Confirmatory method for macrolide residues in bovine tissues by micro-liquid chromatography-tandem mass spectrometry

A new confirmatory method for three macrolides (tylosin, tilmicosin and erythromycin) in bovine muscle, liver and kidney by micro-LC-MS-MS using an atmospheric pressure ionisation source and an ionspray interface has been developed. Roxithromycin was used as internal standard. The molecular related ions, [M+2H]2+, at m/z 435 for tilmicosin, and [M+H]+, at m/z 734 and 916 for erythromycin and tylosin, respectively, were the precursor ions for collision-induced-dissociation and two diagnostic product ions for each macrolide were identified for the unambiguous confirmation by selected reaction monitoring LC-MS-MS. Precision values (relative standard deviations) were all below 14.9%, whereas the overall accuracy (relative error) ranged from -17.7 to -9.8% for tylosin, from -17.5 to -10.7% for tilmicosin and from -19.6 to -13.7% for erythromycin, in all the investigated bovine tissues. The limits of quantification were 30 (muscle) or 40 (liver, kidney) microg kg(-1), 20 (muscle) or 150 (liver, kidney) microg kg(-1), 50 (muscle, liver) or 80 (kidney) microg kg(-1), 20 (muscle, liver) or 50 (kidney) microg kg(-1) for tylosin, tilmicosin, erytromycin and roxithromycin, respectively.     

Development and validation of a method for the confirmation of nicarbazin in chicken liver and eggs using LC-electrospray MS-MS according to the revised EU criteria for veterinary drug residue analysis.

A method is described for the quantitative confirmation of 4,4'-dinitrocarbanilide (DNC), the marker residue for nicarbazin in chicken liver and eggs. The method is based on LC coupled to negative ion electrospray MS-MS of tissue extracts prepared by liquid-liquid extraction. The [M-H]- ion at m/z 301 is monitored along with two transition ions at m/z 137 and 107 for DNC and the [M-H]- ion at m/z 309 for the internal standard, d8-DNC. The method has been validated according to the new EU criteria for the analysis of veterinary drug residues at 100, 200 and 300 microg kg(-1) in liver and at 10, 30 and 100 microg kg(-1) in eggs. Difficulties concerning the application of the new analytical limits, namely the decision limit (CCalpha) and the detection capability (CCbeta) to the determination of DNC in both liver and eggs are discussed.     

Rapid determination of chloramphenicol residues in milk powder by liquid chromatography-elektrospray ionization tandem mass spectrometry

A simple and rapid liquid chromatography tandem mass spectrometry (LC-ESI-MS-MS) confirmation method for the analysis chloramphenicol (CAP) in milk powder has been developed. Samples were extracted by using liquid-liquid extraction steps with ethyl acetate. Lipids were removed using hexsan. LC separation was achieved by using a Phenomenex Luna C-18 column and acetonitryle-water as a mobile phase. The mass spectrometer was operated in multiple reaction monitoring mode (MRM) with negative electro-spray interface (ESI-). The four transitions were monitored m/z 321-->257, 321-->194, 321-->152, 326-->157 (IS) and for quantification, the transition m/z 321-->152 was chosen. Validation of the method was done according to criteria of Decision Commission No 2002/657 EC. Validation includes the determination of specification, linearity, precision (within- and between-day), accuracy, decision limit (CC alpha) and detection capability (CC beta). Samples were fortified at CAP levels 0.30, 0.45 and 0.60 microg/kg with CAP-5d as internal standard. The precision within-day (RSD%) was lower than 12% and accuracy (RE%) ranged from -9.8 to -3.7%. The precision between-day (RSD%) was less than 15%. The limit of decision (CC alpha) and detection capability (CC beta) for milk powder 0.09 and 0.11 microg/kg. Value CC alpha and CC beta were calculated for the 321-->152 ion transition. This method has been successfully used for routine analysis.     

Quantitative determination of chloramphenicol in milk powders by isotope dilution liquid chromatography coupled to tandem mass spectrometry

A method is described for the determination of residues of the illegal antibiotic chloramphenicol (CAP) in milk powders. The analyte is quantified by liquid chromatography coupled to electrospray ionisation tandem mass spectrometry (LC-ESI-MS-MS) operating in negative ion multiple reaction monitoring mode (MRM) after a liquid-liquid extraction followed by a clean-up step on solid phase extraction (SPE) cartridge. Because of the presence of two chlorine atoms in the CAP molecule, four specific transition reactions of CAP were monitored by MS-MS in selecting m/z 321 --> 257, 321 --> 152 (35Cl2) and m/z 323 --> 257, 323 --> 152 (37Cl35Cl). Two calibration curves were constructed by plotting the area ratio of m/z 321 --> 152 versus 326 --> 157 and m/z 321 --> 257 versus 326 --> 262 against their corresponding amount ratio. Indeed, even if m/z 321 --> 152 was found to give a higher MS-MS response (calibration curve used by default), an interfering chemical substance was sometimes observed for some milk extracts and not for the transition m/z 321 --> 257. The quantitation method was validated according to the European Union (EU) criteria for the analysis of veterinary drug residues at 0.1, 0.2 and 0.5 microg/kg concentration levels using d5-CAP as internal standard. The decision limit (CCalpha) and detection capability (CCbeta) of CAP in milk were calculated for m/z 321 --> 152 at 0.02 microg/kg and 0.03 microg/kg, respectively, and for m/z 321 --> 257 at 0.02 microg/kg and 0.04 microg/kg, respectively. At the lowest fortification level (i.e. 0.1 microg/kg), repeatability and within-laboratory reproducibility were calculated for m/z 321 --> 257 both at 0.02 microg/kg and for m/z 321 --> 152 at 0.03 and 0.05 microg/kg, respectively. Moreover, the measurement of uncertainty of the analytical method was calculated at the same spiking levels and falls within the precision values of the within-laboratory reproducibility. This method can be applied to several types of milk powders (e.g. full cream, skim) and can serve as a monitoring tool to avoid that unacceptable levels of residues of CAP enter the food chain.     

气相色谱-质谱联用法测定动物组织中氯霉素、氟甲砜霉素和甲砜霉素的残留量

建立了气相色谱-负离子化学电离源质谱同时测定动物组织中氯霉素(CAP)、甲砜霉素(TAP)和氟甲砜霉素(FF)残留量的方法。样品用乙酸乙酯提取,正己烷分配去脂肪,再用Florisil柱进一步净化,甲苯作为反应介质,用N,O-双(三甲基硅基)三氟乙酰胺(BSTFA)-三甲基氯硅烷(TMCS)(体积比为99∶1)进行硅烷化处理,用间硝基氯霉素(m-CAP)作为内标进行测定。CAP的检测限可达到0.03 μg/kg,TAP和FF的检测限可达到0.2 μg/kg;上述3种药物的标准曲线的线性相关系数均大于0.99。CAP,FF和TAP的批内测定的精密度(以相对标准偏差表示)依次为5.5%,10.4%和8.8%;批间测定的精密度依次为7.4%,20.7%和19.1%。回收率为80.0%~111.5%,相对标准偏差为1.2%~15.4%。该方法前处理步骤简单,处理后杂质干扰少,灵敏度高,适用性强,可用于猪肉及禽类、水产品等多种动物组织中氯霉素类药物残留的检测。     

Determination of the antibiotic chloramphenicol in meat and seafood products by liquid chromatography-electrospray ionization tandem mass spectrometry

A confirmatory method based on isotope dilution liquid chromatography-electrospray ionization tandem mass spectrometry is described for the determination of the antibiotic chloramphenicol (CAP) in foods. The method is quantitative and entails liquid-liquid extraction followed by a clean-up step on a silica gel solid-phase extraction cartridge. Mass spectral acquisition is done in the negative ion mode applying multiple reaction monitoring of two diagnostic transition reactions for CAP (m/z 321 --> 257 and m/z 321--> 152). In addition, the presence of two chlorine atoms in the CAP molecule provides further analyte certainty by assessing the 37Cl/35Cl ratio using the transition reactions m/z 323 --> 257 and m/z 323 --> 152. Validation of the method in chicken meat is conducted according to the latest European Union criteria for the analysis of veterinary drug residues at levels of 0.05, 0.10, and 0.20 microg/kg, employing [2H5]-chloramphenicol as internal standard. The decision limit and the detection capability were calculated at 0.01 microg/kg and 0.02 microg/kg, respectively. At the lowest fortification level (i.e. 0.05 microg/kg), precision values below 14 and 17% were achieved under repeatability and within-laboratory reproducibility conditions, respectively. The accuracy of the method was within 20, 15, and 5% of the target values at the 0.05, 0.10, and 0.20 microg/kg fortification levels, respectively. The applicability of this procedure was demonstrated by the analysis of other meat (turkey, pork, beef) and seafood (fish, shrimps) products. The method is robust and suitable for routine quality control operations, and more than 200 sample injections were performed without excessive pollution of the mass spectrometer or loss of LC column performance.     

Determination of the Fusarium mycotoxins, fusaproliferin and beauvericin by high-performance liquid chromatography-electrospray ionization mass spectrometry.

A method is described using LC-MS for the detection of the mycotoxins fusaproliferin (FUS) and beauvericin (BEA) in cultures of Fusarium subglutinans and in naturally contaminated maize. Protonated molecular ion signals for FUS and BEA were observed at m/z 445 and m/z 784, respectively. Collision induced dissociation of the readily dehydrated protonated molecular ion of the sesterterpene FUS (m/z 427) led to the loss of another water molecule (m/z 409) and acetic acid (m/z 385), while the cyclic lactone trimer BEA fragmented to yield the protonated dimer (m/z 523) and monomer (m/z 262), respectively. Detection of FUS was best performed in the MS-MS mode while BEA displayed a stronger signal in the MS mode. The on-column instrumental detection limits for pure FUS and BEA were found to be 2 ng and 20 pg (S/N=2) while those in naturally contaminated maize were 1 microg/kg and 0.5 microg/kg, respectively. Five South African strains of F. subglutinans were analyzed following methanol extraction of which four produced FUS at levels between 330 mg/kg and 2630 mg/kg while only three produced BEA at levels between 140 mg/kg and 700 mg/kg. Application of this method to naturally contaminated maize samples from the Transkei region of South Africa showed FUS at levels of 8.8-39.6 microg/kg and BEA at 7.6-238.8 microg/kg.     

Quantitative determination of ochratoxin A in kidneys by liquid chromatography/mass spectrometry

A sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for the quantitative determination of ochratoxin A (OTA) in kidney samples was developed. Ochratoxin B (OTB) was used as internal standard. Extraction of homogenized kidney samples was done by adding a chloroform/phosphoric acid mixture. Due to restriction of the sample size, less chloroform could be used than in previously described methods. Two different columns for clean-up were compared: strong anion exchange (Bond Elut SAX) and Extrelut NT columns. The high-performance liquid chromatography (HPLC) was used with gradient elution consisting of variable mixtures of formic acid (0.3%) in acetonitrile and formic acid (0.3%) in water. The mass spectrometer was operated in the positive ESI mode using multiple reaction monitoring. For OTA the precursor ion was m/z 404 while the product ions were at m/z 239 and m/z 341. For OTB the precursor ion was m/z 370 while the product ions were at m/z 205 and at m/z 324. A calibration curve of fortified kidney samples was used to quantify OTA. Method validation was performed according to Commission Decision 2002/657/EC. Decision limit (CCalpha), detection capability (CCbeta), precision, bias, trueness, specificity and measurement uncertainty were determined. In general, the best results were obtained using SAX clean-up. CCalpha and CCbeta were 0.11 and 0.25 microg kg(-1), respectively. Within-laboratory reproducibility (% CV) was 9, 9, and 5% for OTA-fortified kidney samples of 0.5, 1, and 2.5 microg kg(-1), respectively. Trueness (%) was 75, 69, and 57% for OTA-fortified kidney samples at 0.25, 0.5, and 1 microg kg(-1), respectively. Measurement uncertainty and expanded uncertainty were 14.85 and 29.70%, respectively. All criteria as laid down in Commission Decision 2002/657/EC were fulfilled. Therefore, this LC/ESI-MS/MS method can be used to monitor kidneys for OTA in the framework of Council Directive No. 96/23/EC.     

Detection and identification of zeranol in chicken or rabbit liver by liquid chromatography-electrospray tandem mass spectrometry

A sensitive, specific, and reliable liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for detection and identification of zeranol in chicken or rabbit liver. A homogenized liver sample was hydrolyzed with beta-glucuronidase/arylsulfatase, and the hydrolysate was extracted with ethyl ether. The supernatant was evaporated to dryness, and the residue was dissolved in chloroform and re-extracted with sodium hydroxide. After acidification, the extract was cleaned up on a C18 solid-phase extraction cartridge and analyzed by electrospray LC-MS/MS in the negative ion mode. The multiple reaction monitoring transition from both m/z 321 to 277 and m/z 321 to 303 was monitored for confirmation, and the product ion of 277 was used for quantitation. Separation was performed on a Waters XTettra C18 column (50 x 2.1 mm, 3.5 microm) combined with a safeguard column (Symmetry C18, 20 x 3.9 mm, 5 microm), using a gradient elution with acetonitrile and 20 mM ammonium acetate. Calibration curves were prepared and good linearity was achieved over the concentration ranges tested. For all liver samples fortified at 3 different levels of 1, 5, and 50 microg/kg, the overall recoveries and relative standard deviations were in the range of 61-90 and 8-13%, respectively. The limit of quantitation based on the assay validation was 1 microg/kg. The method had been used on a routine basis for detection and identification of zeranol in liver samples.     

Development and validation of an improved method for confirmation of the carbadox metabolite, quinoxaline-2-carboxylic acid, in porcine liver using LC-electrospray MS-MS according to revised EU criteria for veterinary drug residue analysis

A method is described for the quantitative determination of quinoxaline-2-carboxylic acid (QCA), the marker residue for the veterinary drug carbadox, in swine liver. Tissue is subjected to alkaline hydrolysis followed by liquid-liquid extraction. QCA residues are cleaned up using automated solid phase extraction (SPE), before a final liquid-liquid extraction step. Analysis is based on LC coupled to positive ion electrospray MS-MS, monitoring product ions at m/z 129, 102 and 75 for QCA and at m/z 106 for the internal standard (d4-QCA). The method has been validated according to draft revised EU criteria for analysis of veterinary drug residues, and is suitable for monitoring tissues taken under national surveillance schemes. The method has been validated at 3, 10, 30, 100 and 300 microg kg(-1). The method performance characteristics, CCalpha (decision limit) and CCbeta (detection limit) were determined to be 0.16 and 0.27 microg kg(-1), respectively. The described method, which is relatively rapid and applicable to large sample numbers, correlates well (r2 = 0.9799) with a widely used GC-MS assay for QCA.     

Liquid chromatography with electrospray ion-trap mass spectrometry for the determination of anatoxins in cyanobacteria and drinking water

Anatoxin-a (AN) and homoanatoxin-a (HMAN) are potent neurotoxins produced by a number of cyanobacterial species. A new, sensitive liquid chromatography/multiple tandem mass spectrometry (LC/MS(n)) method has been developed for the determination of these neurotoxins. The LC system was coupled, via an electrospray ionisation (ESI) source, to an ion-trap mass spectrometer in positive ion mode. The [M+H](+) ions at m/z 166 (anatoxin-a) and m/z 180 (homoanatoxin-a) were used as the precursor ions for multiple MS experiments. MS(2)bond;MS(4) spectra displayed major fragment ions at m/z 149 (AN), 163 (HMAN), assigned to [Mbond;NH(3)+H](+); m/z 131 (AN), 145 (HMAN), assigned to [Mbond;NH(3)bond;H(2)O+H](+), and m/z 91 [C(7)H(7)](+). Although the chromatographic separation of these neurotoxins is problematic, reversed-phase LC, using a C(18) Luna column, proved successful. Calibration data for anatoxin-a using spiked water samples (10 mL) in LC/MS(n) modes were: LC/MS (25-1000 microg/L), r(2) = 0.998; LC/MS(2) (5-1000(microg/L), r(2) = 0.9993; LC/MS(3) (2.5-1000 microg/L), r(2) = 0.9997. Reproducibility data (% RSD, N = 3) for each LC/MS(n) mode ranged between 2.0 at 500 microg/L and 7.0 at 10 microg/L. The detection limit (S/N = 3) for AN was better than 0.03 ng (on-column) for LC/MS(3) which corresponded to 0.6 microg/L.     

气相色谱-质谱法测定乳制品中光引发剂异丙基硫杂蒽酮的残留量

建立了采用气相色谱（GC）-质谱(MS)检测由包装材料迁移到乳制品中的光引发剂异丙基硫杂蒽酮残留量的方法。使用氘代蒽为内标,样品经Carrez试剂除蛋白质后用丙酮-正己烷(体积比为1∶1)提取,上层提取液用氟罗里硅土固相萃取小柱净化。采用单四极杆质谱进行样品筛选和定量,选取的监测离子为m/z 184,m/z 224,m/z 239,m/z 254(异丙基硫杂蒽酮)和m/z 80,m/z 94,m/z 188,m/z 160(氘代蒽)。疑似样品采用离子阱串联质谱法进行确证,选取的母离子和子离子分别为m/z 254,m/z 239(异丙基硫杂蒽酮)和m/z 188,m/z 160(氘代蒽)。本方法的测定低限(LOQ)分别为7.0 μg/L(GC-MS)和5.0 μg/L(GC-MS/MS),回收率为74.9%~89.6%。采用该方法对11种不同类型的乳制品进行了检测,发现了两例阳性样品。     

Comparative Analysis of Medroxyprogesterone Acetate Residue in Animal Tissues by ELISA and GC‐MS

Abstract

Medroxyprogesterone acetate is a xenobiotic growth promoter of meat‐producing animals. In this study, the liver, kidney, and muscle of rabbits were obtained after the medroxyprogesterone acetate was administrated successively for 5 days at 0.8 mg/kg and withdrawn for 7 days before slaughter. The medroxyprogesterone acetate residues were determined by ELISA method. The average residue in muscle, liver, and kidney, as 7, 6, and 23 µg/kg, respectively. Residues were confirmed by GC/MS by monitoring four ions, 373, 283, 265, and 145 m/z. A good correlation was observed between the GC/MS and ELISA methods.     

Application of positive ion chemical ionisation and tandem mass spectrometry combined with gas chromatography to the trace level analysis of ethyl carbamate in bread

A rapid, sensitive and selective method has been developed and validated for the analysis of the contaminant ethyl carbamate (EC) in bread products at the part-per-billion level. The new procedure uses positive ion chemical ionisation (PICI) and tandem mass spectrometry (MS/MS), combined with gas chromatography (GC), on a 'bench-top' triple-quadrupole mass spectrometer. Ammonia was the PICI reagent gas of choice because of its ability to produce abundant [M+H]+ and [M+NH4]+ ions from EC and deuterium-labelled EC (LEC) used as an internal standard. For identification and quantification, selected reaction monitoring (SRM) was used to follow the precursor-to-product ion transitions of m/z 107 --> 90, m/z 107 --> 62 and m/z 90 --> 62 for EC, as well as m/z 112 --> 63 for the LEC internal standard. The limits of detection and quantification were 0.6 and 1.2 microg kg(-1), respectively, and the recovery of the method was 101 +/- 10% at 10 microg kg(-1) and 98 +/- 5% at 100 microg kg(-1). The precision of the method, established under conditions of intermediate reproducibility, did not exceed a relative standard deviation of 7%. The quantitative performance of the new GC/PICI-SRM procedure compared favourably with that of a reference method based on GC/MS and selected ion monitoring (correlation coefficient, r = 0.997). However, the new method had the advantages of reduced sample preparation time, improved sensitivity and unambiguous identification of EC at all concentrations. Application of the new method to the analysis of 50 UK breads showed that levels of EC ranged from 0.6 to 2.3 microg kg(-1) in retail products and from 3.1 to 12.2 microg kg(-1) for breads prepared using domestic breadmaking machines (dry weight basis). Toasting bread in a domestic toaster led to increases of between two- and three-fold in mean EC concentrations.     

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-电喷雾串联质谱法测定蜂蜜中的林可胺类抗生素残留

建立了蜂蜜中林可胺类抗生素林可霉素和氯林可霉素的高效液相色谱-电喷雾串联质谱(HPLC/ESI-MS/MS)检测方法。样品经固相萃取提取净化、反相液相色谱分离后进行质谱分析,在选择反应监测模式(SRM) 下进行特征母-子离子对信号采集。根据保留时间、母离子和两个特征子离子信息进行定性分析,以共同的基峰离子m/z 126进行定量。两种抗生素的检测限(S/N=3) 为 0.1 μg/kg,定量限为 0.5 μg/kg,在1.0～200 μg/L时峰强度与质量浓度的线性关系良好(r2>0.996)。在1.0,5.0,20.0 μg/kg 3个添加水平,两种抗生素的平均回收率范围为80%～110%,日内测定结果的相对标准偏差小于8%,日间测定结果的相对标准偏差小于15%。结果表明,该法简单、灵敏,特异性强,适用于蜂蜜中林可胺类抗生素残留的分析确证。     

Alternative methodology for the analysis of progesterone, testosterone, and epi-testosterone in bovine liver and veal muscle

Research has shown that traditional solvent extraction procedures used for the analysis of endogenous steroids often give inconsistent recoveries and results. However, a single-laboratory validation of a liquid chromatography/tandem mass specrometry method using 2 product ions per transition for progesterone, testosterone, and epi-testosterone in bovine liver and veal muscle showed accuracy and precision to within 23% at concentrations ranging from 0.5 to 2.0 microg/kg. Homogenized samples were pretreated with methanol to denature endogenous enzymes. Following removal of methanol, samples were treated overnight with Helix pomatia beta-glucuronidase to deconjugate glucuronide conjugates. Alkali digestion of the samples in KOH solutions was done under shaking at 37 degrees C for 30 min. The digestate was extracted with methyl tert-butyl ether, and the extracts were cleaned by partitioning between acetonitrile-hexane, followed by solid-phase extraction cleanup on silica cartridges. In bovine liver, average recoveries exceeded 54% for all analytes, and the within-run assay coefficients of variations were < 6 and 13% for high (2.0 microg/kg) and low (0.3 microg/kg) analyte concentrations, respectively. In veal muscle, average recoveries exceeded 60%, and the analysis of blind spikes gave accuracy estimates of over 85%, with coefficients of variation (CVs) < 15% for all analytes. The CVs for the multiple reaction monitoring ion ratios for all compounds were < 22% for all validation data. The method meets the requirements for confirmatory methods as outlined in 2002/657/EC. An analyst is capable of processing up to 20 samples within 5 days.     

Determination of ethyl glucuronide in hair samples by liquid chromatography/electrospray tandem mass spectrometry

A method for the determination of ethyl glucuronide (EtG) in hair samples, using liquid chromatography/electrospray tandem mass spectrometry (LC/ESI-MS/MS), was developed and validated. The treatment of hair samples was as follows: to 100 mg of washed (dichloromethane followed by methanol, 1 ml each) and cut (1-2 mm) material, 700 microl of water, 20 microl of internal standard solution (pentadeuterated EtG, D(5)-EtG, 500 microg/l) and 20 microl of methanol were added. Samples were incubated at 25 degrees C overnight and then ultrasonicated for 2 h. Finally, 8 microl of the centrifuged solution (13,000 rpm) were analyzed by LC/ESI-MS/MS in negative ion mode. The surviving ions of EtG and D(5)-EtG were monitored together with the following MRM transitions: m/z 221 --> 75, m/z 221 --> 85 (EtG) and m/z 226 --> 75, m/z 226 --> 85 (D(5)-EtG). The method exhibited a mean correlation coefficient better than 0.9998 over the dynamic range (3-2000 pg/mg). The lower limit of quantification (LLOQ) and the limit of detection (LOD) were 3 and 2 pg/mg respectively. The intra- and interday precision and accuracy were studied at four different concentration levels (3, 5, 56 and 160 pg/mg) and were always better than 7% (n = 5). Matrix effects did not exceed 20%. The method was applied to several hair samples taken from autopsies of known alcoholics, from patients in withdrawal treatment, from social drinkers, from adult teetotalers and from children not exposed to ethanol, with EtG concentrations globally ranging from < or =2 to 4180 pg/mg.     

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%.     

Determination of a metabolite of nifursol in foodstuffs of animal origin by liquid–liquid extraction and liquid chromatography with tandem mass spectrometry

An analytical method has been developed for the detection of a metabolite of nifursol, 3,5‐dinitrosalicylic acid hydrazide, in foodstuffs of animal origin (chicken liver, pork liver, lobster, shrimp, eel, sausage, and honey). The method combines liquid chromatography and tandem mass spectrometry with liquid–liquid extraction. Samples were hydrolyzed with hydrochloric acid and derivatized with 2‐nitrobenzaldehyde at 37°C for 16 h. The solutions of derivatives were adjusted to pH 7.0−7.5, and the metabolite was extracted with ethyl acetate. 3,5‐Dinitrosalicylic acid hydrazide determination was performed in the negative electrospray ionization method. Both isotope‐labeled internal standard and matrix‐matched calibration solutions were used to correct the matrix effects. Limits of quantification were 0.5 μg/kg for all samples. The average recoveries, measured at three concentration levels (0.5, 2.0, and 10 μg/kg) were in the range of 75.8–108.4% with relative standard deviations below 9.8%. The developed method exhibits a high sensitivity and selectivity for the routine determination and confirmation of the presence of a metabolite of nifursol in foodstuffs of animal origin.