Shen C

Determination of 17 pyrethroid residues in troublesome matrices by gas chromatography/mass spectrometry with negative chemical ionization

An analytical method with the technique of QuEChERS (quick, easy, cheap, effective, rugged and safe) and gas chromatography (GC)/mass spectrometry (MS) in negative chemical ionization (NCI) has been developed for the determination of 17 pyrethroid pesticide residues in troublesome matrices, including garlic, onion, spring onion and chili. Pyrethroid residues were extracted with acidified acetonitrile saturated by hexane. After a modified QuEChERS clean-up step, the extract was analyzed by GC-NCI/MS in selected ion monitoring (SIM) mode. An isotope internal standard of trans-cypermethrin-D(6) was employed for quantitation. Chromatograms of pyrethroids obtained in all these matrices were relatively clean and without obvious interference. The limits of detection (LODs) ranged from 0.02 to 6 μg kg(-1) and recovery yields were from 54.0% to 129.8% at three spiked levels (20, 40 and 60 μg kg(-1) for chili, and 10, 20 and 30 μg kg(-1) for others) in four different matrices depending on the compounds determined. The relative standard deviations (RSDs) were all below 14%. Isomerization enhancement of pyrethroids in chili extract was observed and preliminarily explained, especially for acrinathrin and deltamethrin.

Analysis of tetracycline residues in royal jelly by liquid chromatography-tandem mass spectrometry

A confirmatory method coupling liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed to determine the concentration of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC) and doxycycline (DC), which make up the tetracycline (TC) groups present in royal jelly. Sample preparation included deproteination, control of pH, extraction and clean-up on a solid-phase extraction (SPE) cartridge. The analyses were achieved by LC/MS/MS in selected reaction monitoring mode (SRM). The overall recovery of fortified royal jelly at the levels of 5.0, 10.0 and 40.0 microg/kg ranged from 62% to 115%, and the coefficients of variation ranged from 3.4% to 16.3% (n=6). The detection limits for TCs were under 1.0 microg/kg. The transformation between the TCs and its epimers (EpiTCs) was studied in standard solution and during the sample preparation process. This method can be used for the detection of tetracycline residues in royal jelly.

Determination of methylene blue residues in aquatic products by liquid chromatography-tandem mass spectrometry.

A method for the determination and confirmation of methylene blue (MB) in aquatic products was developed. Residues of MB were extracted from homogenized tissues with acetonitrile/sodium acetate buffer solution, and simply cleaned up with dichloromethane liquid/liquid extraction. After concentration and dissolution, the sample solutions were cleaned up by the neutral alumina and weak cation-exchange solid phase extraction (SPE) cartridge, prior to LC-MS/MS analysis. MB was determined at 1.0-20 microg/kg in eel, toasted eel and shrimp, with a limit of quantification of 0.5 microg/kg. Recovery for MB was between 73.0% and 108.3%. This method is fast, exact and sensitive. It can be applied to determine MB in aquatic products.

Determination of amitraz and 2,4-dimethylaniline residues in honey by using LC with UV detection and MS/MS.

A method for the determination and confirmation of amitraz and its degradation product 2,4-dimethylaniline (2,4-DMA) in honey is reported. Determination of the two compounds was based on HPLC with UV detection and MS/MS (LC-MS/MS) after a liquid-liquid extraction with hexane and isopropyl alcohol. Chromatographic separation was achieved by using a C18 column with a gradient mobile phase consisting of 0.02 M ammonium acetate and ACN. Recoveries for fortified honey ranged from 83.4 to 103.4% for amitraz and from 89.2 to 104.7% for 2,4-DMA with RSD values lower than 11.6% for HPLC and LC-MS/MS methods. LOD was 6 microg/kg for amitraz and 8 microg/kg for 2,4-DMA, while LOQ was 20 microg/kg for amitraz and 25 microg/kg for 2,4-DMA in HPLC method. LOD was 1 microg/kg for amitraz and 2 microg/kg for 2,4-DMA, while LOQ was 5 microg/kg for amitraz and 10 microg/kg for 2,4-DMA in LC-MS/MS method.

Determination of Three Nitroimidazole Residues in Royal Jelly by High Performance Liquid Chromatography-Tandem Mass Spectrometry

A method for analysis of trace metronidazole (MTZ), dimetridazole (DMZ) and ronidazole (RNZ) residues in royal jelly was developed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After samples were dissolved in sodium hydroxide solution to disassociate target analytes from matrix, liquid-liquid extraction methods by ethyl acetate solvent were used. Matrix effects were minimized and good quantitation results were obtained by using highly-selective reaction monitoring (H-SRM) technology when deuterated dimetridazole (dimetridazole-D3) was selected as internal standard. Limits of detection (LODs) were 1.0 microg/kg for DMZ, 0.5 microg/kg for MTZ and RNZ (S/N > 5). Limits of quantitation (LOQs) were 2.0 microg/kg for DMZ, 1.0 microg/kg for MTZ and RNZ (S/N > 10). The linear ranges were 2.0 - 200 microg/L for all target analytes. Recoveries and relative standard deviations (RSDs) were in the ranges of 96.6% - 110.6% and 2.1% -7.4%, respectively. This method is suitable for statutory residue testing in the National Residue Surveillance Plan in China and meets the requirement for export.

SIMULTANEOUS DETERMINATION OF 14 QUINOLONES IN ROYAL JELLY BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY USING ANION-EXCHANGE SOLID-PHASE EXTRACTION

A new method based on liquid chromatography-tandem mass spectrometry has been developed for simultaneous determination of 14 quinolones (QNs) residues, including ciprofloxacin, danofloxacin, difloxacin, enoxacin, enrofloxacin, flumequine, lomefloxacin, marbofloxacin, norfloxacin, orbifloxacin, ofloxacin, pipemidic acid, pefloxacin, and sarafloxacin in royal jelly. The proposed analytical procedure involves extraction of the QNs from samples by 0.1 M sodium hydroxide aqueous solution, a step for clean-up and preconcentration of the analytes by anion-exchange solid-phase extraction (SPE) and liquid chromatographic separation with mass spectrometric detection. Internal standard calibration was applied with norfloxacin-D5 as internal standard (I.S.). Satisfactory recovery (from 64% to 113%), excellent repeatability precision (relative standard deviations, RSDs below 6%), reproducibility precision (RSDs below 10%), and low limits of quantifications (LOQs from 0.3 to 2.5 µg kg−1) were evaluated from spiked royal jelly samples at 2.5, 5.0, and 10.0 µg kg−1 three concentration levels. This protocol has been validated by five authoritative laboratories and successfully used for analysis of a large number of import–export samples (n > 2000). Norfloxacin and ciprofloxacin were found to be the most common contamination in royal jelly in the ranges of 3.5–30 µg kg−1 and 4.5–20 µg kg−1, respectively.

Simultaneous determination of tocopherols and tocotrienols in vegetable oils by GC-MS

A simple and rapid gas chromatography-mass spectrometry (GC-MS) method was developed and validated for the simultaneous determination of α-, β-, γ- and δ-tocopherols and α-, β-, γ- and δ-tocotrienols in vegetable oils. In this study, tedious sample pretreatments like saponification and derivatization, which are commonly used in previously published related methods, were not adopted. Tocopherols and tocotrienols were isolated from oil samples by ultrasonic extraction with methanol, then centrifuged and the supernatant was directly injected into the GC-MS system for analysis. The results showed that α-, β-, γ- and δ-tocopherols and α-, β-, γ- and δ-tocotrienols were well separated within 14 minutes. The instrumental limits of detection and quantification ranged from 0.3 to 2.5 ng mL−1 and from 1.0 to 8.3 ng mL−1, respectively. Calibration curves were well correlated (r2 > 0.99) within the concentration range of 10 to 1000 ng mL−1 for all eight compounds. Recovery tests were carried out by spiking virgin olive oil with standards at three concentration levels (10, 50 and 250 mg kg−1), in which the average recoveries (n = 6) varied from 83.7% to 117.2%, with relative standard deviations ranging between 1.9% and 7.5%. The proposed method proved to be simple, sensitive and accurate, and was successfully applied to the determination of tocopherols and tocotrienols in vegetable oils.

[Determination of deoxynivalenol in grain and its products by solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry].

A method was established for the determination of deoxynivalenol (vomitoxin) in grain and its products based on solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was firstly extracted by acetonitrile-water (84:16, v/v). The extract was then cleaned-up by an HLB solid phase extraction cartridge. The separation was carried out on a Phenomenex Kinetex C18 column (100 mm x4. 6 mm, 2.6 microm) with a gradient elution using 0.3% per hundred ammonia solution-acetonitrile as mobile phases. The analysis of deoxynivalenol was performed under electrospray negative ionization mode. The limit of detection (LOD, S/N= 3) and the limit of quantification (LOQ, S/N = 10) were 20 microg/kg and 50 microg/kg, respectively. A good linearity (r > 0.99) was achieved for the target compound over the range of 20-1000 pg/L. The recoveries at the three spiked levels (50, 100, 500 microg/kg) in the blank matrices such as flour, barley, soybean, rice, cornmeal, cassava and wheat, were varied from 75.6% to 111.0% with the relative standard deviations no more than 13. 0%. The method is accurate, efficient, sensitive and practical. The cost of pretreatment is obviously reduced by replacing immunoaffinity columns and Mycosep columns with HLB columns which have the same purification effect.

[Determination of five pyrrolizidine alkaloids in honey by liquid chromatography-tandem mass spectrometry].

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of five pyrrolizidine alkaloids (PAs) (monocrotaline, senkirkine, retrorsine, seneciphylline and senecionine) in honey. The honey samples were dissolved in 0.1 mol/L hydrochloric acid solution and a strong-cation exchange column was used to purify and concentrate the target analytes. The separation of the analytes was carried out on a Phenomenex C18 column (100 mm x 4.6 mm, 2.6 microm) using the mobile phases of acetonitrile and 5 mmol/L ammonium acetate-0.1% (volume percentage) formic acid aqueous solution with gradient elution. The separated compounds were detected in multiple reaction monitoring (MRM) mode via positive electrospray ionization (ESI+). The calibration curves were of good linearity in the range of 1-100 microg/L (r > 0.99). The limit of quantification of the method was 1.0 microg/kg. The average recoveries were between 73.1% to 107.1% at three spiked levels (1, 20 and 50 microg/kg) with the relative standard deviations (RSDs) in the range of 4.1% to 17.0%. The proposed method was applied to different kinds of honey from China, New Zealand, Spain and Australia. The samples included rape, vitex, sunflower, cotton, tilia tree, date, acacia, buckwheat, manuka and eucalyptus honey. Monocrotaline, senkirkine and retrorsine were not detected in the collected honey samples. However, seneciphylline and senecionine were found in most of the honey samples. The concentrations of seneciphylline and senecionine were 11.0 -31.1 microg/kg and 8.3-29.1 microg/kg, respectively.

[Determination of kojic acid in foods using high performance liquid chromatography-tandem mass spectrometry].

The quantification method for the determination of kojic acid in foods using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed. For solid samples, the kojic acid was extracted with acetonitrile; for liquid samples, they were diluted with water, then deproteinized by the deposition with zinc acetate and potassium ferrocyanide. The analytes were determined by HPLC-MS/MS on a C18 column with 5 mmol/L ammonium acetate/formic acid solution as mobile phases. The analysis of kojic acid was performed under selected reaction monitoring (SRM) mode by selecting one parent ion and two daughter ions as qualitative ions with [13C6]-kojic acid as the internal standard, and the most abundant daughter ion as quantitative ion. The limits of quantification (S/N > 10) were 0.1 mg/kg for the solid samples, and 2.5 mg/kg for the liquid samples. The good linearity (r > 0.99) was achieved for the target compound over the range of 0.1 - 2.0 mg/L. The recoveries at three levels for kojic acid were from 72.6% to 114% with the relative standard deviations no more than 11.4%. The method is simple and practical, and can be applied to most of matrices which may contain kojic acid as food additives. It can meet the qualitative and quantitative requirements for import and export foods.