Systematic comparison of sensitivity between hydrophilic interaction liquid chromatography and reversed phase liquid chromatography coupled with mass spectrometry

Impact of conditioning runs on hydrophilic interaction chromatography repeatability and its application as a second dimension in online comprehensive two-dimensional liquid chromatography

A common separation approach for polar compounds involves coupling reversed-phase liquid chromatography (RPLC) with hydrophilic interaction chromatography (HILIC) in two-dimensional chromatography. The higher proportion of acetonitrile used in the HILIC mobile phase, which enhances mass spectrometry detection, encourages its use in the second dimension. Previous studies demonstrated that the HILIC column can be partially equilibrated within very short timeframes without compromising retention time stability, rendering it suitable in online comprehensive two-dimensional liquid chromatography (LC×LC) setups. In addition, a specific number of conditioning cycles seems necessary to establish stable retention times. Here, the repeatability of HILIC when employed as second dimension in LC×LC was investigated, with a focus on determining the required number of conditioning cycles to achieve repeatable retention times. Various parameters influenced by the LC×LC online modulation system were studied, such as steep gradient slopes up to 8%, and very short equilibration times, less than or equal to dead time, as well as injection volume and solvent, which depend on the first dimension. Finally, the use of HILIC as a second dimension with tailored conditioning runs was applied to the analysis of hyaluronic acid hydrogel digests. The application of an RPLC×HILIC method using five conditioning runs yielded exceptional stability in second-dimension retention times.

Can plant hormonomics be built on simple analysis? A review

The field of plant hormonomics focuses on the qualitative and quantitative analysis of the hormone complement in plant samples, akin to other omics sciences. Plant hormones, alongside primary and secondary metabolites, govern vital processes throughout a plant's lifecycle. While active hormones have received significant attention, studying all related compounds provides valuable insights into internal processes. Conventional single-class plant hormone analysis employs thorough sample purification, short analysis and triple quadrupole tandem mass spectrometry. Conversely, comprehensive hormonomics analysis necessitates minimal purification, robust and efficient separation and better-performing mass spectrometry instruments. This review summarizes the current status of plant hormone analysis methods, focusing on sample preparation, advances in chromatographic separation and mass spectrometric detection, including a discussion on internal standard selection and the potential of derivatization. Moreover, current approaches for assessing the spatiotemporal distribution are evaluated. The review touches on the legitimacy of the term plant hormonomics by exploring the current status of methods and outlining possible future trends.

Optimization Strategies for Mass Spectrometry-Based Untargeted Metabolomics Analysis of Small Polar Molecules in Human Plasma

The untargeted approach to mass spectrometry-based metabolomics has a wide potential to investigate health and disease states, identify new biomarkers for diseases, and elucidate metabolic pathways. All this holds great promise for many applications in biological and chemical research. However, the complexity of instrumental parameters on advanced hybrid mass spectrometers can make the optimization of the analytical method immensely challenging. Here, we report a strategy to optimize the selected settings of a hydrophilic interaction liquid chromatography-tandem mass spectrometry method for untargeted metabolomics studies of human plasma, as a sample matrix. Specifically, we evaluated the effects of the reconstitution solvent in the sample preparation procedure, the injection volume employed, and different mass spectrometry-related operating parameters including mass range, the number of data-dependent fragmentation scans, collision energy mode, duration of dynamic exclusion time, and mass resolution settings on the metabolomics data quality and output. This study highlights key instrumental variables influencing the detection of metabolites along with suggested settings for the IQ-X tribrid system and proposes a new methodological framework to ensure increased metabolome coverage.

Comparison between 5 extractions methods in either plasma or serum to determine the optimal extraction and matrix combination for human metabolomics

BACKGROUND

Although metabolomics continues to expand in many domains of research, methodological issues such as sample type, extraction and analytical protocols have not been standardized, impeding proper comparison between studies and future research.

METHODS

In the present study, five solvent-based and solid-phase extraction methods were investigated in both plasma and serum. All these extracts were analyzed using four liquid chromatography coupled with high resolution mass spectrometry (LC-MS) protocols, either in reversed or normal-phase and with both types of ionization. The performances of each method were compared according to putative metabolite coverage, method repeatability and also extraction parameters such as overlap, linearity and matrix effect; in both untargeted (global) and targeted approaches using fifty standard spiked analytes.

RESULTS

Our results verified the broad specificity and outstanding accuracy of solvent precipitation, namely methanol and methanol/acetonitrile. We also reveal high orthogonality between methanol-based methods and SPE, providing the possibility of increased metabolome coverage, however we highlight that such potential benefits must be weighed against time constrains, sample consumption and the risk of low reproducibility of SPE method. Furthermore, we highlighted the careful consideration about matrix choice. Plasma showed the most suitable in this metabolomics approach combined with methanol-based methods.

CONCLUSIONS

Our work proposes to facilitate rational design of protocols towards standardization of these approaches to improve the impact of metabolomics research.

Managing sample introduction problems in hydrophilic interaction liquid chromatography

Sample injection can cause serious problems in hydrophilic interaction liquid chromatography (HILIC) when the injection solvent has higher elution strength than the mobile phase (mp). It can lead to asymmetric peak shapes and poor efficiency. The problem can occur when the mp contains a high proportion of organic e.g. 95% acetonitrile (a weak solvent) whereas the injection solvent contains a higher proportion of water (a strong solvent) that is necessary to dissolve polar samples. We investigated different strategies to overcome this problem. A simple method is pre-column dilution where the injector is programmed to deliver a plug of weak solvent (e.g. pure acetonitrile) along with the sample dissolved in a solvent with higher water content than the mp. Another option is to use alternative organic solvents to acetonitrile in the injection solvent, e.g. isopropanol, acetone or tetrahydrofuran, that may give enhanced sample solubility. The role of the volume of injection solvents was investigated as well as the possible effects of mass overload on the results. The use of small sample volumes is always recommended to reduce mismatch effects.

Liquid chromatography-mass spectrometry metabolite library for metabolomics: Evaluating column suitability using a scoring approach

Untargeted metabolomic studies require an extensive set of analyte (metabolic) information to be obtained from each analyzed sample. Thus, highly selective, and efficient analytical methodologies together with reversed-phase (RP) or hydrophilic interaction liquid chromatography (HILIC) are usually applied in these approaches. Here, we present a performance comparison of five different chromatographic columns (C18, C8, RP Amide, zicHILIC, OH5 HILIC phases) to evaluate their sufficiency of analysis for a large analyte library, consisting of 817 authentic standards. By taking into account experimental chromatographic parameters (i.e. retention time, peak tailing and asymmetry, FWHM, signal-to-noise ratio and peak area and intensity), the proposed column scoring approach provides a simple criterion that may assist analysis in the select of a stationary phase for those metabolites of interest. RPLC methods offered better results regarding metabolic library coverage, while the zicHILIC stationary phase delivered a bigger number of properly eluted compounds. This study demonstrates the importance of choosing the most suitable configuration for the analysis of different metabolic classes.

Contribution of ionic interactions to stationary phase selectivity in hydrophilic interaction chromatography

We compared the separation selectivities of 19 different hydrophilic interaction chromatography columns. The stationary phases included underivatized silica and hybrid particles, cyano‐bonded silica, materials with neutral ligands such as amide, diol, pentahydroxy, and urea, zwitterionic sorbents, and mixed‐mode materials with amine functionalities. A set of 77 small molecules was used to evaluate the columns. We visualized the retention behavior of the different columns using retention time correlation plots. The analytes were classified as cations, anions, or neutral based on their estimated charge under the separation conditions. This involved adjusting the dissociation constants of the analytes for the acetonitrile content of the mobile phase and experimentally determining the pH of the mobile phase containing 70% acetonitrile. The retention correlation plots show that the selectivity differences strongly depended on ionic interactions. Comparisons of the neutral stationary phases (e.g., diol vs. amide) showed more similar selectivity than did comparisons of neutral columns versus columns with cation or anion exchange activity (bare silica or amine columns, respectively). The zwitterionic columns did not behave as perfectly neutral. The correlation plots indicated that they exhibited either cation or anion exchange activity, although to a lesser degree than the silica and amine‐containing stationary phases.

Analysis of short-chain bioactive peptides by unified chromatography-electrospray ionization mass spectrometry. Part II. Comparison to reversed-phase ultra-high performance liquid chromatography

In the first part of this study, a unified chromatography (UC) analysis method, which is similar to supercritical fluid chromatography (SFC) but with wide mobile phase gradients of pressurized CO₂ and solvent, was developed to analyse short-chain peptides, with UV and mass spectrometry (MS) detection. In this second part, the method is compared to a reference reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) method, based on the analysis of 43 peptides, including 10 linear peptides and 33 cyclic ones. First, the orthogonality between the two methods was examined, based on the retention patterns. As the UC method was developed on a polar stationary phase (Ascentis Express OH5), the elution orders and selectivities were expected to be significantly different from RPLC on a non-polar stationary phase (ACQUITY CSH C18). Secondly, the success rate of the methods was examined, based on successful retention / elution of the peptides and the absence of observed co-elutions between the main peak and impurities. A successful analysis was obtained for 81% of the peptides in UC and 67% in RPLC. Thirdly, the performance of the methods for the intended application of impurity profiling of peptide drug candidates was assessed, based on the comparison of peak purities, the number of impurities detected and the thorough examination of impurity profiles. Excellent complementarity of the two methods for the specific task of impurity profiling, and for the separation of isomeric species was observed, with only one isomeric pair in this set remaining unresolved. The method sensitivity was however better with RPLC than UC. Finally, the operational costs in terms of solvent cost per analysis were the same between the two methods.

Hydrophilic Interaction Liquid Chromatography (HILIC): Latest Applications in the Pharmaceutical Researches

Background:

Significant advances have been occurred in analytical research since the 1970s by Liquid Chromatography (LC) as the separation method. Reverse Phase Liquid Chromatography (RPLC) method, using hydrophobic stationary phases and polar mobile phases, is the most commonly used chromatographic method. However, it is difficult to analyze some polar compounds with this method. Another separation method is the Normal Phase Liquid Chromatography (NPLC), which involves polar stationary phases with organic eluents. NPLC presents low-efficiency separations and asymmetric chromatographic peak shapes when analyzing polar compounds. Hydrophilic Interaction Liquid Chromatography (HILIC) is an interesting and promising alternative method for the analysis of polar compounds. HILIC is defined as a separation method that combines stationary phases used in the NPLC method and mobile phases used in the RPLC method. HILIC can be successfully applied to all types of liquid chromatographic separations such as pharmaceutical compounds, small molecules, metabolites, drugs of abuse, carbohydrates, toxins, oligosaccharides, peptides, amino acids and proteins.

Objective:

This paper provides a general overview of the recent application of HILIC in the pharmaceutical research in the different sample matrices such as pharmaceutical dosage form, plasma, serum, environmental samples, animal origin samples, plant origin samples, etc. Also, this review focuses on the most recent and selected papers in the drug research from 2009 to the submission date in 2020, dealing with the analysis of different components using HILIC.

Results and Conclusion:

The literature survey showed that HILIC applications are increasing every year in pharmaceutical research. It was found that HILIC allows simultaneous analysis of many compounds using different detectors.

Development of a HILIC-MS/MS method for the quantification of histamine and its main metabolites in human urine samples

An LC-MS/MS method was developed enabling the separation and quantification of histamine and its main metabolites (imidazole acetaldehyde, imidazole acetic acid, methyl imidazole acetic acid, methyl histamine, acetyl histamine) in urine samples. A fast separation was achieved in 10 min on two HILIC columns connected in series by adopting a linear gradient followed by an isocratic hold. The sample preparation consisted of a simple dilution step wherein 10 μL of urine was diluted with acetonitrile (ACN) to a final volume comprising 95% ACN. For methyl imidazole acetic acid, an additional dilution step was incorporated due to its high natural levels. Hereafter, the samples were stored at -20 °C and centrifuged prior to injection. Matrix matched calibrators were unavailable due to the endogenous occurrence of the compounds of interest. The occurrence of matrix effects and the lack of labeled internal standards prompted the use of the standard addition method as a viable alternative to solvent calibration. The validation of the method entailed matrix effects, accuracy and precision and was performed in compliance with the recent guidelines on endogenous compounds issued by the International Conference of Harmonization (ICH). The method was then adopted for the quantification of histamine and its metabolites in human urine samples collected from healthy volunteers and patients suffering from gastrointestinal discomfort.

Implementation of liquid chromatography-high resolution mass spectrometry methods for untargeted metabolomic analyses of biological samples: A tutorial

Untargeted metabolomics is now widely recognized as a useful tool for exploring metabolic changes taking place in biological systems under different conditions. By its nature, this is a highly interdisciplinary field of research, and mastering all of the steps comprised in the pipeline can be a challenging task, especially for those researchers new to the topic. In this tutorial, we aim to provide an overview of the most widely adopted methods of performing LC-HRMS-based untargeted metabolomics of biological samples. A detailed protocol is provided in the Supplementary Information for rapidly implementing a basic screening workflow in a laboratory setting. This tutorial covers experimental design, sample preparation and analysis, signal processing and data treatment, and, finally, data analysis and its biological interpretation. Each section is accompanied by up-to-date literature to guide readers through the preparation and optimization of such a workflow, as well as practical information for avoiding or fixing some of the most frequently encountered pitfalls.

Analytical strategies for the determination of amino acids: Past, present and future trends

This review describes the analytical methods that have been developed over the years to tackle the high polarity and non-chromophoric nature of amino acids (AAs). First, the historical methods are briefly presented, with a strong focus on the use of derivatization reagents to make AAs detectable with spectroscopic techniques (ultraviolet and fluorescence) and/or sufficiently retained in reversed phase liquid chromatography. Then, an overview of the current analytical strategies for achiral separation of AAs is provided, in which mass spectrometry (MS) becomes the most widely used detection mode in combination with innovative liquid chromatography or capillary electrophoresis conditions to detect AAs at very low concentration in complex matrixes. Finally, some future trends of AA analysis are provided in the last section of the review, including the use of supercritical fluid chromatography (SFC), multidimensional liquid chromatography and electrophoretic separations, hyphenation of ion exchange chromatography to mass spectrometry, and use of ion mobility spectrometry mass spectrometry (IM-MS). Various application examples will also be presented throughout the review to highlight the benefits and limitations of these different analytical approaches for AAs determination.

Choosing an Optimal Sample Preparation in Caulobacter crescentus for Untargeted Metabolomics Approaches

Untargeted metabolomics aims to provide a global picture of the metabolites present in the system under study. To this end, making a careful choice of sample preparation is mandatory to obtain reliable and reproducible biological information. In this study, eight different sample preparation techniques were evaluated using Caulobacter crescentus as a model for Gram-negative bacteria. Two cell retrieval systems, two quenching and extraction solvents, and two cell disruption procedures were combined in a full factorial experimental design. To fully exploit the multivariate structure of the generated data, the ANOVA multiblock orthogonal partial least squares (AMOPLS) algorithm was employed to decompose the contribution of each factor studied and their potential interactions for a set of annotated metabolites. All main effects of the factors studied were found to have a significant contribution on the total observed variability. Cell retrieval, quenching and extraction solvent, and cell disrupting mechanism accounted respectively for 27.6%, 8.4%, and 7.0% of the total variability. The reproducibility and metabolome coverage of the sample preparation procedures were then compared and evaluated in terms of relative standard deviation (RSD) on the area for the detected metabolites. The protocol showing the best performance in terms of recovery, versatility, and variability was centrifugation for cell retrieval, using MeOH:H₂O (8:2) as quenching and extraction solvent, and freeze-thaw cycles as the cell disrupting mechanism.

The Emergence of Universal Chromatographic Methods in the Research and Development of New Drug Substances

Manufacturing process development of new drug substances in the pharmaceutical industry combines numerous chemical challenges beyond the efficient synthesis of complex molecules. Optimization of a synthetic route involves the screening of multiple reaction variables with a desired outcome that not only depends on an increased product yield but is also highly influenced by the removal efficacy of residual chemicals and reaction byproducts during the subsequent synthetic route. Consequently, organic chemists must survey a wide array of synthetic variables to develop a highly productive, green, and cost-effective manufacturing process. The time constraints of developing robust quantitative methods prior to each processing step can easily lead to sample analysis becoming a bottleneck in synthetic route development. In this regard, conventional "on demand" analytical method development and optimization approaches, traditionally used for guiding synthetic chemistry efforts, become unsustainable. This Account introduces recent efforts to address the aforementioned challenges through the development and implementation of generic or more universal chromatographic methods that can cover a broad spectrum of targeted compound classes. Such generic methods require significant resolving power to enable baseline resolution of multicomponent mixtures in a single experimental run without additional method customization but must be simple enough to allow for routine use by chemists, chemical engineers and other researchers with little experience in chromatographic method development. These powerful analytical methodologies are often employed to minimize the time spent developing new analytical assays, while also facilitating method transfer to manufacturing facilities and application in regulatory settings. Diverse examples of universal and fit-for-purpose analytical procedures are presented herein, illustrating the power of modern readily available analytical technology for streamlining the development of new drug substances in organic chemistry laboratories across both academic and industrial sectors. With recent advances in analytical instrumentation and column technologies, universal chromatographic methods are quickly becoming a proactive and effective strategy to accelerate the discovery and implementation of new synthetic methodologies, especially but not limited to laboratories where the synthetic process route is undergoing rapid change and optimization. Targets of these generic methods include analysis of organic solvents, acid and basic additives, nucleotide species, palladium scavengers, impurity mapping, enantiopurity, synthetic intermediates, active pharmaceutical ingredients and their counterions, dehalogenation byproducts, and mixtures of organohalogenated pharmaceuticals, among other chemicals used or formed in process chemistry reactions.

Untargeted LC/MS-based metabolic phenotyping (metabonomics/metabolomics): The state of the art

Liquid chromatography (LC) hyphenated to mass spectrometry is currently the most widely used means of determining metabolic phenotypes via both untargeted and targeted analysis. At present a range of analytical separations, including reversed-phase, hydrophilic interaction and ion-pair LC are employed to maximise metabolome coverage with ultra (high) performance liquid chromatography (UHPLC) increasingly displacing conventional high performance liquid chromatography because of the need for short analysis times and high peak capacity in such applications. However, it is widely recognized that these methodologies do not entirely solve the problems facing researchers trying to perform comprehensive metabolic phenotyping and in addition to these "routine" approaches there are continuing investigations of alternative separation methods including 2-dimensional/multi column approaches. These involve either new stationary phases or multidimensional combinations of the more conventional materials currently used, as well as application of miniaturization or "new" approaches such as supercritical HP and UHP- chromatographic separations. There is also a considerable amount of interest in the combination of chromatographic and ion mobility separations, with the latter providing both an increase in resolution and the potential to provide additional structural information via the determination of molecular collision cross section data. However, key problems remain to be solved including ensuring quality, comparability across different laboratories and the ever present difficulty of identifying unknowns.

Toward a better understanding of chronic kidney disease with complementary chromatographic methods hyphenated with mass spectrometry for improved polar metabolome coverage

The prevalence of chronic kidney disease (CKD) is increasing worldwide. New technical approaches are needed to improve early diagnosis, disease understanding and patient monitoring, and to evaluate new therapies. Metabolomics, as a prime candidate in the field of CKD research, aims to comprehensively analyze the metabolic complexity of biological systems. An extensive analysis of the metabolites contained in biofluids is therefore needed, and the combination of data obtained from multiple analytical platforms constitutes a promising methodological approach. This study presents an original workflow based on complementary chromatographic conditions, reversed-phase and hydrophilic interaction chromatography hyphenated to mass spectrometry to improve the polar metabolome coverage coupled with a univocal metabolite annotation strategy enabling a rapid access to the biological interpretation. This multiplatform workflow was applied in a CKD cohort study to assess plasma metabolic profile modifications related to renal disease. Multivariate analysis of 278 endogenous annotated metabolites enabled patient stratification with respect to CKD stages and helped to generate new biological insights, while also confirming the relevance of tryptophan metabolism pathway in this condition.

A scoring approach for multi-platform acquisition in metabolomics

Since the ultimate goal of untargeted metabolomics is the analysis of the broadest possible range of metabolites, some new metrics have to be used by researchers to evaluate and select different analytical strategies when multi-platform analyses are considered. In this context, we aimed at developing a scoring approach allowing to compare the performance of different LC-MS conditions for metabolomics studies. By taking into account both chromatographic and MS attributes of the analytes' peaks (i.e. retention, signal-to-noise ratio, peak intensity and shape), the newly proposed score reflects the potential of a set of LC-MS operating conditions to provide useful analytical information for a given compound. A chemical library containing 597 metabolites was used as a benchmark to apply this approach on two RPLC and three HILIC methods hyphenated to high resolution mass spectrometry (HRMS) in positive and negative ionization modes. The scores not only allowed to evaluate each analytical platform, but also to optimize the number of analytical methods needed for the analysis of metabolomics samples. As a result, the most informative combination of three LC methods and ionization modes was found, leading to a coverage of nearly 95% of the detected compounds. It was therefore demonstrated that the overall performance reached with three selected methods was almost equivalent to the performance reached when five LC-MS conditions were used.

Metabolomics in chronic kidney disease: Strategies for extended metabolome coverage

Chronic kidney disease (CKD) is becoming a major public health issue as prevalence is increasing worldwide. It also represents a major challenge for the identification of new early biomarkers, understanding of biochemical mechanisms, patient monitoring and prognosis. Each metabolite contained in a biofluid or tissue may play a role as a signal or as a driver in the development or progression of the pathology. Therefore, metabolomics is a highly valuable approach in this clinical context. It aims to provide a representative picture of a biological system, making exhaustive metabolite coverage crucial. Two aspects can be considered: analytical and biological coverage. From an analytical point of view, monitoring all metabolites within one run is currently impossible. Multiple analytical techniques providing orthogonal information should be carried out in parallel for coverage improvement. The biological aspect of metabolome coverage can be enhanced by using multiple biofluids or tissues for in-depth biological investigation, as the analysis of a single sample type is generally insufficient for whole organism extrapolation. Hence, recording of signals from multiple sample types and different analytical platforms generates massive and complex datasets so that chemometric tools, including data fusion approaches and multi-block analysis, are key tools for extracting biological information and for discovery of relevant biomarkers. This review presents the recent developments in the field of metabolomic analysis, from sampling and analytical strategies to chemometric tools, dedicated to the generation and handling of multiple complementary metabolomic datasets enabling extended metabolite coverage to improve our biological knowledge of CKD.

Handling Complexity in Animal and Plant Science Research-From Single to Functional Traits: Are We There Yet?

The current knowledge of the main factors governing livestock, crop and plant quality as well as yield in different species is incomplete. For example, this can be evidenced by the persistence of benchmark crop varieties for many decades in spite of the gains achieved over the same period. In recent years, it has been demonstrated that molecular breeding based on DNA markers has led to advances in breeding (animal and crops). However, these advances are not in the way that it was anticipated initially by the researcher in the field. According to several scientists, one of the main reasons for this was related to the evidence that complex target traits such as grain yield, composition or nutritional quality depend on multiple factors in addition to genetics. Therefore, some questions need to be asked: are the current approaches in molecular genetics the most appropriate to deal with complex traits such as yield or quality? Are the current tools for phenotyping complex traits enough to differentiate among genotypes? Do we need to change the way that data is collected and analysed?

Method optimization of hydrophilic interaction chromatography separation of nucleotides using design of experiment approaches I: Comparison of several zwitterionic columns

A systematic method in hydrophilic interaction chromatography (HILIC) was developed for the separation of four monophosphate nucleotides using design of experiment (DOE) approaches. Three HPLC parameters, the buffer concentration (ammonium acetate concentration), gradient time, and temperature, were evaluated within the quality design framework, and the effects on chromatographic parameters were investigated. Four zwitterionic columns (ZIC-HILIC, ZIC-cHILIC, NUCLEODUR HILIC, and PC HILIC) were used to separate four nucleotides, and the HPLC conditions for each column were successfully optimized, although PC HILIC did not give peaks that were suitable for optimization. In addition, it was proved that optimized HPLC conditions differed from column to column even when the same types of zwitterionic sulfobetaine-functionalized columns were applied. This tendency was explained by differences in the separation characteristics of each column, the thickness of the water-enriched layer on the surface of the silica supports, and the pH. DOE for development of the HPLC method provides an effective explanation of the interactions among the variable parameters, especially in HILIC mode. Finally, a robust analytical method could be established by setting the optimum parameters. Among the employed columns, ZIC-cHILIC provided the widest range of suitable analytical conditions. NUCLEODUR HILIC was difficult to build a robust analytical method since the elution order of cytidine monophosphate and guanosine monophosphate was reversed.

Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes

Presently, routine screening misses many cases of prediabetes and early type 2 diabetes (T2D). Therefore, better biomarkers are needed for a simple and early detection of abnormalities of glucose metabolism and prediction of future T2D. Possible candidates for this include plasma or serum amino acids because glucose and amino acid metabolism are closely connected. This review presents the available evidence of this connectivity and discusses its clinical implications. First, we examine the underlying physiological, pre-analytical, and analytical issues. Then, we summarize results of human studies that evaluate amino acid levels as markers for insulin resistance, prediabetes, and future incident T2D. Finally, we illustrate the interconnection of amino acid levels and metabolic syndrome with our own data from a deeply phenotyped human cohort. We also discuss how amino acids may contribute to the pathophysiology of T2D. We conclude that elevated branched-chain amino acids and reduced glycine are currently the most robust and consistent amino acid markers for prediabetes, insulin resistance, and future T2D. Yet, we are cautious regarding the clinical potential even of these parameters because their discriminatory power is insufficient and their levels depend not only on glycemia, but also on other components of the metabolic syndrome. The identification of more precise intermediates of amino acid metabolism or combinations with other biomarkers will, therefore, be necessary to obtain in order to develop laboratory tests that can improve T2D screening.

Simultaneous determination of hydrophilic and lipophilic constituents in herbal medicines using directly-coupled reversed-phase and hydrophilic interaction liquid chromatography-tandem mass spectrometry

Limitations in the separation ability of conventional liquid chromatography system remains a challenge in developing a versatile method for simultaneously determining both hydrophilic and lipophilic constituents in herbal medicines (HMs). To measure compounds covering a broad polarity span in HMs, we developed a directly-coupled reversed-phase and hydrophilic interaction liquid chromatography-tandem mass spectrometry system. Samples were firstly separated according to lipophilicity by using a C₁₈ column. Utilizing a T-piece as connector, the eluent was then pumped into an amide column to get further separation that mainly based on the hydrogen bonding effects. Dan-Qi pair, an extensively used herb-combined prescription in China, was selected to test the practicability and performance of the established system. A total of 27 components, containing 9 hydrophilic and 18 lipophilic constituents, were simultaneously determined using a schedule multiple reaction monitoring method in 15 min. Up to 69.9% content could be monitored in one injection in Dan-Qi pair extract, showing a significant advantage over previous methods. The proposed method was expected to benefit the controllability of herbal medicines.

Quantitation of γ-aminobutyric acid in equine plasma by hydrophilic interaction liquid chromatography with tandem mass spectrometry

γ-Aminobutyric acid is the principal inhibitory neurotransmitter in the central nervous system and regulates the neuronal excitability. There has been anecdotal evidence that γ-aminobutyric acid has been used within a few hours prior to competition in equine sports to calm down nervous horses. However, regulating the use of γ-aminobutyric acid is challenging because it is an endogenous substance in the horse. γ-Aminobutyric acid is usually present at low ng/mL levels in equine plasma; therefore, a sensitive method has to be developed to quantify these low background levels. Measuring low concentrations of endogenous γ-aminobutyric acid is essential to establish a threshold that can be used to differentiate levels attributable to exogenous administrations of γ-aminobutyric acid. A hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry method was developed and validated for the quantitation of γ-aminobutyric acid in equine plasma. Calibrators were prepared in artificial surrogate matrix consisting of 35 mg/mL equine serum albumin in phosphate buffered saline. Samples were prepared by protein precipitation with acetonitrile. Utilizing this methodology, a total of 403 equine plasma samples collected post-competition from horses participating in equestrian events in Canada were analyzed.

Comprehensive metabonomic analysis of heart tissue from isoproterenol-induced myocardial infarction rat based on reversed-phase and hydrophilic interaction chromatography coupled to mass spectrometry

We aim to describe the metabonomic characteristics of myocardial infarction rats. High-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry was utilized to develop a metabonomic method of the heart homogenates of myocardial infarction rats. Hydrophilic interaction chromatography allows the analysis of high polar metabolites, providing complementary information to reversed-phase liquid chromatography. We combined reversed phase and hydrophilic interaction chromatographic separations to analyze 18 samples, ten from myocardial infarction rat hearts and eight from normal rat hearts. A total of 16 potential biomarkers in rat heart tissue were screened out, primarily related to oxidative stress, nitric oxide damage, taurine, and hypotaurine metabolism and sphingolipid metabolism. This research showed that a comprehensive metabonomic study is a useful tool to reveal the underlying mechanism of myocardial infarction.

Quantitative mass spectrometry methods for pharmaceutical analysis

Quantitative pharmaceutical analysis is nowadays frequently executed using mass spectrometry. Electrospray ionization coupled to a (hybrid) triple quadrupole mass spectrometer is generally used in combination with solid-phase extraction and liquid chromatography. Furthermore, isotopically labelled standards are often used to correct for ion suppression. The challenges in producing sensitive but reliable quantitative data depend on the instrumentation, sample preparation and hyphenated techniques. In this contribution, different approaches to enhance the ionization efficiencies using modified source geometries and improved ion guidance are provided. Furthermore, possibilities to minimize, assess and correct for matrix interferences caused by co-eluting substances are described. With the focus on pharmaceuticals in the environment and bioanalysis, different separation techniques, trends in liquid chromatography and sample preparation methods to minimize matrix effects and increase sensitivity are discussed. Although highly sensitive methods are generally aimed for to provide automated multi-residue analysis, (less sensitive) miniaturized set-ups have a great potential due to their ability for in-field usage.This article is part of the themed issue 'Quantitative mass spectrometry'.

Study of matrix effects for liquid chromatography-electrospray ionization tandem mass spectrometric analysis of 4 aminoglycosides residues in milk

Matrix effect (ME) is always a major issue for the development of LC-MS/MS method. ME resulting from co-eluting residual matrix components can affect the ionization efficiency of target analytes, leading to quantification errors of the analytes of interest. The present work evaluates MEs of milk samples on simultaneous analysis of four aminoglycosides residues via LC-ESI/MS/MS including streptomycin, dihydrostreptomycin, spectinomycin and kanamycin. Approaches to reduce MEs were examined: optimization of the sample preparation, sample dilution and lower flow rate used. Three commercial sorbents were tested including Oasis MCX, Oasis HLB and Oasis WCX. WCX behaved better for all analytes, but high MEs (80.8-134.9%) were obtained. Therefore, a consecutive SPE of tC18-WCX was found to effectively reduce ME. Milk samples from different manufacturers were analyzed and low MEs (85.6-112.9%) were obtained.

Recent advances in the application of hydrophilic interaction chromatography for the analysis of biological matrices

Hydrophilic interaction chromatography (HILIC) is being increasingly used for the analysis of hydrophilic compounds in biological matrices. The complexity of biological samples demands adequate sample preparation procedures, specifically adjusted for HILIC analyses. Currently, most bioanalytical assays are performed on bare silica and ZIC-HILIC columns. Trends in HILIC for bioanalysis include smaller particle sizes and miniaturization of the analytical column. For complex biological samples, multidimensional techniques can separate and identify more compounds than 1D separations. The high volatility of the mobile phase, the added separation power and high sensitivity make MS the detection method of choice for bioanalysis using HILIC, although other detectors such as evaporative light scattering detection, charged aerosol detection and nuclear magnetic resonance have been reported.