Wrong-Way-Round Ionization of Sulfonamides and Tetracyclines Enables Simultaneous Analysis with Free and Conjugated Estrogens by Liquid Chromatography Tandem Mass Spectrometry

The effects of modifiers on electrospray ionization for small-to-medium-sized molecules in comparison with solution-phase ionization

Modifiers are essential additives in electrospray ionization (ESI) mass spectrometric analysis to enhance the production of ionic species in the gas phase for the detection of small-to-medium-sized molecules in biological and aqueous samples. Therefore, an appropriate modifier, in conjunction with the right ionization polarity, is crucial for sensitive ESI mass spectrometric analysis. However, the charge carried by basic and acidic functional groups in solution is neither quantitatively nor qualitatively reflected in the MS spectrum. For example, adding an acidic modifier will cause sufficient protonation of a basic functional group in solution; however, this may result in inferior positive ESI compared to using a basic modifier. Another example is when the MS spectrum does not reflect the charge distribution of multiply charged molecules in solution. Therefore, this review will summarize and discuss the proposed mechanisms by which modifiers induce and influence ESI. It will also cover molecular characteristics that affect ESI, such as charge state and polarity, which result in a difference between solution-phase ionization and ESI.

Evaluating the "wrong-way-round" electrospray ionization of antiretroviral drugs for improved detection sensitivity

The presence of antiretroviral drugs (ARVDs) in the aquatic environment poses a significant health risk to the ecosystem. The dilution of these compounds during wastewater treatment processes, followed by discharge into the environment, results in extremely low concentrations in the range of ng/L. Therefore, to enable detection of these low concentrations, it is important to determine the most efficient electrospray ionization (ESI) mode using the right mobile phase modifier and to establish a selective extraction procedure. In this study, we compared the ESI intensity in the positive and negative mode using both formic acid (FA) and ammonium hydroxide (NH₄OH) as mobile phase modifiers. The results revealed a phenomenon known as the "wrong-way-round" (WWR) ESI in which high intensity [M + H]⁺ ions were detected under basic conditions using NH₄OH as modifier and, similarly, high intensity [M-H]^- ions were detected under acidic conditions using FA as modifier. Furthermore, mixed-mode strong cation (MCX) and mixed-mode strong anion (MAX) exchange sorbents were evaluated for extraction recoveries, which yielded extraction recoveries between 60 and 100%. Finally, the recoveries obtained using mixed-mode ion exchange sorbents compared to ion production during the ESI process provide evidence that ions produced in solution do not necessarily reflect the ions that are produced during the ESI process. Based on the results of this study, it is recommended to evaluate the optimal ionization mode under basic and acidic conditions, instead of defaulting to the use of acidic modifiers with positive ion detection.

Standard-Free Quantification of Dicarboxylic Acids: Case Studies with Salt-Rich Effluents and Serum

The present study evaluates the ionization efficiency (IE) of linear and branched C₂-C₁₄ dicarboxylic acids (DCAs) by electrospray ionization (ESI) under different conditions. The influence of the concentration of organic modifier (MeOH); mobile phase additive; and its concentration, pH, and DCA structure on IE values is studied using flow injection analysis. The IE values of DCAs increase with the increase of MeOH concentration but also decrease with an increase of pH. The former is due to the increase in solvent evaporation rates; the latter is caused by an ion-pairing between the diacid and the cation (ammonium), which is confirmed by the study with different amines. The investigation of DCA ionization in the presence of different acidic mobile phase additives showed that a significant improvement in the (-)ESI responses of analytes was achieved in the presence of weak hydrophobic carboxylic acids, such as butyric or propanoic acid. Conversely, the use of strong carboxylic acids, such as trichloroacetic acid, was found to cause signal suppression. The results of the IE studies were used to develop the liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method that provided instrumental limits of detection in the range from 6 to 180 pg. Furthermore, upon applying the nonparametric Gaussian process, a model for the prediction of IE values was developed, which contains the number of carbons in the molecule and MeOH concentration as model parameters. As a case study, dicarboxylic acids are quantified in salt-rich effluent and blood serum samples using the developed LC-HRMS method.

Strategies for effective development of ultra-sensitive LC–MS/MS assays: application to a novel STING agonist

Background: The continual need for the development and validation of ultra-sensitive (low pg/ml) LC–MS/MS assays in the pharmaceutical industry is largely driven by the ultra-low analyte exposure or very low sample volume. Methodology: Strategies and systematic approaches for sensitivity enhancement are provided which cover all aspects of a LC–MS/MS bioanalysis. A case study where such strategies were applied for the validation of a 5.0 pg/ml assay for a STING agonist is discussed. Conclusion: Analytical protocols were developed to extract analytes from large volume of plasma samples (600 and 400 μl) with high throughput. The guidance provided in this publication can serve as a resource to influence LC–MS/MS method development activities.

Quantification of organic contaminants in urban stormwater by isotope dilution and liquid chromatography-tandem mass spectrometry

Pollutants transported in urban stormwater runoff induce pervasive water quality degradation in receiving waters. To accurately characterize stormwater quality and treatment system performance across the range of possible contaminant characteristics, comprehensive multi-residue analytical methods are necessary. Here, we developed a solid-phase extraction (SPE) and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method to quantify representative stormwater-derived organic contaminants across multiple chemical classes, including vehicle-related chemicals, corrosion inhibitors, industrial chemicals, pesticides, pharmaceuticals and personal care products, and antioxidants. Extraction conditions, isotope-labeled internal standards, and LC-MS/MS parameters were optimized to enhance recovery, minimize matrix effects, and maximize selectivity and sensitivity. The developed method was sensitive (method quantification limits < 10 ng/L for > 80% of selected analytes) and accurate (mean relative recoveries in the range of 70-130%, with relative standard deviations < 25% for 77% of the analytes) for most of the analytes. The method was used to analyze samples collected from nine urban watersheds during a storm event; 62% of the 39 analytes were detected at least once at concentrations up to 540 ng/L (1,3-diphenylguanidine). Spatial trends in detection and concentration were observed for vehicle-related and industrial chemicals that correlated with vehicle traffic. Total concentrations of pesticides suggested that residential uses could be more important sources than agriculture. This study illustrates the pervasive occurrence of a wide variety of stormwater-derived chemicals in urban receiving waters and highlights the need to better understand their environmental fate and ecological implications. Graphical abstract.

Use of high-pH (basic/alkaline) mobile phases for LC-MS or LC-MS/MS bioanalysis

High-pH or basic/alkaline mobile phases are not commonly used in LC-MS or LC-MS/MS bioanalysis because of the deeply rooted concern with column instability and reduced detection sensitivity for basic compounds in high-pH mobile phases owing to charge neutralization. With the advancement of LC column technology and the wide recognition of the "wrong-way-round" phenomena, high-pH mobile phases are more and more used in LC-MS or LC-MS/MS bioanalysis to improve chromatographic peak shape, retention, selectivity, resolution, and detection sensitivity, not only for basic compounds, but also for many other compounds. In this article, the benefits, practical considerations, application examples and cautions for using high-pH mobile phases in LC-MS or LC-MS/MS bioanalysis are reviewed, with a focus on quantification. Furthermore, the future trends in this field are also envisaged. A total of 84 references are cited in this review.

Fully compatible and ultra-sensitive micellar electrokinetic chromatography-tandem mass spectrometry using sheathless porous-tip interfacing

The on-line coupling of micellar electrokinetic chromatography and mass spectrometry (MEKC-MS) is often hampered by incompatibility problems leading to reduced separation performance and unfavorable limits of detection (LODs). Here we propose a new selective and highly sensitive MEKC-MS/MS method employing a sheathless porous-tip interface in combination with a micellar phase comprised of semi-volatile surfactant molecules. Carbamate pesticides (CRBs) were selected as representative model compounds being neutral toxic pollutants potentially present at trace levels in environmental water samples. A background electrolyte of 75mM perfluorooctanoic acid adjusted to pH 9.0 with ammonium hydroxide allowed efficient separation of 15 CRBs and appeared fully compatible with electrospray ionization (ESI)-MS. Interfacing parameters, such as the distance between the capillary tip and mass-spectrometer inlet, ESI voltage, and dry gas temperature and flow were optimized in order to attain good spray stability and high analyte signal-to-noise ratios. For CRBs the LODs ranged from 0.2 to 3.9ngL^-1 (13nL injected, i.e., 2% of capillary volume), representing an improvement for certain CRBs of more than 300-fold when compared with conventional sheath-liquid interfacing. Good linearity (R²>0.99) and satisfactory reproducibility were obtained for all CRBs with interday RSD values for peak area and migration time of 4.0-11.3% and below 1.5%, respectively. Analysis of spiked mineral water showed that the new MEKC-MS/MS method allows selective and quantitative determination of CRB concentrations below the maximum residue limit of 100ngL^-1 without the need for sample preconcentration.

A comprehensive profiling of sulfatides in myelin from mouse brain using liquid chromatography coupled to high-resolution accurate tandem mass spectrometry

Sulfatides are sulfoglycolipids found in the myelin sheath. The composition ratio of sulfatide molecular species changes with age, and it has also been associated with the pathogenesis of various human central nervous system diseases. However, profiling sulfatides in biological samples is difficult, due to the great variety of molecular species. In this work, a new, easy and reliable liquid chromatography-electrospray tandem mass spectrometry (LC-ESI(+)-MS/MS) method has been developed to profile sulfatide content in biological samples of myelin. The 'wrong-way-round' ionization effect has been described for this type of molecules for the first time, making it possible to correctly identify as many as 37 different sulfatides in mouse brain myelin samples, including molecules with different fatty acid chain lengths and varying degrees of unsaturation and hydroxylation. A chemometric analysis of their relative abundances showed that the main difference among individuals of different ages was the content of sulfatides with odd-numbered fatty acid chains, in addition to hydroxylated species.

Enhancing Extraction and Detection of Veterinary Antibiotics in Solid and Liquid Fractions of Manure

Analysis of veterinary antibiotics in separated liquid and solid fractions of animal manures is vital because of wide variations in the composition of agriculturally applied manure. Differentiation of antibiotic concentrations is important between liquid and solid manures, as their sorption onto the solid fraction depends on physicochemical properties of each antibiotic and manure composition (e.g., organic content, pH) and because each fraction may be treated and reused differently. Here, an efficient and sensitive method for the analysis of 22 veterinary antibiotics in the liquid and solid fractions of manure is reported. Tetracycline (TC), macrolide, and sulfonamide antibiotics were extracted from liquid manure by liquid-liquid extraction (LLE) with methanol following acidification with acetic acid. Extraction from solids was performed by sonication with acetonitrile, methanol, and 0.1 M EDTA-McIlvaine buffer. Cleanup of extracts was achieved by solid-phase extraction with hydrophilic-lipophilic balance (HLB) cartridges or tandem amino (NH2) and HLB cartridges. Quantification of antibiotics was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) under wrong-way-round (WWR) ionization for sulfonamides and TCs and right-way-round ionization for macrolides. Recoveries of 58 to 94.7% and 62 to 94.3% were obtained in liquid and solid manure, respectively. Method detection limits range from 1.2 to 12 ng L and 0.5 to 7.9 μg kg dry wt. in liquids and solids, respectively. This method allows for extraction and analysis of both mobile antibiotics in liquid phase and hydrophobic antibiotics adsorbed on the solids. Without separate analysis, antibiotic concentrations may be improperly estimated by analyzing whole manure, as reported in many studies to date.

Application of metabolite profiling tools and time-of-flight mass spectrometry in the identification of transformation products of iopromide and iopamidol during advanced oxidation

The efficiency of wastewater treatment systems in removing pharmaceuticals is often assessed on the basis of the decrease in the concentration of the parent compound. However, what is perceived as "removal" during treatment may not necessarily mean mineralization of the pharmaceutical compound but simply conversion into different transformation products (TPs). Using liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer (LC-QToF-MS), we demonstrated conversion of iopromide in wastewater to at least 14 TPs after an advanced oxidation process (AOP) using UV (fluence = 1500 mJ/cm(2)) and H2O2 (10 mg/L). Due to the complexity of the wastewater matrix, the initial experiments were performed using a high concentration (10 mg/L) of iopromide in order to facilitate the identification of TPs. Despite the high concentration of iopromide used, cursory inspection of UV and mass spectra only revealed four TPs in the chromatograms of the post-AOP samples. However, the use of METLIN database and statistics-based profiling tools commonly used in metabolomics proved effective in discriminating between background signals and TPs derived from iopromide. High-resolution mass data allowed one to predict molecular formulas of putative TPs with errors below 5 ppm relative to the observed m/z. Tandem mass spectrometry (MS/MS) data and isotope pattern comparisons provided necessary information that allowed one to elucidate the structure of iopromide TPs. The presence of the proposed iopromide TPs was determined in unspiked wastewater from a municipal wastewater treatment plant, but no iopromide and TPs were detected. Using analogous structural modifications and oxidation that results from the AOP treatment of iopromide, the potential TPs of iopamidol (a structurally similar compound to iopromide) were predicted. The same mass fragmentation pattern observed in iopromide TPs was applied to the predicted iopamidol TPs. LC-QToF-MS revealed the presence of two iopamidol TPs in unspiked AOP-treated wastewater.

Alkaline conditions in hydrophilic interaction liquid chromatography for intracellular metabolite quantification using tandem mass spectrometry

Modeling of metabolic networks as part of systems metabolic engineering requires reliable quantitative experimental data of intracellular concentrations. The hydrophilic interaction liquid chromatography-electrospray ionization-tandem mass spectrometry (HILIC-ESI-MS/MS) method was used for quantitative profiling of more than 50 hydrophilic key metabolites of cellular metabolism. Without prior derivatization, sugar phosphates, organic acids, nucleotides, and amino acids were measured under alkaline and acidic mobile phase conditions with pre-optimized multiple reaction monitoring (MRM) transitions. Irrespective of the polarity mode of the acquisition method used, alkaline conditions achieved the best quantification limits and linear dynamic ranges. Fully 90% of the analyzed metabolites presented detection limits better than 0.5pmol (on column), and 70% presented 1.5-fold higher signal intensities under alkaline mobile phase conditions. The quality of the method was further demonstrated by absolute quantification of selected metabolites in intracellular extracts of Escherichia coli. In addition, quantification bias caused by matrix effects was investigated by comparison of calibration strategies: standard-based external calibration, isotope dilution, and standard addition with internal standards. Here, we recommend the use of alkaline mobile phase with polymer-based zwitterionic hydrophilic interaction chromatography (ZIC-pHILIC) as the most sensitive scenario for absolute quantification for a broad range of metabolites.

Analysis of trace organic pollutants in wastewater to assess biodegradation using wrong-way-round ionization in liquid chromatography/tandem mass spectrometry

RATIONALE

Monitoring the concentrations of pharmaceuticals and personal care products (PPCPs) in wastewater is an integral step toward understanding the fate of these contaminants in wastewater treatment plants (WWTPs). This paper aims to develop a method that allows for the simultaneous analysis of multiple classes of PPCPs that can be used as tracers to assess the performance of WWTPs.

METHODS

Five PPCP tracers - carbamazepine (CBZ), 17α-ethinylestradiol (EE2), nonylphenol (NP), salicylic acid (SA), and trimethoprim (TMP) - were analyzed by liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) using a highly basic mobile phase (pH 10.3). Conventionally, TMP (pKa 7.12) and CBZ (pKa 13.94) are analyzed in positive ion mode using an acidic mobile phase. However, the high pH mobile phase allowed the quantification of all the tracers by polarity switching, with TMP undergoing wrong-way-round (WWR) ionization.

RESULTS

The instrument limits of detection for the five tracers, without solid-phase extraction, were in the range of 1.3 to 5.9 ng/mL, except for NP, which was 238 ng/mL. The signal-to-noise (S/N) ratios for TMP and CBZ with the mobile phase at pH 10.3 were higher than the S/N ratios observed at pH 2.7 under positive electrospray ionization. The mechanism of WWR ionization for TMP was investigated, and we propose that a charge transfer from solvent clusters to TMP molecules due to electrolytic reactions at the surface of the droplet leads to WWR ionization in electrospray.

CONCLUSIONS

A method to simultaneously analyze five representative PPCP tracers with a wide range of pKa values using WWR ionization in LC/MS/MS with polarity switching was developed. The method was successfully used to monitor the selected PPCPs in samples from full-scale WWTPs to assess their biodegradation under various treatment conditions.

Rapid and comprehensive impurity profiling of synthetic thyroxine by ultrahigh-performance liquid chromatography-high-resolution mass spectrometry

Rapid and efficient quality control according to the public authority regulations is mandatory to guarantee safety of the pharmaceuticals and to save resources in the pharmaceutical industry. In the case of so-called "grandfather products" like the synthetic thyroid hormone thyroxine, strict regulations enforce a detailed chemical analysis in order to characterize potentially toxic or pharmacologically relevant impurities. We report a straightforward workflow for the comprehensive impurity profiling of synthetic thyroid hormones and impurities employing ultrahigh-performance liquid chromatography (UHPLC) hyphenated to high-resolution mass spectrometry (HRMS). Five different batches of synthetic thyroxin were analyzed resulting in the detection of 71 impurities within 3 min total analysis time. Structural elucidation of the compounds was accomplished via a combination of accurate mass measurements, computer based calculations of molecular formulas, multistage high-resolution mass spectrometry (HRMS(n)), and nuclear magnetic resonance spectroscopy, which enabled the identification of 71 impurities, of which 47 have been unknown so far. Thirty of the latter were structurally elucidated, including products of deiodination, aliphatic chain oxidation, as well as dimeric compounds as new class of thyroid hormone derivatives. Limits of detection for the thyroid compounds were in the 6 ng/mL range for negative electrospray ionization mass spectrometric detection in full scan mode. Within day and day-to-day repeatabilities of retention times and peak areas were below 0.5% and 3.5% R.SD. The performance characteristics of the method in terms of robustness and information content clearly show that UHPLC-HRMS is adequate for the rapid and reliable detection, identification, and semiquantitative determination of trace levels of impurities in synthetic pharmaceuticals.

'Wrong-way-round ionization' and screening for doping substances in human urine by high-performance liquid chromatography/orbitrap mass spectrometry

To free analytical resources for new classes of doping substances, such as banned proteins, maximization of the number of compounds that can be determined with high sensitivity in a single run is highly urgent. This study demonstrates an application of 'wrong-way-round ionization' for the simultaneous detection of multiple classes of doping substances without the need to switch the polarity. A screening method for the detection of 137 compounds from various classes of prohibited substances (stimulants, diuretics, β(2)-agonists, β-blockers, antiestrogens, glucocorticosteroids and anabolic agents) has been developed. The method involves an enzymatic hydrolysis, liquid-liquid extraction and detection by liquid chromatography/orbitrap mass spectrometry with wrong-way-round ionization. Up to 64% of compounds had a 10-fold lower limit of detection (LOD) than the minimum required performance limit. To compare the efficiency of conventional ionization relative to wrong-way-round ionization of doping substances in + ESI, a fortified blank urine sample at the minimum required performance limit was analyzed using two ESI approaches. All compounds were detected with markedly better S/N in a high-pH mobile phase, with the exception of acetazolamide (minimal change in S/N, < 20%).The method was validated by spiking 10 different blank urine samples at five different concentrations. Validation parameters included the LOD, selectivity, ion suppression, extraction recovery and repeatability.

Simultaneous analysis of free and conjugated estrogens, sulfonamides, and tetracyclines in runoff water and soils using solid-phase extraction and liquid chromatography-tandem mass spectrometry

The ability to monitor multiple analytes from various classes of compounds in a single analysis can increase throughput and reduce cost when compared to traditional methods of analyses. This method for analyzing free (parent estrogen) and conjugated estrogens (metabolites) along with sulfonamides and tetracyclines utilizes a high pH (10.4) mobile phase with an ammonium hydroxide buffer for both positive- and negative-mode electrospray ionization. A single-step sample preparation by solid-phase extraction (SPE) was used to isolate and concentrate all analytes simultaneously. The analytical method was developed and validated for recoveries at 3 concentration levels for water and soil and produced recoveries of 42-123% and 21-105% respectively. Method detection limits ranged from 0.3 to 1.0 ng/L for water samples and 0.01 to 0.1 ng/g for soils. The method quantification limit ranged from 0.9 to 3.3 ng/L for water samples and 0.06 to 0.7 ng/g for soils. The single-point standard addition calibration procedure was validated across a linear range of MQL to 100 ng/L with ≥82% accuracy against a matrix matched standard curve. Furthermore, sorption of tetracyclines onto glassware was investigated and minimized by 10% using nitric acid-rinsed glassware, while separation parameters were further optimized based on retention time and signal responses. This method has been used for the quantification of estrogens, tetracyclines, and sulfonamides in soil and runoff waters with multiple compounds detected simultaneously in a single analysis.