MS/MS: Application to a pharmacokinetic study

The purpose of this study was to develop and validate an LC–MS/MS method for simultaneous determination of idelalisib and GS‐563117 in dog plasma. The analytes were extracted using ethyl acetate and then separated on a Waters Acquity UPLC BEH C₁₈ column (50 × 2.1 mm, i. d., 1.7 μm) using 0.1% formic acid in water and acetonitrile as mobile phase at a flow rate of 0.3 mL/min in gradient elution mode. The analytes were quantified using selected reaction monitoring with precursor‐to‐product transitions at m/z 416.2 → 176.1, m/z 432.2 → 192.1 and m/z 421.2 → 176.1 for idelalisib, GS‐563117 and [²H₅]‐idelalisib (internal standard). The assay showed good linearity (r > 0.9992) over the tested concentration range of 0.1–600 ng/mL for idelalisib and 0.1–300 ng/mL for GS‐563117. The intra‐ and inter‐day RSD values for idelalisib and GS‐563117 were <8.84 and 12.41%, respectively. The intra‐ and inter‐day RE values were within the range of ?7.21–8.52%, and ?6.44–14.23%, respectively. The extraction recovery was found to be >84.59% and no matrix effects were observed. The validated LC–MS/MS method has been successfully applied for the simultaneous determination of idelalisib and GS‐563117 in a pharmacokinetic study in dogs. Our results suggested that idelalisib was rapidly metabolized into its metabolite GS‐563117 in dog and the in vivo exposure of GS‐563117 was 17.59% of that of idelalisib.     

Determination of silodosin and its active glucuronide metabolite KMD‐3213G in human plasma by LC–MS/MS for a bioequivalence study

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method is described for the simultaneous determination of silodosin (SLD) and its active metabolite silodosin β‐d ‐glucuronide (KMD‐3213G) in human plasma. Liquid–liquid extraction of plasma samples was carried out with ethyl acetate and methyl tert‐butyl ether solvent mixture using deuterated analogs as internal standards. The extraction recoveries of SLD and KMD‐3213G were in the ranges 90.8–93.4 and 87.6–89.9%, respectively. The extracts were analyzed on a Symmetry C₁₈ (50 × 4.6 mm, 5 μm) column under gradient conditions using 10 mm ammonium formate in water and methanol–acetonitrile (40:60, v/v), within 6.0 min. For MS/MS measurements, ionization of the analytes was carried out in the positive ionization mode and the transitions monitored were m/z 496.1 → 261.2 for SLD and m/z 670.2 → 494.1 for KMD‐3213G. The method showed good linearity, accuracy, precision and stability in the range 0.10–80.0 ng/mL for SLD and KMD‐3213G. The IS‐normalized matrix factors obtained were highly consistent, ranging from 0.962 to 1.023 for both analytes. The method was used to support a bioequivalence study of SLD and its metabolite in healthy volunteers after oral administration of 8 mg silodosin capsules.     

Simultaneous quantification of antofloxacin and its major metabolite in human urine by HPLC–MS/MS,and its application to a pharmacokinetic study

This study presents a high‐performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method for the simultaneous determination of antofloxacinin and its main metabolite – N ‐demethylated metabolite (N‐ DM) – in human urine. Ornidazole was used as the internal standard. This was a clinical urine recovery study, in which 10 healthy Chinese volunteers were intravenously administered a single 200 mg dose of antofloxacin hydrochloride. Compounds were extracted by albumen precipitation, after which samples were isocratically eluted using a Poroshell 120 SB‐C₁₈ column, and were analysed using HPLC–MS/MS under electronic spray ionization positive ion mode. The method was successfully applied in a urine pharmacokinetic study of antofloxacinin, with a detection range of 0.02/0.01 to 200/100 μg/mL (for antofioxacin/N‐ DM).The average percentages of antofioxacin/N‐ DM measured in urinary excretion frp, 10 volunteers were 54.9 ± 5.7/8.2 ± 2.5% in 120 h duration.     

A fast and accurate isotope dilution GC‐IT‐MS/MS method for determination of eugenol in different tissues of fish: Application to a depletion study in mandarin fish

An accurate, rapid and effective method was established for determination of eugenol in plasma, muscle, skin, liver, kidney and gill of fish using gas chromatography–ion trap tandem mass spectrometry. Samples of muscle, skin, liver, kidney and gill were prepared using the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure, and a plasma sample was prepared by a liquid–liquid extraction procedure. Eugenol was monitored in <7 min using an electron‐ionization source in MS/MS mode and quantified by an internal standard of eugenol‐d₃. The limit of detection was 5.0 μg/kg, and the limit of quantification was 10.0 μg/kg. The calibration curve was linear in the range of 5–1000 μg/L (R² = 0.9996). Intra‐ and inter‐day precisions of eugenol expressed as relative standard deviation were within 9.74%, and the accuracy exhibited a relative error ranging from −2.20 to 8.89%. The developed method was successfully used to study the elimination regularity of eugenol in mandarin fish.     

Simultaneous quantitation of IC87114, roflumilast and its active metabolite roflumilast N‐oxide in plasma by LC‐MS/MS: application for a pharmacokinetic study

A sensitive and reliable high‐performance liquid chromatography–mass spectrometry (LC–MS/MS) was developed and validated for simultaneous quantification IC87114, roflumilast (RFM), and its active metabolite roflumilast N‐oxide (RFN) using tolbutamide as an internal standard. The analytes were extracted by using liquid–liquid extraction and separated on a reverse phase C₁₈ column (50 mm × 3 mm i.d., 4.6 µ) using methanol: 2 mM ammonium acetate buffer, pH 4.0 as mobile phase at a flow rate 1 mL/min in gradient mode. Selective reaction monitoring was performed using the transitions m/z 398.3 > 145.9, 403.1 >186.9, 419.1 > 187.0 and 271.1 > 155.0 to quantify quantification IC87114, RFM, RFN and tolbutamide, respectively. The method was validated over the concentration range of 0.1–60 ng.mL^?1 for RFM and RFN and 6 to 2980 ng.mL^?1 for IC87114. Intra‐ and inter‐day accuracy and precision of validated method were within the acceptable limits of <15% at all concentrations. Coefficients of correlation (r²) for the calibration curves were >0.99 for all analytes. The quantitation method was successfully applied for simultaneous estimation of IC87114, RFM and RFN in a pharmacokinetic drug–drug interaction study in Wistar rats. Copyright © 2012 John Wiley & Sons, Ltd.     

A Multiresidue Method for Simultaneous Determination of 116 Pesticides in <Emphasis Type="Italic">Notoginseng Radix et Rhizoma</Emphasis> Using Modified QuEChERS Coupled with Gas Chromatography Tandem Mass Spectrometry and Census 180 Batches of Sample from Yunnan Province

A method was established for the simultaneous determination of 116 pesticide residues in Notoginseng Radix et Rhizome with a combination of the modified QuEChERS method and GC–MS/MS. The sample was extracted with acetonitrile, cleaned up by primary–secondary amine and octadecyl-modified silica (C18) sorbents and determined by GC–MS/MS in multireaction monitoring mode. Matrix-matched calibration coupled with internal standard method was applied to compensate for the matrix effect and to quantify the pesticides. The results of all the 116 pesticides showed good linearity in the respective linear range with correlation coefficients (r²) > 0.99. The method limits of quantification were between 0.01 and 0.05 mg kg^?1. The recoveries were between 64.3 and 119.4%, with RSD values typically lower than 18.3% at three spiked levels of 0.05, 0.10 and 0.20 mg kg^?1. The validated methodology is easy, fast, highly accurate, reliable and sensitive for monitoring and quantification of the 116 pesticide residues in Notoginseng Radix et Rhizoma. In 180 batches of real samples, 11 pesticides were detected and among these quintozene and cyfluthrin were in excess of the standard of European Union maximum residue level for herbs.     

Nanobiocomposite Modified Carbon‐Ceramic Electrode Based on Nano‐TiO2‐Plant Tissue and Its Application for Electrocatalytic Oxidation of Dopamine

A new modified carbon‐ceramic electrode was prepared by incorporating TiO₂ nanoparticle into sol‐gel network by accompanying apple tissue. A mixture of fine graphite powder with 15 wt% of TiO₂ nanoparticle was used for the preparation of the carbon matrix and finally modification with a known amount weighted of apple tissue. The apple tissue containing polyphenol oxidase enzyme acts as molecular recognition element. The electrocatalytic oxidation of dopamine was investigated on the surface of the nanobiocomposite modified carbon‐ceramic electrode using cyclic voltammetry, chronoamperometry and amperometry techniques. Effect of pH, scan rate, TiO₂ percentage on the response of modified electrode was studied. The prepared modified electrode presented a linear range for dopamine from 5.0×10^?6 to 1.2×10^?3 M in buffered solutions with pH 7.4 by amperometry. The detection limit was 3.41×10^?6 M dopamine. The response of the modified carbon‐ceramic electrode and unmodified carbon‐ceramic electrode was compared.     

Determination of 19 sulfonamides residues in pork samples by combining QuEChERS with dispersive liquid–liquid microextraction followed by UHPLC–MS/MS

A new simple and rapid pretreatment method for simultaneous determination of 19 sulfonamides in pork samples was developed through combining the QuEChERS method with dispersive liquid–liquid microextraction followed by ultra‐high performance liquid chromatography with tandem mass spectrometry. The sample preparation involves extraction/partitioning with QuEChERS method followed by dispersive liquid–liquid microextraction using tetrachloroethane as extractive solvent and the acetonitrile extract as dispersive solvent that obtained by QuEChERS. The enriched tetrachloroethane organic phase by dispersive liquid–liquid microextraction was evaporated, reconstituted with 100 μL acetonitrile/water (1:9 v/v) and injected into an ultra‐high performance liquid chromatography with a mobile phase composed of acetonitrile and 0.1% v/v formic acid under gradient elution and separated using a BHE C₁₈ column. Various parameters affecting the extraction efficiency were investigated. Matrix‐matched calibration curves were established. Good linear relationships were obtained for all analytes in a range of 2.0–100 μg/kg and the limits of detection were 0.04–0.49 μg/kg. Average recoveries at three spiking levels were in the range of 78.3–106.1% with relative standard deviations less than 12.7% (n = 6). The developed method was successfully applied to determine sulfonamide residues in pork samples.