Validated method for determination of ultra-trace closantel residues in bovine tissues and milk by solid-phase extraction and liquid chromatography-electrospray ionization-tandem mass spectrometry

A liquid chromatographic-electrospray ionisation-tandem mass spectrometry method (LC-ESI-MS/MS) with solid extraction was developed and validated for the detection and determination of closantel residues in bovine tissues and milk. An acetonitrile-acetone mixture (80:20, v/v) was used for one-stage extraction of closantel residues in bovine tissues and milk samples, and the extract was cleaned by solid phase extraction with Oasis MAX cartridges. The mass spectrometer was operated in multiple reactions monitoring mode with negative electrospray interface. The limits of detection in different matrices were in the range of 0.008-0.009 microg/kg. The overall recoveries for bovine muscle, liver, kidney and milk samples spiked at four levels including MRL were in the range of 76.0-94.3%. The overall relative standard deviations were in the range of 3.57-8.61%. The linearity is satisfactory with a correlation coefficient (r(2)) of 0.9913-0.9987 at both concentration ranges of 0.02-100 microg/kg and 200-5000 microg/kg. The method is capable of identifying closantel residues at > or =0.02 microg/kg levels and was applied in the determination of closantel residues in animal origin foods.     

Determination of nitroimidazoles and their metabolites in swine tissues by liquid chromatography

A liquid chromatographic method was developed for determination of metronidazole (MNZ), ronidazole (RNZ), dimetridazole (DMZ), and 2-hydroxymethyl-1-methyl-5-nitroimidazole (DMZOH) in swine tissue. After extraction with ethyl acetate and evaporation, the nitroimidazoles were redissolved in hydrochloric acid. Hexane was used in the liquid-liquid extraction to remove fat. An Oasis HLB solid-phase extraction was performed after neutralization of the acidic extract. The limits of detection were 1.0-2.0 microg/kg for DMZOH, MNZ, RNZ, and DMZ in muscle and liver. Average recoveries ranged from 80.1 to 83.9% in muscle fortified at 10, 20, and 50 microg/kg; average recoveries in liver ranged from 78.9 to 82.3%. The procedure provides a simple and sensitive method for monitoring DMZOH, MNZ, RNZ, and DMZ residues in swine tissues.     

Determination of residues of tricaine in fish using liquid chromatography tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the determination of residues of the anaesthetic tricaine mesilate (MS222) in fish tissues is described. Residues were extracted from homogenized tissues with McIllvaine buffer/methanol and purified over a C18 solid-phase extraction column followed by LC-MS/MS analysis. In the multiple-reaction monitoring mode of the mass spectrometer, chromatograms were recorded by monitoring the m/z 166-->m/z 138 and m/z 166-->m/z 94 transitions for quantification and confirmation of the residues in the finfish matrix, respectively. Recoveries were in the range of 67%+/-10% (n=6) for tilapia at 2 microg kg(-1), 95%+/-7% (n=6) at 2 microg kg(-1) in salmon and 92%+/-3% (n=5) for trout at 2.5 microg kg(-1). The limits of detection were 0.5, 0.6 and 0.6 microg kg(-1) in trout, salmon and tilapia, respectively. No residues of tricaine were found in eight sampled aquacultured fish (salmon and trout) bought from the local market.     

高效液相色谱-串联质谱法测定食品中多杀菌素A和D的残留量

建立了食品中多杀菌素(spinosyn) A和D残留的液相色谱-串联质谱(HPLC-MS/MS)检测方法。甘蓝等食品样品经乙腈-水(50:50, v/v)提取、HLB固相萃取柱净化后,采用HPLC-MS/MS进行检测分析,利用外标法定量。质谱分析采用电喷雾电离,正离子扫描,多反应监测模式。结果表明,柱净化后无明显的基质效应,多杀菌素在1～20 μg/L内具有较好的线性关系,其相关系数可达0.9999;样品中添加1～10 μg/kg的多杀菌素,其回收率为76.2%～114.0%,相对标准偏差(n=10)小于10%;检出限(信噪比（S/N）=3): 多杀菌素A为0.2 μg/kg,多杀菌素D为0.5 μg/kg;定量限(S/N=10): 多杀菌素A为0.5 μg/kg,多杀菌素D为1.0 μg/kg。在最佳实验条件下,对来自福建厦门的969份食品样品进行了检测,其中15份样品检测结果呈阳性。实验结果表明,该方法提取效果好,具有良好的灵敏度、回收率和重复性。     

Application of hollow fiber supported liquid membrane extraction to the simultaneous determination of pesticide residues in vegetables by liquid chromatography/mass spectrometry

A new analytical procedure using a hollow fiber supported liquid membrane (HFSLM) has been developed for the simultaneous determination of pesticide residues in vegetables by liquid chromatography (LC) coupled with electrospray mass spectrometry (MS). The extraction technique requires minimal sample preparation and solvent consumption. Optimum extraction conditions have been evaluated with respect to sample pH, ionic strength, liquid membrane composition, extraction time, stirring rate and acceptor composition. The extraction method has been validated for matrices such as cucumber, tomato and pepper, indicating that cucumber can be selected as representative matrix for routine analysis of these food commodities. Linear ranges of pesticides in vegetable samples were 10 to 200 microg/kg, and the repeatability of the method was less than 20% for the lowest calibration point. The limits of detection ranged from 0.06 to 2.7 microg/kg and the limits of quantification from 0.2 to 9.0 microg/kg, which were low enough to determine the pesticide residues at concentrations below or equal to the maximum residue levels (MRLs) specified by European Union. The method was finally applied to the determination of more than 20 pesticides in market vegetable samples and the concentrations found in these samples were always lower than the MRLs. This new approach can be considered as a powerful alternative to the traditional extraction techniques.     

Development of methods for determination of the residues of 15 pesticides in medicinal herbs Isatis indigotica Fort. by capillary gas chromatography with electron capture or flame photometric detection

Two multiresidue methods were developed for the determination of 15 pesticides (organochlorines, organphosphorus compounds, pyrethroids, and fungicides) in medicinal herbs Isatis indigotica Fort. and its formulations. The analytical procedure is based on ultrasonic assisted extraction and liquid-liquid extraction (LLE). After solvents were added, the raw material or granule sample was sonicated in an ultrasonic water bath and then centrifuged, filtered, and cleaned up by LLE. The infusion sample was extracted with petroleum ether by LLE. The pesticide residues were determined by capillary gas chromatography with electron-capture or flame photometric detection. Recoveries with the method at concentrations between 0.4 microg/kg and 10 mg/kg ranged from 70.2 to 119.5% for raw material, 73.2 to 105.1% for granule formulation, and 72.8 to 113.3% for infusion formulation. The relative standard deviation values were <20% for all of the pesticides studied. The pesticide detection limits were within the ranges 0.3-0.5 microg/L for endosulfan, 3-7.5 microg/L for pyrethroids, 0.7-32.5 microg/L for organophosphorus pesticides, and 0.1-0.6 microg/L for the other pesticides. The proposed methods are simple and rapid and provide simultaneous determination of pesticide residues in Isatis indigotica Fort. with acceptable recoveries and repeatability and an adequate limit of determination.     

气相色谱-质谱法分析蜂蜜中的多种农药残留

开展了蜂蜜中23种农药残留的气相色谱-电子轰击离子源质谱(GC-EI/MS)分析方法的研究,并对其中3种农药的EI/MS碎片离子的断裂机理与结构进行了初步解析。探讨了蜂蜜试样前处理条件的优化与选择。将蜂蜜试样用乙酸乙酯提取剂超声提取、Florisil硅藻土色谱柱净化和正己烷-乙酸乙酯(体积比为7∶3)混合洗脱剂洗脱后,以PCB103为内标物,采用选择离子监测(SIM)方式下的GC-EI/MS分析。当试样的加标浓度为50,100和200 μg/kg时,加标回收率为82%～120%,相对标准偏差小于11.0%。23种农药的检测限都小于10.0 μg/kg,线性范围为10～500 μg/kg,相关系数都大于0.995。此分析方法已成功地应用于蜂蜜中23种痕量农药残留的分析。     

Determination of eight sulfonamides in bovine kidney by liquid chromatography/tandem mass spectrometry with on-line extraction and sample clean-up

A sensitive, high performance liquid chromatography/tandem mass spectrometric (i.e. mass spectrometry/mass spectrometry; LC/MS/MS) method with on-line extraction and sample clean-up for the screening and confirmation of residues of sulfonamides in kidney is described. The sulfonamides are extracted from homogenized kidney with methanol. After centrifugation of the extract, an aliquot of the extract is directly injected on the LC/MS/MS system with further extraction and clean-up of the sample on-line. Detection of the analytes was achieved by positive electrospray ionization (ESI) followed by multiple reaction monitoring. For each sulfonamide the collisional decomposition of the protonated molecule to a common, abundant fragment ion was monitored. The method has been validated for sulfadimethoxine, sulfaquinoxaline, sulfamethazine, sulfamerazine, sulfathiazole, sulfamethoxazole, sulfadiazine and sulfapyridine. Calibration curves resulting from spiked blank kidney samples at the 10-200 microg/kg level showed good linear correlation. At the level of 50, 100 and 200 microg/kg both within- and between-day precision, as measured by relative standard deviation (RSD), were less than 16%. The limits of detection (LODs) ranged from 5 to 13.5 microg/kg. The recoveries ranged from 78 to 82%. The procedure provides a rapid, reliable and sensitive method for the determination of residues of sulfonamides in bovine kidney. The advantage of this method over existing methods is its decreased sample preparation and analysis time, which makes the method more suitable for routine analysis.     

固相萃取–气相色谱–串联质谱法测定茶叶中9种农药残留量

建立固相萃取净化–气相色谱–串联质谱法同时测定茶叶中9种农药残留量的方法。茶叶样品用乙腈均质提取,提取液经固相萃取净化处理后,采用DB–5MS毛细管色谱柱分离,在多反应监测模式下测定,外标法定量。9种农药组分的质量浓度在0.01~0.50 mg/L范围内与其色谱峰面积呈良好线性,相关系数r~2大于0.998,方法测定下限(10 S/N)为0.002~0.01 mg/kg。以空白绿茶、红茶、普洱茶和乌龙茶为基体,在0.05,0.1,0.2 mg/kg 3个添加水平进行加标回收试验,加标回收率在73.6%~99.7%之间,相对标准偏差为4.2%~8.7%(n=6)。该法操作简便、快速,适用于茶叶中多种农药残留的测定。     

液相色谱-串联质谱法测定肉及肉制品中利谷隆及其代谢产物3,4-二氯苯胺残留

建立了液相色谱-串联质谱分析多种肉及肉制品中利谷隆及其代谢产物3,4-二氯苯胺残留的方法。样品用丙酮-乙腈(5:95, v/v)提取,冷冻去脂,经弗罗里硅土固相萃取柱净化后进行液相色谱-串联质谱检测,采用内标法定量。利谷隆及3,4-二氯苯胺在1～500 μg/L范围内呈良好的线性关系,相关系数(r)均大于0.998,方法的定量限(信噪比(S/N)＞10)为10 μg/kg,检出限(S/N＞3)为5 μg/kg。在各种肉及肉制品基质中添加低、中、高3种不同水平的利谷隆及3,4-二氯苯胺,其回收率范围分别为88.3%～101.2%和91.6%～101.6%,相对标准偏差(RSD)分别为4.8%～13.7%和4.7%～11.8%。结果表明所建立的方法可以满足肉及肉制品中利谷隆和3,4-二氯苯胺残留量的检测需要。     

Multi-class confirmatory method for analyzing trace levels of tetracyline and quinolone antibiotics in pig tissues by ultra-performance liquid chromatography coupled with tandem mass spectrometry

An ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC/MS/MS) method was developed to screen and confirm multi-class veterinary drug residues in pig tissues including pig kidney, liver and meat. Twenty-one drugs of two different classes including seven tetracyclines and four types of quinolones (quinoline, naphthyridine, pyridopyrimidine and cinoline) were determined simultaneously in a single run. The homogenized sample tissues were extracted with EDTA-McIlvaine buffer solution and further purified using a polymer-based Oasis HLB solid-phase extraction (SPE) cartridge. An ACQUITY UPLC BEH C18 column was used to separate the analytes followed by tandem mass spectrometry using an electrospray ionization source. MS data acquisition was performed in the positive ion multiple reaction monitoring mode, selecting two ion transitions for each target compound. Recovery studies were performed at different fortification levels. The overall average recoveries from pig muscle, kidney, and liver fortified with quinolones and tetracyclines at three levels ranged from 80.2 to 117.8% based on the use of matrix-fortified calibration with the coefficients of variation ranging from 2.1 to 17.8% (n=6). The limits of quantitation (LOQs) of quinolones and tetracyclines in different tissues ranged from 0.03-4.50 microg/kg and 0.16-10.00 microg/kg, respectively. The effects of the extraction solvent, SPE cartridge, elution solvent and sample matrix on the analyte recovery as well as the effects of the mobile phase composition and column temperature on the chromatographic behavior were also studied.     

Rapid determination of nitroimidazole residues in honey by liquid chromatography/tandem mass spectrometry

We developed a rapid and efficient means of determining residues of four nitroimidazoles-i.e., dimetridazole, ipronidazole, metronidazole, and ronidazole-and three hydrophilic metabolites- i.e., 2-hydroxymethyl-1-methyl-5-nitroimidazole, 1 -methyl-2-(2'-hydroxyisopropyl)-5-nitroimidazole, and 1-(2-hydroxyethyl)-2-hydroxymethyl-nitroimidazole--in honey. We applied a QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) procedure improved to suit a nitroimidazole analysis, which is fast (approximately 30 min) and uses less organic solvent. The procedure involves initial single-phase extraction of 5 g of honey with acetonitrile containing 1% acetic acid, followed by liquid-liquid partitioning involving the addition of 5 g sodium chloride, 1.5 g trisodium citrate dihydrate, and 4 g magnesium sulfate. Moreover, matrix from honey was reduced by an SPE method with an alumina-N cartridge. The samples were analyzed using LC/MS/MS. Chromatographic separation of these nitroimidazoles and metabolites was performed in the gradient mode on a pentafluorophenylpropyl-bonded silica column (150x2.0 mm, 3 pm particle size) at 40 degrees C. The mobile phase consisted of a 0.01% acetic acid solution and acetonitrile, and the flow rate was 0.2 mL/min. The method was validated using honey spiked with these nitroimidazoles from 0.1 to 0.5 microg/kg. The overall recovery of the seven nitroimidazoles ranged from 76.1 to 98.5%; intra- and interassay CV values were <9.5 and <14.2%, respectively. The LOQ ranged from 0.1 to 0.5 microg/kg. LC/MS/MS coupled with the QuEChERS method showed good potential as a method for determining nitroimidazole residues in honey.     

Confirmatory assay for the simultaneous detection of penicillins and cephalosporins in milk using liquid chromatography/tandem mass spectrometry

A high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the detection of residues of penicillins and cephalosporins in milk has been developed. After a simple extraction with acetonitrile, the extract was directly injected into the LC/MS/MS system on a C(18) column. A gradient consisting of acetonitrile and water, each containing 0.1% formic acid, was applied. The abundant parent ions [M + H](+) produced by positive electrospray ionisation were selected for fragmentation with argon. For each compound at least one fragment was recorded with multiple reaction monitoring. The limits of detection ranged from 1.5 to 25 microg/kg and the limits of quantification ranged from 4 to 50 microg/kg. Recoveries were examined at three levels (MRL, 0.5 x MRL, 2 x MRL) and ranged from 57 to 88%. The coefficients of variation obtained for the repeatability experiments were in agreement with those specified by the Horwitz equation. Linearity was checked by injecting extracts of samples spiked with increasing amounts of the different standards ranging from 0 to 150 microg/kg. The advantage of this method over existing methods is the very simple sample pre-treatment which makes the method very suitable for routine analysis.     

A novel approach for simultaneous determination of 2-mercaptobenzimidazole and derivatives of 2-thiouracil in animal tissue by gas chromatography/mass spectrometry

A novel approach for determination of 2-mercaptobenzimidazole (MBI) and other thyreostatic residues in animal tissues by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring mode was developed. The analytes in animal tissues (including hypothyroid, pork muscle and beef samples) were extracted by acetonitrile, and then purified by a matrix solid-phase dispersion (MSPD) procedure after the extraction residues had been dissolved in water. The thyreostatic residues were derivatized by pentafluorobenzyl bromide (PFBBr) under strong basic conditions and then N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) before GC/MS analysis. Different kinds of solid supports with various polarities for the MSPD procedure were investigated, and it was found that silica gel was suitable for the purpose. The average recoveries of the thyreostatic drugs in animal tissues ranged from 71.5-96.9% with the relative standard deviations below 10%. By using the developed method, the limits of detection were 10 microg/kg for MBI; 5 microg/kg for 6-phenyl-2-thiouracil; and 2 microg/kg for 2-thiouracil, 6-methyl-2-thiouracil and 6-propyl-2-thiouracil. The stability of the thyreostatic drugs in spiked animal tissues was tested, and the results showed that the thyreostatic drugs did not decompose within 3 months if the sample was stored in darkness below -20 degrees C.     

高效液相色谱-串联质谱法测定食品中20种氨基甲酸酯类农药残留

建立了食品中20种氨基甲酸酯类农药残留量的高效液相色谱-串联质谱联用(HPLC-MS/MS)测定与确证方法。20种氨基甲酸酯类农药在0.005～0.1 mg/kg范围内线性良好,相关系数为0.991 7～0.999 6;在0.005～0.025 mg/kg范围内, 20种目标物的回收率为51.2%～125.0%,相对标准偏差为1.4%～19.8%。该方法准确、灵敏、快速,可满足国际上对食品中这20种氨基甲酸酯类农药残留量的检测需要。     

液相色谱-电喷雾串联四极杆质谱法测定鸡肉中17种磺胺类药物的残留

建立了鸡肉中17种磺胺类药物残留量的液相色谱-电喷雾串联四极杆质谱测定方法。以稳定同位素13C6-磺胺二甲基嘧啶作为内标,采用多反应监测定量。样品经过匀浆、乙腈提取、正己烷脱脂、硅胶柱净化后进行液相色谱-质谱分析。采用Capcell Pak C8DD色谱柱,以均含0.2%甲酸的水和甲醇为流动相进行梯度洗脱。方法检出限为0.02~1 μg/kg,17种磺胺类药物的加标回收率为52.3%~124.9%（添加水平为1,5,10　μg/kg),相对标准偏差为1.0%~17.6%。     

Development of a rapid and sensitive method for the simultaneous determination of 1,2-dibromoethane, 1,4-dichlorobenzene and naphthalene residues in honey using HS-SPME coupled with GC-MS

A new method for the simultaneous determination of 1,4-dichlorobenzene (p-DCB), naphthalene and 1,2-dibromoethane (1,2-DBE) residues in honey has been developed. Analysis is carried out using gas chromatography-mass spectrometry (GC/MS) in selected ion monitoring mode (SIM), after extraction and preconcentration of target analytes by headspace solid-phase microextraction (HS-SPME), with a 100 microm film thickness polydimethylsiloxane (PDMS) fiber. Several parameters affecting the extension of the adsorption process (i.e., addition of salt, extraction time, extraction temperature) were studied. The optimal conditions for the determination of these analytes were established. The proposed HS-SPME method showed good sensitivity, without carryover between the samples. Linearity was studied from 5 to 2500 microg kg(-1) for p-DCB, 0.5 to 500 microg kg(-1) for naphthalene and 5 to 500 microg kg(-1) honey for 1,2-DBE with correlation coefficients (r(2)) ranging from 0.9901 to 0.9999. Precision was assessed and both intra and inter-day R.S.D.s (%) were below 6.3%. The detection limits were found to be 1, 0.1 and 2 microg kg(-1) honey for p-DCB, naphthalene and 1,2-DBE, respectively. The percentage recoveries that were evaluated with the proposed HS-SPME method and the standard addition calibration technique gave values among 72.8 and 104.3% for measurements in samples spiked with one target analyte or mixtures of the three. This method has been applied for the analysis of unknown honey samples. The results showed an excellent applicability of the proposed method for the determination of the target compounds in honey samples.     

Application of a mixed-mode solid-phase extraction and cleanup procedure for LC/MS determination of thiabendazole and carbendazim in apple juice

Recently, a mixed-mode solid-phase extraction (SPE) procedure was developed for rapid extraction and cleanup for determination of the fungicides thiabendazole and carbendazim in various fruit juices. This paper reports the application of that sample preparation procedure to the liquid chromatographic/mass spectrometric determination of these fungicides in apple juice with detection by positive electrospray ionization mass spectrometry (ESI/MS). Response was linear for sample concentrations from 2 to 500 microg/L (ppb). Recoveries averaged 74% (9% RSD) for carbendazim and 93% (9% RSD) for thiabendazole. After SPE cleanup, no matrix supression was observed for the ESI+ response for either compound studied. The method was applied to the analysis of incurred residues in 4 store-bought apple juices; carbendazim levels ranged from 10 to 70 microg/L and thiabendazole levels ranged from less than 2 to 130 microg/L.     

超高效液相色谱-电喷雾三重四极杆质谱法测定中药中马兜铃酸A和B的含量

利用超高效液相色谱-电喷雾三重四极杆质谱仪建立了中药中马兜铃酸A和B的定性定量分析方法。选取柴胡、生甘草、桔梗、龙胆泻肝丸、消胖丸、减肥茶等14种代表性样品,用甲醇-水(70:30, v/v)溶液加热回流提取,经Oasis MAX固相萃取柱富集净化后,在Eclipse RP HD C18反相柱(150 mm×2.1 mm, 1.8 μm)上进行分离;流动相为5 mmol/L乙酸铵水溶液(pH 7.5)-乙腈(75:25, v/v)。采用电喷雾离子源正离子模式(ESI+)和多反应监测模式(MRM)进行质谱分析。马兜铃酸A和B的线性范围分别为0.5～200 μg/L和1～200 μg/L,相关系数(r2)均大于0.995;检出限(LODs)分别为5 μg/kg和7.5 μg/kg;定量限(LOQs)分别为12.5 μg/kg和25 μg/kg。在100 μg/kg和500 μg/kg添加水平下,马兜铃酸A和B的回收率(n=6)范围分别为60.3%～96.4%和61.3%～94.7%,相对标准偏差均不大于10.2%。该方法灵敏度高,重复性好,操作简便,适用于中药材、饮片及中成药中马兜铃酸A和B的痕量检测。     

Multiwalled carbon nanotubes as a solid-phase extraction adsorbent for the determination of three barbiturates in pork by ion trap gas chromatography-tandem mass spectrometry (GC/MS/MS) following microwave assisted derivatization

A new method was developed for the rapid screening and confirmation analysis of barbital, amobarbital and phenobarbital residues in pork by gas chromatography-tandem mass spectrometry (GC/MS/MS) with ion trap MSD. The residual barbiturates in pork were extracted by ultrasonic extraction, cleaned up on a multiwalled carbon nanotubes (MWCNTs) packed solid phase extraction (SPE) cartridge and applied acetone-ethyl acetate (3:7, v/v) mixture as eluting solvent and derivatized with CH3I under microwave irradiation. The methylated barbiturates were separated on a TR-5MS capillary column and detected with an ion trap mass detector. Electron impact ion source (EI) operating MS/MS mode was adopted for identification and external standard method was employed for quantification. One precursor ion m/z 169 was selected for analysis of barbital and amobarbital and m/z 232 was selected for phenobarbital. The product ions were obtained under 1.0 V excitation voltage. Good linearities (linear coefficient R > 0.99) were obtained at the range of 0.5-50 microg kg(-1). Limit of detection (LOD) of barbital was 0.2 microg kg(-1) and that of amobarbital and phenobarbital were both 0.1 microg kg(-1) (S/N > or = 3). Limit of quantification (LOQ) was 0.5 microg kg(-1) for three barbiturates (S/N > or = 10). Satisfying recoveries ranging from 75% to 96% of the three barbiturates spiked in pork were obtained, with relative standard deviations (R.S.D.) in the range of 2.1-7.8%.