Quantitation of small molecules using high-resolution accurate mass spectrometers - a different approach for analysis of biological samples

Biomonitoring urinary organophosphorus flame retardant metabolites by liquid-liquid extraction and ultra-high performance liquid chromatography-tandem mass spectrometry and their association with oxidative stress

Organophosphate flame retardants (OPFRs) are widely used as substitutes for traditional brominated flame retardants, necessitating a reliable and sensitive method for biomonitoring their urinary metabolites to assess human exposure. This study conducted biomonitoring of 10 metabolites of OPFRs in 152 adults and assessed their association with oxidative stress biomarkers 8-hydroxydeoxyguanosine and 8-hydroxyguanosine. Urinary metabolites of OPFRs were released via enzymatic deconjugation. The addition of sodium chloride to the urine samples increases the ionic strength, inducing a salting-out effect that reduces the solubility of these compounds, thereby facilitating their extraction with a mixture of ethyl acetate and acetonitrile. Then, the metabolites of OPFRs were quantified by ultra-high performance liquid chromatography-tandem mass spectrometry, and we validated the method for linear range, precision, matrix effect, and method detection limit. The detection limit of the metabolites of OPFRs ranged from 0.01 to 0.2 μg/L, and these metabolites were detected with high frequencies ranging from 25.0 to 98.68% in the urine samples. The concentration of bis (2-chloroethyl) phosphate was significantly higher in males than in females, with the geometric mean concentration of 0.88 μg/L for males and 0.53 μg/L for females, respectively. Spearman correlation analysis revealed weak but statistically significant positive correlations among the urinary metabolites. Bayesian kernel machine regression analysis showed a significant positive association between elevated urinary concentrations of metabolites of OPFRs and increased oxidative stress levels. Di-n-butyl phosphate was identified as the metabolite that significantly contributed to the elevated level of 8-hydroxyguanosine.

LC-HRMS methods for the quantification of two artemisinin drugs and their metabolites in rat blood and plasma

As first-line antimalarials used in the artemisinin combination therapy, artemisinin drugs exert their action inside red blood cells. However, the blood pharmacokinetic characteristics of artemisinin drugs have not been fully revealed owing to their built-in chemical instability initiated by Fe2+ released from hemoglobin, with limited information on their metabolites. In this study, liquid chromatography tandem high-resolution mass spectrometric (LC-HRMS) methods were developed for the quantification of two representative artemisinin drugs (artemisinin, ART; dihydroartemisinin, DHA) and their respective metabolite (deoxyartemisinin, D-ART; dihydroartemisinin glucuronide, DHA-Glu) in rat blood/plasma. The blood samples were pretreated with the stabilizer (0.4 m potassium dichromate and 3% EDTA-2Na). The methods displayed excellent specificity, linearity, accuracy and precision for ART (17.7-709.2 nm) and its metabolite D-ART (18.8-751.9 nm), and the linear range was 40.0-4,000.0 nm for both DHA and DHA-Glu. The methods were successfully applied to the pharmacokinetic studies of ART and DHA in rats. The blood-to-plasma ratio was 0.8-1.5 for ART, 1.0-1.5 for D-ART, 1.2-2.2 for DHA and 0.9-1.3 for DHA-Glu, which was time dependent. The results indicated that artemisinin drugs and their metabolites showed a high but different blood-to-plasma ratio, which should be considered when optimizating their dosing regimens or evaluating their clinical outcomes.

Determination of alkaloid-inspired molecule vindeburnol in rabbit plasma by UPLC-HRMS and its application to pharmacokinetic studies and preliminary metabolite identification

The eburnamine-vincamine alkaloids exhibit a range of pharmacological activities. There is a limited understanding of the pharmacokinetics and pharmacodynamics of vindeburnol, a synthetic derivative of this chemical class of alkaloids. A fast and reliable UPLC-HRMS method was developed and validated to quantify vindeburnol in Soviet Chinchilla rabbit plasma from pharmacokinetics studies. An ultra-performance liquid chromatography system equipped with a Waters Acquity UPLC HSS T3 column was used for chromatographic separation by gradient elution with 0.1% (v/v) formic acid in water and acetonitrile. An Impact II QqTOF high-resolution mass spectrometer equipped with an Apollo II electrospray ionization source was used for analysis in positive mode; the ions [M+H]+m/z 269.1648 ± 0.003 and m/z 351.2067 ± 0.003 were monitored for vindeburnol and internal standard (vinpocetine), respectively. Preliminary metabolite profiling was also performed, and the pharmacokinetics of the identified metabolites were evaluated. The mean retention times for vindeburnol and vinpocetine were 2.0 and 3.5 min. The UPLC-HRMS method was validated with accuracy and precision within the 15% acceptance limit (8.2% and 11.0%, respectively). The mean extraction recovery value of vindeburnol from rabbit plasma was 77%. Pharmacokinetic evaluation of vindeburnol revealed that the compound is distributed rapidly with a short elimination half-life. Vindeburnol undergoes extensive first-pass metabolism and is metabolized into hydroxyvindeburnol and vindeburnol glucuronide.

Analytical Approaches in Official Food Safety Control: An LC-Orbitrap-HRMS Screening Method for the Multiresidue Determination of Antibiotics in Cow, Sheep, and Goat Milk

The presence of unauthorized substances, such as residues of veterinary medicines or chemical contaminants, in food can represent a possible health concern. For this reason, a complete legislative framework has been established in the European Union (EU), which defines the maximum limits allowed in food and carries out surveillance programs to control the presence of these substances. Official food control laboratories, in order to ensure a high level of consumer protection, must respond to the challenge of improving and harmonizing the performance of the analytical methods used for the analysis of residues of authorized, unauthorized, or prohibited pharmacologically active substances. Laboratories must also consider the state of the art of the analytical methodologies and the performance requirements of current legislation. The aim of this work was to develop a multiresidue method for the determination of antibiotics in milk, compliant with the criteria and procedures established by Commission Implementing Regulation (EU) 2021/808. The method uses an LC-Orbitrap-HRMS for the determination of 57 molecules of antibiotic and active antibacterial substances belonging to different chemical classes (beta-lactams, tetracyclines, sulfonamides, quinolones, pleuromutilins, macrolides, and lincosamides) in bovine, ovine, and goat milk samples. It provides a simple and quick sample pretreatment and a subsequent identification phase of analytes, at concentrations equal to or lower than the maximum residual limit (MRL), in compliance with Commission Regulation (EU) 2010/37. The validation parameters: selectivity, stability, applicability, and detection capability (ccβ), are in agreement with the requirements of Commission Implementing Regulation (EU) 2021/808 and demonstrated the effectiveness of the method in detecting veterinary drug residues at the target screening concentration (at the MRL level or below), with a false positive rate of less than 5%. This method represents an effective solution for detecting antibiotics in milk, which can be successfully applied in routine analyses for official food control plans.

Optimization, validation, and comparison of a rapid method for the quantification of insulin-like growth factor 1 in serum using liquid chromatography-high-resolution mass spectrometry

Human insulin-like growth factor 1 (IGF-I) is the primary mediator of the effects of the growth hormone (GH). Therefore, it has been used as a biomarker to detect the abuse of GH in sports. The measurement of IGF-I relies on mass-based and immunological approaches to analysis. Among the mass-based analysis methods, liquid chromatography-mass spectrometry (LC-MS) has a number of functional advantages. LC-MS measurements based on the quantification of IGF-I, according to trypsin digestion, are used in the most common method of analyzing doping. However, this method is time-consuming and subject to experimental variability. In this study, we optimized a rapid method for detecting IGF-I without the trypsin digestion step. This method of analysis uses an ultra-centrifugal filter and an LC-HRMS through narrow-range mass scan method. To verify the validity of this method, eight categories of validation testing were applied with the following results: linearity, R² > 0.99; limit of detection, 15 ng/ml; limit of quantification, 20 ng/ml; accuracy, >99%; recovery rate, >95%; carryover, <0.03; and inter- and intra-day precision values, %CV < 2% and %CV < 6%, respectively. Furthermore, we discussed the correlation of the quantified concentration from two other methods, immunoradiometric assay (IRMA) and parallel reaction monitoring method, using 209 serum samples. In conclusion, although both mass spectrometry-based methods worked equally well in terms of analytical performance and correlation with IRMA results, narrow-range mass scan method had several advantages, such as time and cost savings and reliable reproducibility, over the existing methods.

Accurate, sensitive determination of omega-6 and omega-3 polyunsaturated fatty acids in human plasma, urine samples

Quantitative determination of omega-6 and omega-3 polyunsaturated fatty acids in human plasma and urine with high accuracy and precision provides significant information to monitor the underlying etiology of several diseases. In this regard, liquid chromatography-mass spectrometry is a good choice owing to its great selectivity and sensitivity. Additionally, the hybrid quadrupole-time of flight-mass spectrometer systems provides easy identification of target compounds with superior mass measurements. In this study, an analytical method has been developed for simple, accurate and simultaneous determination of linoleic acid, arachidonic acid, docosahexaenoic acid and eicosapentaenoic acid in a short chromatographic analysis period. The developed method is suitable for the quantitative detection of these four compounds with detection limits ranging between 1.1-3.0 ng ml^-1 and its applicability was assessed in human urine and plasma samples. As a result, acceptable accuracy (between 83 and 111%) and good precision (<6%) were obtained for target compounds using matrix matching calibration strategy.

Reorientation of Polymers in an Applied Electric Field for Electrochemical Sensors

This mini review investigates the relationship and interactions of polymers under an applied electric field (AEF) for sensor applications. Understanding how and why polymers are reoriented and manipulated by under an AEF is essential for future growth in polymer-based electrochemical sensors. Examples of polymers that can be manipulated in an AEF for sensor applications are provided. Current methods of monitoring polymer reorientation will be described, but new techniques are needed characterize polymer response to various AEF stimuli. The unique and reproducible stimuli response of polymers elicited by an AEF has significant potential for growth in the sensing community.

Analysis of Tryptophan Metabolites in Serum Using Wide-Isolation Strategies for UHPLC-HRMS/MS

Current targeted metabolomic workflows are limited by design and thus sacrifice crucial information from a profiling standpoint that could lead to a more fundamental understanding of the metabolic processes of interest. One drawback to performing targeted analysis on ion trapping instruments is the potential for increased variability in analysis when analytes and standards are isolated and trapped individually for fragmentation. In addition, this sequential isolation process increases the duty cycle of the mass spectrometer and reduces the number of points collected across a chromatographic peak. To address this, the use of a wide-isolation window (12 Da) to encompass the target analyte and the isotope standard within a single fragmentation window ensures that fragmentation is consistent when quantitation relies on the ratio of the target to the internal standard. Additionally, the preservation of a faster scan rate ensures that optimal representation of chromatographic peaks is preserved for the purposes of both quantitative and qualitative analyses that require peak integration for statistical analysis. The use of this flexible method is promising in the investigation of pathways that require multiple targets and are highly integrated within the system. Here, we demonstrate the application of this method in a fast ultra-high performance liquid chromatography (UHPLC) analysis to integrate wide-isolation quantitative strategies for high-resolution mass spectrometry (HRMS) combined with profiling qualitative metabolomics for the analysis of tryptophan degradation metabolites in mouse serum. Analysis of tryptophan-deficient states as compared to control in both germ-free or E. coli gut microbiota states was used to quantitate pathway-specific metabolites as well as obtain full profiling information. The quantitative and qualitative results revealed the preservation of the primary pathways of degradation in the kynurenine pathway to potentially produce primary products such as nicotinamide during stress-induced dietary states.

Towards Mass Spectrometry-Based Chemical Exposome: Current Approaches, Challenges, and Future Directions

The proposal of the “exposome” concept represents a shift of the research paradigm in studying exposure-disease relationships from an isolated and partial way to a systematic and agnostic approach. Nevertheless, exposome implementation is facing a variety of challenges including measurement techniques and data analysis. Here we focus on the chemical exposome, which refers to the mixtures of chemical pollutants people are exposed to from embryo onwards. We review the current chemical exposome measurement approaches with a focus on those based on the mass spectrometry. We further explore the strategies in implementing the concept of chemical exposome and discuss the available chemical exposome studies. Early progresses in the chemical exposome research are outlined, and major challenges are highlighted. In conclusion, efforts towards chemical exposome have only uncovered the tip of the iceberg, and further advancement in measurement techniques, computational tools, high-throughput data analysis, and standardization may allow more exciting discoveries concerning the role of exposome in human health and disease.

Ultra-Performance Liquid Chromatography-High-Resolution Mass Spectrometry and Direct Infusion-High-Resolution Mass Spectrometry for Combined Exploratory and Targeted Metabolic Profiling of Human Urine

The application of metabolic phenotyping to epidemiological studies involving thousands of biofluid samples presents a challenge for the selection of analytical platforms that meet the requirements of high-throughput precision analysis and cost-effectiveness. Here direct infusion–nanoelectrospray (DI–nESI) was compared with an ultra-performance liquid chromatography (UPLC)–high-resolution mass spectrometry (HRMS) method for metabolic profiling of an exemplary set of 132 human urine samples from a large epidemiological cohort. Both methods were developed and optimized to allow the simultaneous collection of high-resolution urinary metabolic profiles and quantitative data for a selected panel of 35 metabolites. The total run time for measuring the sample set in both polarities by UPLC–HRMS was 5 days compared with 9 h by DI–nESI–HRMS. To compare the classification ability of the two MS methods, we performed exploratory analysis of the full-scan HRMS profiles to detect sex-related differences in biochemical composition. Although metabolite identification is less specific in DI–nESI–HRMS, the significant features responsible for discrimination between sexes were mostly the same in both MS-based platforms. Using the quantitative data, we showed that 10 metabolites have strong correlation (Pearson’s r > 0.9 and Passing–Bablok regression slope of 0.8–1.3) and good agreement assessed by Bland–Altman plots between UPLC–HRMS and DI–nESI–HRMS and thus can be measured using a cheaper and less sample- and time-consuming method. A further twenty metabolites showed acceptable correlation between the two methods with only five metabolites showing weak correlation (Pearson’s r < 0.4) and poor agreement due to the overestimation of the results by DI–nESI–HRMS. 

Improving selectivity and sensitivity of protein quantitation by LC–HR–MS/MS: determination of somatropin in rat plasma

Aim: Protein quantitation by digestion of a biological sample followed by LC–MS analysis of a signature peptide can be a challenge because of the high complexity of the digested matrix. Results/methodology: The use of LC with high-resolution (quadrupole-TOF) MS detection allowed quantitation of the 22-kDa biopharmaceutical somatropin in 60 μl of rat plasma down to 25 ng/ml with minimal further sample treatment. Reducing the mass extraction window to 0.01 Da considerably decreased the interference of tryptic peptides, enhanced sensitivity and improved accuracy and precision. Analysis with LC–MS/MS resulted in a less favorable limit of quantitation of 100 ng/ml. Conclusion: HRMS is an interesting option for the quantitation of proteins after digestion and has the potential to improve sensitivity with minimal method development.

Fully-automated systems and the need for global approaches should exhort clinical labs to reinvent routine MS analysis?

Today, many LC–high-resolution MS instruments have become affordable, easy-to-use, sensitive and quantitative. Meanwhile, there is an increased need for more comprehensive approaches. However, omics analyses are still restricted to specialists whereas, in hospitals, routine analyses are targeted and quantitative and represent the main and heavy tasks. But the availability of fully automated LC–MS instruments that can handle independently from sample extraction to result reporting, as well as the increasing biomedical interest for global approaches, clinical analytical workflow should be reorganized. Bioanalysts are now in the position to develop/implement clinical metabolomics or proteomics as routine analyses. In this article, this coming evolution and the reasons to implement global/omics determinations as routine analysis, is described.

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

Multiple stage MS in analysis of plasma, serum, urine and in vitro samples relevant to clinical and forensic toxicology

This paper reviews MS approaches applied to metabolism studies, structure elucidation and qualitative or quantitative screening of drugs (of abuse) and/or their metabolites. Applications in clinical and forensic toxicology were included using blood plasma or serum, urine, in vitro samples, liquids, solids or plant material. Techniques covered are liquid chromatography coupled to low-resolution and high-resolution multiple stage mass analyzers. Only PubMed listed studies published in English between January 2008 and January 2015 were considered. Approaches are discussed focusing on sample preparation and mass spectral settings. Comments on advantages and limitations of these techniques complete the review.

Modify on the fly: triple quad to high resolution in support of a dermal clinical study requiring an ultra low LLOQ

Background: FTIH studies can be challenging due to the varying dosing regimens and rapid data delivery. Chemists are asked to provide ultra-low limits of quantitation to provide an understanding of patient efficacy and safety in order to progress drug development. In a recent dermal study it became necessary to reduce the LLOQ of a small molecule drug from 50 to 1 pg/ml due to reductions in the dose and surface area of drug application. Methodology: The 50-fold increase in assay sensitivity necessitated the use of a high-resolution mass spectrometer (LC–HRMS) to separate matrix interferences observed when using a unit resolution triple quadrupole MS. Conclusion: A sensitive, robust assay was validated to support of a FTIH study using a LC–HRMS.

Assessment of tandem mass spectrometry and high-resolution mass spectrometry for the analysis of bupivacaine in plasma

Triple quadrupole mass spectrometers coupled with high performance liquid chromatography are workhorses in quantitative bioanalyses. They provide substantial benefits including reproducibility, sensitivity and selectivity for trace analysis. Selected reaction monitoring allows targeted assay development but datasets generated contain very limited information. Data mining and analysis of nontargeted high-resolution mass spectrometry profiles of biological samples offer the opportunity to perform more exhaustive assessments, including quantitative and qualitative analysis. The objectives of this study were to test method precision and accuracy, to statistically compare bupivacaine drug concentration in real study samples and to verify if high-resolution and accurate mass data collected in scan mode can actually permit retrospective data analysis, more specifically, extract metabolite related information. The precision and accuracy data presented using both instruments provided equivalent results. Overall, the accuracy ranged from 106.2 to 113.2% and the precision observed was from 1.0 to 3.7%. Statistical comparisons using a linear regression between both methods revealed a coefficient of determination (R(2)) of 0.9996 and a slope of 1.02, demonstrating a very strong correlation between the two methods. Individual sample comparison showed differences from -4.5 to 1.6%, well within the accepted analytical error. Moreover, post-acquisition extracted ion chromatograms at m/z 233.1648 ± 5 ppm (M - 56) and m/z 305.2224 ± 5 ppm (M + 16) revealed the presence of desbutyl-bupivacaine and three distinct hydroxylated bupivacaine metabolites. Post-acquisition analysis allowed us to produce semi-quantitative evaluations of the concentration-time profiles for bupicavaine metabolites.

Clinical assays for quantitation of insulin-like-growth-factor-1 (IGF1)

Insulin-like growth factor 1 (IGF1), a 70 amino acid peptide hormone is the principal mediator of effects of growth hormone (GH). Since GH secretion is pulsatile in nature and is affected by many factors including sleep, feeding and exercise it is not a reliable marker for diagnosis of GH related disorders. On the other hand, IGF1 levels does not undergo short-term fluctuations in the manner that GH does making it the preferred IGF1 biomarker for the diagnosis of growth related disorders. There are several immunoassays available for IGF1 determination. Since majority (>90%) of IGF1 circulates as a ternary complex bound to its principal carrier/binding protein, IGF binding protein 3 (IGFBP3) and acid labile subunit (ALS), the assay methodology used to quantitate IGF1 has to dissociate IGF1 from IGFBPs prior to quantitation. IGFBPs are known to be a source of interference in immunoassays and many techniques have been employed to circumvent this issue. Immunoassays rely on antibody specificity towards IGF1 and differential cross reactivity towards IGFBPs. Mass spectrometry (MS) has also been employed for quantitation of IGF1. Liquid chromatography tandem mass spectrometry (LC-MS/MS) assays for IGF1 rely on generating tryptic peptides followed by selective reaction monitoring (SRM) while LC high resolution accurate-mass mass spectrometry (LC-HRAMS) approaches for intact IGF1 rely on mass accuracy for reliable, robust and accurate quantitation. This review article will focus on the clinical assays available and the clinical utility of quantitative assessment of IGF1. IGF1 quantitation using diverse assay platforms including immunoassay, LC-MS/MS and LC-HRAMS are discussed in detail.

Challenges of analyzing different classes of metabolites by a single analytical method

Complex biological samples include thousands of metabolites that range widely in both physiochemical properties and concentration. Simultaneously analyzing metabolites with different properties using a single analytical method is very challenging. The analytical process for metabolites comprises multiple steps including sampling, quenching, sample preparation, separation and detection. Each step can have a significant effect on the reliability and precision of ultimate analytic results. The aim of review is a discussion of considerations and challenges for the simultaneous analysis of metabolites using LC– and GC–MS systems. The review discusses available methodology for each analytical step, and presents the limitations and advantages of each method for the large-scale targeted metabolomics analysis of human and animal biological samples.

High resolution mass spectrometry based techniques at the crossroads of metabolic pathways

The metabolome is the set of small molecular mass compounds found in biological media, and metabolomics, which refers to as the analysis of metabolome in a given biological condition, deals with the large scale detection and quantification of metabolites in biological media. It is a data driven and multidisciplinary approach combining analytical chemistry for data acquisition, and biostatistics, informatics and biochemistry for mining and interpretation of these data. Since the middle of the 2000s, high resolution mass spectrometry is widely used in metabolomics, mainly because the detection and identification of metabolites are improved compared to low resolution instruments. As the field of HRMS is quickly and permanently evolving, the aim of this work is to review its use in different aspects of metabolomics, including data acquisition, metabolite annotation, identification and quantification. At last, we would like to show that, thanks to their versatility, HRMS instruments are the most appropriate to achieve optimal metabolome coverage, at the border of other omics fields such as lipidomics and glycomics.

Comparison of triple quadrupole mass spectrometry and Orbitrap high-resolution mass spectrometry in ultrahigh performance liquid chromatography for the determination of veterinary drugs in sewage: benefits and drawbacks

This paper presents a comparison of triple quadrupole tandem mass spectrometry (MS/MS) and Orbitrap high-resolution mass spectrometry (HRMS) combined to ultrahigh performance liquid chromatography for the determination of glucocorticoids and polyether ionophores in sewage, in order to show the major benefits and drawbacks for each mass spectrometry analyser. Overall, HRMS measurements have enhanced performance in terms of confirmatory capabilities than MS/MS measurements. Moreover, similar limits of quantification, limits of detection, linear range and repeatability for glucocorticoids with both the MS/MS and HRMS methods were compared, but in the case of polyether ionophores, slightly better limits of detection and limits of quantification were obtained with the HRMS method because of the high sensitivity obtained when diagnostic ions are used for quantification instead of selected reaction monitoring transitions for these compounds. The two methods have been applied to the analysis of several influent and effluent sewage samples from sewage treatment plants located in the Tarragona region (Catalonia, Spain), showing an excellent correlation between the two methods.

Validation of a dual LC-HRMS platform for clinical metabolic diagnosis in serum, bridging quantitative analysis and untargeted metabolomics

Mass spectrometry-based metabolomics is a rapidly growing field in both research and diagnosis. Generally, the methodologies and types of instruments used for clinical and other absolute quantification experiments are different from those used for biomarkers discovery and untargeted analysis, as the former requires optimal sensitivity and dynamic range, while the latter requires high resolution and high mass accuracy. We used a Q-TOF mass spectrometer with two different types of pentafluorophenyl (PFP) stationary phases, employing both positive and negative ionization, to develop and validate a hybrid quantification and discovery platform using LC-HRMS. This dual-PFP LC-MS platform quantifies over 50 clinically relevant metabolites in serum (using both MS and MS/MS acquisitions) while simultaneously collecting high resolution and high mass accuracy full scans to monitor all other co-eluting non-targeted analytes. We demonstrate that the linearity, accuracy, and precision results for the quantification of a number of metabolites, including amino acids, organic acids, acylcarnitines and purines/pyrimidines, meets or exceeds normal bioanalytical standards over their respective physiological ranges. The chromatography resolved highly polar as well as hydrophobic analytes under reverse-phase conditions, enabling analysis of a wide range of chemicals, necessary for untargeted metabolomics experiments. Though previous LC-HRMS methods have demonstrated quantification capabilities for various drug and small molecule compounds, the present study provides an HRMS quant/qual platform tailored to metabolic disease; and covers a multitude of different metabolites including compounds normally quantified by a combination of separate instrumentation.

Characterisation of the metabolism of pogostone in vitro and in vivo using liquid chromatography with mass spectrometry

INTRODUCTION

Pogostone possesses potent anti-bacterial and anti-fungal activities and has been used for the quality control of essential oil of Pogostemon cablin. Pogostone is easily absorbed after oral administration but its metabolism in mammals remains elusive.

OBJECTIVE

To investigate the metabolic profile of pogostone in vitro and in vivo.

METHODS

High-performance liquid chromatography coupled with mass spectrometry (LC–MS) techniques were employed. Orbitrap MS and ion trap tandem mass spectrometry (MS/MS) were utilised to analyse the metabolism of pogostone by virtue of the high sensitivity and high selectivity in the measurement. In vitro experiment was carried out using rat liver microsomes while the in vivo study was conducted on rats, which were orally administered with pogostone (80 mg/kg).

RESULTS

In total, three mono-hydroxylated, one di-hydroxylated, one mono-oxygenated, one di-oxygenated metabolite, one hydrolysis and one hydroxy conjugated metabolites were found. In addition hydroxylation was demonstrated to be a major metabolic pathway of pogostone.

CONCLUSION

LC–MS was demonstrated to be a powerful tool for the metabolite identification of pogostone. The tentative identification of metabolites provides an insight for the metabolic clues of pogostone.

Method development and validation of six bile acids for regulated bioanalysis: improving selectivity and sensitivity

BACKGROUND

Quantification of bile acids using LC-MS has previously been very challenging on triple quadrupole MS systems due to the absence of a primary fragment ion for unconjugated bile acids.

RESULTS

A LC-high-resolution/accurate mass MS method for the analysis of six bile acids (cholic acid, chenodeoxycholic acid, taurocholic acid, deoxycholic acid, lithocholic acid and ursodeoxycholic acid) was developed and successfully validated. The method includes a single extraction and a single injection with all analytes separated using target-selected ion monitoring (SIM) mode in two periods with a resolution of 70,000 and 140,000, respectively.

CONCLUSION

This is the first LC-high-resolution/accurate mass assay fully validated to quantify six bile acids for regulated bioanalysis.

Comparison of high-resolution and tandem mass spectrometry for the analysis of nerve agent metabolites in urine

RATIONALE

Although use is prohibited, concerns remain for human exposure to nerve agents during decommissioning, research, and warfare. High-resolution mass spectrometry (HRMS) was compared to tandem mass spectrometry (MS/MS) analysis for the quantitation of five urinary metabolites specific to VX, Russian VX, soman, sarin and cyclosarin nerve agents. The HRMS method was further evaluated for qualitative screening of metabolites not included in the test panel.

METHODS

Nerve agent metabolites were extracted from urine using solid-phase extraction, separated using hydrophilic interaction chromatography and analyzed using both tandem and high-resolution mass spectrometry. MS/MS results were obtained using selected reaction monitoring with unit resolution; HRMS results were obtained using a mass extraction window of 10 ppm at a mass resolution of 50 000. The benchtop Orbitrap HRMS instrument was operated in full scan mode, to measure the presence of unexpected nerve agent metabolites.

RESULTS

The assessment of two quality control samples demonstrated high accuracy (99.5-104%) and high precision (2-9%) for both HRMS and MS/MS. Sensitivity, as described by the limit of detection, was overlapping for both detectors (0.2-0.7 ng/mL). Additionally, the HRMS method positively confirmed the presence of a nerve agent metabolite, not included in the test panel, using the accurate mass and relative retention time.

CONCLUSIONS

The precision, accuracy, and sensitivity were comparable between the current MS/MS method and this newly developed HRMS analysis for five nerve agent metabolites. HRMS showed additional capabilities beyond the current method by confirming the presence of a metabolite not included in the test panel.

Comparison of the quantitative performance of a Q-Exactive high-resolution mass spectrometer with that of a triple quadrupole tandem mass spectrometer for the analysis of illicit drugs in wastewater

RATIONALE

Analysis of drugs in wastewater is gaining more interest, as new approaches to estimate drug consumption from the amount of drug residues in wastewater have been proposed. The aim of this study was to compare the quantitative performance of high-resolution mass spectrometry with that of triple quadrupole mass spectrometry.

METHODS

A Q-Exactive mass spectrometer was operated in full scan (HRFS) (70 000 FWHM) and product scan (HRPS) (17 500 FWHM) modes. The first and third quadrupoles of the QqQ MS/MS instrument were operated at 0.7 FWHM. A mass-extracted window of 5 ppm around the theoretical m/z of each analyte was used to construct chromatograms. An HESI-II ion source was used for the ionization of target compounds. In-line-SPE-LC configuration was used for the extraction and separation of target analytes.

RESULTS

All three methods showed good linearity and repeatability. High-resolution detection of product ions exhibited better sensitivity and selectivity for some compounds. For most of the tested compounds, LOQs ranged from 0.46 to 20 ng L(-1) . Good agreement between measured and nominal concentrations was observed for most of the compounds at different levels of fortification. Both MS/MS methods showed good selectivity, while HRFS gave some false positive results.

CONCLUSIONS

The Q-Exactive mass spectrometer proved to be suitable for trace detection and quantification of most of the tested drugs in wastewater, with performance comparable to that of the commonly used MS/MS triple quadrupole, but with better selectivity.

Applications of high-resolution MS in bioanalysis

High-resolution MS (HRMS) in conjunction with LC (LC–HRMS) has become available to many laboratories in the pharmaceutical industry. Due to its enhanced, though sometime perceived, specificity using the high-resolution power and its capability of simultaneous quantitation and structural elucidation using the post-acquisition data mining feature, utilization of LC–HRMS for bioanalysis could lead to potential rapid and reliable method development as well as sample analysis, thus generating both cost and resource savings. Here, we would like to share our perspectives about several current and future applications of LC–HRMS in bioanalysis. We will also discuss the factors influencing the quality of method establishment and potential pitfalls that need to be considered for the utilization of LC–HRMS in the field of regulated bioanalysis. We believe when utilized appropriately, LC–HRMS will play a significant role in the future landscape of quantitative bioanalysis.

High-resolution MS in regulated bioanalysis: where are we now and where do we go from here?

While triple quadrupole MS remains the workhorse of bionanalytical laboratories, LC coupled with high-resolution MS (LC–HRMS) is making headway in drug discovery. LC–HRMS is well suited for quantitative bioanalysis with the inherent advantage of post-acquisition data mining, which is not possible with triple quadrupole systems operated in SRM mode. LC–HRMS can, thus, accomplish the core task of a bioanalytical laboratory – accurate determination of a targeted analyte – with the added bonus of being able to monitor other compounds of interest either at the time of sample analysis, or as an afterthought, after sample analysis, with no additional effort in sample preparation, chromatographic optimization or sample reinjection. Despite these advantages, LC–HRMS has not been broadly adopted in regulated bioanalytical laboratories. The slow progress in embracing the technology may be due, in part, to difficulties in replacing an entire fleet of triple quadrupole MS. Additional reasons are that data mining is of less benefit in development, especially late-stage, than in discovery and that the technical and regulatory challenges associated with the change of platform are perceived to be significant. In addition, the current platform of LC–HRMS introduced by instrument companies has not been tailored to the core responsibility of the bioanalytical community. In marketing current LC–HRMS systems, there is a tendency to combine the needs of the bioanalytical community with those of the drug metabolism community, despite their inherent differences. As a result, the current HRMS systems available lack some basic features desired for bioanalysis, but include features that are not important for bioanalysis making the systems unnecessarily complex and expensive. A simple, cost effective, ideal HRMS system for a bioanalytical laboratory would provide HRMS with high resolving power (the higher the better), no MS/MS capability, and with software suitable for quantitative analysis and appropriate for use in regulated laboratories. Under this scenario, one can foresee a future where part of the regulated bioanalytical work will be accomplished using LC–HRMS, reserving triple quadrupole-based LC–MS/MS for assays that require exquisite sensitivity.

High-throughput liquid chromatography/mass spectrometry method for the quantitation of small molecules using accurate mass technologies in supporting discovery drug screening

RATIONALE

Drug discovery samples are routinely analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods on triple quadrupole mass spectrometers employing multiple reaction monitoring (MRM). In order to improve analysis throughput, quantitation of small molecules on a quadrupole time-of-flight (QqTOF) instrument using TOF scan and high-resolution MRM (MRM-HR) modes was evaluated in this study.

METHODS

Cassette dosed plasma and brain samples from nine compounds were extracted using a protein precipitation method. Separation was achieved by reversed-phase liquid chromatography. Mass spectrometric analysis was performed using TOF scan and high-resolution MRM approaches on a QqTOF mass spectrometer with turbo-ionspray ionization. Results were compared to those obtained on a triple quadrupole mass spectrometer.

RESULTS

The dynamic range varied depending on compounds and instruments and was similar between the MRM on QqQ and full TOF scan mode on QqTOF. Linear or quadratic regression and 1/x(2) weighting were used. Resolution on the QqTOF instrument was around 32000 and mass accuracy was within 4.4 ppm. The MRM-HR method showed better sensitivity compared to the TOF scan method, and was comparable to the MRM on a QqQ mass spectrometer. Assay accuracy was within ±25%.

CONCLUSIONS

A TOF scan method allowed the use of the generic method without compound-specific optimization and was an alternative choice for routine high-throughput quantitation of small molecules. The MRM-HR method on the QqTOF showed good sensitivity which was comparable to that obtained by the MRM method on the triple quadrupole mass spectrometer.

Metabolite structure analysis by high-resolution MS: supporting drug-development studies

Effective characterization of drug metabolites in complex biological matrices is facilitated by mass spectrometers with high resolving power, mass accuracy and sensitivity. This review begins with an overview of high-resolution MS terminology and the different types of instrumentation that are currently available. Metabolite structure analysis offers unique challenges and, therefore, the different types of approaches used to solve problems are highlighted through specific examples. Overall, this review describes the value that high-resolution MS brings to drug-metabolism studies.

Global metabolic profiling of animal and human tissues via UPLC-MS

Obtaining comprehensive, untargeted metabolic profiles for complex solid samples, e.g., animal tissues, requires sample preparation and access to information-rich analytical methodologies such as mass spectrometry (MS). Here we describe a practical two-step process for tissue samples that is based on extraction into 'aqueous' and 'organic' phases for polar and nonpolar metabolites. Separation methods such as ultraperformance liquid chromatography (UPLC) in combination with MS are needed to obtain sufficient resolution to create diagnostic metabolic profiles and identify candidate biomarkers. We provide detailed protocols for sample preparation, chromatographic procedures, multivariate analysis and metabolite identification via tandem MS (MS/MS) techniques and high-resolution MS. By using these optimized approaches, analysis of a set of samples using a 96-well plate format would take ~48 h: 1 h for system setup, 8-10 h for sample preparation, 34 h for UPLC-MS analysis and 2-3 h for preliminary/exploratory data processing, representing a robust method for untargeted metabolic screening of tissue samples.

The future key role of LC–high-resolution-MS analyses in clinical laboratories: a focus on quantification

For the last decade, high-resolution (HR)-MS has been associated with qualitative analyses while triple quadrupole MS has been associated with routine quantitative analyses. However, a shift of this paradigm is taking place: quantitative and qualitative analyses will be increasingly performed by HR-MS, and it will become the common ‘language’ for most mass spectrometrists. Most analyses will be performed by full-scan acquisitions recording ‘all’ ions entering the HR-MS with subsequent construction of narrow-width extracted-ion chromatograms. Ions will be available for absolute quantification, profiling and data mining. In parallel to quantification, metabotyping will be the next step in clinical LC–MS analyses because it should help in personalized medicine. This article is aimed to help analytical chemists who perform targeted quantitative acquisitions with triple quadrupole MS make the transition to quantitative and qualitative analyses using HR-MS. Guidelines for the acceptance criteria of mass accuracy and for the determination of mass extraction windows in quantitative analyses are proposed.

Clinical utility of insulin-like growth factor 1 and 2; determination by high resolution mass spectrometry

Measurement of insulin-like growth factor-1 (IGF-I) has utility for the diagnosis and management of growth disorders, but inter-assay comparison of results has been complicated by a multitude of reference standards, antibodies, detection methods, and pre-analytical preparation strategies. We developed a quantitative LC-MS method for intact IGF-I, which has advantages in throughput and complexity when compared to mass spectrometric approaches that rely on stable isotope dilution analysis of tryptic peptides. Since the method makes use of full-scan data, the assay was easily extended to provide quantitative measurement of IGF-II using the same assay protocol. The validated LC-MS assay for IGF-I and IGF-II provides accurate results across the pediatric and adult reference range and is suitable for clinical use.

Quantitation of DNA adducts by stable isotope dilution mass spectrometry

Exposure to endogenous and exogenous chemicals can lead to the formation of structurally modified DNA bases (DNA adducts). If not repaired, these nucleobase lesions can cause polymerase errors during DNA replication, leading to heritable mutations and potentially contributing to the development of cancer. Because of their critical role in cancer initiation, DNA adducts represent mechanism-based biomarkers of carcinogen exposure, and their quantitation is particularly useful for cancer risk assessment. DNA adducts are also valuable in mechanistic studies linking tumorigenic effects of environmental and industrial carcinogens to specific electrophilic species generated from their metabolism. While multiple experimental methodologies have been developed for DNA adduct analysis in biological samples, including immunoassay, HPLC, and ³²P-postlabeling, isotope dilution high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) generally has superior selectivity, sensitivity, accuracy, and reproducibility. As typical DNA adduct concentrations in biological samples are between 0.01-10 adducts per 10⁸ normal nucleotides, ultrasensitive HPLC-ESI-MS/MS methodologies are required for their analysis. Recent developments in analytical separations and biological mass spectrometry, especially nanoflow HPLC, nanospray ionization MS, chip-MS, and high resolution MS, have pushed the limits of analytical HPLC-ESI-MS/MS methodologies for DNA adducts, allowing researchers to accurately measure their concentrations in biological samples from patients treated with DNA alkylating drugs and in populations exposed to carcinogens from urban air, drinking water, cooked food, alcohol, and cigarette smoke.