[Determination of amitraz and its metabolites in vegetables and fruits by high performance liquid chromatography-tandem mass spectrometry].

A method was established for the determination of amitraz (AMZ), and its metabolites semiamitraz (DMPF), 2,4-dimethylformamidine (DMF) and 2,4-dimethylaniline (DMA) in vegetables and fruits by using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The samples were diluted with 0.1 mol/L sodium hydroxide and extracted with n-hexane-isopropanol (2:1, v/v). The separation was performed on a Phenomenex Kinetex C18 column (100 mm×4.6 mm, 2.6 µm) with gradient elution using 0.1% (v/v) formic acid aqueous solution-methanol as the mobile phase. The analysis of amitraz and its metabolites were detected under electrospray positive ionization mode. The limits of quantification (LOQs) were between 0.01 and 0.4 µg/kg. The good linearities (r>0.99) were achieved for the target compounds in the range of 1.0-200.0 µg/L. The recoveries at three spiked levels (0.5, 5.0 and 20 µg/kg) in blank matrix were in the range of 62.5%-105.0% with the relative standard deviations between 7.5% and 17.6%. The method is convenient, rapid, accurate, efficient, sensitive and practical. It is suitable for the determination and confirmation of amitraz and its metabolites in vegetables and fruits, and can meet the demands of domestic and foreign regulations.

[Determination of four kinds of illegal additive residues in sprouts and source beans by high performance liquid chromatography-tandem mass spectrometry].

A reversed-phase high performance liquid chromatography coupled with tandem mass spectrometric (LC-MS/MS) method was developed for the determination of 4-chlorophenoxyacetic acid, 6-benzylaminopurine, enrofloxacin and norfloxacin residues in sprouts and source beans. The sample was extracted by acetonitrile containing 0.1% acetic acid and concentrated. The chromatographic analysis was carried out on a C18 column with methanol and 0.1% formic acid solution as the mobile phases in gradient elution program. The MS analysis was set in electrospray ionization mode and separated to two segments of positive and negative modes. The precursor ions were m/z 189.9, 226.1, 359.9 and 320.1, while the product ions for quantification were m/z 127.0, 91.2, 315.9 and 276.2 for 4-chlorophenoxyacetic acid, 6-benzylaminopurine, enrofloxacin and norfloxacin, respectively. The calibration curves showed good linearity in the range of 5 - 200 microg/L with correlation coefficients more than 0.995. The limits of detection (LODs) were 1 microg/kg and the limits of quantification (LOQs) were 5 microg/kg for the four compounds spiked in mung bean sprouts and mung beans. The recoveries of the four compounds spiked at three levels of 5.0, 10.0 and 20.0 microg/kg ranged from 70% to 91%, with the relative standard deviations (RSDs) less than 14%. The method established is accurate, sensitive, simple, and has considerable advantages in the analysis of the four kinds of illegal additive residues in sprouts and beans simultaneously.

[Determination of cyanuric acid in milk and milk powder by high performance liquid chromatography-tandem mass spectrometry].

A method for the determination of cyanuric acid (CYA) in milk and milk powder was developed using high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI MS/MS). The target analyte was extracted from samples by acetonitrile, and the proteins were precipitated at the same time. The supernatant was cleaned up and enriched with a strong anion exchange column, analysed by HPLC-MS/MS with an AX column, and quantified by internal standard method. Good linearity was obtained in the range of 50-2000 microg/L. The recoveries were all ranged from 97% to 121% at three levels, 200, 500 and 1000 microg/kg, and the relative standard deviations (RSDs) were all below 4.8%. Limit of quantification (LOQ) was 200 microg/kg. The method has high accuracy and precision, the operation is fast, easy and suitable for the determination of CYA in milk and milk powder.

[Determination of 107 pesticide residues in vegetables using off-line dispersive solid-phase extraction and gas chromatography-tandem mass spectrometry].

A screening method was developed for the determination of 107 pesticide residues in vegetables using off-line dispersive solid-phase extraction (DSPE) and gas chromatography-tandem mass spectrometry (GC-MS/MS). The pesticides interested were extracted from the samples with acetonitrile (saturated by n-hexane) containing 1% acetic acid and simultaneously separated by liquid-liquid partitioning with adding anhydrous magnesium sulfate plus sodium acetate following by a simple cleanup step known as dispersive solid-phase extraction. The extracts were determined by GC-MS/MS using external standard method. The method was reliable and stable that the recoveries of almost all pesticides were in the range from 60% to 130% at the spiked level of 10 microg/kg into four vegetable matrixes (garlic, green bean, radish 8 and spinach) and the relative standard deviations (RSDs) were all not more than 15.3%. The linearity of the method was good between 0.05 mg/L and 1 mg/L, and all limits of quantification (LOQs) less than 10 microg/kg. The method is selective with no interference, especially in the complicated garlic matrix.

[Determination of 20 kinds of pesticide residues in soybeans and corn using gas chromatography-negative chemical ionization mass spectrometry coupled with offline disperse solid-phase extraction].

A method was developed for the determination of 20 kinds of pesticide residues in soybeans and corn with the technique of offline disperse solid-phase extraction and gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS). The pesticides interested were extracted twice from the samples with acetonitrile. The combined extract was concentrated to dryness and redissolved in acetonitrile, then cleaned up by dispersive solid-phase extraction with sorbents of N-propyl ethylene diamine (PSA), graphited carbon black, and C18, and determined and confirmed by GC-NCI/MS. The recoveries of all pesticides were in the range of 70%-130% at three spiked levels (5, 10 and 20 microg/kg), and the relative standard deviations were below than 17%. The linearity of the method was good in the concentration range of 20-400 microg/L, and limits of quantification (LOQs) were no more than 2 microg/kg. The method is selective well with no interference and suitable for the confirmatory of pesticide residues in soybeans and corn.

[Determination of 12 azole fungicide residues in beans and corn by offline disperse solid phase extraction and gas chromatography-negative chemical ionization mass spectrometry].

A confirmatory method is proposed for the determination of 12 azole fungicide residues in beans and corn with the technique of offline disperse solid phase extraction (DSPE) and gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS). The pesticides interested were extracted from the samples with acetonitrile containing 1% acetic acid and simultaneous liquid-liquid partitioning formed by adding anhydrous magnesium sulfate plus sodium acetate followed by a simple cleanup step known as dispersive solid-phase extraction. The aliquot was determined and confirmed by GC-NCI/MS using external standard method. The recoveries of all pesticides were between 70% and 130% at the three spiked levels, 10 microg/kg, 20 microg/kg and 40 microg/kg. The relative standard deviations were less than 13.9%. The linearity of method was good from 50 to 1 000 microg/L. The limits of quantification (LOQ) were less than 8 microg/kg. The method is selective with no interference and is suitable for the confirmatory of pesticide residues in beans and corn.