Fragmentation analysis of water-soluble atmospheric organic matter using ultrahigh-resolution FT-ICR mass spectrometry

Isolated water-soluble atmospheric organic matter (AOM) analytes extracted from radiation fogwater samples were analyzed using collision induced dissociation with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Tandem mass analysis was performed on several mass ranges between 100 and 400 Da to characterize the functional groups of AOM species. Compounds containing nitrogen and/or sulfur were targeted because of the high number of oxygen atoms contained in their molecular formulas. Due to the large number of isobaric ions in the precursor isolation ranges, large numbers of product ions resulted from collision induced dissociation. Common neutral losses were assigned by matching the molecular formulas of the expected product ions with the detected product ions within the appropriate mass spectra. Since polar functional groups are expected to affect the hygroscopic properties of aerosols, the losses of H(2)O, CO(2), CH(3)OH, HNO(3), CH(3)NO(3), SO(3), SO(4) and combinations of these were specifically targeted. Among the 421 compounds studied, the most frequently observed neutral losses were CO(2) (54%), H(2)O (43%) and CH(3)OH (40%). HNO(3) losses were observed for 63% of the studied nitrogen containing compounds and 33% of the studied compounds containing both nitrogen and sulfur. SO(3) losses were observed for 85% of the studied sulfur containing compounds and 42% of studied compounds containing both nitrogen and sulfur. A number of molecular formulas matching those of monoterpene ozonolysis SOA were observed; they include organonitrates, organosulfates, and nitroxy-organosulfates. Overall, the results of fragmentation analysis of 400+ individual molecular precursors elucidate the complexity and multifunctional nature of the isolated water-soluble AOM.     

Fulvic acids as transition state of organic matter: indications from high resolution mass spectrometry

Fulvic acids are one of the largest classes of dissolved organic matter, but they are poorly defined and of unclear origin. Three fulvic acid isolates of different origin were analyzed by size-exclusion chromatography coupled to electrospray ionization-Fourier-transform ion cyclotron resonance (FTICR)-mass spectrometry, and molecular formulas for 700-1900 species in these isolates were derived. All three isolates show the same pattern in the elemental composition of their molecules and a large congruence in the molecular sets. It is proposed that the elemental and structural regularity of fulvic acid molecules does not indicate one common precursor material and formation process, but that this regularity is due to both the strong reworking of source materials in the environment and the valency of the three elements (C, H, O) from which most fulvic acid molecules are formed. Potential molecular formulas of fulvic acids were predicted for a mass range of 60 amu based on a few presumptions. A good agreement was found between the predicted and the detected molecular formulas, and it is concluded that (poly-)carboxylic acids with very limited number of hydroxy groups are the major compound class in fulvic acid isolates. It appears that fulvic acids are metastable molecules that characterize a state of transition of diverse precursor compounds during their oxidation.     

Rapid detection of chloramphenicol in animal products without clean-up using LC-high resolution mass spectrometry

A rapid confirmatory and quantitative method using liquid chromatography-high resolution mass spectrometry (LC-HRMS) was developed to determine sub-μg/kg levels of chloramphenicol (CAP) in meat products. The sample plus deuterated chloramphenicol internal standard was homogenised, extracted with ethyl acetate, centrifuged and the supernatant evaporated to dryness. The residue was re-dissolved in methanol/5% ammonium acetate solution (20:80, v/v), defatted with hexane and directly injected into the LC-MS. Chromatographic separation was performed on a C(18) column using methanol/water (60:40, v/v) as the mobile phase. CAP was detected using selected ion monitoring of the high accurate mass of the molecular ion [M-H](-) of CAP using a LTQ-Orbitrap mass spectrometer in negative electrospray ionisation mode (ESI(-)). The limit of quantification of the method was 0.1?μg/kg using isotope internal standard. Recoveries of CAP spiked at levels of 0.1-1.0?μg/kg ranged from 73 to 99%, and the relative standard deviation ranged 3.9-8.1%.     

Monitoring OH-initiated oxidation kinetics of isoprene and its products using online mass spectrometry

A novel technique has been developed to simultaneously monitor the kinetics of the OH radical-initiated oxidation of isoprene and formation and oxidation of its products (methyl vinyl ketone, methacrolein, 3-methylfuran, and formaldehyde) using online mass spectrometry. The kinetics of isoprene and its products were investigated at 323 K and at 1 atm total pressure. The responses of 30 representative ions for isoprene and its products were monitored during the reaction, and their concentration profiles were calculated by linear algebraic equations, which resolve the measured mass spectra of representative ions into the responses of individual target organics, and by calibrations, which converted the responses to individual target concentrations. Using this method, yields of methyl vinyl ketone, methacrolein, and 3-methylfuran at 323 K were measured to be 14.4+/-0.1%, 19.0+/-0.2%, and 2.9+/-0.2%, respectively, in excellent agreement with previously reported yields under NOx-free conditions. The reaction kinetics of isoprene and its oxidation products measured by the experimental procedure developed in this study were compared with those estimated by a kinetic model of isoprene oxidation. The observed methacrolein concentrations as a function of time were reproduced reasonably well by this model, while the observed methyl vinyl ketone concentration could be reproduced by including secondary reactions of some of the hydroperoxide products of isoprene oxidation. The observed 3-methylfuran concentrations could be reproduced using secondary cyclization reactions of some of the 1,4-hydroxycarbonyl products of isoprene oxidation. These results suggest that under low NOx conditions reactions of some of the hydroperoxides and hydroxycarbonyls produced from the OH-initiated oxidation of isoprene may be a significant source of methyl vinyl ketone and 3-methylfuran in the atmosphere.     

基于高分辨质谱法筛查养殖水体中地西泮含量

目的 探索养殖水体中地西泮残留情况并进行风险评估.方法 水体中的地西泮采用大容量固相萃取圆盘(HLB)富集,水产品采用SN/T 3235—2012方法进行前处理,利用超高压液相色谱串联静电场轨道离子阱质谱法对地西泮残留含量进行筛查与定量.结果 60个水体样品中共有38个筛查出地西泮残留,检出率为63.3％.在检出的水样...     

Fractionation of UV and VUV pretreated natural organic matter from drinking water

Recent studies have examined the potential of ultraviolet (UV, 254 nm) and vacuum ultraviolet (VUV, 185 nm + 254 nm) irradiation as either a pretreatment for a biological process or as a sole treatment for the removal of natural organic matter as dissolved organic carbon from drinking water. To understand the potential of UV and VUV irradiation followed by subsequent biological treatment, treated water was fractionated into four components: very hydrophobic acid (VHA), slightly hydrophobic acid (SHA), hydrophilic charged (CHA), and hydrophilic neutral (NEU). The VHA fraction was found to be very susceptible to both UV and VUV irradiation, and the fragmentation products of the high molecular weight VHA and SHA molecules contributed to the CHA and NEU fractions to form a pool of biodegradable, non-UV-absorbing, low molecular weight moieties. The NEU fraction was the most difficult to remove, as most of the components in this fraction were refractory to both the biological and photo-oxidative processes. Therefore, enhanced removal of the NEU fraction is required to increase the effectiveness and potential of the treatment process.     

Characterization and source apportionment of water-soluble organic matter in atmospheric fine particles (PM2.5) with high-resolution aerosol mass spectrometry and GC-MS

Water-soluble organic matter (WSOM) in fine particles (PM(2.5)) collected at one rural and three urban sites from the Southeastern Aerosol Research and Characterization network were characterized with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). These samples were also analyzed for a suite of molecular markers by Gas Chromatography-Mass Spectrometry (GC-MS) to assist in the interpretation of WSOM sources. The HR-ToF-AMS measurements allow a direct determination of the organic mass-to-carbon ratios (average ± 1σ = 1.93 ± 0.12) and hence the quantification of WSOM on the same filters used to close the aerosol mass budget. WSOM constitutes a major fraction of total PM(2.5) mass (26-42%) and organic mass (50-90%) at all sites. The concentrations of WSOM are substantially higher in summer, mainly due to enhanced production of biogenic secondary organic aerosol (SOA). WSOM is composed mainly of oxygenated species with average oxygen-to-carbon (O/C) ratio of 0.56 (± 0.08). Positive matrix factorization (PMF) of the high resolution mass spectra of WSOM identifies a less oxidized component (denoted as lOOA, O/C = 0.50) associated with biogenic SOA and a more oxidized component (denoted as mOOA, O/C = 0.60) associated with WSOM contributed by wood combustion. On average, lOOA accounts for 75 (± 13) % of WSOM in summer while mOOA accounts for 78 (± 21) % in winter, suggesting that WSOM in the southeastern U.S. is primarily contributed by SOA production from biogenic species in summer and by wood burning emissions in winter. This work also demonstrates the utility of HR-ToF-AMS for investigating the bulk chemical composition of WSOM as well as for evaluating its source contributions.     

Effect of UV irradiation on organic matter extracted from treated Ohio River water studied through the use of electrospray mass spectrometry

Ohio River water was treated by settling, sand filtration, and granular activated carbon filtration. It was then irradiated by low-pressure (monochromatic) and medium-pressure (polychromatic) UV lamps to investigate the effects of UV irradiation on the extracted organic matter (EOM). When the EOM, collected by solid phase extraction cartridges, was analyzed by conventional UV spectroscopy and size exclusion chromatography (SEC), no significant changes in the EOM were revealed for various UV doses. Positive and negative electrospray ionization mass spectrometry (ESI-MS) of the EOM produced mass spectra that vary significantly with UV dose. The UV dosage conditions also appear to affect the reactivity of the EOM to subsequent chlorination. The magnitude of the spectral changes is generally greater for medium-pressure lamps than for low pressure and increases with UV exposure. Based on the observed MS peaks, the changes may be due to the presence of lignin, resulting perhaps from photooxidation and/or photo rearrangement of macromolecules in the sample. When chlorination is used for secondary disinfection, these results suggest that it may be important to consider the effects of UV irradiation on the organic matter in the water before applying UV disinfection technology to a particular source water.     

Total determination of residual flutolanil and its metabolites in livestock products and seafood using liquid chromatography-tandem mass spectrometry

ABSTRACT

We have developed a simple and sensitive LC-MS/MS analytical method for the determination of residual flutolanil and its principal metabolites, including α,α,α-trifluoro-3′-hydroxy-o-toluanilide (M-4) and its conjugates, in livestock and seafood products. Both flutolanil and its metabolites contain the 2-(trifluoromethyl)benzoic acid (2-TFMBA) moiety. In this method, flutolanil and its metabolites are converted to 2-TFMBA by hydrolysis. The method involves direct hydrolysis with sodium hydroxide at 200°C, acidification, partitioning into a mixture of ethyl acetate-n-hexane (1:9, v/v), clean-up using a strong anion exchange cartridge (InertSep SAX), and then quantification using LC-MS/MS. The optimal conditions for the complete hydrolysis of flutolanil to 2-TFMBA are an incubation time of 6 h and a temperature of 200°C. The developed method was evaluated using seven types of food: bovine samples of muscle, fat, liver and milk, as well as egg, eel, and freshwater clam. Samples were spiked both at 0.01 mg/kg and at the Japanese maximum residue limit (MRL) established for each food type. The validation results show excellent recoveries (88–107%) and precision (< 10%) for flutolanil and M-4. The limit of quantification (S/N ≥ 10) of the developed method is 0.01 mg/kg. The developed method is applicable to the definition of residual flutolanil for animal-based food commodities and MRLs established by the Codex Alimentarius, and will be useful for the regulatory monitoring of residual flutolanil and its metabolites in food products.     

超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法测定动物源性产品中磺酰草吡唑及其代谢物残留量

目的 建立超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法测定动物源性产品中磺酰草吡唑及其代谢物残留量的分析检测方法。方法 样品经甲酸-乙腈溶液提取,提取液先经低温冷冻除脂后,再采用十八烷基键合硅胶、石墨化碳黑和无水硫酸镁分散固相萃取进行净化,以Waters Acquity UPLC HSS T3色谱柱为分析柱,甲醇-0.2%甲酸溶液为流动相进行梯度洗脱分离,采用高分辨质谱平行反应监测扫描模式,以正离子采集进行定性定量分析,基质匹配外标法定量。结果 磺酰草吡唑和磺酰草吡唑-脱甲基在0.5～50.0μg/L范围内线性关系良好,相关系数均大于0.995。空白样品在4个加标水平下的平均回收率为82.4%～114.6%,相对标准偏差(n=6)为3.1%～8.9%;方法检出限为0.3μg/kg,定量限为1.0μg/kg。结论 该方法操作简单快速、灵敏度高、结果准确,可应用于动物源性产品中磺酰草吡唑及其代谢物的检测。     

Determination of nequinate and buquinolate in livestock products using liquid chromatography-tandem mass spectrometry

We studied the simultaneous determination of nequinate and buquinolate, which are used as feed additives to prevent coccidiosis, by means of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The sample was extracted with acetonitrile, then loaded onto an HLB mini-column with 20% methanol. After clean-up with 20% methanol, the analytes were eluted with acetonitrile-methanol (1 : 1). The coccidiostats in the purified samples were determined using ESI-MRM mode LC-MS/MS with a sample matrix calibration curve. Mean recoveries of nequinate and buquinolate from 8 kinds of livestocks samples (chicken muscle, chicken liver, chicken heart, swine muscle, swine heart, cattle muscle, sheep muscle, egg) were in the range of 89.5% to 108.6%, and the relative standard deviation values were <20% (n=10) at the levels of 0.01 μg/g and 0.05 μg/g, respectively. The limits of quantification of these compounds were 0.001 μg/g in each sample.     

Direct hydrodynamic radius measurement on dissolved organic matter in natural waters using diffusion NMR

Dissolved organic matter from natural waters is a complex mixture of various chemical components, which play vital roles in many environmental processes such as the global carbon cycle and the fate of many key anthropogenic pollutants. Despite its environmental significance, dissolved organic matter in natural form has never been studied using nuclear magnetic resonance based hydrodynamic radius measurements due to its extremely low concentration (e.g., a few mg/L) in natural waters. In this study, NMR-based hydrodynamic radius measurements were performed directly on unconcentrated pond, river, and sea waters. The key chemical components of the dissolved organic matters from different sources were identified as carbohydrates, carboxyl-rich alicyclic molecules, and aliphatic molecules. By using the Stokes-Einstein-Sutherland equation, the average hydrodynamic radii of the three key components were calculated.     

Extra-cellular polysaccharides, soluble microbial products, and natural organic matter impact on nanofiltration membranes flux decline

Extra-cellular polysaccharides (EPS), soluble microbiological products (SMP), dispersed bacterial cells, and a well-characterized natural organic matter (NOM) isolate were observed to determine their influence on the flux decline of model nanofiltration membrane systems. Biofouling tests were conducted using bench-scale, flat-sheet membrane modules, fed with particle-free (laboratory) waters and natural waters, some of which were augmented with readily biodegradable organic carbon. The modules were operated 6.7 x 10(5) Pa, and 21+/- 2 degrees C. Membrane flux-decline was associated with increases in surface EPS mass: between 30 and 80% of normalized flux decline occurred when membrane-associated EPS content increased from 5to 50 microg/ cm2. As judged by standard culturing, heterotrophic cell densities recovered from membrane biofilm samples showed no significant correlations with the different carbon sources present in the feedwaters, or flux decline rates. Results suggested that, in the absence of microbiological activity, SMP and NOM have intrinsic membrane fouling properties at levels that are operationally significant to commercial-scale membrane treatment practices. Results also suggested that SMP may have a biofouling potential significantly greater than some types of NOM. Trends obtained relating these compounds with flux decline were successfully described by expanding existing resistance-in-series models.     

基于超高效液相色谱-四极杆/静电场轨道阱高分辨质谱技术研究全氟化合物质谱裂解规律

目的 采用超高效液相色谱-四级杆/静电场轨道阱高分辨质谱研究全氟化合物的质谱裂解规律。方法 采用Thermo Hypersil GOLD aQ色谱柱（100 mm×2.1 mm,1.9 μm）,以甲醇和0.1%甲酸水溶液为流动相进行梯度洗脱,在电喷雾负离子模式下采集数据,采用全扫描和数据依赖的二级扫描模式,根据一、二级质谱离子的精确质荷比推导全氟化合物可能的裂解途径。 结果 全氟磺酸类化合物主要发生CC键和CS键断裂,产生特征碎片[·C3F6-SO3]- m/z 229.94和[SO3]- m/z 79.95;全氟羧酸类化合物首先丢失中性分子CO2,产生[M-O-CO2]-碎片离子,继而发生不同数量的CC键断裂,产生m/z 218.98、168.98、118.99等特征碎片离子。结论 该研究提出的质谱裂解规律对快速鉴定和分析复杂体系中全氟化合物具有重要作用。     

Fouling and natural organic matter removal in adsorbent/membrane systems for drinking water treatment

Adsorbent particles added to ultrafiltration (UF) systems treating drinking water can remove natural organic matter (NOM) and some other contaminants from the water, but their effect on membrane fouling is inconsistent-in some cases, fouling is reduced, and in others, it is exacerbated. This research investigated the behavior of UF systems to which powdered activated carbon (PAC), heated iron oxide particles (HIOPs), or (nonadsorbent) SiO2 particles were added. On a mass basis, the PAC removed the most NOM from solution, the HIOPs removed less, and the SiO2 removed essentially none. However, in the case of both PAC and SiO2, increasing the dose of solids led to a steady increase in fouling, whereas the opposite trend applied when HIOPs were added. In the absence of NOM, none of the solids fouled the membrane significantly. Thus, even though NOM is a causative agent for fouling, removing it from solution does not necessarily reduce fouling; the mechanism of removal can be just as important as the absolute amount removed, if the removal occurs in a cake layer near the membrane surface. Scanning electron microscopy images of the cake layers formed in the three systems suggest that the NOM binds PAC or SiO2 particles to one another and to the membrane surface, so that the particles become part of the foulant in the system. By contrast, the NOM appears to bind HIOPs to one another but not to the membrane. This process leaves enough pore space in the cake layer for water to reach the membrane with minimal resistance, and it reduces the tendency for either the NOM or the HIOPs to foul the membrane surface.