Low-resolution Mass Spectrometry Research Articles

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.

Anthocyanin composition and content of the Vaccinium uliginosum berry

Anthocyanins are polyphenols that are widely distributed in plants, and contribute to the brilliant blue, red or purple colour in leaves, flowers or fruits. Their attractive colours and their abundance in the north-east of China make the berries of Vaccinium uliginosum a new and excellent source of natural pigments. The pigments were extracted from the V. uliginosum berry using 0.5% TFA in ethanol solution, purified by an X-5 resin column and characterised by HPLC–DAD analysis. All of the peak assignments were confirmed by low-resolution electrospray mass spectrometry. The results showed that 11 anthocyanins and 2 flavonols were present in the V. uliginosum berry.

Determination of organochlorine pesticide residues in soil/sediment using isotope dilution gas chromatography-mass spectrometry

A method was developed for the determination of organochlorine pesticide (OCP) residues in soil/sediment using high resolution gas chromatography coupled with low resolution mass spectrometry. The analytical procedures consisted of Soxhlet extraction, sulfur removal with copper powder, clean-up with gel permeation chromatography (GPC) and a florisil column of solid phase extraction (SPE). The analytes were separated on an HP-5MS capillary column, detected in selected ion monitoring ( SIM) mode and quantified using internal standard calibration curves of isotope dilution technique. The linear correlations of calibration standard solutions were good for all the OCPs. The recoveries and relative standard deviations of labeled compound solutions ranged from 60% to 110% and from 1.5% to 18%, respectively. The limits of detection ranged from 0.20 to 10.3 microg/kg were established for the 23 OCPs. The method showed satisfactory clean-up effect and precision quantification. It is suitable for the determination and confirmation of pesticides in complex matrices such as soil, sediment.

An analytical method for chlorinated paraffins and their determination in soil samples

Short chain chlorinated paraffins (SCCPs) are possibly persistent organic pollutants (POPs), and are candidate POPs of the Stockholm Convention. In this study, three quantitative methods for analyzing CPs were compared using a gas chromatograph-electron capture detector (GC-ECD), gas chromatograph-electron capture negative ion low resolution mass spectrometry (GC-ECNI-LRMS) and gas chromatograph-electron ionization tandem mass spectrometry (GC-EI-MS2). A quantitative method for the analysis of total CPs in soil samples was established. The environmental levels of CPs in an e-waste dismantling area in China were evaluated.

Sensitivity Study of Naphthenic Acids from Flow Assurance Deposits Characterized by Low-Resolution Mass Spectrometry

Soaps constitute one of the more recent challenges in exploration and production flow assurance. In this work, the naphthenic acids from a field soap deposit were extracted and analyzed using low-resolution mass spectrometry, with the aim of examining the effects of ionization sources, operational settings, and the impact of solvents. Results suggest that fast atom bombardment (FAB), atmospheric pressure chemical ionization (APCI), and electrospray (ES) ionization sources have different effects on the samples and lead to different spectra. FAB led to the highest signal for the so-called ARN acids, as well as a range of signals for monocarboxylic acids. The signals for ARN acids obtained using both the ES and APCI sources were similar to each other in terms of intensity. Nevertheless, because of the differences in monocarboxylic acid signals between these sources, the spectrum obtained with APCI, most likely, suggests favorable ionization of ARN acids. This was supported by the analysis of the spectra of a commercial naphthenic acid mixture using the three ionization sources. Mass spectrometry data also showed that the APCI source led to the formation of multimers of higher molecular-weight naphthenic acid for the concentrations studied. More detailed investigations of the operation of the ES source demonstrated that a decrease in source voltage resulted in favored ionization and detection of the ARN acids over the monocarboxylic acids. Moreover, the use of more polar solvents in combination with the ES source also resulted in favored ionization of ARN acids. Use of selected conditions with liquid chromatography followed by tandem mass spectrometry allowed for the identification of four carboxylic acid functionalities for a selected ARN acid ion. Overall, this information points to the importance of various mass spectrometry variables in naphthenic acid detection, particularly with different acid families, and will aid in the development of a combination of quantitative methods for use with field samples. On the basis of our work and the sources examined, the ES source would be the preferred setting for an overview of the general fingerprinting of the naphthenic acids in deposits. The APCI source may be the preferred setting for work focusing on ARN identification and characterization. The ES source was also used to investigate soaps formed in the laboratory conditions using aqueous phases of varying ionic composition. The presence of ARN and non-ARN species in the soap generated in the laboratory suggests competing effects during the soap formation process, as well as the availability of mono- or divalent ions in the parent aqueous phase for the precipitation mechanism.

Pre-Colonial Herding Strategies in the Shashe-Limpopo Basin, Southern Africa, Based on Strontium Isotope Analysis of Domestic Fauna

Archaeological sites in the Shashe-Limpopo River Basin, southern Africa, reflect marked population growth and increased socio- political complexity between ca AD 880 and 1290, but the nature of agropastoral management that underpinned these extensive, more complex societies is not well understood. One key question concerns whether localized or more widespread regional strategies were employed to manage large herds of domestic animals. In order to identify potential herding areas we carried out strontium isotope analyses on tooth enamel from domestic fauna recovered at Shashe-Limpopo River Basin sites and compared them with those of modern wild and domestic fauna sampled from the greater region. Values were determined via low-resolution Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) and Laser-ablation ICP-MS and high-resolution, standard Thermal Ionization Mass Spectrometry (TIMS). The low-resolution approaches gave values comparable to data produced by TIMS, within the level of precision required to distinguish geological areas contained in this exceptionally isotopically variable environment. The less invasive laser-ablation ICP-MS method provided a means to sample tooth enamel increments for indications of inter-seasonal movement of livestock. The archaeological data suggest that an inter-seasonal geographical expansion of herd management took place as socio-political complexity increased. A trans-humance or relocating herding strategy would have limited overgrazing of the local river basin landscape and results allow us to revisit hypotheses that overgrazing and environmental deterioration contributed to the subsequent political collapse and abandonment of the river basin at ca AD 1290.

Characterization of an abundant and novel methyl- and methoxy-substituted brominated diphenyl ether isolated from whale blubber

A previously unidentified yet abundant substituted polybrominated diphenyl ether (PBDE) was isolated from a northern bottlenose whale ( Hyperoodon ampullatus) found dead in the Skagerrak, North Sea. A combination of gas chromatography, high and low resolution mass spectrometry and nuclear magnetic resonance spectroscopy (NMR) ( 1H, 1H– 1H and 1H– 13C) after isolation with preparative capillary gas chromatography (PCGC) lead to the identification of the unknown substance as 6-MeO-5-Me-2,2′,3,4′-tetrabromo diphenyl ether (6-MeO-5-Me-BDE42). To our knowledge this is only the second time PCGC has been used to isolate individual organohalogen compounds present in trace amounts for identification with NMR. The concentration of this novel bioaccumulated compound was estimated to be about 100 ng g −1 lipid, which was 2.5 times higher compared with the most abundant MeO-PBDE congeners.

Dioxins in beef samples from Mexico using a low resolution GC/MS screening method

Dioxins in beef were quantified by high resolution gas chromatography coupled to low-resolution mass spectrometry (GC/LRMS). The analyses were performed according to the minimum requirements described in the USEPA 1613 method with some minor modifications. Levels found in the samples were in the range 1.02–8.04 pg WHO-TEQ PCDDs/PCDFs g−1 fat. For comparison purposes, the maximum level allowed by the European Union is 3 pg WHO-TEQ PCDDs/PCDFs g−1 fat, and some of these samples surpassed the above-mentioned limit and can be considered as contaminated food. The results confirm that a preliminary screening of dioxins in beef can be performed by GC/LRMS. As far as we know, this is the first report of dioxins in beef in Mexico. After the appropriated tests, the applied methodology could be considered as an alternative screening method for the analysis of PCDD/Fs in other food products.

CHEMICAL COMPOSITION OF ESSENTIAL OIL OF BACCHARIS SALICIFOLIA (RUIZ & PAVON) PERS. AND ANTIBACTERIAL ACTIVITY

The essential oil of the aerial parts of Baccharis salicifolia was examined by GC and GC-MS and the major components were identified as α-pinene, camphene, β-pinene, α-phellandrene, α-cubebene, β-cariophyllene, 6,9-guaiadiene, germacrene D and germacrone. The essential oil was tested against eight Gram positive and Gram negative bacteria. The essential oil was found to exhibit moderate antibacterial activity against Gram positive bacteria tested with MIC values from 0.47 to 0.94 (µg/ml). . Raw and/or processed food is open to contamination during the production, sale and distribution steps. Food preservation is a relevant and complex problem. Food products require a longer shelf life and greater assurance of being free from food-borne pathogenic and spoilage organism. The excessive use of synthetic preservatives has resulted in an increasing pressure on food manufacturers either to completely remove chemical preservatives or by the use of new alternatives that consumers conceive as natural or safe 5 . The distillated oil (0.56 g / Kg) was dried over anhydrous sodium sulfate and stored in tightly closed darks vials at 4 oC until analysis. The oil has a golden color with an herbal odor. Identification of components. The B. salicifolia EO composition was determined by GC-MS through comparison of the major signals with previously published spectra. Retention times and mass spectral data were checked with those obtained from authentic samples and/or from the MS instrument library. Relative percentages of the major components were calculated by integrating the registered peaks. GC-MS experiments were performed on a ion trap GCQ-Plus (Finnigan, ThermoQuest, Austin, TX, USA) instrument with MS-MS program using a silica capillary column Rtx® -5MS (30 m x 0.25 mm ID, 0.25 µm). The carrier gas was helium (40 cm.s -1 ). The port temperature was 200 oC in the splitless mode with 1.0 ml injection volume. The initial GC temperature was maintained at 40 oC for 2 min, then increased to 210 oC at 2 oC min -1 , and maintained at this temperature up to 120 min. For the analysis of low resolution MS, the ion trap mass detector was set in full scan mode from m/z 50 to m/z 450. For the analysis of product, the collision inducted detection (CID) method was used. The precursor was selected using tandem mass spectrometry (MS/MS) scan standard function, with 0.5 daltons peak-widths for the parent ion and dynamically programmed scans, as described previously 9 . The main components detected in the samples here analyzed were: α-pinene (6.6x10-4 %), camphene (8.2x10-4 %), β-pinene (4.06x 10-3 %), α-phellandrene (0.0272 %), α-cubebene (5.176 %), β-cariophyllene (65.16 %), 6,9-guaiadiene (5.18 %), germacrene-D (6.6 %) and germacrone (17.85 %) which represent a 99.99 % of the total area. In order to find some correlations between the identified compounds (GC- MS) and the 1 H NMR spectral data, a sample of the whole essential oil was analyzed by this technique. A series of multiplets at δ 0.70-1.20 was consistent with several methyl groups on sp 3

A software program for more reliable precursor ion assignation from LC-MS analysis using LTQ ultra zoom scan

We developed a software program (titled Precursor Ion Calibration software for LTQ or, in short, PICsL) that increases the reliability of precursor ion assignations from LC-MS analysis using ultra zoom scanning of LTQ linear ion trap MS and automatically corrects the assignations. Although existing software calculates the theoretical isotopic distribution according to m/z with a computational algorithm, our method simply searches for ions close to the theoretical mass value using both MS/MS raw data and Mascot search result files, followed by a second database search that identifies the proteins using the regenerated peak list files. Our software program mimics the manual inspection of the spectral data of precursor ions and is expected to be applicable not only for low resolution MS, such as LTQ, but also for a wide variety of MS instruments.

A simple and fast method for the determination of selected organohalogenated compounds in serum samples from the general population

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) have been widely used in industry and agriculture. Due to their persistence and bioaccumulation, they were globally spread in the environment and may still be found in environmental and biological media, despite the international restrictions on production and use. The main aim of our study was to develop a simple and fast method suitable for the establishment of the reference values for 15 PCB congeners and 16 OCPs in general population subgroups. A cost- and time-saving screening procedure using gas chromatography coupled with low-resolution mass spectrometry, was improved and validated before application to the analysis of real samples. The overall method was validated including uncertainty measurement. Preliminary field data were collected from 95 volunteers living in two Italian areas. HCB, p,p′-DDE, PCB 153, PCB 138 and PCB 180 were the most frequently detected compounds. Age and residence area were found to be significant variables for the most abundant compounds, while no correlation between serum concentrations and gender was observed. Our results suggest that long-banned substances, including PCBs and the pesticides HCB and DDT's breakdown product, are still detectable in the general population.

Analysis of whole congener mixtures of polybromodiphenyl ethers by gas chromatography–mass spectrometry in both environmental and biological samples at femtogram levels

A sensitive and selective method for the determination of the whole congener distribution of polybromodiphenyl ethers in environmental and biological samples in one single instrumental run is described. The method is based on gas chromatography coupled to low-resolution mass spectrometry in negative ion chemical ionization mode. It allows determination of these compounds at concentration levels lower than 10 −14 g. A programmed temperature vaporization injector has been used to ensure maximum compound transfer to the chromatographic column while maintaining low thermal degradation levels of the more brominated congeners. Selectivity was increased by modification of the MS source parameters for optimization of the abundance of the high mass fragment ions. Under optimized condition, good repeatability (1.7–9.1%) and reproducibility (4.1–20%), and low detection limits, ranging between 1.5 and 15 pg ml −1, were obtained. These features afforded reliable quantification of these compounds in snow and human samples at the concentrations in which these compounds are found.

Evaluation of alternative approaches for screening contaminated sediments and soils for polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans

Traditional high resolution mass spectrometry (HRMS) analysis for polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) can be time consuming and expensive. Consequently, alternative methods are of great interest to regulatory agencies and others characterizing contaminated sites. One factor that hinders acceptance of alternative methods is a lack of performance information that assesses the alternative method's impacts on analytical results. The U.S. Environmental Protection Agency's Superfund Innovative Technology Evaluation Monitoring and Measurement Technologies Program (EPA SITE MMT) encourages the development and implementation of innovative and alternative monitoring methods by providing performance information on site characterization technologies. This paper presents a comparison of the results obtained from laboratory-based alternative approaches for screening sediment and soil samples for dioxin toxicity equivalents (TEQ D/F) to results obtained using traditional HRMS. The laboratory-based approaches included modifying the traditional HRMS analysis to make it more cost-effective (alternate 1613B), analyzing extracts that had been prepared for HRMS using low resolution mass spectrometry, and determining total organic carbon (TOC) content as an indicator of PCDD/F content. These comparisons demonstrated that TEQ D/F values generated using toxicity equivalency factors proposed by the World Health Organization in 1998 applied to alternate 1613B and LRMS analyses have a strong linear correlation to the TEQ D/F values derived in the same fashion from traditional HRMS analysis. These results would have placed >90% of the samples within the same concentration intervals using ranges of <0.05, 0.05–0.50, 0.50–5, and >5 ng TEQ/g. Natural log transformed data for TOC had significantly weaker correlation to TEQ D/F, indicating that TOC is not a reliable indicator of TEQ D/F concentrations.

Pentachlorphenol migration from treated wood exposed to simulated rainfall

Abstract The leaching of toxins from treated wood poses an, as yet, poorly quantified risk to both plant and animal life. In particular, the leaching of pentachlorophenol (PCP) into rainwater falling on treated wood over aquatic environments, such as bridges, is understudied. Computer models have been developed which predict the leaching of creosote from marine pilings. If data were available, similar models could be developed for PCP-treated bridges and the risk to waterways determined for various structural designs. Providing such data is the objective of this study, where the migration of PCP from treated wood under the influence of simulated rainfall was studied using a simulation system that delivered uniform rainfall rates over-treated wood. The runoff from the treated wood was captured and analyzed with high resolution gas chromatography combined with low resolution mass spectrometry. PCP migrated from treated wood into rainwater runoff at a fairly constant rate of approximately 0.15 g l-1 m-2. Small non-significant deviations were observed with rainfall rate, time, and temperature. We suggest that PCP migration rates from exposed treated wood can be modeled and thereby predict the migration of PCP from this source into the environment.

Baseline levels of dioxin and furan emissions from waste thermal treatment in Colombia

Background data of polychlorinated dibenzodioxin and dibenzofuran (PCDD/Fs) emissions from the incineration sector in Colombia are presented. Monitoring was carried out during a two-year period, 2003–2005. Twelve plants were sampled for stack gas emissions of dioxins and total solid particulate (TSP). Additionally, PCDD/Fs in several fly ash samples were analyzed. Most incinerators burned industrial refuse materials and medical residues. A wide range of PCDD/Fs emission levels were found. In particular, levels ranging from 6.9 to 343.8 ng I-TEQ/N m 3 were determined in plants without any air pollution control system (APCS). In contrast, 0.5–39.2 ng I-TEQ/N m 3 levels were found in plants with APCS while 8.5–67.5 ng I-TEQ/g were measured in fly ash samples. TSP values ranged from 14 to 448 mg/N m 3. This study also evaluated the impact of implementing different control systems in an incinerator. Finally, for comparison purposes several samples were analyzed by both high resolution gas chromatography coupled to high resolution mass spectrometry (HRGC-HRMS) and high resolution gas chromatography coupled to ion-trap low resolution mass spectrometry–mass spectrometry (HRGC-IT LRMS/MS). Overall, I-TEQ values deviated about 20–30% between both techniques.

A quantitative analysis software tool for mass spectrometry–based proteomics

We describe Census, a quantitative software tool compatible with many labeling strategies as well as with label-free analyses, single-stage mass spectrometry (MS1) and tandem mass spectrometry (MS/MS) scans, and high- and low-resolution mass spectrometry data. Census uses robust algorithms to address poor-quality measurements and improve quantitative efficiency, and it can support several input file formats. We tested Census with stable-isotope labeling analyses as well as label-free analyses.

Optimization of Large-Volume Injection for the Determination of Polychlorinated Biphenyls in Childrenʼs Fast-Food Menus by Low-Resolution Mass Spectrometry

This study includes the determination of five indicator polychlorinated biphenyls (PCBs) (52, 101, 153, 138, and 180), six non-ortho PCBs (35, 80, 81, 77, 126, and 169), and two mono-ortho PCBs (28 and 118) in fast food for children. A freeze-dried sample of 10 g is extracted by using pressurized n-hexane in two 5 min cycles at 120 degrees C and 100 mbar. Fatty extracts were cleaned up by means of acetonitrile/n-hexane partitioning and gel-permeation chromatography. The fractionation of non-ortho, mono-ortho, and indicator PCBs was made on graphitized carbon solid-phase extraction cartridges by using n-hexane, n-hexane/toluene (99:1, v/v), and toluene as elution solvents. Gas chromatography coupled to tandem mass spectrometry and large-volume injections with a programmed-temperature vaporizer (PTV-LV) were used to increase sensitivity and selectivity of the PCB determination. The PTV-LV injection settings, that is, vaporizing temperature, vaporizing time, and purge flow, were optimized by using a central composite design. A 15-40 times increased sensitivity was reached as compared with that obtained with the conventional 1 microL splitless injection. The limits of detection achieved were between 0.3 and 1.2 pg/g, and repeatability data, as relative standard deviation varied, ranged from 2 to 9% for the 0.05 ng/mL PCB level.

Identification of a Novel Glucosylsulfate Conjugate as a Metabolite of 3,4-Dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione (ARQ 501, β-Lapachone) in Mammals

3,4-Dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione (ARQ 501) is a fully synthetic version of the natural product beta-lapachone, which has been isolated from the lapacho tree (Tabebuia impetiginosa or Tabebuia avellanedae) and has demonstrated promising anticancer activity. ARQ 501 formulated with hydroxypropyl-beta-cyclodextrin has successfully completed phase I clinical trials and is currently in several phase II human clinical trials for the treatment of pancreatic cancer, head and neck cancer, and leiomyosarcoma. The metabolites of ARQ 501 were investigated by low-resolution and high-resolution mass spectrometry in plasma from (nu/nu) mice, rats, and humans treated with the compound. The data for one of the metabolites identified are consistent with conjugation of ARQ 501 with a glucosylsulfate moiety (m/z 241; fragment ion). Although other glucosylsulfate conjugates have been identified as metabolites of pesticides in cotton plants and in crustaceans as phase II metabolites of pyrenes, none have been previously identified in mammals. Data reported here identify a novel metabolic pathway for humans.

Historical Profiles of Chlorinated Paraffins and Polychlorinated Biphenyls in a Dated Sediment Core from Lake Thun (Switzerland)

A dated sediment core from Lake Thun covering the last 120 years was analyzed to get an overview of the historical trend of the chlorinated paraffin (CP) and polychlorinated biphenyl (PCB) deposition, because CPs and PCBs have/had similar applications as plasticizers and flame retardants. Total CP concentrations (sum of short chain (SCCP), medium chain (MCCP), and long chain CPs (LCCP)) showed a steep increase in the 1980s and a more-or-less stable level of 50 ng g(-1) dry weight (dw) since then. The concentration-time profile is in good agreement with the available information on global production data. The quantification of higher chlorinated SCCPs using electron capture negative ionization low resolution mass spectrometry (ECNI-LRMS) revealed an increase in recent years. In addition, the degree of chlorination of SCCPs has strongly increased during the past 40 years, which may indicate its use as an additive for plastics, paints, and coatings. Furthermore, PCBs were analyzed in dated sediment slices. The PCB concentrations (sum of the six indicator congeners) peaked around 1969 (18 ng g(-1) dw) and decreased to 1.3 ng g(-1) dw in the surface layer corresponding to 2004. The peak level of CPs exceeded those of PCBs by about a factor of 3.

Identification of the Novel Cycloaliphatic Brominated Flame Retardant 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane in Canadian Arctic Beluga (Delphinapterus leucas)

1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) is used primarily as an additive flame retardant. Technical grade TBECH consists of near equimolar amounts of two (of a possible four) diastereoisomers: rac-(1R,2R)-1,2-dibromo-(4S)-4-((1S)-1,2-dibromoethyl)cyclohexane ((alpha-TBECH) and rac-(1R,2R)-1,2-dibromo-(4S)-4-((1R)-1,2-dibromoethyl)cyclohexane (beta-TBECH). The two other possible isomers, gamma- and delta-TBECH, appear in the technical mixture when heated at temperatures above 120 degrees C. Careful selection of GC-capillary column length was critical in resolution of the two main diastereoisomers. Column lengths of 60 or 30 m (0.25 microm film thickness) resulted in incomplete separation of the alpha- and beta-isomers, while on a 10 m column, the isomers were baseline separated. The gamma- and delta-isomers could not be resolved on any column length in this study. Increased injector port temperature induced thermal conversion of the alpha- and beta-isomers to gamma- and delta-TBECH. Electron impact ionization (EI) was used to provide specificity because no characteristic ions in the electron capture negative ionization (ECNI) mass spectrum of TBECH were evident. In EI, the dominant ions in the mass spectrum corresponded to a concomitant loss of HBr and Br from the molecular ion; the biggest peak in this ion cluster (m/z 266.9208) was used for quantitation and the second biggest peak (m/z 264.9227) was used for confirmation. Beluga (Delphinapterus leucas) blubber extracts of animals from the Canadian Arctic (n=29) were analyzed using low resolution (LR) MS and high resolution (HR) MS run at a resolving power of 10,000. beta-TBECH was the only isomer observed in the samples and was detected in 17 samples. The LRMS technique appeared to overestimate beta-TBECH concentrations compared to HRMS, suggesting a small interference arose at the nominal mass monitored. This potential interference also led to some false positive and negative values (n=7) based on the expected ion ratio of the quantitation and confirmation ions. Observed concentrations of the beta-isomer as measured by HRMS ranged from 1.1 to 9.3 ng/g (lipid weight).