High-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry for the determination of flocoumafen and brodifacoum in whole blood

A high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) assay was developed and validated to determine quantitatively flocoumafen and brodifacoum in whole blood using warfarin as an internal standard (IS). Liquid-liquid extraction, using ethyl acetate, was used to isolate flocoumafen, brodifacoum and the IS from the biological matrix. Detection was performed on a mass spectrometer by negative electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The calibration curves were linear (r(2) > 0.998) in the concentration range of 0.1-100.0 ng ml(-1) with a lower limit of quantification of 0.05 ng ml(-1) for flocoumafen, and 0.1 ng ml(-1) for brodifacoum in whole blood. Intra-day and inter-day relative standard deviations (RSDs) were less than 8.0% and 10.8%, respectively. Recoveries of flocoumafen and brodifacoum ranged from 78.0% to 83.7%. This assay can be used to determine trace flocoumafen and brodifacoum in whole blood to investigate suspected poisoning of human and animals.     

High sensitive analysis of rat serum bile acids by liquid chromatography/electrospray ionization tandem mass spectrometry

Sensitive liquid chromatography (LC)/electrospray ionization (ESI) tandem mass spectrometry (MS) can be used to analyze the bile acid composition of rat serum. This method can analyze eight common bile acids and their glycine and taurine conjugates in 100 μl rodent serum by gradient elution on a reversed-phase column using a mixture of 20 mM ammonium acetate buffer (pH 8.0), acetonitrile and methanol as a mobile phase. Selected reaction monitoring analysis under negative ion detection mode allowed the achievement of a high sensitive assay with a simple solid phase extraction using an ODS cartridge column. We used this method to investigate the effect of a one-day fast on the concentration and composition of serum bile acids in rats. The results suggested that the method described here is useful for the dynamic analysis of serum bile acids in rats.     

Identification and determination of nucleosides in rat brain microdialysates by liquid chromatography/electrospray tandem mass spectrometry

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the determination of brain basal nucleosides (inosine, guanosine and adenosine) in microdialysates from the striatum and cortex of freely moving rats. A microdialysis probe was surgically implanted into the striatum or cortex of individual rats and Ringer's solution was used as the perfusion medium at a flow rate of 0.3 or 0.5 μl/min. The samples were then analyzed off-line by LC/MS/MS experiments. The separation of inosine, guanosine and adenosine was carried out on a cyano column using a mobile phase of 10 mM ammonium acetate, 1% acetic acid and 8% methanol at a flow rate of 0.4 ml/min. Analytes were detected by electrospray ionization tandem mass spectrometry in the positive ion mode. The detection limit for inosine, guanosine and adenosine was 80, 80 and 40 pg on column, respectively. With this method, the intercellular basal inosine, guanosine and adenosine concentrations in striatum and cortex of rat were determined.     

Simultaneous determination of lithospermic acid B and its three metabolites by liquid chromatography/tandem mass spectrometry

A rapid and sensitive method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed for the simultaneous determination of lithospermic acid B and its three main O-methylated metabolites in rat serum with silibinin as the internal standard. The calibration curves for LSB, and the three metabolites were linear over the ranges of 16–4096, and 8–2048 ng/ml, respectively, with coefficients of correlation >0.998. For LSB, the intra-assay coefficient of variance (CV) was less than 9.3% and the inter-assay CV was less than 8.9%. The inter-assay mean accuracy was between 92.8% and 104.7%. For the three metabolites, the intra-assay CV was less than 8.7% and the inter-assay CV was less than 9.9%. The inter-assay mean accuracy was between 92.5% and 107.9%. This quantitation method was successfully applied to a pharmacokinetic study of LSB in rats. Also, a total recovery of 5.2%was found in bile after oral administration.     

The effect of non-specific tight junction modulators on the transepithelial transport of poorly permeable drugs across airway epithelial cells

The epithelial barrier in the respiratory system is a major obstacle for drug delivery to the systemic circulation in the lung. Epithelial barrier hinders the transport of large macromolecules or polar drugs. Essential components of this epithelial fence are physical intercellular structures termed tight junctions. Therefore, modulating tight junctions can enhance paracellular transport across epithelial barrier. In this study, the effect of some of non-specific tight junction modulators (TJMs); (Sodium (Na) decanoate, oleic acid and ethyleneglycol-bis-(β-aminoethyl ether)-N, N′-tetraacetic acid (EGTA)) with established effect on intestinal tight junctions was evaluated for its effects on bronchial epithelial cells (Calu-3 cells). It was demonstrated that the effect of TJMs especially Na decanoate resulted in a reversible opening of tight junctions evidenced by the decrease in the transepithelial resistance. It was also demonstrated that this reduction of TEER upon exposing the epithelial cells to the TJMs resulted in a significant increase in Flu-Na (paracellular marker) and PXS25 (anti-fibrotic compound) transepithelial transport through this barrier. In conclusion, among the investigated non-specific TJMs, Na decanoate fulfilled the requirements of an effective, non-toxic and reversible tight junction modulator for Calu-3 lung epithelial cells.     

Quantification of arsenic compounds using derivatization, solvent extraction and liquid chromatography electrospray ionization tandem mass spectrometry

The difficulty in detecting inorganic arsenic compounds using conventional settings of mass chromatography has led to the use of derivatizing agents to aid in their detection. A recent study indicated that 2,3-dimercaptopropanol (BAL) could be used to derivatize arsenic compounds to make them detectable by LC coupled to UV detector. A speciation analysis method was then developed for arsenic compounds after derivatization using the LC–MS/MS with the aim to improve the sensitivity and specificity. The arsenic compounds were derivatized with BAL before solvent extraction was carried out. The resultant extract was analyzed using the LC–MS/MS. However, our finding showed that BAL, being a thiol, reduced the pentavalent arsenic compounds, As(V) to a trivalent state, As(III). The arsenic metabolites, monomethyl arsonate (MMA) and dimethyl arsenic acid (DMA) could also be reduced by BAL to As(V)– and As(III)–BAL adducts. Despite this, the assay could be used to quantify the total arsenic concentration as a summation of all these adducts, when speciation of individual arsenic species is not required. The developed LC–MS/MS assay was subsequently applied to detect arsenic compounds in rat urine samples after oral administration of arsenic trioxide.     

Analysis of iridoid glucosides in Hedyotis diffusa by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

An HPLC-DAD-ESI-MS/MS method was developed for analysis of iridoid glucosides (IGs) from Hedyotis diffusa Willd. The optimized separation condition was achieved with the Complex Sample Analysis Software System (CSASS) software, under which the whole analytes were achieved complete resolution especially for some isomeric IGs. Based on the UV and fragmentations, eleven IGs were detected. According to the fragmentation patterns of the three standard IGs, especially those of the isomeric standards, seven IGs including three pairs of isomers were unambiguous/tentatively identified. For the isomeric IGs with methyl ester or carboxyl group at C-4, the extents of the losses of CH(3)OH and/or H(2)O from their molecular and/or the aglycone adducts are useful for the differentiation of the stereoisomers in positive ion (PI) mode, which depends on the stereochemistry of the hydroxyl group on the cyclopentanoid unit.     

Identification of gentamicin impurities by liquid chromatography tandem mass spectrometry

An HPLC/MS/MS method was developed for identification of impurities in gentamicin. The HPLC was performed on a Synergy Hydro-RP column using 50 mM trifluoroacetic acid (TFA), pH 2 adjusted with ammonium solution and methanol as mobile phase. All impurities in gentamicin were separated from main gentamicin components. Atmospheric pressure chemical ionization (APCI) was used and product mass spectra of protonated molecules were acquired. Seventeen impurities were detected in gentamicin. Reference compounds: gentamicins: C_2b, B, B₁, G-418, sisomicin, garamine and gentamines: C₁, C_1a, C₂, C_2a were used for spectra interpretation and impurities identification. All MS/MS spectra were interpreted and fragmentation transitions for gentamicins and in general for aminoglycoside antibiotics (AG) were proposed. All impurities were identified. More than one isomere were proposed for three impurities.     

Comprehensive chemical analysis of Venenum Bufonis by using liquid chromatography/electrospray ionization tandem mass spectrometry

A rapid, sensitive and versatile liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for the comprehensive analyses of the chemical constituents contained in the Chinese medicine-Venenum Bufonis (VB, Chan’ Su in Chinese). LC analysis was carried out on an Agilent Eclipse plus C₁₈ RRHD column (2.1 × 150 mm, 1.8 μm) with a linear gradient solvent system of water (0.1% formic acid) and acetonitrile (0.1% formic acid) as mobile phase. Detection and quantification were performed by multiple reaction monitoring (MRM) transitions via electrospray ionization (ESI) source operating in the positive ionization mode. Through “Molecular Feature Extraction” (MFE), more than 900 features were detected from VB extracts. Among them, a total of 97 components were identified using the Agilent METLIN accurate mass matching database (DB) established according to those reported in the literatures. Further more, 30 high quality matches were obtained by comparisons of their accurate mass and retention times (AMRT) with those imported out in the developed personal database (METLIN DB with AMRT). The characteristic fragmentation pathways were proposed for the tentative characterization of four representative types of bufadienolides in the present work. The targeted MS/MS experiment of the 30 major compounds was performed for their quantification and semi-quantification. And 7 of them were quantified over the assaying concentration range of 5.0-500 pg/μL. The lowest limit of detection and quantification of them were 0.25-0.50 and 1.25-0.25 pg/μL, respectively. The recoveries varied from 83 to 106% depending on the chemical types and different extraction solvents. The remained 23 bufosteroids were simultaneously semi-quantified using three representative standard compounds as their standard references, respectively.     

Analysis of underivatized polyamines by reversed phase liquid chromatography with electrospray tandem mass spectrometry

A reversed phase liquid chromatography-electrospray ionization-tandem mass spectrometric method (RP-LC-ESI-MS/MS) was developed to separate and detect polyamines with minimal sample pre-treatment and without any derivatization. Prior to MS/MS analysis, a complete chromatographic separation of polyamines was achieved by a linear gradient elution using heptafluorobutyric acid as a volatile ion-pair modifier, and signal suppression was prevented by post-column addition of 75% propionic acid in isopropanol to the column flow. The developed method was successfully applied to the identification of metabolites formed from N(1),N(12)-diethylspermine in the reaction catalyzed by recombinant human polyamine oxidase and to the detection of eight different polyamines in a standard mixture.     

LC-ESI-MS/MS法测定人血浆中卢帕他定的浓度（英文）

目的建立测定人血浆中卢帕他定浓度的LC-ESI-MS/MS方法。方法血浆样品加入内标,碱化后用二氯甲烷：乙酸乙酯（20：80）提取,在37℃真空干燥箱中干燥至干,残渣用200μL流动相溶解后进样。色谱条件为：色谱柱为Agilent Eclipse XDB-C18（4.6mm×150mm,5μL）;流动相为乙腈（含1%甲酸）：20mmol·L^-1醋酸铵（76：24,V/V）,流速为0.6mL·min^-1。质谱条件：采用美国安捷仑1100高效液相色谱系统和离子阱（Agilent MSD Trap XCT）检测仪,质谱条件为电喷雾离子源,检测方式为正离子电离、多离子反应监测（MRM）,用于定量分析的离子为卢帕他定m/z416→309,内标氯雷他定m/z383→337。结果该方法应用于检测20名健康志愿者服药后的血浆样品。线性范围为0.05～14ng·mL^-1（r=0.998）,日内和日间精密度均低于15%,方法回收率为85.1%～114.0%。最低检测限为0.05ng·mL^-1（当n=5时,RSD=9.22%）。结论该方法灵敏、准确、快速,可用于该药药代动力学和生物等效性研究。     

基于液相色谱飞行时间质谱的炒川楝子化学成分分析

目的通过液相色谱飞行时间质谱(LC/QTOF MS)联用技术定性分析炒川楝子甲醇提取物中的主要化学成分。方法色谱分离采用Agilent ZORBAX SB-C18色谱柱(4.6 mm×150 mm,5μm),以1%甲酸—乙腈为流动相梯度洗脱,流速:1.0 mL.min-1,质谱定性采用飞行时间质谱,正负离子模式扫描。结果通过正、负离子质谱信息及元素组成分析并结合相关文献数据对照,鉴定出炒川楝子甲醇提取物中的11个成分。结论建立了一种基于LC/QTOF MS技术对炒川楝子中的化学成分进行鉴别的方法,为中药饮片炒川楝子的质量控制奠定了基础并为其深入研究和应用提供了依据。     

Detection of 10 sweeteners in various foods by liquid chromatography/tandem mass spectrometry

The analytical method for sweeteners in various food matrixes is very important for food quality control and regulation enforcement. A simple and rapid method for the simultaneous determination of 10 sweeteners [acesulfame potassium (ACS-K), aspartame (ASP), cyclamate (CYC), dulcin (DUL), glycyrrhizic acid (GA), neotame (NEO), neohesperidin dihydrochalcone (NHDC), saccharin (SAC), sucralose (SCL), and stevioside (STV)] in various foods by liquid chromatography/tandem mass chromatography (LC–MS/MS) was developed. The chromatographic separation was performed on a Phenomenex Luna Phenyl-Hexyl (5 μm, 4.6 mm × 150 mm) column with gradient elution of 10 mM ammonium acetate in water and 10 mM ammonium acetate in methanol. The recoveries of the 10 sweeteners were between 75% and 120%, and the coefficients of variation were less than 20%. The limits of quantification were 0.5 μg/kg for NHDC and SCL. For the other sweeteners, the limits of quantification were 0.1 μg/kg. Compared to the traditional high-performance liquid chromatography method, the LC–MS/MS method could provide better sensitivity, higher throughput, enhanced specificity, and more sweeteners analyzed in a single run. The samples included 27 beverages (16 alcoholic and 11 nonalcoholic beverages) and 15 pickled foods (1 pickled pepper, 3 candies, and 11 candied fruits). Two remanufactured wines were found to contain 7.2, 8.5 μg/g SAC and 126.5, 123 μg/g CYC, respectively. ACS-K, ASP, SCL, and NEO were detected in five beverages and drinks. The pickled peppers and candied fruits were found to contain SAC, GA, CYC, ASP, STV, NEO, and ACS-K. The wine with sweeteners detected was remanufactured wine, not naturally fermented wine. Therefore, the ingredient label for the sweeteners of remanufactured wine should be regulated by the proper authority for inspection of sweeteners.     

Methods for detection of anatoxin-a(s) by liquid chromatography coupled to electrospray ionization-tandem mass spectrometry

Anatoxin-a(s) is a potent irreversible inhibitor of the enzyme acetylcholinesterase with a unique N-hydroxyguanidine methylphosphate ester chemical structure. Determination of this toxin in environmental samples is hampered by the lack of specific methods for its detection. Using the toxic strain of Anabaena lemmermani PH-160 B as positive control, the fragmentation characteristics of anatoxin-a(s) under collision-induced dissociation conditions have been investigated and new LC-MS/MS methods proposed. Recommended ion transitions for correct detection of this toxin are 253 > 58, 253 > 159, 235 > 98 and 235 > 96. Chromatographic separation is better achieved under HILIC conditions employing a ZIC-HILIC column. This method was used to confirm for the first time the production of anatoxin-a(s) by strains of Anabaena oumiana ITEP-025 and ITEP-026. Considering no standard solutions are commercially available, our results will be of significant use for the correct identification of this toxin by LC-MS/MS.     

Plasma pharmacokinetics and tissue distribution study of cajaninstilbene acid in rats by liquid chromatography with tandem mass spectrometry

Cajaninstilbene acid (CSA; 3-hydroxy-4-prenyl-5-methoxystilbene-2-carboxylic acid) is a major active constituent of pigeonpea leaves, has been proven to be effective in clinical treatment of diabetes, hepatitis, measles and dysentery. A rapid and sensitive liquid chromatography tandem mass spectrometry (LC–MS/MS) method was developed and validated for the determination of CSA in rat plasma and various tissues (brain, heart, lung, liver, spleen, small intestine and kidney) of rat for the first time. Rat plasma and tissue distribution pre-treated by protein precipitation with acetoacetate was analyzed using LC–MS/MS with an electrospray ionization (ESI) interface, and isoliquiritigenin was used as an internal standard. Chromatographic separation was achieved on a HIQ Sil C₁₈ column with the mobile phase of water and methanol (9:91, v/v) containing 0.1% formic acid and resulted in a total run time of 10 min. The isocratic elution mode pumped at a flow rate of 1.0 mL/min. The lower limit of quantification (LLOQ) which was 10 ng/mL. The calibration curve was linear from 10 to 6000 ng/mL (R = 0.9967) for plasma samples and 10 to 6000 ng/mL (R ≥ 0.9974) for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 0.6% to 6.1% and 1.5% to 6.6%, respectively, and the intra- and inter-day assay accuracy was 93.5–104.6% and 93.3–107.5%, respectively. Recoveries in plasma and tissues ranged from 95.0% to 106.8%. The method was successfully applied in pharmacokinetic and tissue distribution studies of CSA after oral administration to rats. The pharmacokinetics of CSA showed rapid absorption and elimination (T_max, 10.7 ± 0.31 min; t_1/2, 51.40 ± 6.54 min). After oral administration in rats, CSA was rapidly and widely distributed in tissues. High concentrations were found in liver and kidney indicating that CSA was possibly absorbed by liver and eliminated by kidney.     

Imaging analysis of the gliadin direct effect on tight junctions in an in vitro three-dimensional Lovo cell line culture system

Tight junctions play a pivotal role in maintaining the integrity of the intestinal barrier. Their alteration is involved in the pathogenesis of celiac disease. Our aim was to investigate the gliadin effect on the tight junction proteins in an in vitro three-dimensional cell culture model through imaging analyses.Lovo multicellular spheroids were treated with enzymatically digested (PT) gliadin 500 μg/mL and its effect on actin, occludin and zonula occludens-1, was evaluated by means of confocal laser microscopy, transmission electron microscopy and image capture analysis.Compared to untreated spheroids, PT-gliadin-treated ones showed enlargement of the paracellular spaces (9.0 ± 6.9 vs. 6.2 ± 1.7 nm, p < 0.05) at transmission electron microscopy and tight junction protein alterations at confocal microscopy and image analyses. In untreated cell cultures thickness of the fluorescence contour of actin, zonula occludens-1 and occludin appeared significantly larger and more intense than in the treated ones. In occludin planimetric analysis the lengths of the integral uninterrupted cellular contour appeared longer in untreated than in PT-gliadin treated spheroids (71.8 ± 42.8 vs. 23.4 ± 25.9 μm, p < 0.01).Our data demonstrated that tight junction proteins are directly damaged by gliadin as shown by means of quantitative imaging analysis.     

Identification and determination of coumateralyl and coumafuryl in animal tissues by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) method was developed and validated to determine simultaneously coumafuryl and coumateralyl in animal tissues using warfarin as an internal standard (IS). Animal tissue samples were extracted with ethyl acetate and cleaned by Oasis HLB solid-phase extraction (SPE) cartridges. After pretreatment, the separation was performed on a XDB C18 column with an isocratic mobile phase of acetic acid-ammonium acetate (5 mmol l(-1), pH = 4.5)/methanol (30:70, v/v). Detection was carried out on a mass spectrometer by negative electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The calibration curves were linear (r(2) > 0.998) in the concentration range 0.75-100.0 ng g(-1) with a lower limit of quantification of 0.75 ng g(-1) for coumafuryl, and 0.5 ng g(-1) for coumateralyl in liver and kidney samples. Intra-day and inter-day relative standard deviations (RSDs) were less than 8.6% and 10.9%, respectively. Recoveries of coumafuryl and coumateralyl were in the range 81.5-89.5%. The developed assay has been applied to the determination of trace residues of coumafuryl and coumateralyl in animal tissues to investigate suspected poisoning of human and animals.     

Quantification of nitrated tryptophan in proteins and tissues by high-performance liquid chromatography with electrospray ionization tandem mass spectrometry

Aromatic amino acids are targets of reactive nitrogen species (RNS) such as peroxynitrite (ONOO(-)) and nitrogen dioxide. It is known that tryptophan (Trp) as well as tyrosine is nitrated, generated isomers. However, no quantitative method to determine nitrotryptophan (NO(2)Trp) in proteins has been developed so far. In this study, we have developed a method for the quantification of Trp and NO(2)Trp isomers, 2-, 4- and 6-NO(2)Trp, which uses liquid chromatography with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). In order to confirm the applicability of our method to in vitro and in vivo system, we measured protein-bound NO(2)Trp levels in ONOO(-) treated bovine serum albumin (BSA) and in liver of B6C3F1 mice at 2, 4, and 8h after administration of 300 mg/kg acetaminophen (APAP). A mass spectrometer equipped with an electrospray ionization source using a crossflow counter electrode and ran in the positive ion mode (ESI(+)) was used for multiple reaction monitoring (MRM) of transitions 205-->188, 250-->130, 250-->159 and 250-->233 for Trp, 2-, 4- and 6-NO(2)Trp, respectively. The recoveries from mice liver samples were 98.3-105.9% for each compound. The limits of quantification were 50, 3.0, 10 and 4.0 nM for Trp, 2-, 4- and 6-NO(2)Trp, respectively. In in vitro experiments demonstrated that all isomers of NO(2)Trp were detectable from BSA treated with ONOO(-) and the amount generated decreased in the order of 6-, 4- and 2-NO(2)Trp. In in vivo experiments, 4- and 6-NO(2)Trp were detected in the liver of mice administered APAP. The concentration range of 4- and 6-NO(2)Trp per mol of Trp in the sample was 2.24-3.92 and 26.96-32.71 nmol/mol of Trp, and its existence in vivo was confirmed for the first time with our method. The LC-ESI-MS/MS method was able to determine protein-bound NO(2)Trp in a small amount of tissue sample, and is therefore applicable not only as a biomarker of RNS, but also as a mean to clarify novel mechanisms underlying RNS-related tissue damage.     

高效液相色谱／质谱联用法测定槟榔食品中槟榔碱的含量

目的建立高效液相色谱-紫外-电喷雾质谱（HPLC—UV—ESI／MS）联用测定槟榔食品中槟榔碱的方法。方法以甲醇和0．1％三乙胺水溶液作流动相，在反相C18（5mm，250mm×4．6mm）柱上梯度淋洗，以质谱定性，紫外定量进行检测。结果在0．2～20μg／ml内峰面积和浓度呈良好的线性关系。结论该方法抗干扰能力强，可以快速、准确地测定槟榔食品中的槟榔碱。