Application of ion-exchange cartridge clean-up in food analysis IV. Confirmatory assay of benzylpenicillin, phenoxymethylpenicillin, oxacillin, cloxacillin, nafcillin and dicloxacillin, in bovine tissues by liquid chromatography-electrospray ionization tandem mass spectrometry

A multiresidue analytical method was developed for the confirmation of benzylpenicillin (PCG), phenoxymethylpenicillin (PCV), oxacillin (MPIPC), cloxacillin (MCIPC), nafcillin (NFPC) and dicloxacillin (MDIPC) in bovine tissues using electrospray ionization liquid chromatography-tandem mass spectrometry (LC-ESI-MS-MS) with a product ion scan mode. All penicillins gave [M-H]-, [M-H-CO2]- and [M-H-141]- as the product ion, when [M-H]- was selected as the precursor ion. Combination of an ion-exchange cartridge clean-up and the LC-ESI-MS-MS method can reliably identify all of these penicillins fortified at a concentration of 0.05 mg/kg in bovine tissues, including liver, kidney and muscle. The limits of confirmation satisfy the maximum residue limits for each of the penicillins established by the World Health Organization, US Food and Drug Administration, European Union and Japan.     

液相色谱-电喷雾串联质谱法检测鸡组织中5种聚醚类药物残留

建立了鸡组织中聚醚类药物多残留检测的高效液相色谱-电喷雾串联质谱方法。采用甲醇提取鸡组织中的拉沙洛菌素、盐霉素、莫能菌素、甲基盐霉素和马杜霉素,经硅胶柱净化,以乙腈(含0.1%甲酸)-0.1%甲酸水溶液(体积比为97:3)为流动相,Symmetry Shield RP18作为色谱分析柱,多反应监测(MRM)正离子扫描方式进行质谱检测。当5种聚醚类药物的添加水平为鸡肉0.1～1500 μg/kg、鸡肝0.2～4500 μg/kg时,平均回收率为71.6%～99.1%,日内测定的相对标准偏差(RSD)(n=5)为3.2%～10.7%,日间RSD(n=3)为4.6%～14.7%。2种鸡组织中5种聚醚类药物的定量限为0.1～1.0 μg/kg。该方法的灵敏度、准确度和精密度均符合兽药残留分析技术的要求,适用于鸡肉和鸡肝中5种聚醚类药物的多残留检测。     

液相色谱-电喷雾串联质谱法同时检测鸡组织中5种抗病毒类药物的残留量

建立了鸡组织中抗病毒类药物多残留检测的液相色谱-电喷雾串联质谱法(LC-ESI-MS/MS)。采用三氯乙酸-乙腈溶液提取鸡组织中的金刚烷胺、金刚乙胺、美金刚、咪喹莫特和吗啉胍,离心过滤后经强阳离子交换柱(SCX)净化,色谱柱Xamide(100 mm×2.1 mm, 5 μm)分离,多反应监测(MRM)正离子扫描方式进行质谱检测。结果表明,鸡组织与鸡肝中5种药物的检出限为0.06～0.30 μg/kg,定量限为0.2～1.0 μg/kg。当5种药物的添加水平为0.2～10.0 μg/kg时,在鸡肉中的平均回收率为72.3%～94.2%,相对标准偏差(RSD)(n=6)为3.5%～11.3%;在鸡肝中的平均回收率为70.8%～92.7%, RSD(n=6)为5.3%～12.6%。该方法选择性好,抗干扰能力强,可作为鸡肉和鸡肝中抗病毒药物残留检测的确证方法。     

Determination of tetrodotoxin in puffer-fish by liquid chromatography-electrospray ionization mass spectrometry

A simple and reliable method using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for the determination of tetrodotoxin in the puffer-fish has been developed. The LC separation was performed on a Shodex RSpak NN-414 column (15 cm x 4.6 mm id) using 20 mM ammonium acetate-methanol (75 + 25) as the mobile phase at a flow rate of 0.5 ml min(-1). The positive ionization produced the typical [M + H]+ molecular ion of tetrodotoxin (m/z 320). The calibration graph for tetrodotoxin was rectilinear from 0.01 to 1 microg ml(-1) with selected ion monitoring (SIM). Tetrodotoxin was extracted with 0.1% acetic acid by heating in a boiling water-bath and the extracts were cleaned up on a Bond Elut C18 (500 mg) cartridge. The recoveries of the tetrodotoxin from the puffer-fish fortified at 1 microg g(-1) were 77.7-80.7% and the detection limit was 0.1 microg g(-1) (equivalent to ca. 0.5 mouse units per gram).     

高效液相色谱-串联质谱测定猪肉中3种β-受体激动剂残留量

建立一种同时测定猪肉中3种β-受体激动剂残留量的高效液相色谱-电喷雾串联质谱(HPLC-ESI-MS/MS)确证分析方法。样品经β-葡萄糖醛酸酶/芳基硫酸酯酶酶解、乙酸铵缓冲液提取和MCX固相萃取柱净化,采用Agilent ZorbaxSB-C18(2.1mm×150mm,3.5μm)色谱柱,0.1%的甲酸水溶液、甲醇和乙腈作为流动相进行洗脱,高效液相色谱分离,电喷雾离子源电离,正离子多反应监测模式进行检测,内标法定量。3种药物在0.05～1μg/kg浓度范围内线性良好,相关系数r均大于0.999,0.05、0.1、0.5μg/kg3个浓度水平的添加回收率在89.7%～106.7%之间,相对标准偏差为2.4%～8.6%,3种药物的定量限均为0.05μg/kg。方法适用于猪肉中β-受体激动剂残留的确证分析。     

Quantification of zolpidem in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry

A simple and robust method for quantification of zolpidem in human plasma has been established using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS). Es-citalopram was used as an internal standard. Zolpidem and internal standard in plasma sample were extracted using solid-phase extraction cartridges (Oasis HLB, 1 cm3/30 mg). The samples were injected into a C8 reversed-phase column and the mobile phase used was acetonitrile-ammonium acetate (pH 4.6; 10 mm) (80:20, v/v) at a flow rate of 0.7 mL/min. Using MS/MS in the selected reaction-monitoring (SRM) mode, zolpidem and Es-citalopram were detected without any interference from human plasma matrix. Zolpidem produced a protonated precursor ion ([M+H]+) at m/z 308.1 and a corresponding product ion at m/z 235.1. The internal standard produced a protonated precursor ion ([M+H]+) at m/z 325.1 and a corresponding product ion at m/z 262.1. Detection of zolpidem in human plasma by the LC-ESI MS/MS method was accurate and precise with a quantification limit of 2.5 ng/mL. The proposed method was validated in the linear range 2.5-300 ng/mL. Reproducibility, recovery and stability of the method were evaluated. The method has been successfully applied to bioequivalence studies of zolpidem.     

Determination of quaternary ammonium pesticides by liquid chromatography-electrospray tandem mass spectrometry

A method for the direct determination of paraquat, diquat, chlormequat and difenzoquat in water samples, using an on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry system was developed. No sample preparation was required and the detection limits were below the European Union maximum residue levels. The chromatographic separation was performed using an XTera MS C8 column. The concentration of the ion pair reagent, the pH and the gradient elution were optimized to give high recoveries and good chromatographic resolution between quats. The detection was carried out using an ion trap as mass analyzer. Parameters such as the magnitude and duration of the resonant excitation voltage and the magnitude of the trapping RF voltage for full scan tandem mass spectrometry (MS-MS) experiments were studied to establish the optimal experimental conditions. Moreover, the accurate optimization of these parameters allowed MS-MS experiments of low mass ions, below m/z 200, providing unambiguous peak identification. Finally, the reproducibility of the proposed method was shown by good run-to-run and day-to-day precision values and its applicability to the determination of quats in drinking water was evaluated using spiked samples.     

Determination of the plant growth regulator chlormequat in food by liquid chromatography-electrospray ionisation tandem mass spectrometry

A confirmatory method for the determination of trace levels of chlormequat in a variety of different food matrices was developed. It entails a single clean-up step over a solid-phase cation exchange resin and subsequent liquid chromatography-electrospray ionisation tandem mass spectrometry using a stable isotopically labelled internal standard. Mass spectral acquisition was done in selected reaction monitoring mode, selecting the transitions from both the 35Cl and the 37Cl isotope of chlormequat. Recoveries after extraction and clean-up, determined with radio-labelled chlormequat and averaged over the spiking range (16-65 microg kg(-1)) in four different commodities, were within 88-96%, with a coefficient of variation better than 8%. The method can be applied to pears, pear juice concentrates, fruit purées, and cereal products, with typical limits of detection for chlormequat estimated at 2-5 microg kg(-1). A survey of different food commodities revealed that chlormequat was detectable--albeit at very low levels--in many of the food samples analysed, with the highest concentration recorded in pears purchased in Switzerland and of South African origin (5.5 mg kg(-1)). Measurements were also conducted on two LC-MS instruments and demonstrate the versatility and robustness of the method and its applicability to instruments of different ion source design.     

Determination of pyrrolizidine alkaloids in comfrey by liquid chromatography-electrospray ionization mass spectrometry

Symphytum officinale L. (comfrey) is a medicinal plant commonly used in decoctions and aliments. Besides therapeutic bioactive compounds present in the herb, it is found to contain hepatotoxic pyrrolizidine alkaloids (PAs), such as lycopsamine and others. In the present study, PAs such as lycopsamine, echimidine and lasiocarpine were determined using electrospray liquid chromatography-mass spectrometry (LC-MS) with the method precision (relative standard deviation, RSD) <10%. Detection of lycopsamine, symviridine and their N-oxides could be confirmed with a newly developed method based on HPLC ion-trap and orbitrap MS with electrospray ionization interface. With LC-MS, quantitative analysis of lycopsamine in the botanical extract was carried out. The effect of extraction solvent was optimized by sonication and methanol: H₂O (50:50) was selected. Then a rapid method based on pressurized hot water extraction (PHWE) was employed for the extraction of lycopsamine from comfrey followed by the comparison with heating under reflux with the RSD ranging from 2.49% to 19.32%. Our results showed a higher extraction efficiency for heating under reflux compared with PHWE. It was proposed that the lower extraction efficiency for PHWE was attributable to dissolved nitrogen from air which caused the reduction in the solubility of lycopsamine in the compressed hot solvent. In this study, quantitative analysis of PAs in comfrey was demonstrated. In addition, it was found that the use of subcritical water for extractions depended on the physical properties of the dissolved solutes and their tendency to degrade under the chosen extraction conditions.     

Determination of carnitine and acylcarnitines in urine by high-performance liquid chromatography-electrospray ionization ion trap tandem mass spectrometry

A high-performance liquid chromatography-mass spectrometry method has been developed for the simultaneous determination of native carnitine and eight acylcarnitines in urine. The procedure uses a solid-phase extraction on a cation-exchange column and the separation is performed without derivatization within 17 min on a reversed-phase C8 column in the presence of a volatile ion-pairing reagent. The detector was an ion trap mass spectrometer and quantification was carried out in the MS-MS mode. Validation was done for aqueous standards at ranges between 0.75 and 200 micromol/l, depending on the compound. Carnitine was quantified in urine and comparison with a radioenzymatic assay gave a satisfactory correlation (R2 = 0.981). The assay could be successfully applied to the diagnostic of pathological acylcarnitines profile of metabolic disorders in urines of patients suffering from different organic acidurias.     

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 abamectin in citrus fruits by liquid chromatography-electrospray ionization mass spectrometry

Liquid chromatography coupled to electrospray mass spectrometry (LC-ES-MS) with positive ion detection was used to determine abamectin in oranges. MS conditions were optimized to achieve maximum sensitivity. The main ion for abamectin was [M+Na]+ at a fragmentor voltage of 180 V. Abundant structural information can be obtained at different fragmentor voltages. The detection limit for the standard solution was 12 pg injected, and good linearity and reproducibility were observed. Abamectin residues were extracted using matrix solid-phase dispersion. Orange samples were homogenized with C18 bonded silica placed onto a glass column and eluted with dichloromethane. Recoveries of the abamectin from oranges fortified with approximately 0.01-10 mg/kg ranged from 94 to 99% with an overall average recovery of 96%. The quantification limit is 0.0025 mg/kg, which means detection limit for this analyte could be set at a few hundred picograms per gram of fruit. The presence in the electrosprayed solution of numerous citrus constituents did not interfere significantly with the ionization process of abamectin. The assay procedure provides a simple, rapid, and sensitive method for monitoring residues in oranges. The method was applied to field treatment orange samples.     

超高效液相色谱-串联质谱法同时测定聚合物食品包装材料中8种添加剂

建立了同时测定聚合物食品包装材料中8种常用添加剂Irgafos 168、Irganox 1010、Irganox 1076、丁基羟基茴香醚（BHA）、没食子酸丙酯（PG）、没食子酸十二酯（DG）、叔丁基对苯二酚（TBHQ）和苯三唑甲酚（UV-326）的超高效液相色谱-串联质谱方法。试样以二氯甲烷为溶剂进行超声提取;采用Waters BEH-C18柱（50 mm×2.1 mm,1.7 μm）分离,以0.05%甲酸水溶液和甲醇为流动相进行梯度洗脱;采用电喷雾离子源正、负离子切换模式和多反应监测模式进行检测。8种添加剂在相应的质量浓度范围内定量离子的峰面积与质量浓度均呈良好线性关系（相关系数R²均大于0.993）,回收率为63.9%~127.0%,相对标准偏差（RSD,n=6）≤15.8%,检出限（S/N=3）为0.13~5.50 μg/L,定量限（S/N=10）为0.45~17.50 μg/L。该方法简便快捷、灵敏度高,适合食品包装材料中常用添加剂的分析测定。     

Determination of betaine in Lycium chinense fruits by liquid chromatography-electrospray ionization mass spectrometry.

A rapid and sensitive high-performance liquid chromatography-electrospray mass spectrometric method has been developed for the determination of betaine in Lycium chinense fruits. Betaine was analyzed on a system consisting of a NH2 stationary phase and a mobile phase of water-acetonitrile (25:75) by isocratic elution for 40 min. Betaine was identified and quantitated by electrospray ionization mass spectrometry with selected ion monitoring of the protonated ion [Betaine+H]+ and clustered ions [nBetaines+H]+. The limit of detection for betaine by this method was ca. 0.2 ng/ml and the relative standard deviations of the assay (intra- and inter-day) were less than 8.1%.     

Analysis of sulfophthalimide and some of its derivatives by liquid chromatography-electrospray ionization tandem mass spectrometry.

A system was developed for the separation of sulfophthalimide (SPI), sulfophthalamide (SPAM), sulfophthalamic acid (SPAA) and sulfophthalic acid (SPA) by ion-pair liquid chromatography and their detection by electrospray ionization tandem mass spectrometry (ESI-MS-MS). Except for SPAM, the 3- and 4-sulfo-isomers of the analytes were separated by HPLC using volatile tributylamine as ion-pairing agent. Initial fragmentations of the analytes in the negative mode involve losses of CO2 or HNCO or condensation via H2O or NH3 elimination. ortho-Effects of the sulfonate group were recognized in the fragmentation of the respective 3-sulfo-isomers and allowed us to assign the order of elution of the SPAA isomers. Quantitative analysis of these sulfonated aromatic compounds with MRM detection was elaborated and resulted in detection limits ranging from 1 pg for SPA to 13 pg for SPAA isomers and in limits of quantification of 2-10 microg/L for 5 microL volumes of injected tap water, municipal wastewater or industrial effluents up to salt contents of 0.5-1 g/L. The method was applied to study the isomer-specific chemical and microbial transformations of SPI, which was previously shown to be formed by white-rot fungi from sulfophthalocyanine textile dyes.     

超高效液相色谱-电喷雾电离串联质谱联用法检测茶叶中阿维菌素类药物残留

建立了采用超高效液相色谱-电喷雾电离串联质谱同时检测茶叶中爱比菌素、甲胺基阿维菌素、乙酰胺基阿维菌素、伊维菌素、多拉菌素、莫西丁克残留的方法。试样经饱和氯化钠溶液浸润后,用乙腈提取,C18固相萃取小柱净化,超高效液相色谱-电喷雾串联质谱法(UPLC/ESI-MS/MS)测定。对流动相、监测离子、校正曲线等进行了优化和探讨。6种分析物在2.0～50 μg/L范围内线性关系良好,相关系数均大于0.9920。莫西丁克在5,10,20 μg/kg,其余分析物在2,5,10 μg/kg加标水平的平均回收率为61.7%～85.4%,相对标准偏差为9.37%～17.19%。该方法可靠、稳定,可满足茶叶中阿维菌素类药物残留检测与确证的需要。     

基于氨基柱的反相/正相液相色谱-电喷雾串联质谱法测定纺织品中的二硬脂基二甲基氯化铵

建立了纺织品中二硬酯基二甲基氯化铵(DSDMAC)的反相(RP)/正相(NP)液相色谱-电喷雾串联四极杆质谱(LC-ESI-MS/MS)的分析方法。选用甲醇为提取溶剂,确定了超声功率为420 W、提取温度为70 ℃的超声波辅助提取条件,实现了30 min快速提取样品中的DSDMAC。建立了基于氨基柱的反相和正相两套液相色谱分离系统,采用LC-MS/MS的选择反应监测(SRM)模式检测3个DSDMAC组分。结果显示: RPLC和NPLC对DSDMAC的检出限(S/N=3)分别为0.1 mg/kg和0.01 mg/kg。采用RPLC-MS/MS为定量方法,对8种不同的空白纤维纺织品的添加回收率为85.5%～103%(n=5);平行测试的相对标准偏差(RSD)为4.18%～12.8%(n=5)。5家外部实验室分别采用上述方法对2种参考样品中的DSDMAC进行检测,实验室间测定的RSD分别为7.3%和9.4%。该方法快速、准确、稳定,适用于纺织品中DSDMAC的检测。     

Determination of oxatomide in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry

A rapid, sensitive and specific high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method has been developed and validated for the determination of oxatomide in human plasma. Flunarizine hydrochloride was employed as the internal standard (IS). The analytes were chromatographically separated on a Shimadzu Shim-pack VP-ODS C18 column (250 x 2.0 mm i.d.) with a mobile phase consisting of methanol and aqueous ammonium acetate solution (10 mm, pH 4.0; 85:15, v/v). Detection was performed on a single quadrupole mass spectrometer using an electrospray ionization interface with the selected-ion monitoring (SIM) mode. The method showed excellent linearity (r = 0.9995) over the concentration range of 0.5-500 ng/mL with good accuracy and precision. The intra- and inter-batch precisions were within 10% relative standard deviation. The recoveries were more than 90%. The validated method was successfully applied to a preliminary pharmacokinetic study of oxatomide in Chinese healthy male volunteers.     

液相色谱-电喷雾串联质谱法测定冬青芽中的脱落酸

建立了测定植物中痕量脱落酸 (ABA) 的液相色谱-电喷雾串联质谱联用分析方法. 植物提取液先采用固相萃取 (SPE) 富集脱落酸并消除基体干扰, 然后以C18柱为固定相, V(甲醇)∶V(2 g/L甲酸水溶液)＝50∶50为流动相分离脱落酸. 电喷雾(ESI)串联质谱采用负离子模式. 选择反应监测 (SRM) 模式用于脱落酸定量, 选择的离子对是263→153, 219. 脱落酸的线性范围为0.005～10 μg/mL, 检测限 (S/N=3) 为0.003 μg/mL, 加标0.02 μg和0.05 μg的回收率分别为98.3% 和103.5%. 该方法用于冬青芽中脱落酸的分析, 结果表明所建立的SPE-LC-MS/MS方法对于分析植物中的痕量脱落酸是有效的.     

Determination of cyclamate in foods by high performance liquid chromatography-electrospray ionization mass spectrometry

A high sensitive method for determination of cyclamate in foods by ion-pair high-performance liquid chromatography-electrospray ionization mass spectrometry was developed and validated. The separation was achieved on a C₈ column with 5 mM tris(hydroxymethyl)aminomethane aqueous solution (pH 4.5, adjusted by acetic acid) as mobile phase with an isocratic mode. The quantification of target compound was completed using a selected ion recording (SIR) at m/z 178 obtained from ESI-mode. Tiopronin was used as internal standard for the quantification of cyclamate. The correlation coefficient of the calibration curve were better than 0.996, in the range of 50-5000 ng/mL. The limit of detection is 5 ng/mL, the limit of quantification is 20 ng/mL. The inter- and intra-day accuracy, precision were investigated in detail. The method can be used to monitor effectively the content of the artificial sweetener in foods. The method has obvious merits such as high sensitivity, specificity and simply versus other methods reported.