Evaluation of the potential of thermospray liquid chromatography-mass spectrometry in neurochemistry

Optimized operating conditions previously developed for the determination of neuroactive indoleamines and metabolites were adapted to meet the requirements of thermospray liquid chromatography-mass spectrometry (LC-MS) in terms of the ammonium acetate buffer system needed in this technique. Mass spectra were obtained for nineteen indolic compounds in both the positive and negative ion modes. The positive thermospray mass spectra of indoles with a free primary amino group are characterized by the base peak at [M + H]+, whereas the alcohol and acid metabolites show the base peak at [M + NH4]+. In the negative mode only amino acids and acids give good mass spectra with base peaks at [M - H + ACOOH]-. Detection limits by selected ion monitoring were of the order of 50-100 pg SIM on-column, allowing the direct determination of endogenous serotonin in an extract from rat hypothalamus. Quantitation was performed by isotope dilution MS. In the same way 5-hydroxyindoleacetic, indoleacetic, indolepropionic and indolelactic acids in urine were directly determined in an ethyl acetate extract from acidified urine samples. Likewise, gamma-aminobutyric acid and tricyclic antidepressants gave detection limits of 10 pg whereas only nanogram sensitivity could be achieved with catecholamines.     

Approach to the analysis of diuretics and masking agents by high-performance liquid chromatography-mass spectrometry in doping control

The application of thermospray and plasmaspray high-performance liquid chromatography-mass spectrometry to the analysis of diuretics and probenecid has been investigated. The latter method gave better ionization efficiency than the former, and its response was optimized by altering the solvent composition: best results were obtained with water-methanol-acetonitrile-trifluoroacetic acid. Using different proportions of these solvents, three isocratic systems were developed to separate the compounds under study. The principal characteristic of plasmaspray positive-ion mass spectra was a protonated molecular ion and very little fragmentation was evident. In the negative ionization mode, the plasmaspray method gave mass spectra showing more fragmentation, which resulted in additional structural information. The ability of trifluoroacetic acid to form negative cluster ions precluded its use as a mobile phase component. The minimum detectable amounts determined by the analysis in the positive-ion mode was compound-dependent, but generally ca. 10-150 ng. In many cases the compounds could be detected in urine extracts.     

Positive- and negative-ion chemical ionization gas chromatography/mass spectrometry of polynuclear aromatic hydrocarbons

Four groups of isomeric polynuclear aromatic hydrocarbons (PAH) were examined by gas chromatography/mass spectrometry (GC/MS) using positive-ion chemical ionization and negative-ion chemical ionization with a variety of reagent gases in order to evaluate the utility of each; differentiation of isomers was the ultimate goal. Hydrogen positive-ion chemical ionization (PICI) yielded different spectra for all but one isomer pair while retaining sensitivity comparable to electron-impact mass spectrometry. Several experimental conditions in the negative-ion mode afforded distinctly different spectra for isomeric PAH, but often sensitivities were reduced. The thirteen model compounds divided approximately into three classes according to the types and extent of reactions of the molecular anion. Class 1 gave as good sensitivity as hydrogen PICI; class 2 gave isomer-dependent spectra, but reduced sensitivity; class 3 gave no isomer differentiation, but greatly enhanced sensitivity.     

N-二异丙基磷酰化氨基酸-N-4-氨基吡啶衍生物的合成及对河豚毒素(TTX)解毒生物活性的研究

通过母体化合物4-氨基吡啶(4-AP)与N-二异丙基磷酰化氨基酸(DiPP-AA)在Ph3P和C2Cl6体系下的缩合反应,将具有生物活性的氨基吡啶环引入到磷酸化氨基酸结构中,设计、合成了5个N-二异丙基磷酰化氨基酸-N-4-氨基吡啶衍生物A1～A5.所有目标化合物均经IR,1H NMR,13C NMR,31P NMR,MS的表征.初步生物活性测试结果表明:目标化合物对河豚毒素(TTX)中毒的小鼠均有一定的解毒作用,并不同程度地延长了生存时间,而且毒性比母体化合物降低了.     

Comparison of different analytical methods for speciation of seven gadolinium-based magnetic resonance imaging contrast agents and the applications in wastewater and whole blood

Three methods, high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry, high-performance liquid chromatography-tandem mass spectrometry, and ion chromatography, were compared for simultaneous speciation of seven commercial gadolinium-based contrast agents for magnetic resonance imaging. Optimizations of experimental conditions for individual method were conducted, respectively. Methods of high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry showed the capability of speciation for all seven target compounds, whereas ion chromatography was only suitable for three of them when using electronic conductivity detector. The limits of detection and limits of qualification by the three methods were compared, and high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry was found to be the most sensitive one. The limits of detection for seven target compounds by high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry were in the range of 0.15–0.55 pg. Thus, high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry was chosen as the final method and successfully applied to speciation analysis of seven gadolinium-based contrast agents in wastewater and whole blood. Compounds of gadoxetic acid disodium, gadobenate dimeglumine, gadodiamide, and gadobentetate dimeglumine were found in wastewater.     

Extraction of domoic acid from seawater and urine using a resin based on 2-(trifluoromethyl)acrylic acid

A new solid-phase extraction (SPE) matrix with high affinity for the neurotoxin domoic acid (DA) was designed and tested. A computational modelling study led to the selection of 2-(trifluoromethyl)acrylic acid (TFMAA) as a functional monomer capable of imparting affinity towards domoic acid. Polymeric adsorbents containing TFMAA were synthesised and tested in high ionic strength solutions such as urine and seawater. The TFMAA-based polymers demonstrated excellent performance in solid-phase extraction of domoic acid, retaining the toxin while salts and other interfering compounds such as aspartic and glutamic acids were removed by washing and selective elution. It was shown that the TFMAA-based polymer provided the level of purification of domoic acid from urine and seawater acceptable for its quantification by high performance liquid chromatography-mass spectrometry (HPLC-MS) and enzyme-linked immunosorbent assay (ELISA) without any additional pre-concentration and purification steps.     

Application of pentafluorophenyl hydrazine derivatives to the analysis of nabumetone and testosterone in human plasma by liquid chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry

Two carbonyl compounds, nabumetone and testosterone, were derivatized with pentafluorophenyl hydrazine (PFPH) and analyzed by atmospheric-pressure chemical-ionization mass spectrometry. The PFPH derivatives underwent dissociative electron capture in negative-ion APCI (ECAPCI) and gave intense [M–20]^– ions in the mass spectra. In positive-ion APCI, the PFPH derivatives underwent efficient protonation and gave intense [M+H]⁺ ions in the mass spectra. In CID, the major product ions of the [M–20]^– ions in ECAPCI corresponded to the partial moiety of PFPH. In contrast, the major product ions of [M+H]⁺ corresponded to the partial moiety of the analyte. By using selected reaction monitoring (SRM) detection, low pg of nabumetone (1 pg) and testosterone (7 pg) could be detected in both ECAPCI and positive-ion APCI. In comparison with the detection limits (SRM) of the underivatized analytes, use of the PFPH derivatives resulted in 2500-fold and 35-fold sensitivity enhancements for nabumetone and testosterone, respectively. The PFPH derivatives were applied to the analysis of nabumetone and testosterone in human plasma by both ECAPCI and positive-ion APCI and were found to enable detection of 0.1 ng mL^–1 nabumetone in spiked plasma. For testosterone, endogenous testosterone in female plasma was detected in both ECAPCI and positive-ion APCI.     

Identification of flavonoids and their glycosides by high-performance liquid chromatography with electrospray ionization mass spectrometry and with diode array ultraviolet detection

Identification of flavonoids and flavonoid glycosides was carried out on Psidium guajava Linn leaves by means of high-performance liquid chromatography ultraviolet (HPLC-UV) analysis and HPLC mass spectrometry. By using HPLC-UV, two known phenolics (gallic acid and quercetin) and five newly reported ones (procatechuic acid, chlorogenic acid, caffeic acid, kaempferol and ferulic acid) were identified in alcohol guava leaf extract. Structural information about the compounds was obtained from the retention times, the UV spectra and mass spectra without the need to isolate the individual compounds. Two flavonoids (quercetin and kaempferol) and four flavonoid glycosides (three known components, quercetin 3-O-alpha-L-arabinoside, quercetin 3-O-beta-D-glucoside and quercetin 3-O-beta-D-galactoside, along with one novel compound, kaempferol-glycoside) and three other unknown compounds have been identified in the fractions.     

Influence of the solvent on the gas chromatographic behaviour of urea herbicides

Summary Degradation products of chlorsulfuron, chlortoluron, diuron, fluometuron, isoproturon, linuron, metabenzthiazuron, metobromuron, and monuron formed in the gas chromatographic injector have been used for identification of the respective herbicides. Mass spectra of the derived compounds were obtained with a quadrupole mass spectrometric detector working in scan mode (20–450 amu). The compounds generated often depended on the solvent used for phenylurea herbicide injection (ethanol, methanol, dichloromethane, and acetonitrile). When methanol and ethanol were used as solvents the major products formed from phenylureas were carbamic acid esters. When acetonitrile or dichloromethane were used the main derivatives were phenylisocyanates. Chlorsulfuron and metabenzthiazuron, however, generated a triazine plus a phenylsulfonamide and a benzothiazolamine, respectively, irrespective of the solvent used. Linuron and diuron behaved similarly and gave degradation products with the same mass spectra. The thermal reactions occurred instantaneously in the injector block and were promoted by the high temperature selected (300°C). Detemination of the compounds derived from urea herbicides, by use of a 30 m BP10 column and a selected ion registering (SIR) program based on two or three ions, can be used for sensitive detection of the presence of urea herbicides in environmental extracts. With standards in methanol instrument detection limits ranged from 0.1 pg for chlorsulfuron (detected as 2-chlorobenzensulfonamide) to 1 pg for monuron and metobromuron (both detected as their carbamic acid methyl esters).RSD were below 9% at the 5 ng L⁻¹ level. The response was linearly dependent on quantily (r>0.9986) in the 5 ng L⁻¹ to 25 μg L⁻¹ range. Unequivocal identification of some phenylurea herbicides was not always possible because some herbicides with similar structures, for example diuron and linuron, gave the same derivative.     

液相色谱-电喷雾离子阱质谱联用分析河豚毒素

应用C18反相色谱柱和HILIC亲水作用色谱柱,建立了河豚毒素(TTX)的液相色谱-电喷雾离子阱质谱联用分析方法。应用反相色谱法,在选择离子监测(SIM)模式下,对TTX的分析具有良好的线性响应(r=0.9992),方法检出限(S/N=3)为120pg,相对标准偏差(RSD)低于10%;应用亲水色谱法,在SIM和选择反应监测(SRM)模式下同样具有良好的线性响应(r=0.9996和r=0.9998),检出限(S/N=3)分别为15pg和3.75pg,在SIM模式下RSD低于10%,在SRM模式下RSD处于10%~20%之间。亲水作用色谱柱大大提高了方法的灵敏度,由于SIM模式具有较高的精密度,建议应用HILIC色谱柱的SIM模式定量分析TTX。     

Differentiation of isomeric 5- and 7-oxo derivatives of tetrahydrothiazolo[3,2-a]pyrimidine by electron impact mass spectrometry

The electron impact mass spectra of two series of 5-oxo-tetrahydro-5H-thiazolo [3,2-a]pyrimidine-6-ethylcarboxylates and 7-oxo-tetrahydro-7H-thiazolo [3,2-a]pyrimidine-6-ethylcarboxylates were measured and fragmentation patterns examined. Structures were assigned from analysis of oxo molecular ion fragmentations. Compounds of the 5-oxo series gave an [M – CO₂C₂H₅]⁺ fragmentation whereas compounds of the 7-oxo series gave three characteristic cleavages. This decomposition was confirmed for one pair of isomers by high-resolution mass spectrometry and unimolecular mass-analysed ion kinetic energy spectrometry. Electron impact mass spectrometry is a convenient method for assigning structures of 5- and 7-oxo regioisomers of tetrahydrothiazolo[3,2-a]pyrimidine-6-carboxylates.     

Trace Determination of Domoic Acid in Sea Water and Phytoplankton by High-Performance Liquid Chromatography of the Fluorenylmethoxycarbonyl (FMOC) Derivative

Abstract

A method is presented for the trace determination of domoic acid, a neurotoxic amino acid responsible for cases of Amnesic Shellfish Poisoning resulting from the consumption of contaminated shellfish. The method involves pre-column derivatization with 9-fluorenylmethylchloroformate to form the FMOC derivative followed by reversed-phase HPLC with fluorescence detection. The detection limit for domoic acid in seawater and aqueous extracts is 15pg/mL (50 pM) using gradient elution, a 20μL injection volume, and a 2.1mm I.D. microbore column. Use of dihydrokainic acid as an internal standard improved quantitation. The method was applied to the detection of domoic acid in seawater, in phytoplankton cultures (Nitzschia pungens forma multiseries), and in natural mixed phytoplankton assemblages in estuarine waters.     

Comparison of electron ionization mass spectra of some organic compounds (MW < 200 Da) recorded on mass spectrometers of various types

Low-resolution electron ionization mass spectra recorded on various types of mass spectrometers (time-of-flight, quadrupole, and three-dimensional ion trap) were compared. A model mixture of 10 organic compounds (MW < 200 Da) was analyzed by gas chromatography-mass spectrometry. Pure mass spectra of analytes were extracted using the AMDIS software. The best repeatability was achieved for the time-of-flight mass spectrometer. The mass spectra recorded by a quadrupole and a time-of-flight mass spectrometer were quite similar. In the case of these instruments, library search using a commercial mass spectral data base (NIST’05) gave satisfactory result for each analyte (rank 1 or 2 in the “hit list”; Match > 900). In some cases, the mass spectra of model compounds recorded by the ion trap mass spectrometer differed in intensity of certain mass spectral peaks (but not in the set of peaks) from the mass spectra presented in the library and from the experimental mass spectra recorded by the time-of-flight and quadrupole instruments.     

Determination of arsenic species by inductively coupled plasma mass spectrometry with ion chromatography

Five arsenic species, trimethylarsine oxide, dimethylarsenic acid, monomethylarsonic acid, arsenobetaine and sodium arsenite, in urine were analysed by inductively coupled plasma mass spectrometry with ion chromatography (IC ICP MS). Since the toxicities of different arsenic compounds are different, speciation of arsenic compounds is very important in the investigation of metabolisms. In this paper, we applied ion chromatography (IC) as a separation device and inductively coupled plasma mass spectrometry (ICP MS) as a detection device. For separation of the five arsenic compounds, an anion-exchange column and, as mobile phase, tartaric acid were used. The eluent from the IC column was introduced directly into the nebulizer of the ICP MS and analysed at 75 amu. Detection limits were from 4 to 9 pg as arsenic.     

Identifying the related compounds using electrospray ionization tandem mass spectrometry: bromotyrosine alkaloids from marine sponge Psammaplysilla purpurea

We have investigated extracts of marine sponge Psammaplysilla purpurea during three collections from Mandapam (Tamil Nadu, India) and Okha (Gujarat, India) and indentified two new bromotyrosine alkaloids, purpurealidin I (7) and J (8) using electrospray ionization tandem mass spectrometry (ESI-MS/MS). This sponge has tremendous chemical diversity of bromotyrosine alkaloids. Here we have used the proteomics approach in identifying related bromotyrosine alkaloids based on the predicated mass fragmentation pattern. The focus is on the examination of detailed product ion spectra of six known compounds that allowed identification of new compounds based on its mass fragmentation pattern. The isotopic pattern of the peaks for protonated molecules indicated the number of bromine atoms present in the molecule. During MS/MS studies, the most prominent product ion peak is for the presence of side chain propane with either free NH(2) or NHMe or Nme(2). The cleavage at C-C bond between oxime-amide carbonyl and amide-phenoxy moiety also gave characteristic product ions. The ESI-MS spectra for all three collections show that the bromotyrosine metabolites vary during different season and also geographical location. Although, some common metabolites were observed during the three collections. Thus, ESI-MS/MS is a method of choice in identifying the related compounds.     

Simultaneous determination of twelve inorganic and organic arsenic compounds by liquid chromatography-ultraviolet irradiation-hydride generation atomic fluorescence spectrometry

A coupling between column liquid chromatography (LC) and atomic fluorescence spectrometry was developed for arsenic speciation. After separation, the compounds are oxidised on-line by UV irradiation, volatilised by hydride-generation and carried to the detector by a stream of argon. A combination of anion-exchange and hydrophobic interactions in a single column (Dionex AS7) was found suitable for the simultaneous separation of organic and inorganic species. Twelve compounds (arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, trimethylarsine oxide, tetramethylarsonium ion and four arsenosugars) were separated using an acetate buffer and a nitric acid solution as mobile phases. Limits of detection are 4-22 pg. The technique was applied to three marine samples. Arsenobetaine was detected as the main species in all samples, with concentrations varying from 59 to 1947 ng(As) g(-1) of fresh mass.     

In vivo microdialysis and reverse phase ion pair liquid chromatography/tandem mass spectrometry for the determination and identification of acetylcholine and related compounds in rat brain

A method using liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed for the determination of basal acetylcholine (ACh) in microdialysate from the striatum of freely moving rats. A microdialysis probe was surgically implanted into the striatum of the rats and Ringer's solution was used as the perfusion medium at a flow rate of 2 microL per minute. The samples were then analyzed off-line by LC/MS/MS experiments. The separation of ACh and choline (Ch) was carried out using reverse phase ion pair liquid chromatography with heptafluorobutyric acid as a volatile ion pairing reagent. Analytes were detected by electrospray ionization tandem mass spectrometry in the positive ion mode. The detection limit for ACh was 1.4 fmol on column, which is at least three times lower than previously reported. Three quaternary ammonium compounds in the rat brain microdialysate were also identified by tandem mass spectrometry experiments in which the unknown mass spectra were compared with standard reference compounds. These compounds were identified as carnitine, acetylcarnitine and (3-carboxypropyl)trimethylammonium. This is the first known report of the compound (3-carboxypropyl)trimethylammonium being found in rat brain.     

三唑仑苯二氮(艹卓)类药物的电喷雾质谱裂解特征

采用电喷雾/四极杆飞行时间质谱(ESI-QqTOF)联用技术,对3种三唑仑苯二氮(艹卓)类药物进行CID研究,并以质子化准分子离子[M+H]+作为内标物,对碎片离子进行了准确质量测定,确认了这些碎片离子的元素组成,探讨了该类化合物的质谱裂解规律.研究发现,它们的ESI-MS2(源内)和ESI-MS3质谱分别生成脱去N2分子、HCN或CH3CN分子和Cl原子的碎片离子,其中m/z 205为3种药物共有的碎片离子,这些特征可用于三唑仑苯二氮(艹卓)类药物的体内代谢转化和定量研究.     

Quantitative analysis of multiple components based on liquid chromatography with mass spectrometry in full scan mode

Although liquid chromatography with mass spectrometry in full scan mode can obtain all the signals simultaneously in a large range and low cost, it is rarely used in quantitative analysis due to several problems such as chromatographic drifts and peak overlap. In this paper, we propose a Tchebichef moment method for the simultaneous quantitative analysis of three active compounds in Qingrejiedu oral liquid based on three‐dimensional spectra in full scan mode of liquid chromatography with mass spectrometry. After the Tchebichef moments were calculated directly from the spectra, the quantitative linear models for three active compounds were established by stepwise regression. All the correlation coefficients were more than 0.9978. The limits of detection and limits of quantitation were less than 0.11 and 0.49 μg/mL, respectively. The intra‐ and interday precisions were less than 6.54 and 9.47%, while the recovery ranged from 102.56 to 112.15%. Owing to the advantages of multi‐resolution and inherent invariance properties, Tchebichef moments could provide favorable results even in the situation of peaks shifting and overlapping, unknown interferences and noise signals, so it could be applied to the analysis of three‐dimensional spectra in full scan mode of liquid chromatography with mass spectrometry.     

Computational mass spectrometry for metabolomics: Identification of metabolites and small molecules

The identification of compounds from mass spectrometry (MS) data is still seen as a major bottleneck in the interpretation of MS data. This is particularly the case for the identification of small compounds such as metabolites, where until recently little progress has been made. Here we review the available approaches to annotation and identification of chemical compounds based on electrospray ionization (ESI-MS) data. The methods are not limited to metabolomics applications, but are applicable to any small compounds amenable to MS analysis. Starting with the definition of identification, we focus on the analysis of tandem mass and MS(n) spectra, which can provide a wealth of structural information. Searching in libraries of reference spectra provides the most reliable source of identification, especially if measured on comparable instruments. We review several choices for the distance functions. The identification without reference spectra is even more challenging, because it requires approaches to interpret tandem mass spectra with regard to the molecular structure. Both commercial and free tools are capable of mining general-purpose compound libraries, and identifying candidate compounds. The holy grail of computational mass spectrometry is the de novo deduction of structure hypotheses for compounds, where method development has only started thus far. In a case study, we apply several of the available methods to the three compounds, kaempferol, reserpine, and verapamil, and investigate whether this results in reliable identifications.