Kevin A. Schug

The advantages of ESI-MS detection in conjunction with HILIC mode separations: Fundamentals and applications.

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.

Development of aliphatic biodegradable photoluminescent polymers

None of the current biodegradable polymers can function as both implant materials and fluorescent imaging probes. The objective of this study was to develop aliphatic biodegradable photoluminescent polymers (BPLPs) and their associated cross-linked variants (CBPLPs) for biomedical applications. BPLPs are degradable oligomers synthesized from biocompatible monomers including citric acid, aliphatic diols, and various amino acids via a convenient and cost-effective polycondensation reaction. BPLPs can be further cross-linked into elastomeric cross-linked polymers, CBPLPs. We have shown representatively that BPLP-cysteine (BPLP-Cys) and BPLP-serine (BPLP-Ser) offer advantages over the traditional fluorescent organic dyes and quantum dots because of their preliminarily demonstrated cytocompatibility in vitro, minimal chronic inflammatory responses in vivo, controlled degradability and high quantum yields (up to 62.33%), tunable fluorescence emission (up to 725 nm), and photostability. The tensile strength of CBPLP-Cys film ranged from 3.25 ± 0.13 MPa to 6.5 ± 0.8 MPa and the initial Modulus was in a range of 3.34 ± 0.15 MPa to 7.02 ± 1.40 MPa. Elastic CBPLP-Cys could be elongated up to 240 ± 36%. The compressive modulus of BPLP-Cys (0.6) (1:1:0.6 OD:CA:Cys) porous scaffold was 39.60 ± 5.90 KPa confirming the soft nature of the scaffolds. BPLPs also possess great processability for micro/nano-fabrication. We demonstrate the feasibility of using BPLP-Ser nanoparticles (“biodegradable quantum dots”) for in vitro cellular labeling and noninvasive in vivo imaging of tissue engineering scaffolds. The development of BPLPs and CBPLPs represents a new direction in developing fluorescent biomaterials and could impact tissue engineering, drug delivery, bioimaging.

General method for extraction of blueberry anthocyanins and identification using high performance liquid chromatography–electrospray ionization-ion trap-time of flight-mass spectrometry

A systematic approach for optimizing the extraction and identification of anthocyanins from blueberries was explored using HPLC-UV and HPLC-ESI-IT-TOF-MS. Sample homogenization effects, extraction solvent selection, type of acid, and amount used in extraction solvent were investigated. A mixture of methanol:water:trifluoroacetic acid (70:30:1, v/v/v) was found to be the best solvent system for blueberry anthocyanin extraction. Differences in total anthocyanin content due to commercial blueberry processing were explored as an application using the optimized extraction technique and HPLC-UV analysis. A methodical system for anthocyanin identification by HPLC-ESI-IT-TOF-MS without the use of standards was also reviewed and applied. Consideration was given to elution order by chromatographic separation with selective detection at 520nm, high mass accuracy m/z values, tandem MS fragmentation, and previously published literature. Overall, 25 anthocyanins from a wild type highbush blueberry were identified and reported.

An evaluation of water quality in private drinking water wells near natural gas extraction sites in the Barnett Shale Formation

Natural gas has become a leading source of alternative energy with the advent of techniques to economically extract gas reserves from deep shale formations. Here, we present an assessment of private well water quality in aquifers overlying the Barnett Shale formation of North Texas. We evaluated samples from 100 private drinking water wells using analytical chemistry techniques. Analyses revealed that arsenic, selenium, strontium and total dissolved solids (TDS) exceeded the Environmental Protection Agencys Drinking Water Maximum Contaminant Limit (MCL) in some samples from private water wells located within 3 km of active natural gas wells. Lower levels of arsenic, selenium, strontium, and barium were detected at reference sites outside the Barnett Shale region as well as sites within the Barnett Shale region located more than 3 km from active natural gas wells. Methanol and ethanol were also detected in 29% of samples. Samples exceeding MCL levels were randomly distributed within areas of active natural gas extraction, and the spatial patterns in our data suggest that elevated constituent levels could be due to a variety of factors including mobilization of natural constituents, hydrogeochemical changes from lowering of the water table, or industrial accidents such as faulty gas well casings.

A review of separation methods for the determination of estrogens and plastics-derived estrogen mimics from aqueous systems

Recent methods of separation and detection for the quantification of trace-level concentrations of selected endocrine disrupting compounds (EDCs) from aqueous systems are reviewed. A brief introduction of the selected EDCs (natural and synthetic estrogens and plastics-derived xenoestrogens), including their characteristics and importance, is presented. Sample preparation and extraction trends are discussed. Various types of separation techniques are presented, with the express goal of emphasizing time and cost-effective methods that isolate and quantify trace-levels of multiple endocrine disruptors from aqueous systems.

A Comprehensive Analysis of Groundwater Quality in The Barnett Shale Region

The exploration of unconventional shale energy reserves and the extensive use of hydraulic fracturing during well stimulation have raised concerns about the potential effects of unconventional oil and gas extraction (UOG) on the environment. Most accounts of groundwater contamination have focused primarily on the compositional analysis of dissolved gases to address whether UOG activities have had deleterious effects on overlying aquifers. Here, we present an analysis of 550 groundwater samples collected from private and public supply water wells drawing from aquifers overlying the Barnett shale formation of Texas. We detected multiple volatile organic carbon compounds throughout the region, including various alcohols, the BTEX family of compounds, and several chlorinated compounds. These data do not necessarily identify UOG activities as the source of contamination; however, they do provide a strong impetus for further monitoring and analysis of groundwater quality in this region as many of the compounds we detected are known to be associated with UOG techniques.

Adduct formation in electrospray ionization. Part 1: Common acidic pharmaceuticals

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 pK a and 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 pKa of 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.

Adduct formation in electrospray ionization mass spectrometry II. Benzoic acid derivatives

This work serves as a follow-up to Part I of experiments designed to determine the underlying principles in the formation of pseudomolecular, or adduct, ions during electrospray ionization. Aromatic acids were studied by flow injection analysis in the negative ionization mode of electrospray ionization mass spectrometry. Part I dealt with common acidic anti-inflammatory pharmaceuticals. such as ibuprofen and related analogues. Part II deals with functionally less complex molecules, namely benzoic acid (BA) and substituted benzoic acids. Halide-substituted molecules are investigated to deduce the effect of electron-withdrawing substituents (bromo-, chloro-, and fluoro-) and ring position (ortho-, meta- and para-) on the response of a traditional deprotonated molecular ion ([M-H]-) and a sodium-bridged dimer ion ([2M-2 H+Na]-). Amino-substituted benzoic acids are also analyzed in order to study the effect of an additional ionizable group on the molecule, and para-tert.-butyl-BA is analyzed to study the effect of increased hydrophobicity, as they relate to the formation of pseudomolecular ions. This study shows that solution character [octanol-water partition coefficient (or log P) and pKa] of the model compounds controls the relative efficiency of formation of [M-H]- and [2M-2H+Na]- ions. However the relative gas phase character (gas phase basicity and proton affinity) also has a significant effect on the formation of the sodium-bridged dimer ion. For the halide-substituted species, placement of the electron-withdrawing atom at the meta-position gives the greatest enhancement in sensitivity. Observations also show that as the structural complexity of the model compound increases, predictions relating analyte acidity to sodium-bridged dimer ion formation give way to a stronger dependence between log P values and ionization efficiency. Supporting this hypothesis is the nearly ten-fold enhancement in signal for tert.-butyl BA relative to BA. due to the greater hydrophobicity, and consequently, increased surface activity in an electrosprayed droplet of the analyte molecule.

A mechanistic explanation for pH-dependent ambient aquatic toxicity of Prymnesium parvum carter

The harmful algal bloom species Prymnesium parvum has caused millions of dollars in damage to fisheries around the world. These fish kills have been attributed to P. parvum releasing a mixture of toxins in the water. The characterized toxins, reported as prymnesin-1 and -2, have structural similarities consistent with other known ionizable compounds (e.g., ammonia). We investigated whether pH affects the toxicity of P. parvum under conditions representative of inland Texas reservoirs experiencing ambient toxicity from bloom formation. We evaluated pH influences on toxicity in laboratory and field samples, and modeled the physicochemical properties of prymnesins. Aquatic toxicity to a model fish and cladoceran was reduced by lowering pH in samples obtained from reservoirs experiencing P. parvum blooms; similar observations were confirmed for experiments with laboratory cultures. A pKa value of 8.9 was predicted for the prymnesins, which suggests that ionization states of these toxins may change appreciably over surface water pH of inland waters. These findings indicate that ionization states of toxins released by P. parvum may strongly influence site-specific toxicity and subsequent impacts to fisheries. Consequently, these results emphasize the importance of understanding processes that affect pH during P. parvum blooms, which may improve predictions of ambient toxicity.

Vacuum ultraviolet detector for gas chromatography

Analytical performance characteristics of a new vacuum ultraviolet (VUV) detector for gas chromatography (GC) are reported. GC-VUV was applied to hydrocarbons, fixed gases, polyaromatic hydrocarbons, fatty acids, pesticides, drugs, and estrogens. Applications were chosen to feature the sensitivity and universal detection capabilities of the VUV detector, especially for cases where mass spectrometry performance has been limited. Virtually all chemical species absorb and have unique gas phase absorption cross sections in the approximately 120-240 nm wavelength range monitored. Spectra are presented, along with the ability to use software for deconvolution of overlapping signals. Some comparisons with experimental synchrotron data and computed theoretical spectra show good agreement, although more work is needed on appropriate computational methods to match the simultaneous broadband electronic and vibronic excitation initiated by the deuterium lamp. Quantitative analysis is governed by Beer-Lambert Law relationships. Mass on-column detection limits reported for representatives of different classes of analytes ranged from 15 (benzene) to 246 pg (water). Linear range measured at peak absorption for benzene was 3-4 orders of magnitude. Importantly, where absorption cross sections are known for analytes, the VUV detector is capable of absolute determination (without calibration) of the number of molecules present in the flow cell in the absence of chemical interferences. This study sets the stage for application of GC-VUV technology across a wide breadth of research areas.