Elemental composition of HULIS in the Pearl River Delta Region, China: results inferred from positive and negative electrospray high resolution mass spectrometric data

The HUmic-LIke Substances (HULIS) fraction isolated from aerosol samples collected at a rural location of the Pearl River Delta Region (PRD), China, during the harvest season was analyzed by both positive and negative mode electrospray ionization (ESI) coupled with an ultrahigh resolution mass spectrometer (UHRMS). With the remarkable resolving power and mass accuracy of ESI-UHRMS, thousands of elemental formulas were identified. Formulas detected in the positive (ESI+) and the negative (ESI-) mode complement each other due to differences in the ionization mechanism, and the use of both provides a more complete characterization of HULIS. Compounds composed of C, H, and O atoms were preferentially detected in ESI- by deprotonation, implying their acidic properties. Tandem MS and Kendrick Mass Defect analysis implies that carboxyl groups are abundant in the CHO compounds. This feature is similar to those of natural fulvic acids, but relatively smaller molecular weights are observed in the HULIS samples. A greater number of reduced nitrogen organic compounds were observed in the ESI+ compared to ESI-. Compounds with biomass burning origin including alkaloids, amino acids, and their derivatives are their probable constituents. Sulfur-containing species were dominantly detected in ESI-. The presence of sulfate fragments in the MS/MS spectra of these species and their high O/S ratios implies that they are mainly organosulfates. Organosulfates and nitrooxy-organosulfates were often the most intensive peaks in the ESI- spectra. They are believed to be products of reactive uptake of photooxidation products of reactive volatile organic compounds by acidic sulfate particles. The elemental compositions deduced from the UHRMS analysis confirm the conclusion from our previous study that biomass burning and SOA formation are both important sources of HULIS in the PRD region.     

Chemical characterisation of non-defective and defective green arabica and robusta coffees by electrospray ionization-mass spectrometry (ESI-MS)

The coffee roasted in Brazil is considered to be of low quality, due to the presence of defective coffee beans that depreciate the beverage quality. These beans, although being separated from the non-defective ones prior to roasting, are still commercialized in the coffee trading market. Thus, it was the aim of this work to verify the feasibility of employing ESI-MS to identify chemical characteristics that will allow the discrimination of Arabica and Robusta species and also of defective and non-defective coffees. Aqueous extracts of green (raw) defective and non-defective coffee beans were analyzed by direct infusion electrospray ionization mass spectrometry (ESI-MS) and this technique provided characteristic fingerprinting mass spectra that not only allowed for discrimination of species but also between defective and non-defective coffee beans. ESI-MS profiles in the positive mode (ESI(+)-MS) provided separation between defective and non-defective coffees within a given species, whereas ESI-MS profiles in the negative mode (ESI(−)-MS) provided separation between Arabica and Robusta coffees.     

Secondary organic aerosol formation by glyoxal hydration and oligomer formation: humidity effects and equilibrium shifts during analysis

Glyoxal is a significant atmospheric aldehyde formed from both anthropogenic aromatic compounds and biogenic isoprene emissions. The chemical behavior of glyoxal relevant to secondary organic aerosol (SOA) formation and analysis is examined in GC-MS, electrospray ionization (ESI)-MS, and particle chamber experiments. Glyoxal oligomers are shown to rapidly decompose to glyoxal in GC injection ports at temperatures > or = 120 degrees C. Glyoxal dihydrate monomer is dehydrated at temperatures > or = 140 degrees C during GC analysis but shows only oligomers (n < or = 7) upon ESI-MS analysis. Thus both of these analytical techniques will cause artifacts in speciation of glyoxal in SOA. In particle chamber experiments, glyoxal (at -0.1 Torr) condensed via particle-phase reactions when relative humidity levels exceeded a threshold of -26%. Both the threshold humidity and particle growth rates (-0.1 nm/min) are consistent with a recent study performed at glyoxal concentrations 4 orders of magnitude below those used here. This consistency suggests a mechanism where the surface water layer of solid-phase aerosol becomes saturated with glyoxal dihydrate monomer, triggering polymerization and the establishment of an organic phase.     

新型分子印迹聚合物修饰的选择性离子源结合电喷雾电离质谱快速检测莠灭净和莠去津

基于分子印迹聚合物修饰铁片（molecularly imprinted polymer modified iron sheet,MIPIS）制备了一种选择性的敞开式质谱离子源,结合电喷雾电离质谱,构建一种快速检测食品基质中莠灭净和莠去津痕量残留的方法。分子印迹聚合物以氰草津为模板,使用甲基丙烯酸和苯胺在水溶液中聚合而成。将MIPIS作为萃取尖端对豆奶粉、小麦和牛奶中的莠灭净和莠去津进行富集,随后作为敞开式质谱离子源结合电喷雾电离质谱直接进行检测。结果显示,在0.2～200μg/L范围内线性良好,相关系数R2为0.998 2和0.999 7,检出限和定量限分别为0.2～0.5μg/kg和0.6～1.5μg/kg,在3个加标水平下回收率在81.05%～109.66%。该方法操作简单,灵敏度高,省时高效,无需长时间的色谱分离,适用于食品中痕量三嗪类农药残留的快速检测。     

Formation of nitrogen-containing oligomers by methylglyoxal and amines in simulated evaporating cloud droplets

Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles.     

Particle-phase chemistry of secondary organic material: modeled compared to measured O:C and H:C elemental ratios provide constraints

Chemical mechanisms for the production of secondary organic material (SOM) are developed in focused laboratory studies but widely used in the complex modeling context of the atmosphere. Given this extrapolation, a stringent testing of the mechanisms is important. In addition to particle mass yield as a typical standard for model-measurement comparison, particle composition expressed as O:C and H:C elemental ratios can serve as a higher dimensional constraint. A paradigm for doing so is developed herein for SOM production from a C(5)-C(10)-C(15) terpene sequence, namely isoprene, α-pinene, and β-caryopyhllene. The model MCM-SIMPOL is introduced based on the Master Chemical Mechanism (MCM v3.2) and a group contribution method for vapor pressures (SIMPOL). The O:C and H:C ratios of the SOM are measured using an Aerosol Mass Spectrometer (AMS). Detailed SOM-specific AMS calibrations for the organic contribution to the H(2)O(+) and CO(+) ions indicate that published O:C and H:C ratios for SOM are systematically too low. Overall, the measurement-model gap was small for particle mass yield but significant for particle-average elemental composition. The implication is that a key chemical pathway is missing from the chemical mechanism. The data can be explained by the particle-phase homolytic decomposition of organic hydroperoxides and subsequent alkyl-radical-promoted oligomerization.     

The effect of solvent on the analysis of secondary organic aerosol using electrospray ionization mass spectrometry

This study examined the effect of solvent on the analysis of organic aerosol extracts using electrospray ionization mass spectrometry (ESI-MS). Secondary organic aerosol (SOA) produced by ozonation of d-limonene, as well as several organic molecules with functional groups typical for OA constituents, were extracted in methanol, d3-methanol, acetonitrile, and d3-acetonitrile to investigate the extent and relative rates of reactions between analyte and solvent. High resolution ESI-MS showed that reactions of carbonyls with methanol produce significant amounts of hemiacetals and acetals on time scales ranging from several minutes to several days, with the reaction rates increasing in acidified solutions. Carboxylic acid groups were observed to react with methanol resulting in the formation of esters. In contrast acetonitrile extracts showed no evidence of reactions with analyte molecules, suggesting that acetonitrile is the preferred solvent for SOA extraction. The use of solvent-analyte reactivity as a tool for the improved characterization of functional groups in complex organic mixtures was demonstrated. Direct comparison between mass spectra of the same SOA samples extracted in methanol versus acetonitrile was used to estimate the lower limits for the relative fractions of carbonyls (> or = 42%) and carboxylic acids (> or = 55%) in d-limonene SOA.     

Advanced oxidation of caffeine in water: on-line and real-time monitoring by electrospray ionization mass spectrometry

High performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV), and total organic carbon (TOC) analyses show that caffeine is quickly and completely degraded underthe oxidative conditions of the UV/H2O2,TiO2/ UV, and Fenton systems but that the organic carbon content of the solution decreases much more slowly. Continuous on-line and real-time monitoring by electrospray ionization mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS) as well as high accuracy MS measurements and gas chromatography-mass spectrometry analysis show that caffeine is first oxidized to N-dimethylparabanic acid likely via initial OH insertion to the C4=C8 caffeine double bond. A second degradation intermediate, di(N-hidroxymethyl)parabanic acid, has been identified by ESI-MS and characterized by ESI-MS/MS and high accuracy mass measurements. This polar and likely relatively unstable compound, which is not detected by off-line GC-MS analysis, is likely formed via further oxidation of N-dimethylparabanic acid at both of its N-methyl groups and constitutes an unprecedented intermediate in the degradation of caffeine.     

杜仲雄花化学成分的液相色谱-电喷雾三重四极杆飞行时间质谱分析

采用液相色谱-电喷雾三重四极杆飞行时间质谱法对杜仲雄花中化学成分进行分析。用反相C18色谱柱,以0.1%甲酸溶液（A）-乙腈（B）为流动相进行梯度洗脱;采用电喷雾离子源负离子扫描方式对样品进行分析。根据高分辨质谱提供的准分子离子和碎片离子的精确分子质量信息,结合标准品对照与参考相关文献数据,共鉴定出32?种化学成分,包括2?种木脂素类、9?种环烯醚萜类、8?种苯丙素类、12?种黄酮类和1?种酚苷类成分。上述结果可为探究杜仲雄花的药效物质基础及深度开发利用提供基础资料。     

Source attribution of submicron organic aerosols during wintertime inversions by advanced factor analysis of aerosol mass spectra

Real-time measurements of submicrometer aerosol were performed using an Aerodyne aerosol mass spectrometer (AMS) during three weeks at an urban background site in Zurich (Switzerland) in January 2006. A hybrid receptor model which incorporates a priori known source composition was applied to the AMS highly time-resolved organic aerosol mass spectra. Three sources and components of submicrometer organic aerosols were identified: the major component was oxygenated organic aerosol (OOA), mostly representing secondary organic aerosol and accounting on average for 52-57% of the particulate organic mass. Radiocarbon (14C) measurements of organic carbon (OC) indicated that approximately 31 and approximately 69% of OOA originated from fossil and nonfossil sources, respectively. OOA estimates were strongly correlated with measured particulate ammonium. Particles from wood combustion (35-40%) and 3-13% traffic-related hydrocarbon-like organic aerosol (HOA) accounted for the other half of measured organic matter (OM). Emission ratios of modeled HOA to measured nitrogen oxides (NOx) and OM from wood burning to levoglucosan from filter analyses were found to be consistent with literature values.     

Sorption of Aldrich humic acid onto hematite: insights into fractionation phenomena by electrospray ionization with quadrupole time-of-flight mass spectrometry

Sorption induced fractionation of purified Aldrich humic acid (PAHA) on hematite is studied through the modification of electrospray ionization (ESI) quadrupole time-of-flight (QToF) mass spectra of supernatants from retention experiments. The ESI mass spectra show an increase of the "mean molecular masses" of the molecules that constitutes humic aggregates. The low molecular weight fraction (LMWF; m/z < or = 600 Da) is preferentially sorbed compared to two other fractions. The resolution provided by ESI-QToF mass spectrometer in the low-mass range provided evidence of further fractionation induced by sorption within the LMWF. Among the two latter fractions, the high molecular weight fraction (HMWF; m/z approximately 1700 Da) seems to be more prone to sorption compared to the intermediate molecular weight fraction (IMWF; m/z approximately 900 Da). The IMWF seems to be more hydrophilic as it should be richer in O, N, and alkyl C from the proportion of even mass, and poorer in aromatic structures from mass defect analysis in ESI mass spectra.     

大豆卵磷脂中脑苷脂类物质的分析与检测研究

通过电喷雾质谱(ESI/MS)和高效液相色谱-蒸发光散射器(HPLC-ELSD)鉴定和分析用柱层析法纯化大豆卵磷脂得到的各组分主要成分。经质谱检测纯化的组分中主要有两种分子类型的神经酰胺,分别是C18:0 d18:1Cer和C25:0 h d18:1Cer;主要有两种分子类型的脑苷脂,分别是C16:0 t18:2Ce和C17:0Ce。通过HPLC-ELSD分析,二次柱层析得到的神经酰胺含量99.43%,回收率为98.23%;脑苷脂含量为98.86%,回收率为97.27%。     

Antioxidant activity of Annona crassiflora: Characterization of major components by electrospray ionization mass spectrometry

The polar components of Annona crassiflora pulp, peel and seeds ethanolic extracts were investigated by direct infusion electrospray ionization mass spectrometry (ESI-MS) both in the negative ion mode. Characteristic ESI mass spectra with many diagnostic ions were obtained for the extracts, serving for fast and reliable information. The technique provided information of component structures revealing the presence of important bioactive components widely reported as potent antioxidants such as ascorbic acid, caffeic acid, quinic acid, ferulic acid, xanthoxylin, rutin, caffeoyltartaric acid, caffeoyl glucose and [quercetin+hexose+pentose−H]⁻¹ This is the first report on the composition by ESI-MS of araticum peel and seed ethanolic extracts demonstrating excellent antioxidant activity.     

5种丁香酚类化合物的电喷雾质谱裂解规律研究

目的研究5种渔用麻醉剂的电喷雾质谱裂解规律。方法采用电喷雾离子源(ESI源),对丁香酚、甲基丁香酚、甲基异丁香酚、乙酰基异丁香酚和MS-222进行质谱分析。根据结构分为正、负2种离子检测方式(ESI~(+/-)),含有酚羟基团的丁香酚采用负离子检测方式,其余4种化合物采用正离子检测方式。结果在正、负离子检测模式下,5种渔用麻醉剂准分子离子分别为[M+H]~+和[M-H]~-。对准分子离子进行碰撞诱导解离(collision induced dissociation,CID),得到特征离子碎片。分析了5种化合物在相应离子模式下的电喷雾质谱裂解途径。结论本研究所提出的电喷雾质谱裂解规律,可为同类型分子结构的渔用麻醉剂的结构分析和鉴定研究提供了参考依据。     

Electrospray ionization mass spectrometry fingerprinting of essential oils: Spices from the Labiatae family

Polar components of the methanolic extracts of the essential oils of the spices Origanum dictamnus, Origanum vulgare, Origanum majorana and Rosmarinus officinalis, all four belonging to the Labiatae family, were investigated by direct infusion electrospray ionisation mass spectrometry (ESI-MS) both in the negative and positive ion modes. Characteristic ESI mass spectra with many diagnostic ions were obtained for the extracts of all four spices, serving for fast and reliable identification of these species. Tandem mass spectrometry (ESI-MS/MS), which often forms a series of fragment ions, and this additional MS dimension increases selectivity for authenticity and adulteration tests for spice essential oils. The MS technique also provides complementary information of component structures revealing the presence of important bioactive components.     

高效液相色谱串联质谱法测定鲢鱼中的微囊藻毒素

建立了高效液相色谱/串联质谱法（HPLC-MS/MS）同时定量检测洪泽湖鲢鱼中微囊藻毒素（MC-RR,MC-LR和MC-YR）的方法,用甲醇提取鲢鱼肉中的微囊藻毒素,用C18固相萃取柱净化。以甲醇和0.1%的甲酸水溶液为流动相,采用梯度洗脱用C18色谱柱对鱼肉中的微囊藻毒素进行分离,用电喷雾质谱正离子选择模式进行检测。三种微囊藻毒素MC-RR,MC-LR,MC-YR的线性良好,检出限分别为0.2、0.4、0.4μg·L-1,定量限分别为0.8、0.9、0.9μg·L-1。对链鱼样品进行加标回收,回收率在87.1%～101.2%,10次平行测定的相对标准偏差均小于8%。该方法具有准确、快速、简单以及灵敏度高的特点,能够适应大规模样品的快速分析要求。     

高效液相色谱-电喷雾串联质谱法测定保健食品中水苏糖含量

目的以质谱定性定量,测定保健品中水苏糖含量。方法采用高效液相色谱/电喷雾质谱联用法(HPLC-ESI/MS),色谱柱:瑞典KromasilNH2柱;流动相:甲醇+乙腈+0.1%甲酸氨水溶液=8+52+40(体积比);流速1.0ml/min。质谱采用电喷雾正离子模式(ESI+),对m/z689进行选择离子监测,扫描范围(m/z):620～700amu。结果水苏糖在80～120μg/ml范围内,峰面积和浓度呈良好的线性关系(r=0.9992);相对标准偏差(RSD)为0.73%;在3个添加水平下的回收率均在93.0%～105.8%。结论本方法快速、选择特异性高、分析时间短且无需衍生处理,抗干扰能力强,能准确快速测定水苏糖的含量。     

QuEChERS-超高压液相色谱-串联质谱法同时测定水产品中的6种丁香酚类麻醉剂

建立了同时测定水产品中的丁香酚、异丁香酚、甲基丁香酚、甲基异丁香酚、乙酸丁香酚酯、乙酰基异丁香酚残留量的超高压液相色谱-串联质谱法。样品用乙腈提取,经50 mg乙二胺-N-丙基硅烷、100 mg C₁₈、150 mg Mg SO₄净化,采用Kinetex C₁₈(2.1 mm×100 mm,2.6μm)色谱柱分离,以甲醇-水作为流动相进行梯度洗脱,电喷雾离子源正负快速切换,多反应监测模式检测,内标法定量。丁香酚和异丁香酚的线性范围为2～100 ng/m L,其他4种丁香酚类药物的线性范围为1～100 ng/m L,线性相关系数均不低于0.999。丁香酚类药物检出限(信噪比为3)为0.5～1.5μg/kg,定量限为2.0～5.0μg/kg。6种丁香酚类麻醉剂的方法回收率为67.0%～106.4%,相对标准偏差为1.2%～15.7%。该方法能实现对水产品中丁香酚类麻醉剂的准确、快速检测,测定结果可靠。     

Characterization of high molecular weight disinfection byproducts from chlorination of humic substances with/without coagulation pretreatment using UF-SEC-ESI-MS/MS

Chlorinated disinfection byproducts (DBPs) generated from the reaction of the disinfectant chlorine with naturally occurring humic substances in raw water have been intensively studied over the past three decades, yet only a fraction of the total organic halogen (TOX) formed during chlorination has been chemically identified or even well characterized. The majority of the unknown portion of the TOX is likely attributable to high molecular weight (MW) DBPs (above 500), which may have potential adverse health effects. In this work, typically dosed chlorinated Suwannee River fulvic acid (SRFA) samples with and without coagulation pretreatment were separated and fractionated by using ultrafiltration (UF) and size exclusion chromatography (SEC) techniques. The SEC fractions corresponding to the high MW region were concentrated with nitrogen sparging and characterized by negative ion electrospray ionization mass spectrometry (ESI-MS) and ESI-MS/MS. The results demonstrate that the ESI-MS/MS precursor ion scan is an effective tool for the selective detection of the electrospray ionizable chlorine-containing compounds in a complex mixture. Many high MW chlorine-containing DBPs were tentatively found in the UF-SEC fractions of the chlorinated SRFA samples with/without coagulation pretreatment. The SEC-UV chromatograms and SEC-ESI-MS spectra show that coagulation could significantly reduce the formation of high MW chlorinated DBPs.     

一种小分子生物活性肽(重组BMP)的质谱分析

目的 对一种小分子生物活性肽(重组BMP)样品进行电喷雾质谱测定,初步确定其一级结构.方法 离子化方式:电喷雾离子化;检测方式正离子;质量扫描范围m/z 150～1 000;干燥气(N2)流速5 arb;雾化气(N2)压力35 arb;毛细管出口电压4.5 kV;碎裂器电压100V;碰撞诱导解离技术碎裂器电压为35％;碰撞气流量为电子流量控制器自动控制;进样方式:流动注射进样;流动相为乙腈:水(50:50).结果 利用电喷雾质谱技术,初步测定重组BMP样品的一级结构为H-Lys-Gly-Asp-Glu-Glu-Ser-Leu-Pro-OH.结论 该方法能够初步测定小分子生物活性肤的一级结构,为实验室生物工程菌构建提供准确有效的检测技术.