Simultaneous determination of quinolone antibacterials in bovine milk by liquid chromatography-mass spectrometry

A new liquid chromatography-mass spectrometry (LC-MS) method has been developed and validated for the simultaneous determination of eight quinolone antibacterials for veterinary use in processed bovine milk samples. The quinolones studied included marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid and flumequine. Also, a new sample-treatment procedure was used for extraction and preconcentration of these compounds. It involved defatting by centrifugation, protein precipitation by adding a mixture of glacial acetic acid-acetonitrile and removing acetonitrile with dichloromethane; finally, the acidified aqueous layer was evaporated to dryness in a speed vac system, resuspended in the mobile phase and filtered prior to LC injection. The mobile phase was composed of a formic acid aqueous solution 0.1% (v/v) and acetonitrile, with an initial composition of water-acetonitrile 95: 5 (v/v) and using linear gradient elution. Norfloxacin was used as internal standard. The limits of quantification found (2-7 ng g(-1)) were in all cases lower than the maximum residue limits tolerated by the European Union for these compounds in milk.     

Capillary electrophoretic separation of dicarboxylic acids in atmospheric aerosol particles

2,3-Pyrazinedicarboxylic acid (PZDA), 2,6-pyridinedicarboxylic acid (PDA) and 2,3-pyridinedicarboxylic acid (QUIN) solutions were studied as background electrolytes (BGEs) in the capillary electrophoretic analysis of dicarboxylic acids in aerosol particles with indirect UV detection. The BGEs were selected on the basis of similarity in structure with the analytes so that mobilities would be compatible. Optimised pH values for PZDA, PDA and QUIN solutions were 10.6, 11.0 and 10.2, respectively. Myristyltrimethylammonium hydroxide and myristyltrimethylammonium bromide were added to reverse the electroosmotic flow in the solutions in the direction of anode to enable fast anion detection. Separation was obtained for nine dicarboxylic acids (C₂–C₁₀) differing in the number of CH₂ groups in their skeleton. The electrophoretic mobilities were determined to lie in the range 3.0×10⁻⁴–7.0×10⁻⁴ cm² V⁻¹ s⁻¹. The relative standard deviations (RSDs) for the absolute migration times of the analytes were mostly less than 0.5% (n=6) in PZDA solution. In PDA solution the within-day and day-to-day RSD values for migration were less than 1% and between 2 and 4%, respectively. Peak heights and areas mostly deviated between 1 and 15% in both PZDA and PDA solutions. Detection limits ranged between 1 and 5 mg/l. Methods were applied to the analysis of dicarboxylic acids isolated from aerosol particles.     

Characterization of carboxylic acids in atmospheric aerosols using hydrophilic interaction liquid chromatography tandem mass spectrometry

A sensitive hydrophilic interaction liquid chromatography/electrospray ionization mass spectrometry (HILIC/ESI-MS/MS) method was developed for determination of selected aliphatic (i.e. malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, maleic, fumaric, glycolic and pyruvic acid), alicyclic (i.e. cis-pinonic and pinic acid) and aromatic (i.e. trimesic, phthalic acid and its isomers) carboxylic acids. Analytes were separated on an amide column using a gradient elution with a 10mM constant ionic strength mobile phase containing acetonitrile and aqueous ammonium acetate buffer (pH 5.0). The influence of the buffer type, pH, polar modifier and temperature on analyte retention under HILIC was studied. Static sonication-assisted solvent extraction was optimized for sample preparation prior to analysis. The recoveries obtained were higher than 90% for most analytes. The method was proven to be sensitive with limits of detection ranged from 0.03 to 16.0 μg/L in selected reaction monitoring mode (SRM). The repeatability and intermediate precision of the method, expressed as RSD (%) of the peak area ratio between analytes and their internal standards were generally lower than 5%. The method was successfully applied for determination of the studied acids in samples of ambient aerosol particles. A big advantage of the new method is also its ability to detect and separate the isobaric compounds of the selected carboxylic acids. Our results demonstrate that the method is specific and sensitive for the determination of a wider range of polar carboxylic acids at low concentrations in complex samples of aerosol particles.     

Determination of cyclobenzaprine in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry and its application in a pharmacokinetic study

A sensitive, rapid and simple liquid chromatography–electrospray ionization mass spectrometry (LC‐ESI‐MS/MS) method was developed for the quantitative determination of cyclobenzaprine in human plasma, to study the pharmacokinetic behavior of cyclobenzaprine capsule in healthy Chinese volunteers. With escitalopram as the internal standard (IS), sample pretreatment involved a one‐step liquid–liquid extraction using saturated sodium carbonate solution and hexane–diethyl ether (3:1, v/v). The separation was performed on an Ultimate XB‐CN column (150 × 2.1 mm, 5 µm). Isocratic elution was applied using acetonitrile–water (40:60, v/v) containing 10 m M ammonium acetate and 0.1% formic acid. The detection was carried out on a triple‐quadrupole tandem mass spectrometer in multiple reaction monitoring mode via electrospray ionization. The ion‐pairs including m/z 276.2–216.2 for cyclobenzaprine and m/z 325.2–109.1 for IS were used for monitoring. Linear calibration curves were obtained over the range of 0.049–29.81 ng/mL with the lower limit of quantification at 0.049 ng/mL. The intra‐ and inter‐day precision showed ≤6.5% relative standard deviation. The established method laid the groundwork for follow‐up studies and provided basis for the clinical administration of cyclobenzaprine. Copyright © 2011 John Wiley & Sons, Ltd.     

Confirmation and determination of carboxylic acids in root exudates using LC-ESI-MS

Reversed-phase liquid chromatography with UV detection is of limited applicability in the separation and identification of carboxylic acids because of the column's poor separation efficiency and the non-selective nature of the UV detector. To address this issue, RP-LC with electrospray ionization mass spectrometry has been explored for the confirmation and determination of carboxylic acids in plant root exudates, with ESI-MS providing structural information, high selectivity, and high sensitivity. The separation of 10 carboxylic acids (pyruvic, lactic, malonic, maleic, fumaric, succinic, malic, tartaric, trans-aconitic, and citric acid) was performed on a C(18) column using an eluent containing 0.1% (v/v) acetic acid within 10 min, where the acidic eluent not only suppressed the ionization of the carboxylic acids to be retained on the column, but was also compatible with ESI-MS detection. In addition, an additional standard was used to overcome the matrix effect. The results showed that peak areas correlated linearly with the concentration of carboxylic acids over the range 0.05-10 mg/L. The detection limits of target acids (signal-to-noise S/N ratio of 3) ranged from 20 to 30 microg/L. Finally, the proposed method was used for the confirmation and determination of low-molecular-weight carboxylic acids in plant root exudates, and provided a simple analytical procedure, including sample processing, fast separation, and high specificity and sensitivity.     

Determination of alkylphenol and bisphenol A in beverages using liquid chromatography/electrospray ionization tandem mass spectrometry

A comprehensive analytical method based on liquid chromatography electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS) with negative ionization mode has been developed for measuring of alkylphenols and bisphenol A in beverage samples. Concentration and clean up of samples were performed on 200 mg OASIS HLB solid extraction cartridges. The effects of mobile phases and additives on ionization were assessed. The recoveries for each compound ranged from 76.7 to 96.9% and reproducibilities were represented as having relative standard deviation (R.S.D.) below 10%. The limits of quantification (LOQ) of the method under multiple-reaction monitoring (MRM) acquisition mode were 0.04, 0.03 and 0.2 ng L⁻¹ for 2 L of mineral drinking water and 2.0, 1.8 and 8.0 ng L⁻¹ for 50 mL of soda beverages.     

Analysis of scopolamine and its eighteen metabolites in rat urine by liquid chromatography-tandem mass spectrometry

A rapid and sensitive method is described for the determination of scopolamine and its metabolites in rat urine by combining liquid chromatography and tandem mass spectrometry (LC–MS/MS). Various extraction techniques (free fraction, acid hydrolyses and enzyme hydrolyses) and their comparison were carried out for investigation of the metabolism of scopolamine. After extraction procedure, the pretreated samples were injected into a reversed-phase C18 column with mobile phase of methanol/ ammonium acetate (2 mM, adjusted to pH 3.5 with formic acid) (70:30, v/v) and detected by an on-line MS/MS system. Identification and structural elucidation of the metabolites were performed by comparing their changes in molecular masses (ΔM), retention-times and full scan MSⁿ spectra with those of the parent drug. The results revealed that at least 18 metabolites (norscopine, scopine, tropic acid, aponorscopolamine, aposcopolamine, norscopolamine, hydroxyscopolamine, hydroxyscopolamine N-oxide, p-hydroxy-m-methoxyscopolamine, trihydroxyscopolamine, dihydroxy-methoxyscopolamine, hydroxyl-dimethoxyscopolamine, glucuronide conjugates and sulfate conjugates of norscopolamine, hydroxyscopolamine and the parent drug) and the parent drug existed in urine after ingesting 55 mg/kg scopolamine to healthy rats. Hydroxyscopolamine, p-hydroxy-m-methoxyscopolamine and the parent drug were detected in rat urine for up 106 h after ingestion of scopolamine.     

How to identify and discriminate between the methyl quinates of chlorogenic acids by liquid chromatography-tandem mass spectrometry

The methyl esters of chlorogenic acids, methyl quinates, are widely distributed in plant materials and frequently appear as extraction artifacts in plant samples. This is the first time when liquid chromatography-tandem mass spectrometry methods have been used for the identification and characterization of the methyl quinates. For this purpose, methyl quinates of mono caffeoylquinic acids and mono feruloylquinic acids were synthesized as authentic standards. The methyl quinates of mono and diacyl chlorogenic acids have shown characteristic fragmentation pattern in their tandem mass spectra. MS(n + 1) spectra of the methyl quinates of diacyl chlorogenic acids were identical to MS(n) spectra of mono acyl derivatives. These quinates do not produce any methyl quinate peak at m/z 205 if compared with quinic acid peak at m/z 191 in negative ion mode. In the MS(n) spectra of these quinates, cinnamic acid part or cinnamoyl part was detected as a base peak in negative ion mode. The retention time, order of elution and fragmentation pattern were completely different if compared with LC-MS(n) methods developed for chlorogenic acids. These LC-MS(n) methods have been applied for the identification and regioisomeric characterization of the methyl quinates of chlorogenic acids in maté tea and woodruff (Galium odoratum). Two methyl caffeoylquinates (2 and 4) were identified as methyl 3-caffeoylquinate and methyl 5-caffeoylquinate.     

Determination of sialic acids by liquid chromatography-mass spectrometry

Sialic acids are widely found in nature as components of oligosaccharide units in mucins, glycoproteins and other microbial polymers. Existing methods for determining these acids are long, tedious, and not specific. A simple, rapid, and sensitive method for determining the most commonly occurring acids, N-acetylneuraminic and N-glycolylneuraminic acid, using LC-MS is described. Standard solutions of the sialic acids with the internal standard, N-acetylneuraminic acid methyl ester, were quantitatively analyzed by positive ion electrospray ionization. Fetuin was used as a model glycoprotein and the hydrolysate was injected directly onto an ES Industries AquaSep 3 microm 150x4.6 mm column eluted with a 0.1% aqueous formic acid mobile phase at a flow-rate of 0.5 ml/min. Detection was achieved using the Finnigan Navigator MS system in the selected ion monitoring mode for the protonated molecular ions at m/z 310, 324, and 326. The linearity over the dynamic range 10 to 1000 ng of sialic acids on-column had a correlation coefficient greater than 0.999. The amount of sialic acids found in the fetuin hydrolysate was in agreement with values reported in the literature.     

Liquid chromatography-mass spectrometry method for the determination of venlafaxine in human plasma and application to a pharmacokinetic study

A sensitive and selective liquid chromatographic-mass spectrometric (LC-MS) method for the determination of venlafaxine in human plasma has been developed. Samples were prepared using liquid-liquid extraction and analyzed on a C(18) column interfaced with a triple quadrupole mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase was methanol-water containing 10 mmol/L ammonium acetate, pH 7.9 adjusted with aqueous ammonia (80:20, v/v) at the flow rate of 1.0 mL/min. The analyte and internal standard clozapine were both detected by use of selected ion monitoring mode. The method was linear in the concentration range of 1.0-200.0 ng/mL. The lower limit of quantification (LLOQ) was 1.0 ng/mL. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 10.1%. The accuracy determined at three concentrations (5.0, 50.0 and 150.0 ng/mL for venlafaxine) was within +/-10.0% in terms of relative error (RE). The method was successfully applied for the evaluation of pharmacokinetic profiles of venlafaxine capsule in 20 healthy volunteers. The results show AUC, T(max), C(max) and T(1/2) between the testing formulation and reference formulation have no significant difference (p > 0.05). Relative bioavailability was 103.4 +/- 14.1%.     

Determination of polar organic compounds in atmospheric aerosols by gas chromatography with ion trap tandem mass spectrometry

A gas chromatography with ion trap mass spectrometry method has been developed and validated for the analysis of 27 polar organic compounds in atmospheric aerosols. The target analytes were low‐molecular‐weight carboxylic acids and methoxyphenols, as relevant markers of source emissions and photochemical processes of organic aerosols. The operative parameters were optimized in order to achieve the best sensitivity and selectivity for the analysis. In comparison with the previous gas chromatography with mass spectrometry procedure based on single ion monitoring detection, the tandem mass spectrometry technique increased the analytical sensitivity by reducing detection limits for standard solutions from 1–2.6 to 0.1–0.4 ng/μL ranges (concentrations in the injected solution). In addition, it enhanced selectivity by reducing matrix interferences and chemical noise in the chromatogram. The applicability of the developed method in air quality monitoring campaigns was effectively checked by analyzing environmental samples collected in the Po Valley (Northern Italy) in different seasons. The obtained results indicate that the ion trap mass spectrometer may be an ideal alternative to high‐resolution mass spectrometers for the user‐friendly and cost‐effective determination of a wide range of molecular tracers in airborne particulate matter.     

Use of liquid chromatography-tandem mass spectrometry for the analysis of pentoxifylline and lisofylline in plasma

A method was developed for the quantitation of pentoxifylline [1-(5-oxohexyl)-3,7-dimethylxanthine] and a primary active metabolite, lisofylline [1-(5-hydroxyhexyl)-3,7-dimethylxanthine], using high-performance liquid chromatography (HPLC)-tandem mass spectrometry. This method was developed in order to overcome problems encountered with HPLC-ultraviolet detection. The operating parameters of the electrospray interface (PE SCIEX, TurboIon Spray) and lens voltages of the triple-quadrupole detector (PE SCIEX 365) were optimized in positive ion mode to obtain the best sensitivity of the analytes. Collision-induced dissociation was used to produce fragment ions, and multiple reaction monitoring was used to quantitate pentoxifylline (m/z 279/181) and lisofylline (m/z 263/181). Dichloromethane was used to extract the drug, metabolite, and the internal standard (3-isobutyl-1-methylxanthine) from plasma. A reverse-phase C8(2) 150 x 1.0 mm HPLC column was used to resolve all three compounds in less than 6 min. Calibration curves were generated using peak area and were linear from 1 to 1000 ng/mL (R(2) > 0.99). The small sample volume, ease of extraction, and sensitivity provide advantages over more conventional methods of quantitation.     

Quantitative determination of sulfonamide in meat by liquid chromatography-electrospray-mass spectrometry

This paper describes a newly developed liquid chromatography–electrospray-mass spectrometry (LC–ES-MS) method for the quantitative determination of nine commonly used sulfonamides (sulfadiazine, sulfapyridine, sulfamerazine, sulfamethazine, sulfamonomethoxine, sulfisoxazole, sulfadimethoxine, sulfaquinoaline and sulfaphenazole) in meat. [M+H]⁺ and [M+Na]⁺ were the two major ions detected in positive ion mode. Selective ion monitoring was employed for quantitative determination. Satisfactory linearity, 0.1–10 μg ml⁻¹, of each compound was obtained. Blank meat samples were fortified at levels between 50 and 500 μg kg⁻¹. [Phenyl-¹³C6]sulfamethazine was used as internal standard. Sulfonamides were isolated from meat with a solvent extraction procedure and then determined by LC–ES-MS. The limits of detection were below 10 μg kg⁻¹. The application of this newly developed method was demonstrated by analyzing various beef, pork and chicken samples from local markets.     

Development and validation of liquid chromatography–mass spectrometry method for the determination of telmisartan in human plasma

A sensitive liquid chromatographic–electrospray ionization mass spectrometric method was developed and validated for fast determination of telmisartan in human plasma. Plasma of 0.1 mL was deprotienated with methanol, centrifugation, evaporation to dryness and dissolving in mobile phase, samples were separated using a Hypersil-Keystone C18 reversed-phase column (150 mm × 2.1 mm i.d., 5 μm), together with a mobile phase containing of acetonitrile–10 mM ammonium acetate (42:58, v/v), 0.2% acetic acid and was isocratically eluted at a flow rate of 0.2 mL/min. Telmisartan and its internal standard, valsartan, were measured by electrospray ion source in positive selective ion monitoring mode. The method demonstrated linearity from 1 to 2000 ng/mL (r = 0.9988). The limit of quantification for telmisartan in plasma was 1 ng/mL with good accuracy and precision. The mean sample extract recovery of the method were higher than 82 and 78% for telmisartan and internal standard (IS), respectively. The within-run and between-run precision ranged from 3.4 to 8.9% and 5.9 to 11.2% (relative standard deviation, R.S.D.), respectively.     

Determination of ketamine and metabolites in urine by liquid chromatography-mass spectrometry

We have developed an analytical method by using liquid chromatography-mass spectrometry (LC-MS) to determine ketamine and its metabolites in urine. The ionization efficiency between two ionization modes (ESI and APCI) of LC-MS was compared to each other. An easy and simple sample preparation of urine samples was made by passing samples through a 0.22 μm PVDF syringe filter. The results indicated that the ionization efficiency of positive APCI mode is better than positive ESI mode for determination of trace ketamines. A wide linearity range of the research is from 5 to 250 ng mL⁻¹ and the detection limits for ketamine, norketamine and dehydronorketamine were 0.95, 0.48 and 0.33 ng mL⁻¹, respectively. The proposed method was tested by analyzing ketamine and metabolites in the urines of volunteers. The concentrations of ketamine, norketamine and dehydronorketamine are ranged of 5.4-131.0, 12.5-74.1 and 22.8-278.9 ng mL⁻¹, respectively and the ketamines concentration profiles in human urine were also determined. The results demonstrate the suitability of liquid chromatography-mass spectrometry approach to analyze trace amount of ketamine and its metabolites in urine.     

Determination of sialic acids in infant formula by liquid chromatography tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric method using pneumatically assisted electrospray ionization (LC-ESI-MS/MS) was developed for determination of N-acetylneuramic acid and N-glycolylneuramic acid in infant formula. Reconstituted samples were hydrolysed in dilute sulfuric acid and deproteinized with acetonitrile. The extract was analysed directly without further clean-up by hydrophilic interaction chromatography. The substances were detected in negative ion mode and matrix matched standards were used for calibration. The relative intra-laboratory reproducibility standard deviation was better than 6% for both substances. An R2 of 0.985 was obtained by comparison with a classical colorimetric assay based on reaction with resorcinol. The developed method is expected to be applied for accurate routine analysis of infant formulas.     

超高效液相色谱-质谱法同时快速测定烟叶中的几种芳香酸和酚酸

对烟叶中的苯甲酸、邻苯二甲酸、4-香豆酸、咖啡酸和阿魏酸进行了超高效液相色谱-串联四极杆线性离子肼质谱法(UPLC-MS/MS)同时测定的系统研究,建立了烟叶中5种酸的测定方法.对样品中被测物的萃取溶剂和萃取条件以及相关线性、精密度和回收率进行了考察和实验.该方法的相对标准偏差在0.52%～4.9% 范围内,回收率在93.3%～104.7%之间、检测限为0.05～1 μg/L.该方法适合复杂体系中微量酸的快速检测.     

Characterisation of polycyclic aromatic hydrocarbons in atmospheric aerosols by gas chromatography-mass spectrometry

An accurate and reliable method for determining polycyclic aromatic hydrocarbons (PAHs) in atmospheric aerosols is described. This optimised gas chromatography-mass spectrometry (GC-MS) method permits a wide range of concentrations to be analysed without the influence of interferences.Pre-treatment comparison of four kinds of aerosol collector filters determined that quartz and glass fibre filters were the most suitable. Solvents like cyclohexane, toluene, acetonitrile and dichloromethane were evaluated for their PAH-extraction capacity. Ultrasonic extraction using CH₂Cl₂ was selected because it is rapid and easy; moreover, this solvent increases the sample-throughput capacity.PAH compounds were quantitatively collected and ultrasonically extracted twice using 15 mL of CH₂Cl₂ for 15 min for each replicate. Rotavapor concentration, fractionation and dissolution were also optimised.A certified standard mixture (16 EPA PAHs), a deuterated compound and precision recovery assays were used for validating the proposed methodology. Adequate analytical parameters were obtained. Detection limits were (1.6-26.3) × 10⁻⁵ ng and quantification limits were (5.2-87.6) × 10⁻⁵ ng.Analysis of the environmental samples detected 4-10 EPA list PAH compounds. In addition, 2-11 tentative compounds were found, and their molecular structures were described for the first time.Our study of both Youden method and the standard addition method has shown that the proposed determination of PAHs in environmental samples is free of systematic errors.In conclusion, this unbiased methodology improves the identification and quantification of PAH compounds. High sensitivity as well as acceptable detection and quantification limits were obtained for the environmental applications.     

Testing organic solvents for the extraction from fish of sulfophenylcarboxylic acids, prior to determination by liquid chromatography-mass spectrometry

The present paper describes the use of different solvent mixtures to extract from fish various sulfophenylcarboxylic acids (SPCs of C₆ to C₁₃), and their originating compounds, linear alkylbenzene sulfonates (LAS of C₁₀ to C₁₃). The analytical method utilized involves pressurized liquid extraction, followed by preconcentration of the samples, purification by solid-phase extraction, and finally identification and quantification of the target compounds by high-performance liquid chromatography-mass spectrometry using a system equipped with an electrospray interface operating in negative ion mode. The SPCs and LAS were extracted from spiked fish first with hexane to remove interference from fats, then with different mixtures of solvents: dichloromethane followed by methanol; 50:50 dichloromethane-methanol; and 30:70 dichloromethane-methanol. The LAS recoveries obtained with these three extraction options were high (between 68.5 and 80.8%); however, owing to the low percentages obtained for SPC homologues (13.5, 13.1, and 15.9%, respectively), another extraction procedure with methanol was developed in order to increase these recoveries. The percentage of recovery for total SPCs with the methanolic extraction was higher (90.1%), with a standard deviation of 9.9, and the LAS recoveries also increased (99.9%). Detection limits were between 1 and 22 ng g^?1 for LAS, and between 1 and 58 ng g^?1 for SPCs. Quantitation limits were between 4 and 73 ng g^?1 for LAS, and between 2 and 193 ng g^?1 for SPCs. This method has been applied to measure the biotransformation of 2ØC₁₀ LAS (where Ø is a sulfophenyl group) in fish exposed in a flow-through system, and enabled the separation and identification of SPCs from 5ØC₆ to 9ØC₁₀.     

液相色谱-电喷雾电离质谱法检测尿液中的3种合成类固醇药物

研究建立了合成类固醇药物群勃龙、四氢孕三烯炔酮和孕三烯酮的液相色谱-电喷雾质谱的检测方法。尿样经过β-葡萄糖醛酸酶酶解和叔丁基甲醚提取后,采用Zorbax SB-C18分析柱(150 mm×2.1 mm,5 μm),在流动相为pH 3.5的甲酸铵缓冲液-乙腈的条件下进行梯度洗脱,在正离子模式下检测。考察了不同的质谱条件对这类化合物检测结果的影响。建立了人尿液中合成类固醇药物的液相色谱-电喷雾电离质谱的初筛和确证方法。