Analysis of tomato glycoalkaloids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Steroidal glycoalkaloids (SGAs) extracted from tomato leaves and berries (Lycopersicon esculentum Mill.) were separated and identified using optimized reversed-phase liquid chromatography with electrospray ionization (ESI) and ion trap mass spectrometry (ITMS). The ESI source polarity and chromatographic conditions were evaluated. The ESI spectra contain valuable information, which includes the mass of SGAs, the mass of the aglycones, and several characteristic fragment ions. Cleavage at the interglycosidic bonds proximal to the aglycones is the most prominent process in the ESI process. A protonated molecule, [M+H]+, accompanied by a mixed adduct ion, [M+H+Na]2+, was observed for alpha-tomatine (i.e., m/z 1034.7 and 528.9) and dehydrotomatine (i.e., m/z 1032.6 and 527.9) in positive ion mode spectra. The structures of these tomato glycoalkaloids were confirmed using tandem mass spectrometry. The identification of a new alpha-tomatine isomer glycoalkaloid, named filotomatine (MW 1033), which shares a common tetrasaccharide structure (i.e., lycotretraose) with alpha-tomatine and dehydrotomatine, and soladulcidine as an aglycone, is described for the first time. It occurs in significant amounts in the extracts of wild tomato foliage. Multistage mass spectrometry both of the protonated molecules and of the doubly charged ions was used for detailed structural elucidation of SGAs. Key fragmentations and regularities in fragmentation pathways are described and the fragmentation mechanisms involved are proposed.     

Quantitative analysis of clavulanic acid in porcine tissues by liquid chromatography combined with electrospray ionization tandem mass spectrometry

The purpose of this study was to develop and validate a method for the determination of clavulanic acid (CLAV) residues in edible tissues of swine by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS). After a simple extraction of CLAV using an aqueous phosphate buffer solution of pH 6.0, an ultrafiltration step was performed for protein removal. Chromatography of CLAV and the internal standard tazobactam (TAZO) was achieved on a reversed-phase PLRP-S polymeric column (150 mm × 2.1 mm i.d., 100 Å) using a mixture of 0.05 (v/v)% formic acid in water and acetonitrile. The mass spectrometer was operated in the MS/MS selected reaction monitoring (SRM) mode. The method was validated for the analysis of porcine muscle, skin plus fat, liver and kidney, according to the requirements defined by the European Community. Calibration curves were prepared for all tissues and good linearity was achieved over the concentration ranges tested (correlation coefficient ≥0.99 and goodness-of-fit coefficient ≤10%). Limits of quantification of 50 ng g⁻¹ were obtained for the analysis of CLAV in the various tissues which corresponds in all cases to at least half the maximum residue limits (MRLs). Limits of detection ranged between 8.0 and 15.14 ng g⁻¹. The within-day, between-day precisions and trueness fell within the ranges specified in the EMEA/CVMP/573-00/FINAL document. Biological samples from pigs that received an oral or intravenous bolus of a commercial amoxicillin/clavulanic acid formulation were analyzed using the described method.     

Plasma lipid analysis by hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A novel method for the analysis of endogenous lipids and related compounds was developed employing hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry. A hydrophilic interaction liquid chromatography with carbamoyl stationary phase achieved clear separation of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, ceramide, and mono‐hexsosyl ceramide groups with good peak area repeatability (RSD% < 10) and linearity (R² > 0.99). The established method was applied to human plasma assays and a total of 117 endogenous lipids were successfully detected and reproducibly identified. In addition, we investigated the simultaneous detection of small polar metabolites such as amino and organic acids co‐existing in the same biological samples processed in a single analytical run with lipids. Our results show that hydrophilic interaction liquid chromatography is a useful tool for human plasma lipidome analysis and offers more comprehensive metabolome coverage.     

Determination of acrylamide in food by solid-phase microextraction coupled to gas chromatography-positive chemical ionization tandem mass spectrometry

A method has been developed to determine acrylamide in aqueous matrices by using direct immersion solid-phase microextraction (SPME) coupled to gas chromatography-positive chemical ionization tandem mass spectrometry (GC-PCI-MS-MS) in the selected reaction monitoring (SRM) mode. The optimized SPME experimental procedures to extract acrylamide in water solutions were: use of a carbowax/divinylbenzene (CW/DVB)-coated fiber at pH 7, extraction time of 20 min and analyte desorption at 210 °C for 3 min. A detection limit of 0.1 μg L⁻¹ was obtained. The linear range was 1-1000 μg L⁻¹. The relative standard deviation was 10.64% (n = 7). The proposed analytical method was successfully used for the quantification of trace acrylamide in foodstuffs such as French fries (1.2 μg g⁻¹) and potato crisps (2.2 μg g⁻¹).     

液相色谱-同位素稀释串联质谱法测定动物源性食品中硝基呋喃类代谢物残留

加入同位素标记物的动物源性样品(龙虾、肠衣),在酸性条件下用2-硝基苯甲醛,使样品中呋喃唑酮、呋喃西林、呋喃它酮、呋喃妥因实现衍生。经乙酸乙酯提取浓缩、用甲醇水溶液溶解过滤后,滤液用液相色谱-串联质谱定量。在0.5,1.0和2.0μg/kg3个浓度水平上进行添加回收试验,回收率为80.1％～92.2％,检出限(LOQ)...     

Determination of acrylamide in Chinese traditional carbohydrate-rich foods using gas chromatography with micro-electron capture detector and isotope dilution liquid chromatography combined with electrospray ionization tandem mass spectrometry

The present study developed two analytical methods for quantification of acrylamide in complex food matrixes, such as Chinese traditional carbohydrate-rich foods. One is based on derivatization with potassium bromate and potassium bromide without clean-up prior to gas chromatography with micro-electron capture detector (GC-MECD). Alternatively, the underivatized acrylamide was detected by high-performance liquid chromatography coupled to quadrupole tandem mass spectrometry (HPLC-MS/MS) in the positive electrospray ionization mode. For both methods, the Chinese carbohydrate-rich samples were homogenized, defatted with petroleum ether and extracted with aqueous solution of sodium chloride. Recovery rates for acrylamide from spiked Chinese style foods with the spiking level of 50, 500 and 1000 μg kg⁻¹ were in the range of 79-93% for the GC-MECD including derivatization and 84-97% for the HPLC-MS/MS method. Typical quantification limits of the HPLC-MSMS method were 4 μg kg⁻¹ for acrylamide. The GC-MECD method achieved quantification limits of 10 μg kg⁻¹ in Chinese style foods. Thirty-eight Chinese traditional foods purchased from different manufacturers were analyzed and compared with four Western style foods. Acrylamide contaminant was found in all of samples at the concentration up to 771.1 and 734.5 μg kg⁻¹ detected by the GC and HPLC method, respectively. The concentrations determined with the two different quantitative methods corresponded well with each other. A convenient and fast pretreatment procedure will be optimized in order to satisfy further investigation of hundreds of samples.     

Direct determination of acrylamide in food by gas chromatography-high-resolution time-of-flight mass spectrometry

Simple and rapid gas chromatographic (GC) method employing a high-resolution time-of-flight mass analyzer that enables direct analysis (no derivatization) of acrylamide in various heat-processed foodstuffs has been developed and validated. Co-isolation of acrylamide precursors such as sugars and asparagine, constituting the risk of results overestimation due to additional formation of analyte in hot GC injector, is avoided by the extraction with n-propanol followed by solvent exchange to acetonitrile (MeCN). Introduction of a novel purification strategy, dispersive solid phase extraction, based on addition of primary-secondary amine (PSA) sorbent into deffated extract in MeCN, provides a significant reduction of some abundant matrix co-extracts (mainly free fatty acids). Isotope dilution technique (d₃-acrylamide as an internal standard) is employed for compensation of potential target analyte losses and/or matrix-inducted chromatographic response enhancement. Limits of quantifications (LOQs) ranged between 15 and 40 μg kg⁻¹ and recoveries were between 97 and 108% depending on the examined food matrix. The repeatability of measurements (expressed as relative standard deviation, R.S.D.) was as low as 1.9% for potato crisps containing acrylamide at a level of 1 mg kg⁻¹. Slightly higher values (R.S.D. < 4.0%) were achieved for breakfast cereals and crisp bread with approximately 10 times lower content of this processing contaminant. Trueness of results generated by this new method was demonstrated via FAPAS^® (Food Analysis Performance Assessment Scheme) interlaboratory proficiency tests.     

High-throughput determination of atrasentan in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Atrasentan (A-147627) is an endothelin antagonist receptor being developed at Abbott Laboratories for the treatment of prostate cancer. A quick and sensitive method for the determination of atrasentan in human plasma has been developed and validated using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. A dual-column, single mass spectrometer system is used to provide a reliable and routine means to increase sample throughput. The analytical method involves liquid-liquid extraction and internal standard (A-166790). The plasma samples and internal standard are acidified with 0.3 M hydrochloric acid prior to being extracted into 1:1 (v/v) hexanes--methyl t-butyl ether. The organic extract was evaporated to dryness using heated nitrogen stream and reconstituted with mobile phase. Atrasentan and internal standard were separated with no interference in a Zorbax SB-C(18) analytical column with 2.1 x 50 mm, 5 microm, and a Zorbax C(8) guard column using a mobile phase consisting of 50:50 (v:v) acetonitrile--0.05 M ammonium acetate, pH 4.5, at a flow rate of 0.30 mL/min to provide 4 min chromatograms. For a 250 microL plasma sample volume, the limit of quantitation was approximately 0.3 ng/mL. The calibration was linear from 0.30 to 98.0 ng/mL (r(2) > 0.995). A significant advantage of the method is the ability to employ parallel HPLC separations with detection by a single MS/MS system to provide sensitivity and selectivity sufficient to achieve robust analytical results with a lower limit of quantitation of 0.30 ng/mL and high throughput.     

Direct quantification of creatinine in human urine by using isotope dilution extractive electrospray ionization tandem mass spectrometry

Urinary creatinine (CRE) is an important biomarker of renal function. Fast and accurate quantification of CRE in human urine is required by clinical research. By using isotope dilution extractive electrospray ionization tandem mass spectrometry (EESI–MS/MS) a high throughput method for direct and accurate quantification of urinary CRE was developed in this study. Under optimized conditions, the method detection limit was lower than 50 μg L⁻¹. Over the concentration range investigated (0.05–10 mg L⁻¹), the calibration curve was obtained with satisfactory linearity (R² = 0.9861), and the relative standard deviation (RSD) values for CRE and isotope-labeled CRE (CRE-d3) were 7.1–11.8% (n = 6) and 4.1–11.3% (n = 6), respectively. The isotope dilution EESI–MS/MS method was validated by analyzing six human urine samples, and the results were comparable with the conventional spectrophotometric method (based on the Jaffe reaction). Recoveries for individual urine samples were 85–111% and less than 0.3 min was taken for each measurement, indicating that the present isotope dilution EESI–MS/MS method is a promising strategy for the fast and accurate quantification of urinary CRE in clinical laboratories.     

Identification of isoflavonoids in several kudzu samples by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Pueraria lobata is a rich source of isoflavonoids. The detection and identification of isoflavonoid components from Pueraria radix (RP), callus and cell cultures, is very important for the safest and most effective use of kudzu as a medicinal plant, and for the studies on quantitative analysis and secondary metabolism of isoflavonoids in vitro cultures. Liquid chromatography is coupled with negative and positive electrospray ionization (ESI) tandem mass spectrometry (MS-MS), and photodiode array detection is used to characterize and detect isoflavonoids in root, callus, and cell samples of P. lobata. Characteristic product ions of aglycones, O-glucosides, and C-glucosides were obtained from the full-scan ESI-MS chromatography of the major peaks and the MS-MS spectra of the protonated ions. Five major components of puerarin, daidzin-6"-O-acetylester, genistin-6"-O-malonylester, biochanin A-7-O-glucoside-6"-O-malonylester, and daidzein are detected and identified from the methanolic extract of P. lobata callus cultures. The major isoflavonoid components of P. lobata cell suspension cultures are identified as puerarin, daidzin, daidzin-6"-O-acetylester, genistin-6"-O-malonylester, biochanin A-7-O-glucoside-6"-O-malonylester, genistein-8-C-glucoside-6"-O-malonylester, and daidzein, on the basis of ESI-MS and MS-MS spectra analysis. Likewise, puerarin, daidzin, genistein-6"-O-malonylester, 3'-methoxypuerarin, and daidzein are detected and identified from RP. Of those isoflavonoid components detected, daidzin-6"-O-acetylester is a new isoflavonoid glucoside and is for the first time detected from P. lobata cultures in vitro.     

高效液相色谱-电喷雾串联质谱法测定饲料中的N-氨基甲酰-L-谷氨酸

建立了高效液相色谱-电喷雾串联质谱(HPLC-ESI-MS/MS)测定饲料中N-氨基甲酰-L-谷氨酸(NCG)含量的方法。饲料样品经甲醇提取、混合型强阴离子交换反相固相萃取(PXA)柱净化、HPLC分离后,采用ESI-MS/MS在正离子多反应监测(MRM)模式下进行检测,以碎片离子m/z 148.0和m/z 84.0进行定性,以碎片离子m/z 130.0进行定量。NCG的检出限(S/N >3)为24 μg/kg,定量限(S/N >10)为80 μg/kg,在20~1000 μg/L的质量浓度范围内峰面积与含量的线性关系良好,相关系数为0.9999。对饲料中NCG在80、200、500 mg/kg等3个添加水平下的回收率进行了测定,分别为104.0%、103.5%、95.3%,相对标准偏差分别为7.5%、6.3%、5.8%。结果表明,该方法操作简单,净化效果好,快速,灵敏度和准确度高,符合对饲料样品中NCG检测分析的要求。     

Derivatization reagents in liquid chromatography/electrospray ionization tandem mass spectrometry

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is one of the most prominent analytical techniques owing to its inherent selectivity and sensitivity. In LC/ESI-MS/MS, chemical derivatization is often used to enhance the detection sensitivity. Derivatization improves the chromatographic separation, and enhances the mass spectrometric ionization efficiency and MS/MS detectability. In this review, an overview of the derivatization reagents which have been applied to LC/ESI-MS/MS is presented, focusing on the applications to low molecular weight compounds.     

液相色谱-电喷雾串联质谱法测定生姜中的215种农药残留

建立了生姜中215种农药多残留测定的液相色谱-电喷雾串联质谱(LC-ESI-MS/MS)方法。样品用1%醋酸-乙腈溶液均质提取,经Sep-Pak Vac固相萃取柱净化,乙腈-甲苯(3:1, v/v)洗脱,旋转蒸发浓缩至约0.5 mL后,于室温氮气吹干,用乙腈-水(3:2, v/v)溶解,以电喷雾电离串联质谱在正离子多反应监测(MRM)模式下进行测定。在定量限水平进行添加回收率实验,方法的回收率范围为68.1%～132.6%,其中回收率在70%～120%的占94.4%,相对标准偏差(RSD)范围为0.4%～25.0%。方法的检出限(S/N=3)和定量限(S/N=10)范围分别为0.01～70.45 μg/L和0.04～234.84 μg/L。该方法操作简便,灵敏度、准确度和精密度均符合农药多残留检测技术要求,适用于生姜中215种农药多残留的快速测定。     

Determination of flomoxef in human plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A specific, sensitive, rapid and reproducible method for the determination of flomoxef in human plasma using high‐performance liquid chromatography–tandem mass spectrometry was developed and validated. Flomoxef was detected using an electrospay ionization method operated in negative‐ion mode. Chromatographic separation was performed in gradient elution mode on a Luna® C₁₈(2) column (3 μm , 20 × 4.0 mm) at a flow rate of 1 mL/min and runtime 3.5 min. The mobile phase consisted of acetonitrile and water containing 0.1% formic acid as additive. Extraction of flomoxef from plasma and precipitation of plasma proteins was performed with acetonitrile with an absolute recovery of 86.4 ± 1.6%. The calibration curve was linear with a correlation coefficient of 0.999 over the concentration range 10–5000 ng/mL and the lower limit of quantification was 10 ng/mL. The intra‐ and inter‐day precisions were <11.8%, while the accuracy ranged from 99.6 to 109.0%. A stability study of flomoxef revealed that it could be successfully analyzed at 4ºС over 24 h, but it was unstable in solutions at room temperature during short‐term storage (4 h) and several freeze–thaw cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of Amaryllidaceae alkaloids from Crinum by high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A high‐performance liquid chromatography/electrospray ionization multi‐stage tandem mass spectrometry (HPLC/ESI‐MSⁿ) method was developed to analyze two structurally related groups of Amaryllidaceae alkaloids (AmAs), crinane‐ and tazettine‐type alkaloids, in the species Crinum latifolium and C. asiaticum, as well as different organs of C. latifolium. In ESI‐MSⁿ spectra of the two types of alkaloids, characteristic fragmentation reactions were observed that allowed us to determine and differentiate them. Based on the fragmentation rules of reference standards, crinane‐type alkaloids displayed concurrent neutral loss of C₂H₅N (43 u) and C₂H₆N (44 u) as well as characteristic ions of m/z 213 and 211, whereas tazettine‐type alkaloids exhibited neutral loss of C₃H₇N (57 u) [or C₂H₅N (43 u), C₃H₇NO (73 u)] from the [M+H]⁺ and [M+H–H₂O]⁺ ions. These were supported by quadrupole time‐of‐flight (Q‐Tof)‐MS/MS analysis. The chemical complexity of the mixture was resolved by profiling. The compositions of the main crinane‐ and tazettine‐type alkaloids in the above‐mentioned species and organs were also compared. Overall, 28 AmAs comprising 14 crinane‐type and 14 tazettine‐type alkaloids were identified and studied by MS. Among them, 14 AmAs were tentatively characterized from the two species for the first time. This method allowed a rapid analysis of alkaloid distribution and composition of Crinum species, and may also be used for quality control and screening of extracts designated for pharmaceutical application. Copyright © 2009 John Wiley & Sons, Ltd.     

Screening and characterization of natural antioxidants in four Glycyrrhiza species by liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Licorice, derived from the dried roots and rhizomes of several species of genus Glycyrrhiza L. (Leguminosae family), has been traditionally used in herbal medicine for over 4000 years. In recent years, the interest in antioxidative constituents in licorice has greatly increased. In this work, a new method based on 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) spiking test combined with HPLC coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS) analysis was developed to screen and identify the antioxidants in licorice. The results of the method validation indicated that the developed method was reliable and repeatable. Compared with DPPH on-line method, the HPLC-Q-TOF MS/MS method combined with DPPH spiking test offered much higher sensitivity and resolution. Using this method, 35 radical scavengers were screened from four Glycyrrhiza species (G. inflata, G. glabra, G. pallidiflora and G. uralensis), and 21 of them were unambiguously or tentatively identified by HPLC-Q-TOF MS/MS. Among the 21 identified flavonoids, 10 compounds had been reported to possess antioxidative activities in the previous studies, and the radical scavenging activities of the other 11 compounds were reported for the first time. The effects of six purified flavonoids on DPPH radical and lipid peroxidation were evaluated for validation of the developed method. The results indicated that HPLC-Q-TOF MS/MS coupled with DPPH treatment is an efficient and powerful method to discover the potential antioxidative compounds from the complex natural product mixtures. In this study, the identified components with free radical scavenging activity, would help to explain the therapeutic benefit of licorice in the treatment of human disease associated with oxidative stress.     

Characterization of caffeic acid enzymatic oxidation by-products by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

The products of tyrosinase-catalyzed caffeic acid oxidation at pH 6.5 were investigated using high-performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS). Aliquots of reaction mixtures were withdrawn at different times, varying from 0 to 24 h, and directly analysed by HPLC-ESI-MS and, in the case of 1 and 5 h, by HPLC-ESI-MS/MS to obtain structural information on caffeic acid derivatives. In particular, two different classes of caffeic acid dimers were identified: caffeicins-like structures and dimers originated by CC coupling between the benzene rings. Evidences for the presence of trimeric derivatives of caffeic acid were also obtained from MS data.     

Quantitation of glutathione by liquid chromatography/positive electrospray ionization tandem mass spectrometry

Glutathione (GSH) is a tripeptide composed of glutamate, cysteine, and glycine. It is present in practically all cells and has several important roles, such as preventing the oxidation of the sulfhydryl groups of proteins within a cell. Evidence for GSH deficiency or depletion has been found in a variety of diseases and toxicity-related studies, including diabetes and induction of oxidative stress to form reactive oxygen species which cause DNA, lipid, and protein oxidations. A simple, selective, and sensitive analytical method for measuring low levels of GSH in biological fluids would therefore be desirable to conduct GSH deficiency or depletion-related mechanistic toxicity studies. Here a method for both low- and high-level quantitation of GSH from cultured cells and rat liver tissues via liquid chromatography/positive electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) has been developed. The lower limit of quantitation (LOQ) of the method was 5 ng/mL. The method is linear over a wide dynamic concentration range of 5.0 to 5000.0 ng/mL, with a correlation coefficient R2 > 0.99. The intra-day assay precision relative standard deviation (RSD) values for all quality control (QC) samples were < or =16.31%, with accuracy values ranging from 94.13 to 97.80%. The inter-day assay precision RSD values for all QC samples were < or =15.94%, with accuracy values ranging from 94.51 to 100.29%. With this method, low levels of GSH from diethyl maleate (DEM)-treated mouse lymphoma cells, and GSH in rat liver tissues, were quantified.     

Analysis of chlormequat and mepiquat by hydrophilic interaction chromatography coupled to tandem mass spectrometry in food samples

In this work a LC–MS/MS method for the determination of two quaternary ammonium growth regulators (chlormequat and mepiquat) in food is reported. The separation was based on hydrophilic interaction liquid chromatography (HILIC) without the use of ion-pair reagents. A gradient elution of acetonitrile and formic acid/ammonium formate buffer from 60 to 40% acetonitrile was enough to achieve a resolution >1.5 in less than 4.0 min. The HILIC system was coupled to a triple quadrupole mass spectrometer equipped with a heated electrospray probe (H-ESI) providing sub-pg LODs in SRM mode. A straightforward sample treatment (SPE C18 clean-up) was enough to provide MLODs at low ppb levels when analysing a range of food samples that covered different kinds of matrices such as fresh fruit, vegetables, fruit juices, baby food, bread, coffee and beer. Chlormequat was found in seven samples (0.8–126 ng/g) but mepiquat was only detected in bread and coffee samples (0.9–166 ng/g).