Liquid chromatography combined with mass spectrometry for 13C isotopic analysis in life science research

Among the different disciplines covered by mass spectrometry, measurement of (13)C/(12)C isotopic ratio crosses a large section of disciplines from a tool revealing the origin of compounds to more recent approaches such as metabolomics and proteomics. Isotope ratio mass spectrometry (IRMS) and molecular mass spectrometry (MS) are the two most mature techniques for (13)C isotopic analysis of compounds, respectively, for high and low-isotopic precision. For the sample introduction, the coupling of gas chromatography (GC) to either IRMS or MS is state of the art technique for targeted isotopic analysis of volatile analytes. However, liquid chromatography (LC) also needs to be considered as a tool for the sample introduction into IRMS or MS for (13)C isotopic analyses of non-volatile analytes at natural abundance as well as for (13)C-labeled compounds. This review presents the past and the current processes used to perform (13)C isotopic analysis in combination with LC. It gives particular attention to the combination of LC with IRMS which started in the 1990's with the moving wire transport, then subsequently moved to the chemical reaction interface (CRI) and was made commercially available in 2004 with the wet chemical oxidation interface (LC-IRMS). The LC-IRMS method development is also discussed in this review, including the possible approaches for increasing selectivity and efficiency, for example, using a 100% aqueous mobile phase for the LC separation. In addition, applications for measuring (13)C isotopic enrichments using atmospheric pressure LC-MS instruments with a quadrupole, a time-of-flight, and an ion trap analyzer are also discussed as well as a LC-ICPMS using a prototype instrument with two quadrupoles.     

Analysis of macrolide antibiotics, using liquid chromatography-mass spectrometry, in food, biological and environmental matrices

Macrolides are a group of antibiotics that have been widely used in human medical and veterinary practices. Analysis of macrolides and related compounds in food, biological, and environmental matrices continue to be the focus of scientists for the reasons of food safety, pharmacokinetic studies, and environmental concerns. This article presents an overview on the primary biological properties of macrolides and their associated analytical issues, including extraction, liquid chromatography-mass spectrometry (LC-MS), method validation, and measurement uncertainty. The main techniques that have been used to extract macrolides from various matrices are solid-phase extraction and liquid-liquid extraction. Conventional liquid chromatography (LC) with C18 columns plays a dominant role for the determination of macrolides, whereas ultra-performance liquid chromatography (UPLC) along with sub-2 microm particle C18 columns reduces run time and improves sensitivity. Mass spectrometry (MS), serving as a universal detection technique, has replaced ultraviolet (UV), fluorometric, and electrochemical detection for multi-macrolide analysis. The triple-quadrupole (QqQ), quadrupole ion trap (QIT), triple-quadrupole linear ion trap, time-of-flight (TOF), and quadrupole time-of-flight (QqTOF) mass spectrometers are current choices for the determination of macrolides, including quantification, confirmation, identification of their degradation products or metabolites, and structural elucidation. LC or UPLC coupled to a triple-quadrupole mass spectrometer operated in the multiple-reaction monitoring (MRM) mode (LC/MS/MS) is the first choice for quantification. UPLC-TOF or UPLC-QqTOF has been recognized as an emerging technique for accurate mass measurement and unequivocal identification of macrolides and their related compounds.     

Direct-EI in LC-MS: towards a universal detector for small-molecule applications

This review article will give an up-to-date and exhaustive overview on the efficient use of electron ionization (EI) to couple liquid chromatography and mass spectrometry (LC-MS) with an innovative interface called Direct-EI. EI is based on the gas-phase ionization of the analytes, and it is suitable for many applications in a wide range of LC-amenable compounds. In addition, thanks to its operating principles, it prevents unwelcome matrix effects (ME). In fact, although atmospheric pressure ionization (API) methodologies have boosted the use of LC-MS, the related analytical methods are sometime affected by inaccurate quantitative results, due to unavoidable and unpredictable ME. In addition, API's soft ionization spectra always demand for costly and complex tandem mass spectrometry (MS/MS) instruments, which are essential to acquire an "information-rich" spectrum and to obtain accurate quantitative information. In EI a one-stage analyzer is sufficient for a qualitative investigation and MS/MS detection is only used to improve sensitivity and to cut chemical noise. The technology illustrated here provides a robust and straightforward access to classical, well-characterized EI data for a variety of LC applications, and readily interpretable spectra for a wide range of areas of research. The Direct-EI interface can represent the basis for a forthcoming universal LC-MS detector for small molecules.     

LIQUID CHROMATOGRAPHY–MASS SPECTROMETRY BOTTOM‐UP PROTEOMIC METHODS IN ANIMAL SPECIES ANALYSIS OF PROCESSED MEAT FOR FOOD AUTHENTICATION AND THE DETECTION OF ADULTERATIONS

This review offers an overview of the current status and the most recent advances in liquid chromatography–mass spectrometry (LC‐MS) techniques with both high‐resolution and low‐resolution tandem mass analyzers applied to the identification and detection of heat‐stable species‐speci?c peptide markers of meat in highly processed food products. We present sets of myofibrillar and sarcoplasmic proteins, which turned out to be the source of 105 heat‐stable peptides, detectable in processed meat using LC‐MS/MS. A list of heat‐stable species‐specific peptides was compiled for eleven types of white and red meat including chicken, duck, goose, turkey, pork, beef, lamb, rabbit, buffalo, deer, and horse meat, which can be used as markers for meat authentication. Among the 105 peptides, 57 were verified by multiple reaction monitoring, enabling identification of each species with high specificity and selectivity. The most described and monitored species by LC‐MS/MS so far are chicken and pork with 26 confirmed heat‐stable peptide markers for each meat. In thermally processed samples, myosin, myoglobin, hemoglobin, l ‐lactase dehydrogenase A and β‐enolase are the main protein sources of heat‐stable markers. © 2019 John Wiley & Sons Ltd. Mass Spec Rev     

Recent advances in mycotoxin determination in food and feed by hyphenated chromatographic techniques/mass spectrometry

Mycotoxins are fungal toxins produced by molds, which occur universally in food and feed derivatives, and are produced under certain environmental conditions in the field before harvest, post-harvest, during storage, processing, and feeding. Mycotoxin contamination is one of the most relevant and worrisome problem concerning food and feed safety because it can cause a variety of toxic acute and chronic effects in human and animals. In this review we report the use of mass spectrometry in connection with chromatographic techniques for mycotoxin determination by considering separately the most diffuse class of mycotoxins: patulin, aflatoxins, ochratoxin A, zearalenone, trichothecenes, and fumonisins. Although the selectivity of mass spectrometry is unchallenged if compared to common GC and LC detection methods, accuracy, precision, and sensitivity may be extremely variable concerning the different mycotoxins, matrices, and instruments. The sensitivity issue may be a real problem in the case of LC/MS, where the response can be very different for the different ionization techniques (ESI, APCI, APPI). Therefore, when other detection methods (such as fluorescence or UV absorbance) can be used for the quantitative determination, LC/MS appears to be only an outstanding confirmatory technique. In contrast, when the toxins are not volatile and do not bear suitable chromophores or fluorophores, LC/MS appears to be the unique method to perform quantitative and qualitative analyses without requiring any derivatization procedure. The problem of exact quantitative determination in GC/MS and LC/MS methods is particularly important for mycotoxin determination in food, given the high variability of the matrices, and can be solved only by the use of isotopically labeled internal standards or by the use of ionization interfaces able to lower matrix effects and ion suppressions. When the problems linked to inconstant ionization and matrix effects will be solved, only MS detectors will allow to simplify more and more the sample preparation procedures and to avoid clean-up procedures, making feasible low-cost, high-throughput determination of mycotoxins in many different food matrices.     

Analysis of pesticides in water by liquid chromatography-tandem mass spectrometric techniques

Pesticide residues continue to be the focus of many environmental studies, and the number of articles describing the development of more advanced, multiresidue analytical methodologies does not decline. The use of liquid chromatography-mass spectrometry based on single quadrupole or ion trap analyzers is consolidated for this purpose. The implementation, in the near future, of more sophisticated mass analyzers, such as triple quadrupole and hybrid quadrupole-time-of-flight is anticipated for routine analysis. This article reviews the various works published so far in the literature for the determination of pesticides and transformation products (TPs) in water by means of liquid chromatography (LC) coupled to tandem mass spectrometry. It discusses the various ionization sources and analyzers used for this purpose, as well as the extraction procedures employed for previous sample preconcentration. Because of the widespread use of triple quadrupole analyzers for the generation of pesticides levels in water using tandem mass spectrometry, a table compiling the transitions monitored for ca. 70 compounds is also included.     

High‐precision mass spectrometric analysis using stable isotopes in studies of children

The use of stable isotopes combined with mass spectrometry (MS) provides insight into metabolic processes within the body. Herein, an overview on the relevance of stable isotope methodology in pediatric research is presented. Applications for the use of stable isotopes with MS cover carbohydrate, fat, and amino acid metabolism as well as body composition, energy expenditure, and the synthesis of specific peptides and proteins, such as glutathione and albumin. The main focus of these studies is on the interactions between nutrients and the endogenous metabolism within the body and how these factors affect the health of a growing infant. Considering that the early imprinting of metabolic processes hugely impacts metabolism (and thus functional outcome) later in life, research in this area is important and is advancing rapidly. The major fluxes on a metabolic level are the synthesis and breakdown rates. They can be quantified using kinetic tracer analysis and mathematical modeling. Organic MS and isotope ratio mass spectrometry (IRMS) are the two most mature techniques for the isotopic analysis of compounds. Introduction of the samples is usually done by coupling gas chromatography (GC) to either IRMS or MS because it is the most robust technique for specific isotopic analysis of volatile compounds. In addition, liquid chromatography (LC) is now being used more often as a tool for sample introduction of both volatile and non‐volatile compounds into IRMS or MS for ¹³C isotopic analyses at natural abundances and for ¹³C‐labeled enriched compounds. The availability of samples is often limited in pediatric patients. Therefore, sample size restriction is important when developing new methods. Also, the availability of stable isotope‐labeled substrates is necessary for measurements of the kinetics and concentrations in metabolic studies, which can be a limiting factor. During the last decade, the availability of these substrates has increased. Furthermore, improvements in the accuracy, precision, and sensitivity of existing techniques (such as GC/IRMS) and the development of new techniques (such as LC/IRMS) have opened up new avenues for tackling these limitations. © 2011 Wiley Periodicals, Inc. Mass Spec Rev 31:312–330, 2012     

煤焦油成分的气相色谱－质谱法分析

本文用气相色谱－质谱法对煤焦油进行了分析，确定出９１种化合物，脂肪族和芳香族化合物分别为３２种和５９种。     

The application of mass spectrometry in molecular dosimetry: Ethylene oxide as an example

Mass spectrometry plays an increasingly important role in the search for and quantification of novel chemically specific biomarkers. The revolutionary advances in mass spectrometry instrumentation and technology empower scientists to specifically analyze DNA and protein adducts, considered as molecular dosimeters, derived from reactions of a carcinogen or its active metabolites with DNA or protein. Analysis of the adducted DNA bases and proteins can elucidate the chemically reactive species of carcinogens in humans and can serve as risk‐associated biomarkers for early prediction of cancer risk. In this article, we review and compare the specificity, sensitivity, resolution, and ease‐of‐use of mass spectrometry methods developed to analyze ethylene oxide (EO)‐induced DNA and protein adducts, particularly N7‐(2‐hydroxyethyl)guanine (N7‐HEG) and N‐(2‐hydroxyethyl)valine (HEV), in human samples and in animal tissues. GC/ECNCI‐MS analysis after HPLC cleanup is the most sensitive method for quantification of N7‐HEG, but limited by the tedious sample preparation procedures. Excellent sensitivity and specificity in analysis of N7‐HEG can be achieved by LC/MS/MS analysis if the mobile phase, the inlet (split or splitless), and the collision energy are properly optimized. GC/ECNCI‐HRMS and GC/ECNCI‐MS/MS analysis of HEV achieves the best performance as compared with GC/ECNCI‐MS and GC/EI‐MS. In conclusion, future improvements in high‐throughput capabilities, detection sensitivity, and resolution of mass spectrometry will attract more scientists to identify and/or quantify novel molecular dosimeters or profiles of these biomarkers in toxicological and/or epidemiological studies. © 2011 Wiley Periodicals, Inc., Mass Spec Rev 30:733–756, 2011     

Analytical strategies for identifying drug metabolites

With the dramatic increase in the number of new chemical entities (NCEs) arising from combinatorial chemistry and modern high-throughput bioassays, novel bioanalytical techniques are required for the rapid determination of the metabolic stability and metabolites of these NCEs. Knowledge of the metabolic site(s) of the NCEs in early drug discovery is essential for selecting compounds with favorable pharmacokinetic credentials and aiding medicinal chemists in modifying metabolic "soft spots". In development, elucidation of biotransformation pathways of a drug candidate by identifying its circulatory and excretory metabolites is vitally important to understand its physiological effects. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) have played an invaluable role in the structural characterization and quantification of drug metabolites. Indeed, liquid chromatography (LC) coupled with atmospheric pressure ionization (API) MS has now become the most powerful tool for the rapid detection, structure elucidation, and quantification of drug-derived material within various biological fluids. Often, however, MS alone is insufficient to identify the exact position of oxidation, to differentiate isomers, or to provide the precise structure of unusual and/or unstable metabolites. In addition, an excess of endogenous material in biological samples often suppress the ionization of drug-related material complicating metabolite identification by MS. In these cases, multiple analytical and wet chemistry techniques, such as LC-NMR, enzymatic hydrolysis, chemical derivatization, and hydrogen/deuterium-exchange (H/D-exchange) combined with MS are used to characterize the novel and isomeric metabolites of drug candidates. This review describes sample preparation and introduction strategies to minimize ion suppression by biological matrices for metabolite identification studies, the application of various LC-tandem MS (LC-MS/MS) techniques for the rapid quantification and identification of drug metabolites, and future trends in this field.     

Application of mass spectrometry in the analysis of polybrominated diphenyl ethers

This review summarized the applications of mass spectrometric techniques for the analysis of the important flame retardants polybrominated diphenyl ethers (PBDEs) to understand the environmental sources, fate and toxicity of PBDEs that were briefly discussed to give a general idea for the need of analytical methodologies. Specific performance of various mass spectrometers hyphenated with, for example, gas chromatograph, liquid chromatograph, and inductively coupled plasma (GC/MS, LC/MS, and ICP/MS, respectively) for the analysis of PBDEs was compared with an objective to present the information on the evolution of MS techniques for determining PBDEs in environmental and human samples. GC/electron capture negative ionization quadrupole MS (GC/NCI qMS), GC/high resolution MS (GC/HRMS) and GC ion trap MS (GC/ITMS) are most commonly used MS techniques for the determination of PBDEs. New analytical technologies such as fast tandem GC/MS and LC/MS become available to improve analyses of higher PBDEs. The development and application of the tandem MS techniques have helped to understand environmental fate and transformations of PBDEs of which abiotic and biotic degradation of decaBDE is thought to be one major source of Br_1‐9BDEs present in the environment in addition to direct loading from commercial mixtures. MS‐based proteomics will offer an insight into the molecular mechanisms of toxicity and potential developmental and neurotoxicity of PBDEs. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:737–775, 2010     

间苯氧基苯甲醛及其衍生物的GC／MS研究

本文介绍间苯氧基苯甲醛产品及其原料的GC/MS分析。该系列化合物和它的衍生物的质谱均出现较强的分子离子峰,文中列出了检测到的十六种化合物,并根据基峰的变化确定氯原子取代的位置是在苯环上或是取代在甲基上。此外,还对间苯氧基苯甲醛生产过程中存在的副反应进行了推导,给出三类副反应式,并在GC/MS实验结果中得到证实。     

LABEL‐FREE BIO‐AFFINITY MASS SPECTROMETRY FOR SCREENING AND LOCATING BIOACTIVE MOLECULES

Despite the recent increase in the development of bioactive molecules in the drug industry, the enormous chemical space and lack of productivity are still important issues. Additional alternative approaches to screen and locate bioactive molecules are urgently needed. Label‐free bio‐affinity mass spectrometry (BA‐MS) provides opportunities for the discovery and development of innovative drugs. This review provides a comprehensive portrayal of BA‐MS techniques and of their applications in screening and locating bioactive molecules. After introducing the basic principles, alongside some application notes, the current state‐of‐the‐art of BA‐MS‐assisted drug discovery is discussed, including native MS, size‐exclusion chromatography‐MS, ultrafiltration‐MS, solid‐phase micro‐extraction‐MS, and cell membrane chromatography‐MS. Finally, several challenges and limitations of the current methods are summarized, with a view to potential future directions for BA‐MS‐assisted drug discovery. © 2019 John Wiley & Sons Ltd. Mass Spec Rev     

Structural characterization of bacterial lipopolysaccharides with mass spectrometry and on‐ and off‐line separation techniques

The focus of this review is the application of mass spectrometry to the structural characterization of bacterial lipopolysaccharides (LPSs), also referred to as “endotoxins,” because they elicit the strong immune response in infected organisms. Recently, a wide variety of MS‐based applications have been implemented to the structure elucidation of LPS. Methodological improvements, as well as on‐ and off‐line separation procedures, proved the versatility of mass spectrometry to study complex LPS mixtures. Special attention is given in the review to the tandem mass spectrometric methods and protocols for the analyses of lipid A, the endotoxic principle of LPS. We compare and evaluate the different ionization techniques (MALDI, ESI) in view of their use in intact R‐ and S‐type LPS and lipid A studies. Methods for sample preparation of LPS prior to mass spectrometric analysis are also described. The direct identification of intrinsic heterogeneities of most intact LPS and lipid A preparations is a particular challenge, for which separation techniques (e.g., TLC, slab‐PAGE, CE, GC, HPLC) combined with mass spectrometry are often necessary. A brief summary of these combined methodologies to profile LPS molecular species is provided. © 2012 Wiley Periodicals, Inc., Mass Spec Rev 32:90–117, 2013     

GC-MS/MS方法测定大米中农药残留杀虫环

目前测定大米中杀虫环的农药残留多采用气相色谱方法,样品前处理时试剂需要提纯,既危险又繁琐,目标峰还存在干扰,影响定性;采用液相色谱和液质联用的方法处理样品需使用固相萃取柱,增加了检测成本,也比较费时间,液质联用方法虽然定性比较准确,但其检出限比较高。本文采用溶剂萃取方法处理样品,气质质联用仪测定,样品处理简单,耗材成本低。本方法对仪器条件进行了优化,具有较好的重复性和较低的检出限。测定重复性的标准偏差(RSD)达到4.1%,检出限达到0.8μg/kg,由于本方法较低的检出限,对研究大米中农残杀虫环的降解过程将提供有力的检测手段。     

UHPLC-LTQ Orbitrap MS快速鉴别无患子果皮中部分苷及苷元成分

建立了超高效液相色谱-线性离子阱/静电场轨道阱组合式高分辨质谱(UHPLC-LTQ Orbitrap MS)联用技术整合多种数据采集、挖掘策略快速分析无患子果皮中苷类化合物;总结了两类无患子皂苷标准品的质谱裂解规律及特征碎片离子,用于无患子果皮中苷类成分的快速筛查和鉴别;探索了母离子列表(parent ion list,PIL)-MS2、PIL-MS3和高能碰撞(high energy collision dissociation,HCD)技术,用于无患子果皮中母核结构相近化合物的精细区分和鉴别;最后通过智能化的In silico策略(Mass Frontier软件中的FISH和MS Tree Match技术)对无患子果皮中新的苷类成分进行高通量筛查,并用HCD碎裂模式验证其预测的可靠性。结果表明,在无患子果皮中共鉴别出67个苷类化合物,其中38个化合物被快速筛查和鉴别,18个母核结构相近的化合物得以精细区分,11个新成分被推测。该方法能够为无患子质量控制及药效学研究提供参考数据,有助于复杂中药成分的快速定性分析。     

Metabolomic applications of HILIC–LC–MS

Hydrophilic interaction liquid chromatography (HILIC), although not a new technique, has enjoyed a recent renaissance with the introduction of robust and reproducible stationary phases. It is consequently finding application in metabolomics studies, which have traditionally relied on the stability of reversed phases (RPs), since the biofluids analyzed are predominantly aqueous and thus contain many polar analytes. HILIC's retention of those polar compounds and use of solvents readily compatible with mass spectrometry have seen its increasing adoption in studies of complex aqueous metabolomes. This review describes the stationary phases and their features, surveys HILIC–LC–MS's role in metabolomics experiments, discusses approaches to data extraction and analysis including multivariate analysis, and reviews the literature on HILIC–MS applications in metabolomics. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:671–684, 2010     

质谱新技术在毒品分析中的应用

毒品分析是办理涉毒犯罪案件的重要环节之一,为案件侦破和证据收集提供重要依据。质谱分析法具有灵敏度高、分析速度快、所需样品量少等特点,因其出色的分析性能越来越受到分析人员的重视。本文综述了色谱质谱联用技术和新兴原位直接电离质谱技术在毒品分析领域的应用情况,并展望了质谱新技术在毒品分析领域的发展前景。