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Gaussian and exponentially modified Gaussian functions were incorporated into integrating algorithms used by an open-source, cross-platform tool called CycloBranch. The quantitation is demonstrated on bacterial pyoverdines separated by fine isotope features. Using our algorithm, we can separate the m/z values 694.25802 and 694.26731 (a 0.009 Da difference), where the former belongs to the most intense peak of pyoverdine D (PvdD), and the latter to the second most intense peak of pyoverdine E (PvdE) in the respective isotopic clusters of [M + Fe-H]2+ions. The areas under chromatographic curves of standards were analyzed for the limit of detection (LOD), limit of quantitation (LOQ), and regression coefficient calculations. The quantitative module returned a LOD and LOQ of 1.4 and 4.3 ng/mL, respectively, for both PvdD and PvdE in human urine. If present and detected in mass spectra, the intensities of user-defined [M + H]+, [M + Na]+, [M + K]+, [M + Fe-H]2+, or other ion types, can be accumulated and used for quantitation. The quantitation result is returned by CycloBranch in seconds or minutes, contrary to an hours-long manual approach, prone to user-born errors originating from necessary copying among various software environments. Native Bruker, Waters, Thermo, txt, mgf, mzML, and mzXML data formats are supported in CycloBranch, which is freely available at https://ms.biomed.cas.cz/cyclobranch.

Produced water (PW), a waste byproduct of oil and gas extraction, is a complex mixture containing numerous organic solubles and elemental species; these constituents range from polycyclic aromatic hydrocarbons to naturally occurring radioactive materials. Identification of these compounds is critical in developing reuse and disposal protocols to minimize environmental contamination and health risks. In this study, versatile extraction methodologies were investigated for the untargeted analysis of PW. Thin-film solid-phase microextraction with hydrophilic–lipophilic balance particles was utilized for the extraction of organic solubles from eight PW samples from the Permian Basin and Eagle Ford formation in Texas. Gas chromatography–mass spectrometry analysis found a total of 266 different organic constituents including 1,4-dioxane, atrazine, pyridine, and PAHs. The elemental composition of PW was evaluated using dispersive solid-phase extraction followed by inductively coupled plasma–mass spectrometry, utilizing a new coordinating sorbent, poly(pyrrole-1-carboxylic acid). This confirmed the presence of 29 elements including rare earth elements, as well as hazardous metals such as Cr, Cd, Pb, and U. Utilizing chemometric analysis, both approaches facilitated the discrimination of each PW sample based on their geochemical origin with a prediction accuracy above 90% using partial least-squares-discriminant analysis, paving the way for PW origin tracing in the environment.

Ultraviolet (UV) absorption spectroscopy is a widely used tool for quantitative and qualitative analyses of chemical compounds. In the gas phase, vacuum UV (VUV) and UV absorption spectra are specific and diagnostic for many small molecules. An accurate prediction of VUV/UV absorption spectra can aid the characterization of new or unknown molecules in areas such as fuels, forensics, and pharmaceutical research. An alternative to quantum chemical spectral prediction is the use of artificial intelligence. Here, different molecular feature representation techniques were used and developed to encode chemical structures for testing three machine learning models to predict gas-phase VUV/UV absorption spectra. Structure data files (.sdf) and VUV/UV absorption spectra for 1397 volatile and semivolatile chemical compounds were used to train and test the models. New molecular features (termed ABOCH) were introduced to better capture pi-bonding, aromaticity, and halogenation. The incorporation of these new features benefited spectral prediction and demonstrated superior performance compared to computationally intensive molecular-based deep learning methods. Of the machine learning methods, the use of a Random Forest regressor returned the best accuracy score with the shortest training time. The developed machine learning prediction model also outperformed spectral predictions based on the time-dependent density functional theory.

A proof-of-concept study is presented on the use of comprehensive two-dimensional liquid chromatography mass spectrometry (LC × LC-MS) for the separation of intact protein mixtures using a different mobile phase pH in each dimension. This system utilizes mass spectrometry (MS) friendly pH modifiers for the online coupling of high pH reversed phase liquid chromatography (HPH-RPLC) in the first dimension (1D) followed by low pH reversed phase liquid chromatography (LPH-RPLC) in the second dimension (2D). Owing to the ionic nature of proteins, the use of a different mobile phase pH was successful to provide altered selectivity between the two dimensions, even for closely related protein variants, such as bovine cytochrome cand equine cytochrome c, which differ by only three amino acids. Subminute gradient separation of proteins in the second dimension was successful to minimize analysis time, while maintaining high peak capacity. Unlike peptides, the elution order of studied proteins did not follow their isoelectric points, where acidic proteins would be expected to be more retained at low pH (and basic proteins at high pH). The steep elution isotherms (on–off retention mechanism) of proteins and the very steep gradients utilized in the second-dimension column succeeded in overcoming pH and organic solvent content mismatch. The utility of the system was demonstrated with a mixture of protein standards and an Escherichia coliprotein mixture.

•Methods for analyzing natural cannabis components and contaminants.•Considerations for quality control of cannabis-derived edible products.•Evaluation of different food extraction techniques and their applications.

Chemical cross-linking coupled with mass spectrometry (MS) is becoming a routinely and widely used technique for depicting and constructing protein structures and protein interaction networks. One major challenge for cross-linking/MS is the determination of informative low-abundant inter-cross-linked products, generated within a sample of high complexity. A C18 stationary phase is the conventional means for reversed-phase (RP) separation of inter-cross-linked peptides. Various RP stationary phases, which provide different selectivities and retentions, have been developed as alternatives to C18 stationary phases. In this study, two phenyl-based columns, biphenyl and fluorophenyl, were investigated and compared with a C18 phase for separating BS3(bis(sulfosuccinimidyl)suberate) cross-linked bovine serum albumin (BSA) and myoglobin by bottom-up proteomics. Fractions from the three columns were collected and analyzed in a linear ion trap (LIT) mass spectrometer for improving detection of low abundant inter-cross-linked peptides. Among these three columns, the fluorophenyl column provides additional ion-exchange interaction and exhibits unique retention in separating the cross-linked peptides. The fractioned data was analyzed in pLink, showing the fluorophenyl column consistently obtained more inter-cross-linked peptide identifications than both C18 and biphenyl columns. For the BSA cross-linked sample, the identified inter-cross-linked peptide numbers of the fluorophenyl to C18 column are 136 to 102 in “low confident” results and 11 to 6 in “high confident” results. The fluorophenyl column could potentially be a better alternative for targeting the low stoichiometric inter-cross-linked peptides.

The application of continuous flow–extractive desorption electrospray ionization (CF-EDESI), an ambient ionization source demonstrated previously for use with intact protein analysis, is expanded here for the coupling of reversed phase protein separations to mass spectrometry. This configuration allows the introduction of charging additives to enhance detection without affecting the chromatographic separation mechanism. Two demonstrations of the advantages of CF-EDESI are presented in this work. First, a proof-of-principle is presented to demonstrate the applicability of hyphenation of liquid chromatography (LC) to CF-EDESI. LC-CF-EDESI-MS has good sensitivity compared to LC–electrospray ionization (ESI)–mass spectrometry. Second, the supercharging mechanism investigated in CF-EDESI provides an insight into a highly debated supercharging process in ESI. The results indicate that the mechanism of protein charging seen in HPLC-CF-EDESI is different from supercharging phenomena in conventional ESI. The surface tension mechanism and binding mechanism may both contribute to protein supercharging in ESI.

Matrix effects of different biological samples, including phosphate‐buffered saline–bovine serum albumin (PBS‐BSA), gelded horse serum, mouse serum, and mouse brain, were investigated for the determination of 17α‐ and β‐estradiol using derivatization with dansyl chloride prior to LC‐MS/MS. Matrix effects were evaluated based on the slopes of regression lines plotted from results obtained in biological matrices versus pure standard solutions. Such plots indicate the enhancement or suppression of signal based on the presence of a particular biological fluid for a particular method. The matrix effects from PBS‐BSA were similar to those of mouse serum. In contrast, analyses performed from horse serum and mouse brain yielded significant ion suppression, especially for 17β‐estradiol. Precipitation during derivatization was observed when pre‐concentrated samples were processed with ethyl acetate as an extraction solvent. This was overcome with the use of methyl tert‐butyl ether; however, matrix effects from this preparation were still present, evidenced by signal suppression and poor linearity in the standard curve. This work affirms that caution should be taken in the transfer of methods for use with different biological matrices, especially in the case where surrogate matrices are necessary for calibration purposes.

The effect of solvent systems on previously‐reported ESI‐MS based proton‐assisted enantioselective molecular recognition phenomena of tartar emetic, L‐antimony(III)‐tartrate, was evaluated. This was achieved by carrying out a series of competitive binding experiments using chiral selectors, bis(sodium) D‐ and ‐L‐antimony(III)‐tartrates with chiral selectands, neutral side‐chain amino acid enantiomeric isotopomers of alanine (Ala), valine (Val), leucine (Leu) and phenylalanine (Phe), in three different solvent systems, ACN/H2O (75/25 v/v), H2O (100%) and H2O/MeOH (25/75 v/v). Observations from these experiments suggest that the effect of solvent systems on previously reported proton‐assisted chiral recognition capacity of D,L‐antimony(III)‐tartrates is small, but not negligible. It was observed that an ACN/H2O (75/25 v/v) solvent system facilitates and enhances the chiral discrimination capacity of protonated {[D,L‐Sb2‐tar2][H]}−ionic species. Further, amino acid enantiomers showed a general trend of increasing selectivity order, Val ≤ Ala < Leu ≈ Phe towards the protonated {[D,L‐Sb2‐tar2][H]}−ionic species which was independent of the solvent system employed. The lack of enantioselective binding for {[D,L‐Sb2‐tar2]}2−ionic species was consistently recorded in respective mass spectra from all performed experiments, which suggests that ESI‐friendly solvent systems have no effect and do not influence this phenomenon. Chirality, 2011. © 2010 Wiley‐Liss, Inc.

Estrogens and estrogen metabolites are important biological mediators of the endocrine system. They have also been implicated in detrimental carcinogenesis and beneficial neuroprotective processes. The retention behavior of estrogen metabolites was investigated on five polar stationary phases, used for hydrophilic interaction chromatography, and coupled with ESI‐MS. Data were fit to partitioning and surface adsorption models. Retention of the compounds, especially estrogen glucuronides, on the amide‐ and diol‐bonded stationary phases, could be best described by the surface adsorption model; however, mixed modes of retention were observed on most stationary phases. Retention time increased while the peak efficiency decreased proportional to the number of hydroxyl groups in the analytes. The effects of salt concentration and salt type were also investigated. The presence of solvated salt ions, which interact with the stationary phase and the analyte, enhanced retention of the analytes. This was believed to be due to two effects. The increased ionic strength reduced the contribution of secondary electrostatic interactions (mixed‐mode effects). It also enhanced hydrogen‐bonding and partitioning (hydrophilic interaction) between the analyte and the stationary phase, likely facilitated by the associated solvated salt ions.

Because of the generally different interaction of enantiomers with biological systems, there has been an ever increasing demand for artificial highly enantioselective systems that can facilitate separation processes involved in the research and development of enantiomerically pure drugs. Such systems may be discovered by large‐scale screening of compound libraries which warrants rapid and cost‐efficient screening methods. Here, we demonstrate enantioselectivity determination for systems of cinchona alkaloid carbamates and N‐blocked amino acids using HPLC‐MS and the recently developed dynamic titration technique (Fryčák P, Schug KA. Anal Chem 2008;80:1385‐1393). A mixture of nine N‐blocked amino acids (either Dor Lenantiomers) was separated on a reversed‐phase column with cinchona alkaloid carbamates added postcolumn. Dissociation constants of the observed noncovalent complexes were determined from the HPLC‐MS data. Enantioselectivity was then calculated from the dissociation constants, pointing out the best performing systems. For these systems, apparent dissociation constants were measured for the whole range of enantiomeric composition and were shown to obey a proposed theoretical model. Chirality, 2009. © 2009 Wiley‐Liss, Inc.

Solution phase and gas phase chiral molecular recognition properties of tartrates (salts or esters of tartaric acid) and metal tartrates (binuclear tartrato(4‐)‐metal‐bridged complexes) are reviewed in conjunction with their applications in enantiomeric separation science and their mass spectrometric chiral discrimination properties.

The analysis of highly hydrophilic, ionic, and polar compounds has been performed by HILIC‐ESI‐MS for the last few years. The use of low aqueous/high polar organic solvent content in HILIC separation mobile phase is almost ideal for ESI‐MS detection in many cases, resulting in increased sensitivity. Although the addition of modifiers such as acids or salts is necessary in some circumstances for a good separation, the optimum concentrations used are still highly amenable for ESI‐MS analysis, showing few deleterious effects. In this review, the mechanism of HILIC separation and ESI ion generation will be briefly discussed, followed by a summary of method development and applications in several fields of research including pharmaceutical, biomolecular, food, metabolic, and environmental analysis.

A review is given from the stand-point of applying methods utilizing electrospray ionization - mass spectrometry (ESI-MS) for quantitative binding (affinity and selectivity) determinations in small molecule host-guest (receptorligand, selector-selectand, etc.) systems. Advantages over more commonly utilized and traditional solution phase approaches, both in the context of developing new chiral selector molecules for separation and purification of enantiomers and in drug discovery applications, are presented. Although the majority of studies employing methods such as host-guest screening, competitive binding, and titrations have focused on large protein-ligand, DNA-ligand, and RNA-ligand systems, the use of ESI-MS for studying small molecule and chiral recognition systems is growing. For the latter case, greater care must be given to considering the effects of the ESI process on the ionization of the species involved in equilibria of interest. Some basic mechanistic and practical concerns for performing solution-phase-targeting quantitative measurements by ESI-MS are given in this light. Finally, an account of the application of these methods in a high throughput format is given, highlighting the potential of traditional and novel screening and titration approaches which allow scientists to screen the performance of hundreds, if not thousands, of compounds in a single day.

Deuterium isotope effects are reported for binding between tert‐butylcarbamoyl‐quinine/quinidine chiral selectors and isotopomeric quasienantiomers of N‐(3,5‐dinitrobenzoyl)leucine measured using electrospray ionization‐mass spectrometry (ESI‐MS) and competitive binding. Evaluation of mixtures of each selector with one labeled and one unlabeled enantiomeric selectand of identical configuration showed a significant difference in measured ion abundances of diastereomeric complexes between the selector and each selectand. It was found that in some cases, the complex containing the nondeuterated selectand was 15% more abundant than its deuterated counterpart. On the basis of an assessment of solution‐ and gas‐phase isotope effects reported in the literature, a series of control experiments were performed to study the origin of the effects. On the basis of these measurements, our preliminary conclusion is that the differing gas‐phase physicochemical nature of the deuterated versus nondeuterated selectand represents the strongest contribution to the observed effect in this chiral molecular recognition system. Copyright © 2006 John Wiley & Sons, Ltd.

As of late, mass spectrometric methods for analysis of enantiomer discriminating systems have received considerable attention. In the last ten years, specific methods focused on measuring enantioselectivitiesviadiastereomeric host–guest associations, collisional dissociation of diastereomeric complexes, and ion‐molecule reactions using chiral selectors have been developed. The ability to evaluate the performance of new chiral selector molecules by MS is particularly intriguing in this context; providing complementary technology to enantioselective gas‐ and liquid‐phase separation strategies already in place. Still, a number of question marks remain to be answered before these methods become commonplace. This review surveys the aspects of the mass spectrometric methods listed above and describes how they can be used to evaluate enantiomer discriminating systems. A short overview comparing the different ionization sources and mass analyzers which are used is also offered. Overall, we seek to address the advantages and limitations of each method, citing specific examples of their use from the literature, for the purpose of understanding what could be done to expand the scope of their implementation. In doing so, we also highlight some of those facets that relate directly to using MS for evaluating molecular recognition, and in particular, chiral molecular recognition systems.

This study focuses on pseudo‐molecular ion formation in electrospray ionization mass spectrometry (ESI‐MS) of six anti‐inflammatory pharmaceuticals with similar functionality. The formation of particular pseudo‐molecular ions depends on ion affinity and molecular structure of the analyte as well as the solvent/buffer conditions used. Six common anti‐inflammatory agents are mixed 1:1 with six different acetonitrile/aqueous buffer solutions at varying concentrations. The analytes are ibuprofen, carprofen, naproxen, ketoprofen, flurbiprofen, and fenoprofen. The pKaand surface activity of the analytes and the pH, concentration, and type of the solvent system strongly affect the ions formed [1,2]. The additives are common liquid chromatography (LC) mobile phase modifiers. The spectral intensities of three major pseudo‐molecular ions were measured by flow injection analysis ESI‐MS. The ions studied correspond to the deprotonated molecular ion ([M – H]–), a deprotonated dimer ion ([2M – H]–), and a deprotonated dimer ion pair with sodium ([2M – 2H+Na]–). These ions were chosen due to their high relative abundance in a majority of the spectra. The pKaof the analytes studied range from 4.1 to 4.4, due to their aromatic acetic acid moiety. The common carboxylic acid group facilitates ESI of the compounds in the negative ionization mode. The changes in molecular structure of these model compounds allows for a wide variety of solution interactions. Some analytes are effectively declustered under the set conditions creating an intense [M – H]–peak, whereas others prefer to form dimers or complexes with sodium.

The relative abundances of ternary diastereomeric complexes (composed each from a cinchonane-type chiral selector, a model chiral acid, and an alkali cation) are shown to change remarkably and fortuitously with variation in concentration and type of alkali metal using electrospray ionization-mass spectrometry and competitive binding analysis.

Here we present data using a bioluminescent dinoflagellate, Pyrocystis lunula, in a toxicological bioassay to rapidly assess potential instances of groundwater contamination associated with natural gas extraction. P. lunula bioluminescence can be quantified using spectrophotometry as a measurement of organismal viability, with normal bioluminescent output declining with increasing concentration(s) of aqueous toxicants. Glutaraldehyde and hydrochloric acid (HCl), components used in hydraulic fracturing and shale acidization, triggered significant toxicological responses in as little as 4 h. Conversely, P. lunula was not affected by the presence of arsenic, selenium, barium, and strontium, naturally occurring heavy metal ions potentially associated with unconventional drilling activities. If exogenous compounds, such as glutaraldehyde and HCl, are thought to have been introduced into groundwater, quantification of P. lunula bioluminescence after exposure to water samples can serve as a cost-effective detection and risk assessment tool to rapidly assess the impact of putative contamination events attributed to unconventional drilling activity.

For Abstract see ChemInform Abstract in Full Text.