Alexandra C. Stenson

Release of drinking water contaminants and odor impacts caused by green building cross-linked polyethylene (PEX) plumbing systems

Green buildings are increasingly being plumbed with crosslinked polyethylene (PEX) potable water pipe. Tap water quality was investigated at a six month old plumbing system and chemical and odor quality impacts of six PEX pipe brands were examined. Eleven PEX related contaminants were found in the plumbing system; one regulated (toluene) and several unregulated: Antioxidant degradation products, resin solvents, initiator degradation products, or manufacturing aides. Water chemical and odor quality was monitored for new PEX-a, -b and -c pipes with (2 mg/L free chlorine) and without disinfectant over 30 days. Odor and total organic carbon (TOC) levels decreased for all pipes, but odor remained greater than the USAs Environmental Protection Agencys (USEPA) secondary maximum contaminant level. Odors were not attributed to known odorants ethyl-tert-butyl ether (ETBE) or methyl-tert-butyl ether (MTBE). Free chlorine caused odor levels for PEX-a1 pipe to increase from 26 to 75 threshold odor number (TON) on day 3 and affected the rate at which TOC changed for each brand over 30 days. As TOC decreased, the ultraviolet absorbance at 254 nm increased. Pipes consumed as much as 0.5 mg/L as Cl2 during each 3 day stagnation period. Sixteen organic chemicals were identified, including toluene, pyridine, methylene trichloroacetate and 2,4-di-tert-butylphenol. Some were also detected during the plumbing system field investigation. Six brands of PEX pipes sold in the USA and a PEX-a green building plumbing system impacted chemical and drinking water odor quality.

On the Formation of a Protic Ionic Liquid in Nature

The practical utility of ionic liquids (ILs) makes the absence (heretofore) of reported examples from nature quite puzzling, given the facility with which nature produces many other types of exotic but utilitarian substances. In that vein, we report here the identification and characterization of a naturally occurring protic IL. It can be formed during confrontations between the ants S. invicta and N. fulva. After being sprayed with alkaloid-based S. invicta venom, N. fulva detoxifies by grooming with its own venom, formic acid. The mixture is a viscous liquid manifestly different from either of the constituents. Further, we find that the change results as a consequence of formic acid protonation of the N centers of the S. invicta venom alkaloids. The resulting mixed-cation ammonium formate milieu has properties consistent with its classification as a protic IL.

Chromatographic reduction of isobaric and isomeric complexity of fulvic acids to enable multistage tandem mass spectral characterization.

Humic substances and related material commonly grouped under the designation of natural organic matter (NOM) are of interest in fields ranging from marine chemistry and geochemistry to industry, agriculture, and pharmacology. High-field Fourier transform ion cyclotron resonance mass spectrometry enables resolution and identification of elemental compositions of up to thousands of components from a single mass spectrum. Here, we introduce an offline prefractionation to reduce the number of species of the same nominal (nearest-integer) mass, allowing for isolation of ions of one or a few m/z values, from which structural information can be obtained by low-resolution multistage tandem mass spectrometry (MS(n)). Alternatively, precharacterized fractions can be generated for other types of analysis. As an example, we demonstrate significant reduction of isomeric and isobaric complexity for Suwannee River fulvic acid (SRFA). The combined MS and MS(n) analyses support the hypothesis that early eluting material comprises older, highly oxidized SRFA, whereas later eluting material is younger, retaining some similarity with precursor material.

Fourier transform ion cyclotron resonance mass spectral characterization of metal-humic binding

The interaction between metals and naturally occurring humic substances and the thereby induced issues of bioavailability and hydrogeochemical turnover of metal ions in natural waters have been the subject of intense study for decades. Traditional bulk techniques to investigate metal-humic binding (e.g. potentiometry and inductively coupled plasma mass spectrometry (ICP-MS)) can provide quantitative results for the relative abundance and distribution of metal species in humic samples and/or overall binding constants. The shortcoming of these bulk techniques is the absence of structural detail. Ultra-high-resolution mass spectrometry, currently the only technique demonstrated to resolve individual humic ions, is not generally employed to provide the missing qualitative information primarily because the identification of metal complexes within the already complex mixtures of humic substances is non-trivial and time-consuming to the extent of eliminating any possibility for real-time manipulation of chelated analytes. Here, it is demonstrated that with tailored selection of the metal ion, it is possible to visually identify large numbers of metal-humic complexes ( approximately 500 for Be2+, approximately 1100 for Mn2+, and approximately 1500 for Cr3+) in real-time as the spectra are being acquired. Metal ions are chosen so that they form primarily even-m/z complexes with humic ions. These even-m/z complexes stand out in the spectrum and can readily be characterized based on molecular formulae, which here revealed for example that Suwannee River fulvic acid (SRFA) complexes encompassed primarily highly oxygenated fulvic acids of relatively low double-bond equivalence. Facile, real-time identification of even-m/z metal-humic complexes additionally allows for the specific selection of metal-humic complexes for MS(n) analysis and in-trap ion-neutral reactions enabling investigation of metal-humic complex structure. MS/MS data were collected to demonstrate the potential of the technique as well as highlight some of the remaining challenges.

A simple and rapid route to novel tetra(4-thiaalkyl)ammonium bromides

A simple approach for the preparation of symmetrical quaternary ammonium bromides employing thiol–ene click chemistry is used to synthesize tetra(4-thiaalkyl)ammonium bromides. This approach allows the incorporation of a variety of alkyl moieties onto the nitrogen center with a one-step synthesis involving easy work-up, no side reactions and environmentally friendly reagents. To elucidate information regarding the behaviour of this novel class of compounds, comparisons to tetraalkylammonium analogues have been made. These include melting points, activity as phase-transfer catalysts, and conformational predictions from computational modelling. All results are consistent in indicating stronger bonding between the quaternary cation and the anion for the salts with 4-thiaalkyl chains as compared to those with n-alkyl chains.

Fact or artifact: the representativeness of ESI-MS for complex natural organic mixtures

Because mass spectrometers provide their own dispersion and resolution of analytes, electrospray ionization mass spectrometry (ESI-MS) has become a workhorse for the characterization of complex mixtures from aerosols to crude oil. Unfortunately, ESI mass spectra commonly contain multimers, adducts and fragments. For the characterization of complex mixtures of unknown initial composition, this presents a significant concern. Mixed-multimer formation could potentially lead to results that bare no resemblance to the original mixture. Conversely, ESI-MS has continually reflected subtle differences between natural organic matter mixtures that are in agreement with prediction or theory. Knowing the real limitations of the technique is therefore critical to avoiding both over-interpretation and unwarranted skepticism. Here, data were collected on four mass spectrometers under a battery of conditions. Results indicate that formation of unrepresentative ions cannot entirely be ruled out, but non-covalent multimers do not appear to make a major contribution to typical natural organic matter spectra based on collision-induced dissociation results. Multimers also appear notably reduced when a cooling gas is present in the accumulation region of the mass spectrometer. For less complex mixtures, the choice of spray solvent can make a difference, but generally spectrum cleanliness (i.e. representativeness) comes at the price of increased selectivity.

Click chemistry mediated synthesis of bio-inspired phosphonyl-functionalized ionic liquids†

This study focuses on the synthesis of a class of novel biologically-inspired ionic liquids coupled with a phosphonate group containing short to long side chains (C3–C11) via the Pudovic reaction. The ionic liquids exhibited very low glass transition temperatures and were hydrophobic in character. This method has the attributes of “click” chemistry with outstanding efficiency, simplicity, yields and regioselectivity. The results of their calcium(II) ligating capability are also presented.

Characterization of Disinfection By-Products from Chromatographically Isolated NOM through High-Resolution Mass Spectrometry.

As levels of natural organic matter (NOM) in surface water rise, the minimization of potentially harmful disinfection by-products (DBPs) becomes increasingly critical. Here, we introduce the advantage that chromatographic prefractionation brings to investigating compositional changes to NOM caused by chlorination. Fractionation reduces complexity, making it easier to observe changes and attribute them to specific components. Under the conditions tested (0.1-0.4 g of Cl to g of C without further additives), the differences between highly and less oxidized NOM were striking. Highly oxidized NOM formed more diverse Cl-containing DPB, had a higher propensity to react with multiple Cl, and tended to transform so drastically as to no longer be amenable to electrospray-ionization mass spectral detection. Less-oxidized material tended to incorporate one Cl and retain its humiclike composition. N-containing, lipidlike, and condensed aromatic structure (CAS)-like NOM were selectively enriched in mass spectra, suggesting that such components do not react as extensively with NaOCl as their counterparts. Carbohydrate-like NOM, conversely, was selectively removed from spectra by chlorination.

HPLC–MS/MS method for quantification of paclitaxel from keratin containing samples

HIGHLIGHTSPaclitaxel was quantified from keratin containing samples via HPLC‐MS/MS.Tert‐butyl methyl ether and ethanol were evaluated as extraction solvents.The method was validated based on linear range and intra‐ and inter‐day precision.The developed method is applicable to any aqueous paclitaxel samples. ABSTRACT Local drug delivery of paclitaxel is becoming ever more prevalent. As complex drug/excipient combinations are being developed and tested, new high performance liquid chromatography‐mass spectrometry (HPLC‐MS) techniques capable of quantifying paclitaxel from such formulations are needed. Here a method for quantifying paclitaxel from aqueous, protein and oil containing samples was developed and validated. Keratin, derived from human hair, is the protein component/paclitaxel excipient in the development and validation of said method. The novelty of this method is described by its ability to overcome water solubility issues and address clean‐up of residual solvents in clinical grade paclitaxel injection composition. The method evaluates tert‐butyl methyl ether and ethanol as extraction solvents with an extraction efficiency of 31.9 ± 2.3% and 86.4 ± 4.5% respectively. Upon evaporation and rehydration, samples were evaluated by HPLC‐MS and a method was developed for paclitaxel quantification. The method developed had an inter‐day precision of 9.1% relative standard deviation and an intra‐day precision of 4.3% relative standard deviation normalized to a docetaxel internal standard. The described method is applicable to any aqueous paclitaxel sample containing protein and/or oils.

Benefits of multidimensional fractionation for the study and characterization of natural organic matter.

The belief that chromatographic separation of complex environmental mixtures or natural organic matter (NOM) produces featureless humps from which little, if anything, can be learned is still pervasive. Meanwhile improvements in chromatography and the use of information-rich detection methods have led to meaningful fractionation and revealed consistent data. Here, we build on this work and developed a robust, facile two-dimensional separation with high orthogonality between dimensions. We illustrate that re-injections of fractions (both in the first and in the second dimension) leads to individual peaks at the expected retention times and use information-rich detection to investigate the basis on which NOM is fractionated. We demonstrate unprecedentedly feature-rich chromatograms are observed even with standard UV detection for polar NOM fractions. The second stage of fractionation is demonstrated to separate isomers, providing a direct look at isomeric complexity in NOM as well as a tool to reduce it. Consistent with expectation, but confirmed for the first time through mass spectral data, radicals were detected for NOM components that were generally nonpolar and grouped in the condensed aromatic structure - like region of van Krevelen plots. High-resolution tandem mass spectral data, furthermore, suggests that many higher-MW components of fulvic acids (especially the highly oxidized ones) have formulas that do not match any known compounds in the literature, supporting the hypothesis that fulvic acids are a unique compound-class. Combined, the data illustrate that meaningful reduction in complexity reveals new compositional and structural detail and avails new avenues of investigation.