Electron Capture Negative Ionization Research Articles

Chlorinated paraffin analysis by gas chromatography Orbitrap high-resolution mass spectrometry: Method performance, investigation of possible interferences and analysis of fish samples

For decades, high quantities of short-chain chlorinated paraffins (SCCP) and medium-chain chlorinated paraffins (MCCP) have been widely used, for instance as plasticizers or flame retardants, leading to global pollution due to unintentional emissions from products or waste. Due to the high complexity of chlorinated paraffins with several thousand congeners there is no consensus on an analytical procedure for SCCPs and MCCPs in food samples. Amongst the multitude of methods currently in use, high-resolution mass spectrometry is particularly valuable for in-depth studies of homologue patterns. Here we analyse SCCPs and MCCPs with gas chromatography coupled to high-resolution Orbitrap mass spectrometry (GC-Orbitrap-HRMS) operated in full-scan acquisition in electron capture negative ion (ECNI) mode at 60,000 and 120,000 resolution (FWHM, m/z 200, equals roughly 30,000 and 60,000 at 5% peak height). Linear dynamic range, selectivity and sensitivity tests confirmed an excellent linearity in a concentration range of 25–15,000 pg/μL with very low limits of detection (LODs) in the low pg/μL range. Spiking experiments with high levels of native mono- and di-ortho-polychlorinated biphenyls (PCBs) and mixtures of MCCP and SCCP standards did not have a negative impact on isotope ratios of the examined homologues. Besides the [M−Cl]− fragment ions used for quantification, the mass spectra of homologues also featured [M−HCl]− ions whose abundance increased with decreasing chlorination degree. In addition, [M−HCl−Cl]− ions were detected with a relative abundance of 5–10%. Three salmon (Salmo salar) samples farmed in Norway showed a consistent CP homologue pattern which differed both from the CP pattern in a sample from Scottish aquaculture and a wild salmon sample. These measurements produce evidence that discretely different CP patterns may exist in different areas of origin. Our results demonstrate that GC/ECNI-Orbitrap-HRMS is well-suited for the analysis of CPs by overcoming a range of mass interference problems and due to its thus far unmatched sensitivity.

GC-MS Analysis of Lipid Oxidation Products in Blood, Urine, and Tissue Samples.

Oxidant stress has been identified as important in the pathology of many diseases. Oxidation products of polyunsaturated fatty acids collectively termed isoprostanes, neuroprostanes, and isofurans are considered the most reliable measures of in vivo lipid oxidation, and they are widely used to assess oxidant stress in various diseases. Here we describe the measurement of these lipid oxidation products using gas chromatography mass spectrometry with electron capture negative ionization.

Determination of short-chain chlorinated paraffins in multiple matrices of Arctic using gas chromatography-electron capture negative ion-low resolution mass spectrometry

Gas chromatography-electron capture negative ion-low resolution mass spectrometry (GC-ECNI-MS) was used for the quantification of short-chain chlorinated paraffins (SCCPs) in multiple matrices of Arctic. Samples were spiked with surrogate standards (13C10-trans-chlordane) and extracted with dichloromethane and hexane (1:1, v/v) using accelerated solvent extraction (ASE). The extract was cleaned using a multilayer Silica-Florisil column and e-HCH was added before instrument analysis. The SCCPs were analyzed using a gas chromatograph (GC) in electron capture negative ion (ECNI) mode coupled with a 7000B triple quadruple mass spectrometer (MS) in single quad mode. The calibration is performed using three commercial standards (chlorine contents of 51.5%, 55.5%, and 63.0%). A reasonable linear correlation for commercial standards was found between chlorine content and total response factor (R2?=?0.96). To ensure instrument sensitivity, the SCCP congeners were divided into four groups by the optimized combinations (C10, C11, C12 and C13) and subjected to analysis by four individual injections. This method is suited to analyse the total concentration of SCCPs and individual SCCP congener groups in the environmental analysis.• Accelerated solvent extraction offers a lower cost of time for per sample and reducing solvent consumption.• The presented quantification procedure makes the quantification of SCCPs independent from the chlorine content of the used standard mixtures.• The samples were subjected to analysis by four individual injections for the instrument sensitivity, and the total concentration of SCCPs and CP congener groups can be obtained at the same time.

Replacing H+ by Na+ or K+ in phosphopeptide anions and cations prevents electron capture dissociation.

By successively replacing H+ by Na+ or K+ in phosphopeptide anions and cations, we show that the efficiency of fragmentation into c and z˙ or c˙ and z fragments from N-Cα backbone bond cleavage by negative ion electron capture dissociation (niECD) and electron capture dissociation (ECD) substantially decreases with increasing number of alkali ions attached. In proton-deficient phosphopeptide ions with a net charge of 2-, we observed an exponential decrease in electron capture efficiency with increasing number of Na+ or K+ ions attached, suggesting that electrons are preferentially captured at protonated sites. In proton-abundant phosphopeptide ions with a net charge of 3+, the electron capture efficiency was not affected by replacing up to four H+ ions with Na+ or K+ ions, but the yield of c, z˙ and c˙, z fragments from N-Cα backbone bond cleavage generally decreased next to Na+ or K+ binding sites. We interpret the site-specific decrease in fragmentation efficiency as Na+ or K+ binding to backbone amide oxygen in competition with interactions of protonated sites that would otherwise lead to backbone cleavage into c, z˙ or c˙, z fragments. Our findings seriously challenge the hypothesis that the positive charge responsible for ECD into c, z˙ or c˙, z fragments can generally be a sodium or other metal ion instead of a proton.

Dietary Habits and Cooking Methods Could Reduce Avoidable Exposure to PCBs in Maternal and Cord Sera

Polychlorinated biphenyls (PCBs), like other persistent organic pollutants, are accumulating throughout the food chain and pose health threats to humans, especially children and foetuses. There is no protocol for reducing the contamination levels of the PCBs in humans. This study identified food items and cooking methods that reduce serum PCB levels by analysing data collected from the Chiba Study of Mother and Child Health. The sample size was 194 subjects. Serum PCB levels were measured using gas chromatography–electron capture negative ionization quadrupole mass spectrometry. Information on dietary habits was obtained from a brief diet history questionnaire that included questions about food items and cooking methods. Food items were categorized into food groups, and nutrient levels were calculated based on food item consumption. Principal component analysis and lasso regression were used as statistical methods. The analyses of food items and nutrients suggested that food items rich in dietary fibre reduce avoidable exposure to PCBs, as could grilling and deep frying of food, which could reduce avoidable exposure to serum PCBs in mothers and foetuses. (174 words).

Occurrence and human exposure to brominated and organophosphorus flame retardants via indoor dust in a Brazilian city.

Indoor dust is considered an important human exposure route to flame retardants (FRs), which has arised concern due the toxic properties of some of these substances. In this study, ten organophosphorus flame retardants (OPFRs), eight polybrominated diphenyl ethers (PBDEs) and four new brominated flame retardants (NBFRs) were determined in indoor dust from different places in Araraquara-SP (Brazil). The sampled places included houses, apartments, offices, primary schools and cars. The analysis of the sample extracts was performed by gas chromatography coupled to mass spectrometry and two ionization techniques were used (electron ionization - EI; electron capture negative ionization - ECNI). OPFRs were the most abundant compounds and tris(2-butoxyethyl) phosphate (TBOEP), tris(phenyl) phosphate (TPHP), tris(1,3-dichloroisopropyl) phosphate (TDCIPP) and tris(2-chloroisopropyl) phosphate (TCIPP) were present at the highest concentrations. Among the brominated FRs, the most ubiquitous compounds were BDE-209, bis(2-ethylhexyl) tetrabromophthalate (BEH-TEBP) and decabromodiphenyl ethane (DBDPE). Statistical analysis revealed that there were differences among dust typologies for TBOEP, TDCIPP, ethylhexyl diphenyl phosphate (EHDPHP), BDE-209, 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (EH-TBB), BEH-TEBP and DBDPE, which were attributed to different construction materials in each particular environment and to the age of the buildings. The highest levels of brominated FRs were observed in offices, TBOEP was at high concentration in primary schools, and TDCIPP was at high concentration in cars. A preliminary risk assessment revealed that toddlers were exposed to TBOEP levels higher than the reference dose when considering the worst case scenario. The results obtained in this study showed for the first time that although Brazil does not regulate the use of FRs, these substances are present in indoor dust at levels similar to the observed in countries that have strict fire safety standards, and that humans are exposed to complex mixtures of these contaminants via indoor dust.

Dietary exposure to short- and medium-chain chlorinated paraffins in meat and meat products from 20 provinces of China.

Food intake is one of the main pathways of human exposure to chlorinated paraffins (CPs). This study assessed the dietary exposure for the general Chinese population to short-chain chlorinated paraffin (SCCPs) and medium-chain chlorinated paraffins (MCCPs) through meat and meat products. Twenty samples of meat and meat products from 20 Chinese provinces were collected in 2011. As the sampling sites covered about two-thirds of the Chinese population, the meat samples were considered to be representative of the true characteristics of CPs contamination in Chinese meat products. The concentrations of SCCPs and MCCPs in the meat samples were measured using the comprehensive two-dimensional gas chromatography electron capture negative ionization high-resolution time-of-flight mass spectrometry method. Forty-eight SCCP and MCCP homolog groups were detected in the meat samples. The mean SCCP and MCCP concentrations in all meat samples were 129±4.1ngg-1 wet weight and 5.7±0.59ngg-1 wet weight, respectively. The concentrations of SCCPs and MCCPs varied in samples from different provinces. The geographical distribution of CP concentrations was similar to the distribution of CPs manufacturing plants in China. The most abundant groups of SCCPs in all samples were C10-11 Cl6-7, and the most abundant groups of MCCPs in most samples were C14 Cl7-8. The possible sources of SCCPs and MCCPs in meat and meat products might be CP-42 and CP-52. The 50th percentile estimated daily intakes of SCCPs and MCCPs through meat consumption for a "standard" Chinese adult male were 0.13 and 0.0047μgkg-1 bw d-1, respectively, both much lower than the tolerable daily intakes (TDIs) for SCCPs and MCCPs. This preliminary risk assessment has indicated that the indirect exposure of SCCPs and MCCPs through meat consumption does not pose significant risk to human health in China.

Measurement of urinary Benzo[a]pyrene tetrols and their relationship to other polycyclic aromatic hydrocarbon metabolites and cotinine in humans

Biomonitoring of exposure to polycyclic aromatic hydrocarbons (PAHs) typically uses measurement of metabolites of PAHs with four or less aromatic rings, such as 1-hydroxypyrene, even though interest may be in exposure to larger and carcinogenic PAHs, such as benzo[a]pyrene (B[a]P). An improved procedure for measuring two tetrol metabolites of B[a]P has been developed. Using 2 mL urine, the method includes enzymatic deconjugation of the tetrol conjugates, liquid-liquid extraction, activated carbon solid phase extraction (SPE) and Strata-X SPE, and gas chromatography–electron capture negative ionization–tandem mass spectrometric determination. Limits of detection were 0.026 pg/mL (benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol, BPT I-1) and 0.090 pg/mL (benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol, BPT II-1). We quantified BPT I-1 and BPT II-1 in urine from a volunteer who consumed one meal containing high levels of PAHs (barbequed chicken). We also measured urinary concentrations of BPT I-1 and BPT II-1 in smokers and nonsmokers, and compared these concentrations with those of monohydroxy PAHs (OH-PAHs) and cotinine. Urinary elimination of BPT I-1 and BPT II-1 as a function of time after dietary exposure was similar to that observed previously for OH-PAHs. While the median BPT I-1 concentration in smokers’ urine (0.069 pg/mL) significantly differs from nonsmokers (0.043 pg/mL), BPT I-1 is only weakly correlated with cotinine. The urinary concentration of BPT I-1 shows a weaker relationship to tobacco smoke than metabolites of smaller PAHs, suggesting that other routes of exposure such as for example dietary routes may be of larger quantitative importance.

Brominated flame retardants (BFRs) in eggs from birds of prey from Southern Germany, 2014

In Southern Germany, peregrine falcons (Falco peregrinus), which almost exclusively prey on other birds, are top predators of the terrestrial food chain. These animals accumulate persistent organic pollutants (POPs) and halogenated flame retardants (HFRs) with mothers transferring these lipophilic contaminants to their eggs. Here we analyzed unhatched eggs of eleven peregrine falcons and six of other species, and report concentrations of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), hexabromobenzene (HBB), 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE) and its metabolites, pentabromoethylbenzene (PBEB), pentabromotoluene (PBT), and tribromophenol (TBP). The extract of one purified peregrine falcon egg sample was comprehensively analyzed in a non-target (NT) approach by gas chromatography with mass spectrometry in the electron capture negative ion mode. A total of ∼400 polyhalogenated compounds were detected, among them dechloranes and possibly transformation products, two tetrabrominated metabolites of PBT and several compounds unknown to us which could not be identified.

Simultaneous determination of dechloranes, polybrominated diphenyl ethers and novel brominated flame retardants in food and serum.

A sensitive method for the simultaneous quantification of dechloranes, polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) has been developed for gas chromatography (GC) coupled to tandem mass spectrometry operating in electron capture negative ionization (ECNI) mode. The major advance has been achieved by combining selected ion monitoring (SIM) and multiple reaction monitoring (MRM) modes in well-defined time windows, to determine dechloranes, PBDEs and NBFRs at picogram per gram level in one single analysis in complex matrix biological samples. From the chromatographic point of view, efforts were devoted to study several injection modes using multimode inlet (MMI) in order to obtain low instrumental detection limits, necessary for trace compounds such as Dechlorane Plus (DP) isomers. Method performance was also evaluated: calibration curves were linear from 20fgμL-1 to 100pgμL-1 for the studied compounds, with method detection limits at levels of 50fgg-1 for DPs. Repeatability and reproducibility, expressed as relative standard deviation, were better than 5% even in solvent vent mode for the injection of standards. The application to a wide range of complex samples (including food, human and animal serum samples) indicated a sensitive and reliable way to quantify at the picogram per gram level 4 halogenated norbornenes (HNs), Dechlorane Plus (anti-DP and syn-DP) and 2 of their homologues (Dechlorane-602 and Dechlorane-603), 11 PBDE congeners (no. 28, 47, 49, 66, 85, 99, 100, 153, 154, 183 and 209) and 5 novel BFRs, i.e. decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), hexabromobenzene (HBB), 2,3,4,5-tetrabromo-ethylhexyl-benzoate (TBB) and tetrabromophthalate (TBPH). Graphical Abstract GC-ECNI-MS/MS chromatograms showing the most sensitive transition for DPs when injecting 2 μL of a 16 fg/μL standard solution of s-DP and a-DP at three different source temperatures.

Estimating electron affinity from the lifetime of negative molecular ions: Cycloheptatriene derivatives

Cycloheptatriene derivatives are studied by means of resonance electron capture negative ion mass spectrometry (REC NIMS). The average lifetimes of molecular negative ions (NIs) are measured with respect to electron autodetachment. Using the Arrhenius approach, electron affinity EAa of the molecules under study is estimated, and the effective temperature of the resulting negative molecular ions is determined as a function of the electron energy. It is assumed that the dissociation of negative molecular ions in the ground electronic state is a process similar to that of the thermal degradation of molecules.

Occurrence, homologue patterns and source apportionment of short- and medium-chain chlorinated paraffins in suburban soils of Shanghai, China

In order to systematically investigate the spatial distribution, homologue profiles, and sources of short- and medium-chain chlorinated paraffins (SCCPs and MCCPs) in suburban soils in Shanghai, SCCPs and MCCPs in soils were analyzed using gas chromatography coupled with low resolution mass spectrometry in electron capture negative ion (ECNI) mode (GC-ECNI-MS). The CP concentrations in soils were between not detected (ND) – 697 ng g−1 with a median value of 3.52 ng g−1 for SCCPs, and ND – 666 ng g−1 with a median value of 15.3 ng g−1 for MCCPs, respectively. The concentrations of MCCPs in most soils were higher than that of SCCPs. The total CP concentrations (sum of SCCPs and MCCPs) in soils varied from ND to 964 ng g−1 with a median value of 20.5 ng g−1. The concentration of MCCPs was higher than that of SCCPs in most soils. The levels of SCCPs and MCCPs in suburban soils in Shanghai were at the medium level when compared to other areas around the world. No significant correlation was observed between soil CP concentrations and total organic carbon contents (p > 0.05). For different use type of soils, the median concentrations of CPs in soils were found higher in greenland than that in other areas probably due to busy traffic, sewage sludge application and/or wastewater irrigation. All soils were divided into two groups by hierarchical cluster analysis (HCA) both for SCCPs and MCCPs. Three discharge sources of CPs in suburban soil of Shanghai were identified by PMF model.

Health risks posed to infants in rural China by exposure to short- and medium-chain chlorinated paraffins in breast milk

Chlorinated paraffins (CPs) are complex mixtures of synthetic chemicals found widely in environmental matrices. Short-chain CPs (SCCPs) are candidate persistent organic pollutants under the Stockholm Convention. There should be great concern about human exposure to SCCPs. Data on CP concentrations in human breast milk is scarce. This is the first study in which background SCCP and medium-chain CP (MCCP) body burdens in the general rural population of China have been estimated and health risks posed to nursing infants by CPs in breast milk assessed. The concentrations of 48 SCCP and MCCP formula congeners were determined in 24 pooled human milk samples produced from 1412 individual samples from eight provinces in 2007 and 16 provinces in 2011. The samples were analyzed by comprehensive two-dimensional gas chromatography electron capture negative ionization high-resolution time-of-flight mass spectrometry. The median SCCP and MCCP concentrations were 303 and 35.7ngg−1 lipid weight, respectively, for the 2007 samples and 360 and 45.4ngg−1 lipid weight, respectively, for the 2011 samples. The C10 and C14 homologs were the dominant CP carbon-chain-length groups, contributing 51% and 82% of the total SCCP and MCCP concentrations, respectively. There are probably multiple CP sources to the general Chinese population and numerous exposure pathways. The median estimated daily SCCP and MCCP intakes for nursing infants were 1310 and 152ngkg−1d−1, respectively, in 2007 and 1520 and 212ngkg−1d−1, respectively, in 2011. SCCPs do not currently pose significant risks to infants in China. However, it is necessary to continuously monitor CP concentrations and health risks because CP concentrations in Chinese human breast milk are increasing.

Elevated Concentrations of 4-Bromobiphenyl and 1,3,5-Tribromobenzene Found in Deep Water of Lake Geneva Based on GC×GC-ENCI-TOFMS and GC×GC-μECD.

We quantified the concentrations of two little-studied brominated pollutants, 1,3,5-tribromobenzene (TBB) and 4-bromobiphenyl (4BBP), in the deep water column and sediments of Lake Geneva. We found aqueous concentrations of 625 ± 68 pg L–1 for TBB and 668 ± 86 pg L–1 for 4BBP over a depth range of 70–191.5 m (near-bottom depth), based on duplicate measurements taken at five depths during three separate 1 month sampling periods at our sampling site near Vidy Bay. These levels of TBB and 4BBP were 1 or 2 orders of magnitude higher than the quantified aqueous concentrations of the components of the pentabrominated biphenyl ether technical mixture, which is a flame retardant product that had a high production volume in Europe before 2001. We observed statistically significant vertical concentration trends for both TBB and 2,2′,4,4′,6-pentabromobiphenyl ether in the deep water column, which indicates that transport and/or degradation processes affect these compounds. These measurements were enabled by application of a comprehensive two-dimensional gas chromatograph coupled to an electron capture negative chemical ionization time-of-flight mass spectrometer (GC×GC-ENCI-TOFMS) and to a micro-electron capture detector (GC×GC-μECD). GC×GC-ENCI-TOFMS and GC×GC-μECD were found to be >10× more sensitive toward brominated pollutants than conventional GC×GC-EI-TOFMS (with an electron impact (EI) ionization source), the latter of which had insufficient sensitivity to detect these emerging brominated pollutants in the analyzed samples. GC×GC also enabled the estimation of several environmentally relevant partitioning properties of TBB and 4BBP, further confirming previous evidence that these pollutants are bioaccumulative and have long-range transport potential.

Lactational exposure to short-chain chlorinated paraffins in China, Korea, and Japan

To investigate short-chain chlorinated paraffin (SCCP) levels in human breast milk, pooled breast milk samples (BMSs) collected between 2007 and 2010 from Chinese (Beijing, n = 17), Korean (Seoul, Busan, n = 16), and Japanese (Kyoto, Sendai, n = 44) women were analyzed. SCCPs found in air samples in Beijing (n = 4, in 2008) were also analyzed and compared with BMSs to estimate the possible source of contamination in Beijing. The electron-capture negative ionization method demonstrated the different sensitivities for SCCPs, and pentachlorinated alkanes had the highest method detection limit (MDL) among congeners. In Beijing, SCCPs were detected in 8 of 17 pooled BMSs at concentrations more than the highest MDL of each homolog. The total SCCP concentration ranged from below the MDL to 54 ng g−1 lipid weight. Among the SCCP homologs, polychlorinated tridecanes were most frequently detected in Beijing. In Korea and Japan, no samples contained detectable total SCCP concentrations at more than the highest MDL. In Seoul, only two samples showed trace levels of polychlorinated undecanes. In Kyoto and Sendai, congeners of polychlorinated dodecanes were most frequently detected. C10 components were the major contributors to the SCCPs in the atmosphere of Beijing. Congener profiles in breast milk in Beijing provided a clear contrast to the profiles found in food and air. The unique congener profiles necessitate the monitoring of breast milk for exposure of infants to SCCPs. The calculated mean exposure of SCCPs in 1-year-olds in China was 337 ng (kg body weight)−1 d−1. These results demonstrate the body burden of SCCPs in the study areas and potential lactational exposure to SCCPs in Asian countries.

Measurement of emerging dechloranes in human serum using modulated gas chromatography coupled to electron capture negative ionization time-of-flight mass spectrometry.

Quite recently, the presence of significant amounts of several emerging Dechlorane (Dec) flame retardants (FRs) was reported in environmental and biota samples, principally from Canada and China, but also from Europe. Several molecules were identified, e.g. Dec 602, 603, 604, Dechlorane Plus (DP), and Chlordene Plus (CP). Gas chromatography (GC) coupled to electron ionization (EI) high-resolution mass spectrometry (HRMS) is typically used for their measurement in various matrices based on hexachlorocyclopentadiene (HCCPD) fragment ions at m/z 271.8102/273.8072. We investigated the use of GC with cryogenic zone compression and electron capture negative ionization time-of-flight mass spectrometry (CZC-GC/ECNI-TOFMS) to measure Dechlorane compounds at low levels in human serum. The TOFMS instrument provided a resolving power of 5000 (FWHM) with an acquisition rate of 25Hz and was equipped with a specific low thermal emission filament, which allowed it to perform reproducibly in ECNI mode at ion source temperatures as low as 140°C, thus yielding a signal for the molecular ion cluster. The method provided comparable sensitivity to the GC/EI-SectorHRMS technique used in selected ion monitoring (SIM) mode, and specificity for the target Dechlorane compounds. The method was applied on human serum samples and quantification was performed for Dec 602, Dec 603, and CP, ranging from 0.1 to 10ng/g lipid weight levels. The main drawbacks of the method are the high instrument detection limits (IDLs) obtained for DP and Dec 604. The method would benefit from even softer ionization and better ion transmission. The main advantages of the present method are the selectivity, as detection is based on the molecular ion signal, and the use of good mass accuracy combined with isotopic distribution calculation for molecular formulae investigation of halogenated compounds. This methodology should facilitate the monitoring of emerging Dechlorane contaminants in future studies, and possibly extend the scope to untargeted emerging analogues. Copyright © 2016 John Wiley & Sons, Ltd.

Deconvolution of Soft Ionization Mass Spectra of Chlorinated Paraffins To Resolve Congener Groups.

We describe and illustrate a three-step data-processing approach that enables individual congener groups of chlorinated paraffins (CPs) to be resolved in mass spectra obtained from either of two soft ionization methods: electron capture negative ionization mass spectrometry (ECNI-MS) or atmospheric pressure chemical ionization mass spectrometry (APCI-MS). In the first step, general fragmentation pathways of CPs are deduced from analysis of mass spectra of individual CP congeners. In the second step, all possible fragment ions in the general fragmentation pathways of CPs with 10 to 20 carbon atoms are enumerated and compared to mass spectra of CP mixture standards, and a deconvolution algorithm is applied to identify fragment ions that are actually observed. In the third step, isotope permutations of the observed fragment ions are calculated and used to identify isobaric overlaps, so that mass intensities of individual CP congener groups can be deconvolved from the unresolved isobaric ion signal intensities in mass spectra. For a specific instrument, the three steps only need to be done once to enable deconvolution of CPs in unknown samples. This approach enables congener group-level resolution of CP mixtures in environmental samples, and it opens up the possibility for quantification of congener groups.

Isobutane Made Practical as a Reagent Gas for Chemical Ionization Mass Spectrometry.

As a reagent gas for positive- and negative-mode chemical ionization mass spectrometry (CI-MS), isobutane (i-C4H10) produces superior analyte signal abundance to methane. Isobutane has never been widely adopted for CI-MS because it fouls the ion source more rapidly and produces positive CI spectra that are more strongly dependent on reagent gas pressure compared with methane. Isobutane was diluted to various concentrations in argon for use as a reagent gas with an unmodified commercial gas chromatograph-mass spectrometer. Analyte spectra were directly compared using methane, isobutane, and isobutane/argon mixtures. A mixture of 10% i-C4H10 in argon produced twice the positive-mode analyte signal of methane, equal to pure isobutane, and reduced spectral dependence on reagent gas pressure. Electron capture negative chemical ionization using 1% i-C4H10 in argon tripled analyte signal compared with methane and was reproducible, unlike pure isobutane. The operative lifetime of the ion source using isobutane/argon mixtures was extended exponentially compared with pure isobutane, producing stable and reproducible CI signal throughout. By diluting the reagent gas in an inert buffer gas, isobutane CI-MS experiments were made as practical to use as methane CI-MS experiments but with superior analytical performance. Graphical Abstract ᅟ.

Simultaneous pentafluorobenzyl derivatization and GC-ECNICI-MS measurement of nitrite and malondialdehyde in human urine: Close positive correlation between these disparate oxidative stress biomarkers.

Urinary nitrite and malondialdehyde (MDA) are biomarkers of nitrosative and oxidative stress, respectively. At physiological pH values of urine and plasma, nitrite and MDA exist almost entirely in their dissociated forms, i.e., as ONO- (ONOH, pKa=3.4) and -CH(CHO)2 (CH2(CHO)2, pKa=4.5). Previously, we reported that nitrite and MDA react with pentafluorobenzyl (PFB) bromide (PFB-Br) in aqueous acetone. Here, we report on the simultaneous derivatization of nitrite and MDA and their stable-isotope labeled analogs O15NO- (4μM) and CH2(CDO)2 (1μM or 10μM) with PFB-Br (10μL) to PFBNO2, PFB15NO2, C(PFB)2(CHO)2), C(PFB)2(CDO)2 by heating acetonic urine (urine-acetone, 100:400μL) for 60min at 50°C. After acetone evaporation under a stream of nitrogen, derivatives were extracted with ethyl acetate (1mL). A 1-μL aliquot of the ethyl acetate phase dried over anhydrous Na2SO4 was injected in the splitless mode for simultaneous GC-MS analysis in the electron capture negative-ion chemical ionization mode. Quantification was performed by selected-ion monitoring (SIM) the anions [M-PFB]-m/z 46 for ONO-, m/z 47 for O15NO-, m/z 251 for -C(PFB)(CHO)2, and m/z 253 for -C(PFB)(CDO)2. The retention times were 3.18min for PFB-ONO2/PFB-O15NO2, and 7.13min for -C(PFB)(CHO)2/-C(PFB)(CDO)2. Use of CH2(CDO)2 at 1μM but not at 10μM was associated with an unknown interference with the C(PFB)2(CDO)2 peak. Endogenous MDA can be quantified using O15NO- (4μM) and CH2(CDO)2 (10μM) as the internal standards. The method is also useful for the measurement of nitrate and creatinine in addition to nitrite and MDA. Nitrite and MDA were measured by this method in urine of elderly healthy subjects (10 females, 9 males; age, 60-70 years; BMI, 25-30kg/m2). Creatinine-corrected excretion rates did not differ between males and females for MDA (62.6 [24-137] vs 80.2 [52-118]nmol/mmol, P=0.448) and for nitrite (102 [71-174] vs. 278 [110-721]nmol/mmol P=0.053). We report for the first time a close correlation (r=0.819, P<0.0001) between MDA and nitrite in human urine. This correlation is assumed to be due to involvement of myeloperoxidase which catalyzes the formation of hypochlorite (-OCl) from chloride and hydrogen peroxide. In turn, hypochlorite reacts both with nitrite and with polyunsaturated fatty acids such as arachidonic acid, with the later reaction generating MDA. The proposed mechanisms are supported by the literature but remain to be fully explored.

A Novel Method for Profiling and Quantifying Short- and Medium-Chain Chlorinated Paraffins in Environmental Samples Using Comprehensive Two-Dimensional Gas Chromatography-Electron Capture Negative Ionization High-Resolution Time-of-Flight Mass Spectrometry.

Chlorinated paraffins (CPs) are complex technical mixtures containing thousands of isomers. Analyzing CPs in environmental matrices is extremely challenging. CPs have broad, unresolved profiles when analyzed by one-dimensional gas chromatography (GC). Comprehensive two-dimensional GC (GC×GC) can separate CPs with a high degree of orthogonality. A novel method for simultaneously profiling and quantifying short- and medium-chain CPs, using GC×GC coupled with electron capture negative ionization high-resolution time-of-flight mass spectrometry, was developed. The method allowed 48 CP formula congener groups to be analyzed highly selectively in one injection through accurate mass measurements of the [M - Cl](-) ions in full scan mode. The correlation coefficients (R(2)) for the linear calibration curves for different chlorine contents were 0.982 for short-chain CPs and 0.945 for medium-chain CPs. The method was successfully used to determine CPs in sediment and fish samples. By using this method, with enhanced chromatographic separation and high mass resolution, interferences between CP congeners and other organohalogen compounds, such as toxaphene, are minimized. New compounds, with the formulas C9H14Cl6 and C9H13Cl7, were found in sediment and biological samples for the first time. The method was shown to be a powerful tool for the analysis of CPs in environmental samples.