Trace sulfide determination in oxic freshwaters

A simplified method for determination of reduced sulfur species in natural waters is presented. Reduced sulfur species were separated from a natural water matrix, using purge-and-trap (PT), after reacting with acid (acid volatile sulfide—AVS) or Cr(II) in acidic medium (chromium reducible sulfur—CRS). Sulfide in the trapping medium (0.05 M NaOH), was analyzed spectrophotometrically after derivatization to form methylene blue (MB). AVS precision for Na₂S and zinc sulfide clusters in synthetic solutions was ≤8.5% RSD at concentrations ranging from 48 to 503 nM. Spike recoveries of zinc sulfide clusters were 75-98% in a variety of freshwaters using the AVS procedure. Spike recoveries of Cu sulfide colloids were 94-109% in the same freshwater samples using the CRS procedure. During the analytical procedure an interfering compound was produced due to the reaction of mixed diamine reagent with itself. Lowering the pH of the reaction mixture minimized the formation of this compound. Minimizing contamination from particulates was necessary to achieve sub-nanomolar detection limits. The detection limit for AVS in a 500 ml sample with a 10 cm spectrophotometer cell was 0.1-0.3 nM (3×S.D. blank). The CRS procedure was calibrated with a synthetic CuS colloid. Interferences to the CRS method included finely divided pyrite, polysulfide, thiosulfate, sulfite and some elemental sulfur. The Cr(II) reagent did not reduce sulfate under our experimental conditions. The degree to which zinc sulfide clusters were adsorbed on membrane filters during filtration was mitigated if the clusters were synthesized in the presence of natural organic matter. Examples of AVS and CRS concentrations determined in oxygenated waters using the PT method were comparable to those reported recently by other methods. This method offers greater simplicity than other methods for trace dissolved sulfide determination in natural waters.     

Coulometric determination of total sulfur and reduced inorganic sulfur fractions in environmental samples

Evaluation of the solid-phase partitioning of sulfur is frequently an important analytical component of risk assessments at hazardous waste sites because minerals containing reduced-sulfur can significantly affect the transport and fate of organic and inorganic contaminants in natural environments. We applied selected methods for the determination of total sulfur, acid-volatile sulfide (AVS), chromium-reducible sulfur (CRS), and extractable-sulfate in standard reference materials and sediment samples from a contaminated site. A coulometric titration method is presented and evaluated for total sulfur, AVS, and CRS. This method is especially advantageous for AVS and CRS determinations because hydrogen sulfide gas evolved during chemical extraction is detected and quantitated in-line; consequently, measurement endpoints can be precisely determined without need for setting arbitrary time limits. The coulometric method allows for improved data quality and increased laboratory throughput of samples. Data on sulfur partitioning are presented for four standard reference materials (NIST 1646a, NIST 2780, CCRMP LKSD-1, CCRMP RTS-3) for the purpose of supporting quality control in environmental studies involving the geochemical and biochemical cycling of sulfur.     

Determination of acid volatile sulphur in river sediments by ICP-OES coupled with purge and trap method

The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S^2? ? L^?1 in the absorption solution which corresponds to 0.23 mg S^2?·kg^?1 in a sediment. Value of LOD is comparable with the iodometric determination.     

电感耦合等离子体原子发射光谱法测定废蓄电池硫酸铅及其脱硫物中的硫

建立废蓄电池硫酸铅及其脱硫物中硫含量的测定方法。样品采用硝酸、盐酸消解样品,电感耦合等离子体原子发射光谱法测定废蓄电池硫酸铅及其脱硫物中硫的含量。在选定的仪器工作条件下,大量Pb,Al,Fe等基体元素的存在不影响硫的测定。硫的质量浓度在0.00~80.00 mg/L范围内与其光谱强度具有良好的线性关系,线性相关系数为0.999 9,检出限为0.14 mg/L。测定结果的相对标准偏差为2.18%~5.22%(n=11),样品加标回收率在95.0%~104.2%之间。该方法的测定结果与重量法测定结果一致。该方法简单易行,测定结果准确可靠,重复性好,可用于废蓄电池硫酸铅及其脱硫物中硫的测定。     

主成分分析-支持向量回归建模方法及应用研究

将主成分分析(PCA)用于近红外光谱的特征提取,并与支持向量回归(SVR)相结合,实现了主成分分析-支持向量回归(PCA-SVR)用于近红外光谱定量分析的建模方法。与单纯的SVR方法相比,不仅提高了运算速度,而且提高了模型的预测准确度。将PCA-SVR方法用于烟草样品中总糖和总挥发碱含量的测定,所得结果的预测均方根误差分别为1.323和0.0477;回收率分别为91.8%~112.6%和88.9%~120.2%。     

在线裂解-气相色谱-质谱法研究灵香草浸膏的热裂解

为了研究灵香草浸膏的热裂解行为,采用在线有氧热裂解-冷阱捕集-气相色谱-质谱联用技术,模拟卷烟燃吸状态对灵香草浸膏进行了热裂解分析,并对灵香草浸膏热裂解前后的挥发性成分进行了比较分析。从灵香草浸膏的热裂解产物中共鉴定出64种成分,占总峰面积的88.27%,主要成分为高级脂肪酸及其酯类;灵香草浸膏热裂解后的挥发性成分数量多于裂解前（45个）,说明灵香草浸膏经热裂解生成了新的化合物。热裂解前后共有的化合物有20个,主要是高级脂肪酸及其酯类、新植二烯、5-（羟甲基）-2-呋喃甲醛、3-羟基-4,5-二甲基-2（5H）-呋喃酮等化合物。在线有氧裂解模式更接近烟用添加剂样品的真实裂解状态,操作简单、快捷,结果准确。     

吹扫捕集-气相色谱联用测定城市河流中的挥发性硫化物

建立了一种吹扫捕集 气相色谱联用测定城市河流中挥发性硫化物的方法。二甲基硫、甲基乙基硫、二甲基二硫最低检测质量浓度分别为80,80和100ng/L,水样加标回收率在91%～101%之间。方法操作简单,灵敏度高,成功应用于城市河流中水样中挥发性硫化物的测定。     

顶空气相色谱质谱法快速测定液体食品中的挥发性酸

建立了一种用于快速测定食品中挥发性有机酸的分析方法.利用顶空技术对样品进行前处理,并与气相色谱质谱联用,用离子选择对11种挥发性有机酸进行定量分析.在优化的实验条件下,方法线性关系良好,线性范围为0.20 ～5 mg/L.11种挥发性有机酸的相关系数均大于0.998 6,检出限为0.000 2 ～35.5 mg/L,比全扫描检出限低1 ～3个数量级.11种挥发性有机酸的回收率为93% ～99%,相对标准偏差均小于10%.该方法简便、快速、重复性好、定性定量准确,适于食品中挥发性有机化合物的检测.     

Separate vaporisation of boric acid and inorganic boron from tungsten sample cuvette-tungsten boat furnace followed by the detection of boron species by inductively coupled plasma mass spectrometry and atomic emission spectrometry (ICP-MS and ICP-AES)

Utilising extremely different vaporisation properties of boron compounds, the determination procedures of volatile boric acid and total boron using tungsten boat furnace (TBF) ICP-MS and TBF-ICP-AES have been investigated. For the determination of volatile boric acid by TBF-ICP-MS, tetramethylammonium hydroxide (TMAH, Me₄NOH) was used as a chemical modifier to retain it during drying and ashing stages. As for the total boron, not only non-volatile inorganic boron such as boron nitride (BN), boron carbide (B₄C), etc. but also boric acid (B(OH)₃) was decomposed by a furnace-fusion digestion with NaOH to produce sodium salt of boron, a suitable species for the electrothermal vaporisation (ETV) procedure. The proposed method was applied to the analysis of various standard reference materials. The analytical results for various biological and steel samples are described.     

A simple diffuse reflectance Fourier transform infrared spectroscopic determination of sulfur dioxide in ambient air using potassium tetrachloromercurate as the absorbing reagent

This paper presents development of a simple, rapid, and precise analytical method for determination of sulfur dioxide in ambient air by a gas to solid-phase conversion method. Sulfur dioxide is determined in the form of sulfite (SO3(2-)) because the absorbing reagent, potassium tetrachloromercurate (TCM), used in this method absorbs sulfur dioxide from the atmosphere in the form of sulfite. Determination of submicrogram levels of sulfur dioxide was based on the selection of a quantitative analytical peak at 495 cm(-1) among the 3 observed vibrational peaks for the dichlorosulfitomercurate complex formed after reaction of sulfur dioxide with TCM and measurement of absorbance using diffuse reflectance Fourier transform infrared spectroscopy. The limits of detection and quantification of the method were found to be 0.09 and 0.4 microg/g SO3(2-), respectively. The precision in terms of standard deviation and relative standard deviation (RSD) at a level of 2 microg SO3(2-)/10.1 g KBr for n = 10 was found to be 0.036 microg SO3(2-) and 1.8%, respectively. The RSD (n = 10) for determination of sulfur dioxide in ambient air was observed to be in the range of 2.7-4.2%. The method proposed is time saving and eliminates the slow and cumbersome steps of pH maintenance of the reaction mixture and color formation of the U.S. Environmental Protection Agency recommended West and Gaeke spectrophotometric method and other methods for quantitative determination of sulfur dioxide.     

管式炉燃烧–碘量库仑滴定法测定石油焦中总硫含量

建立一种管式炉内燃烧石油焦样品前处理,然后用自动碘量库仑滴定法测定石油焦中总硫含量的方法。探讨了影响实验结果的因素,电解液采用10 m L冰乙酸溶解于250 m L蒸馏水中,避光保存,实验环境温度为20℃以上,电解液中搅拌转子的转速为500 r/min。在优化的实验条件下,测定结果的相对标准偏差在2.36%~3.94%(n=6)之间,3种石油焦样品加标回收率在82.0%~101.5%之间。该方法可应用于石油焦中总硫含量的测定。     

原子吸收光谱法间接测定萤石中的全硫

基于SO42-和BaCrO4溶液反应生成BaSO4沉淀, 置换出定量的CrO42-, 通过原子吸收法测定Cr, 建立了间接测定萤石中硫的原子吸收光谱法. 方法的工作曲线范围0.05～20 μg/mL SO42-, 检出限为0.017 μg/mL S, 适用于硫质量分数在0.01%～3%范围内萤石样品的测定.     

Determination and Application of Nineteen Monoamines in the Gut Microbiota Targeting Phenylalanine,Tryptophan, and Glutamic Acid Metabolic Pathways

It has been reported that monoamine neurotransmitters can be produced by gut microbiota, and that several related metabolites of amino acids in these pathways are associated with nervous system (NVS) diseases. Herein, we focused on three pathways, namely, phenylalanine (Phe), tryptophan (Trp), and glutamic acid (Glu), and established an underivatized liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of nineteen monoamine neurotransmitters and related metabolites in the gut microbiota. The neurotransmitters and related metabolites included Phe, tyrosine (Tyr), l-dopa (Dopa), dopamine (DA), 3-methoxytyramine, Trp, hydroxytryptophan, 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), kynurenine (KN), kynurenic acid (KYNA), melatonin, tryptamine (TA), indole-3-lactic acid (ILA), indole-3-acetic acid (IAA), indolyl-3-propionic acid (IPA), Glu, gamma-aminobutyric acid (GABA), and acetylcholine (Ach). A fluoro-phenyl bonded column was used for separation, and the mobile phase consisted of methanol:acetonitrile (1:1) and water, with 0.2% formic acid in both phases. The compounds exhibited symmetric peak shapes and sufficient sensitivity under a total analysis time of 8.5 min. The method was fully validated with acceptable linearity, accuracy, precision, matrix effect, extraction recovery, and stability. The results showed that neurotransmitters, such as Dopa, DA, 5-HT, GABA, and Ach, were present in the gut microbiota. The metabolic pathway of Trp was disordered under depression, with lower levels of 5-HT, 5-HIAA, KN, KYNA, TA, ILA, IAA, IPA, and Glu, and a higher ratio of KYNA/KN. In addition, some first-line NVS drugs, such as sertraline, imipramine, and chlorpromazine, showed regulatory potential on these pathways in the gut microbiota.     

TS3000总硫分析仪分析低压力硫化氢的研究

通过时TS3000 总硫分析仪气体进样模块的简单改装,利用仪器的富集功能,使其可以分析由质量流量控制器原理发生的低含量、低压力的硫化氢气体,解决了TS3000 总硫分析仪不能检测压力较低样品的难题.对不同含量硫化氢样气体的分析结果表明,改装后的仪器仍具有很好的线性及准确度,同时验证了仪器改装方法的可行性.     

微库仑法测定石油硫含量

建立了测定石油中硫含量的微库仑法。用硫标准样品对库仑仪的最佳工作参数进行试验和调整,结果表明:裂解段温度为1 000℃,空气流量为1 L/min,裂解段停留时间至少2.5 min时测定结果较为理想。低硫含量、中硫含量、高硫含量油品的取样量分别为10~20 mg,9.5~11.5 mg,5.5 mg左右。该方法测量结果的相对标准偏差小于3%(n=6),两种硫标准样品回收率分别为100.2%,101.9%。该法适用于石油中硫含量的测定。     

气相色谱-质谱联用法测定腌制水产品中的挥发性N-亚硝胺类化合物

建立了气相色谱-质谱(GC-MS)快速测定腌制水产品中挥发性N-亚硝胺含量的分析方法。采用GC-MS测定了N-二甲基亚硝胺(NDMA)、N-二乙基亚硝胺(NDEA)、N-二丙基亚硝胺(NDPA)、N-亚硝基吡咯烷(NPYR)、N-亚硝基哌啶(NPIP)、N-二丁基亚硝胺(NDBA)6种化合物,考察了样品不同提取方法、不同固相萃取小柱、不同色谱柱对分离检测的影响。结果显示: 在10～1000 μg/L范围内,线性相关系数可达0.9998以上;重现性良好,相对标准偏差小于8%;回收率可达79%～105%;灵敏度高,检出限低,除NDPA为0.03 μg/kg外,其他5种N-亚硝胺为0.05 μg/kg。该方法前处理快速简捷,易于操作,适用于腌制水产品中N-亚硝胺残留量的检测工作。     

Measuring bioavailable trace metals from freshwater sediments by diffusive gradients in thin films (DGT) in monitoring procedures for quality assessment

An experimental design using passive samplers was set up in our laboratories with the aim of preparing a procedure for the assessment of trace metals bioavailability in freshwater sediments. Trace metal (Cd, Cu, Pb, Ni, and Zn) bioavailability in sediment samples were measured by diffusive gradients in thin films (DGT) devices and compared to those simultaneously extracted (SEM) in 1N HCl with acid-volatile sulfide (AVS). During experiments DGT devices were exposed at various times (from 4 to 336 h) in sediments with different physical and chemical properties and metal content, after equilibration with ambient water (1:2) for 24 h. Trace metal were progressively accumulated in DGT units and after at least 24-48 h metal fluxes became constant. No relation was found between metal available fractions measured by DGTs and total concentrations in sediments or pore waters. On the contrary good relations were found between available metals measured by DGT and metals simultaneously extracted (SEM) in HCl 1N with acid volatile sulfide (AVS).     

Rapid and accurate determination of trace volatile sulfur compounds in human halitosis by an adaptable active sampling system coupling with gas chromatography

Halitosis with the main components of trace volatile sulfur compounds widely affects the quality of life. In this study, an adaptable active sampling system with two sample‐collection modes of direct injection and solid‐phase microextraction was developed for the rapid and precise determination of trace volatile sulfur compounds in human halitosis coupled with gas chromatography–flame photometric detection. The active sampling system was well designed and produced for efficiently sampling and precisely determining trace volatile targets in halitosis under the optimized sampling and detection conditions. The analytical method established was successfully applied for the determination of trace targets in halitosis. The limits of detection of H₂S, CH₃SH, and CH₃SCH₃ by direct injection were 0.0140–23.0 μg/L with good recoveries ranging from 82.2 to 118% and satisfactory relative standard deviations of 0.4–9.5% (n = 3), respectively. The limit of detections of CH₃SH and CH₃SCH₃ by solid‐phase microextraction were 2.03 and 0.186 × 10^?3 μg/L with good recoveries ranging from 98.3 to 108% and relative standard deviations of 5.9–9.0% (n = 3). Trace volatile targets in positive real samples could be actually found and quantified by combination of direct injection and solid‐phase microextraction. This method was reliable and efficient for the determination of trace volatile sulfur compounds in halitosis.     

Determination of ultra-micro amounts of sulfur in igneous rocks by spectrofluorimetry using 2-(o-hydroxyphenyl) benzoxazole derivatization and tin(II)-strong phosphoric acid-assisted reduction

A new and very sensitive method was developed for the determination of ultra-micro amounts of sulfur in igneous rock samples. The sulfur compounds in an igneous rock sample are reduced and released in the form of hydrogen sulfide by heating with a tin(II)-strong phosphoric acid (SPA) reagent. The liberated hydrogen sulfide is carried by a flow of nitrogen into a copper(II) absorbing solution to obtain a precipitate of copper(II) sulfide. The remaining copper(II) ion forms a chelate with 2-(o-hydroxyphenyl)benzoxazole (HPB) and quenches the fluorescence of HPB. The amount of sulfide is determined by measuring the HPB fluorescence intensity. The optimum reaction conditions were stoichiometrically investigated. By the present method using 0.1-0.2 g of rock sample, ultramicro amounts of sulfur (0.1-12.8 mug) could be quantitatively separated, collected, and determined with a relative standard deviation of 1.37% for a sample containing 5.7 mug of sulfur (95% confidence level).     

Total sulfur determination in gasoline,kerosene and diesel fuel using inductively coupled plasma optical emission spectrometry after direct sample introduction as detergent emulsions

Herein, we present the development of a procedure for the determination of total sulfur in petroleum-derived products (gasoline, kerosene and diesel fuel) employing inductively coupled plasma optical emission spectrometry (ICP OES). For this procedure, samples were prepared as emulsions that were made using concentrated nitric acid, Triton X-100, sample, and ultra pure water in proportions of 5/10/7/78% (v/v), respectively. Sample volumes were weighed because of the density differences, and oxygen was added to the sheat gas entrance of the ICP OES in order to decrease carbon deposition in the torch and to minimize background effects. A Doehlert design was applied as an experimental matrix to investigate the flow ratios of argon (sheat and plasma gas) and oxygen in relation to the signal-to-background ratio. A comparative study among the slopes of the analytical curves built in aqueous media, surfactant/HNO₃, and by spike addition for several sample emulsions indicates that a unique solution of surfactant in acidic media can be employed to perform the external calibration for analysis of the emulsions. The developed procedure allows for the determination of the total sulfur content in petroleum derivatives with a limit of detection (LOD) and limit of quantification (LOQ) of 0.72 and 2.4 μg g^− 1, respectively. Precision values, expressed as the relative standard deviations (% RSD, n = 10) for 12 and 400 μg g^− 1, were 2.2% and 1.3%, respectively. The proposed procedure was applied toward the determination of total sulfur in samples of gasoline, kerosene, and diesel fuel commercialized in the city of Niterói/RJ, Brazil. The accuracy of the proposed method was evaluated by the determination of the total sulfur in three different standard reference materials (SRM): NIST 2723a (sulfur in diesel fuel oil), NIST 1616b (sulfur in kerosene), and NIST 2298 (sulfur in gasoline). The data indicate that the methodology can be successfully applied to these types of samples. Spiking tests, conducted with the analyzed samples, indicate that recoveries are between 97 and 103%.