Dynamic headspace enrichment/reinjection for open tubular GC/FTIR analysis of volatiles in polymers

An analytical system for the analysis of volatiles entrained in polymers is described. This system is based on a thermal desorption oven connected to a cold trap. After enrichment of headspace vapor, trapped material is reinjected and analyzed by open tubular gas chromatography/Fourier transform infrared spectroscopy, OTGC/FTIR. The thermal desorption oven is designed to provide different modes of sample introduction: use of a pyroprobe; insertion of a piece of quartz tubing with applied sample; or syringe injection. Headspace enrichment is carried out in a piece of fused silica capillary tubing filled with glass beads. The trap may be cooled either electrically using Peltier elements or with liquid nitrogen. A six-port rotary valve is used for flow switching between enrichment and reinjection modes. All system parameters, temperatures, and timed events, are controlled from the gas chromatograph. Dynamic headspace analysis is demonstrated as a method for polymer characterization.     

The evaluation of recovery rate associated with the use of thermal desorption systems for the analysis of atmospheric reduced sulfur compounds (RSC) using the GC/PFPD method

In this work, the recovery rate (RR) of preconcentration technique was examined using a combination of the Peltier cooling (PC) and thermal desorption (TD) system for the gas chromatographic (GC) analysis of reduced sulfur compounds (RSC) in air. The possible loss or gain of analytes resulting from the use of the PC/TD system was estimated by analyzing equimolar standards (10 ppm) of four S compounds including H₂S, CH₃SH, DMS, and DMDS in two different manners: (1) by injecting directly the four S compounds into the GC via injector and (2) by introducing them through the PC/TD system. When a series of tests were conducted on different types of gas media (ultrapure air versus N₂) and across varying relative humidity (RH), it was found that the RR values for the four S compounds vary from 80 to 110% range. The overall results of our study thus indicate that the RR for the PC/TD system is fairly good and that subtle differences in their RR values may reflect the combined effects of different factors investigated in this study such as types of gas media, RH change, and properties of target analytes (e.g., recovery rate of the least (H₂S) versus the highest compound (DMDS)).     

On the suitability of Peltier cooled Si-PIN detectors in transmission experiments

The performance of a Peltier cooled Si-PIN detector is compared with that for a Freolectric cooled Si(Li) detector, references being made to transmission experiments that evaluate total cross sections at low photon energies. The results of these measurements are discussed.     

Improved real-time puff-by-puff GC-MS system for whole smoke analysis

An automated puff-by-puff mainstream smoke (MSS) system is developed to monitor real-time whole smoke in mainstream cigarette smoke using gas chromatography (GC)-mass spectrometry (MS). The whole-smoke analysis is based on automated sample collection and injection into the GC-MS system. The important feature of this system is the real-time rapid analysis that is simple, sensitive, precise, flexible, and exhibits low carryover of volatile and semivolatile smoke constituents. The system is equipped with an automated sampling and switching valve and a smoking machine. The key improvements of the system, as compared with current and alternative methodologies, include minimizing variations caused by operator sampling techniques, the real-time analysis of MSS, the detection of flavorants in MSS from a single puff of cigarette smoke, the ability to analyze numerous smoke constituents from either whole smoke or the gas phase of a single puff, the ability to monitor a few selected smoke constituents in whole smoke using multiple puffs, and its good feasibility compared with solvent extraction and impinger trapping procedures for volatile organic compounds in MSS. System configuration and sampling methodologies are described. Sensitivity, flexibility, precision, feasibility, carryover, and applications of the system are discussed.     

A high performance liquid chromatography – inductively coupled plasma-mass spectrometry interface employing desolvation for speciation studies of platinum in chemotherapy drugs

A novel interface between high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS) is described. The eluent from the HPLC is nebulised into a heated cyclone spray-chamber and the solvent removed using a Nafion membrane drier, held at 75 degrees C, and a cryogenic condenser. The condenser consists of 6 Peltier heat pumps connected to liquid cooled aluminium blocks. At a nebuliser gas flow rate of 0.6 l min(-1), the membrane drier removes 58% of the vapour and the Peltier condenser 75% of the remaining vapour, i.e. a total desolvation efficiency of 89%. This enables the use of HPLC solvents which otherwise would destabilise the ICP, e.g. 100% acetonitrile or methanol, and permits the use of solvent gradients with minimal baseline drift. The system has been applied to the determination of platinum species in an organoplatinum drug used for chemotherapy in human plasma ultrafiltrate of patients treated with this new drug (JM-216). The limit of detection for platinum species has been 0.6 ng nl(-1) (i.e. 120 pg of Pt) and several species have been separated with good resolution.     

Combining membrane extraction with mobile gas chromatography for the field analysis of volatile organic compounds in contaminated waters

A mobile gas chromatographic device (Airmobtx HC 1000 monitor manufactured by Airmotec, Germany), originally designed for the analysis of benzene, toluene, ethylbenzene and xylenes (BTEX) in air, was connected to a flow cell for dynamic membrane extraction. Volatile organic compounds (VOCs) diffuse out of a water stream through a hollow fibre, are enriched onto sorption tubes integrated in the mobile device, and are then thermally desorbed and analysed by gas chromatography-flame ionisation detection. Battery operation of the device enables continuous on-site analysis of VOCs. Influences of the water flow-rate on system response and memory effects were investigated. The linear range of the method depends on the flow-rate of the water sample and did not exceed two orders of magnitude. The detection limits for trichloroethene, chlorobenzene and the BTEX compounds were found to be between 0.1 and 1.0 microg/l using a water flow-rate of 30 ml/min. Dynamic membrane extraction combined with the mobile gas chromatographic device was used for the on-site analysis of contaminated waters in the area of Leipzig.     

Advances in coupling a commercial total organic carbon analyser with an isotope ratio mass spectrometer to determine the isotopic signal of the total dissolved nitrogen pool

A new method has been developed to analyse 15N of the total dissolved nitrogen (TDN) pool. The method operates on a commercial total organic carbon (TOC) analyser coupled to an elemental analyser/isotope ratio mass spectrometer (EA-IRMS). Nitrogen compounds are combusted to nitric oxide (NO) and nitrogen dioxide (NO2) by high-temperature catalytic oxidation (HTCO), after which the NOx gas is transferred to an EA-IRMS for isotopic nitrogen analysis. The system is described, including five modifications of the system in order to overcome analytical problems. First, flow paths were modified to run both systems on helium as carrier gas, while complete sample oxidation was maintained. Secondly, the catalyst structure was adapted to allow high injection volumes at the given backpressures delivered by the EA system. Thirdly, we installed a Permapure dehumidification system as the standard Peltier element did not satisfy dehumidification requirements. Finally, we prevented the inflow of atmospheric nitrogen into the system. In a final stage, we are planning to automate the coupled system in order to run a continuous batch of up to 60 samples. We have obtained satisfactory results on the accuracy and precision of 180+/-1 per thousand potassium nitrate samples (IAEA, USGS-32). Running a batch of five samples resulted in a mean isotopic value of 178.8 per thousand with a standard deviation of 2.8 per thousand. Some important issues could not yet be addressed here, and will have to be evaluated once the system is running on a continuous base. However, the results appear promising and this system has the potential to become a method for TD15N analysis. An appropriate TD15N analysis method might open new challenges in aquatic and terrestrial ecosystem nitrogen studies, including a more comprehensive study of the dissolved organic nitrogen pool.     

Radio gas chromatography on capillary columns using a multi-column system (column-switching)

Summary A gas chromatographic system with capillary columns (fused silica) for the analysis of radiolabelled compounds is described. The system presented is based on a dual column gas chromatograph equipped with column switching facllity and a variable splitter at the column outlet combined with a dead-volume free adapter for the radioactivity monitor for continous measurement of radioactivity in the column effluent. The first column works as a separation column and the second is roughly shortened and used as a feed to the mass detector. The adjustment of the split ratio is regulated by the inlet pressures for the carrier gas supplying both columns. For mass detection all conventional systems can be used. Detection of radioactivity by a gas proportional counter (system based on a combustion technique). Three flow modes can be adjusted: a) total column effluent to the mass detector or b) to the radioactivity monitor, and c) simultaneous flow (dependent on the chosen split ratio) to mass-and radioactivity detectors. The system was developed for use in clinical chemistry and tested with labelled and unlabelled steroids. The method for peak identification by means of relative retention times and methylene units was possible also for radioactive peaks when a heart cutting technique was used. The radio gas chromatographic system presented allows the development of radiochromatograms with the same peak characteristics as in conventional capillary gas chromatography.Presented at the 14th International Symposium on Chromatography London, September, 1982     

The effect of cold trap adsorbents on the gas chromatographic analysis of ambient VOCs under Peltier cooling conditions

In this work, the relative analytical performance of the GC-based detection method was investigated with a major focus on cold trap (CT) adsorbent materials against four aromatic volatile organic compounds (VOCs) (e. g., benzene, toluene, xylene, and styrene). A series of calibration experiments were hence conducted under cryofocusing conditions formed by the Peltier cooling system in a thermal desorber (TD) unit. During the course of this study, comparative calibration datasets were acquired for each of the three CT types: (i) CT (I) = Carbopack B + Carbopack C, (ii) CT (II) = Carbopack B + Carboxen 1000, and (iii) CT (III) = Tenax TA. All calibration datasets were obtained under subambient temperature (-10 degrees C) conditions controlled by the Peltier cooling system. The reliability of the calibration data was also assessed in an ancillary experiment with the aid of the modified injection through a thermal desorber (MITD) method. The results demonstrated that the GC detection properties of different VOCs were not altered significantly between different CT applications under Peltier conditions, although relative sensitivity could be distinguished moderately depending on the CT type.     

Identification of Non‐Faradaic Processes by Measurement of the Electrochemical Peltier Heat during the Silver Underpotential Deposition on Au(111)

We measured the heat which is reversibly exchanged during the course of an electrochemical surface reaction, i.e., the deposition/dissolution of the first two monolayers of Ag on a Au(111) surface in (bi)sulfate and perchlorate containing electrolytes. The reversibly exchanged heat corresponds to the Peltier heat of the reaction and is linearly related to its entropy change, including also non‐Faradaic side processes. Hence, the measurement of the Peltier heat provides thermodynamic information on the electrochemical processes which is complementary to the current–potential relations usually obtained by conventional electrochemical methods. From the variation of the molar Peltier heat during the various stages of the deposition reaction we inferred that co‐adsorption processes of anions and Ag do not play a prominent role, while we find strong indications for a charge neutral substitution reaction of adsorbed anions by hydroxide, which would not show up in cyclic voltammetry.     

Outgassng of polymers by thermal-desorption gas chromatography/fourier-transform infrared spectrometry

Applicatons of on-line thermal-desorption gas chromatography/Fourier-transform infrared spectroscopy are described for the evaluation of outgassing phenomena of polymers. Details of the experimental configuration and system operation are given. Examples discussed are degradation products in a dimethylsiloxane rubber, trioxane formation in polyacetal production, and monomers and additives in poly(methyl- methacrylate). The detection limits are in the μg g^?1 range for 100-mg samples.     

Synthesis of Organic Compounds from Mixtures of Methane with Carbon Dioxide in Dielectric-Barrier Discharges at Atmospheric Pressure

The entire range of gas phase reaction products, depending on the composition of initial binary mixtures of methane and carbon dioxide in dielectric barrier discharges, has been determined (saturated as well as unsaturated hydrocarbons and oxygenated organic compounds). The macro-kinetics of the basic chemical pathways of the system under consideration has been investigated. This system is found to display a strong feedback effect (positive or negative, depending on the initial state of the surfaces, as well as the chemical composition of the feed-gas mixture). It is demonstrated that these properties undergo significant changes during operation, due to surface modification processes (polymer film deposition, its oxidation or reduction). They are found to exert a considerable influence on the chemical efficiency of the discharge (for example, on the absolute and relative chemical yields of the reaction products), the Lissajous figures appear to be a sensitive tool to monitor the operation conditions of the discharge.     

三通道气相色谱法监测大气中CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)北大核心CSCD

我国正处于“碳达峰、碳中和”的关键时期,准确认识我国温室气体浓度时空格局以及变化对于评估“碳达峰”和“碳中和”行动成效非常重要。当前我国近地面温室气体高精度监测主要依赖进口的光学监测主机,单台仪器成本高且监测要素有限。为此,该研究基于传统的气相色谱法,自主设计了一套三通道气相色谱分析系统,在单台仪器上实现了5种主要长寿命温室气体(CH_(4)、CO、CO_(2)、N_(2)O和SF_(6))的高精度监测。对该系统的精密度、线性响应情况和准确度进行的针对性测试实验表明系统检测性能满足世界气象组织/全球大气观测(WMO/GAW)质控标准。针对环境浓度的CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)的连续分析精密度分别达0.08%、1.90%、0.05%、0.08%、0.66%。准确度测试中,5种气体(CH_(4)、CO、CO_(2)、N_(2)O和SF_(6))使用回归方程计算所得值与标称摩尔分数间的偏差分别达0.15×10-9、0.20×10-9、0.37×10-6、0.35×10-9、0.02×10-12(摩尔分数),CH_(4)、CO、CO_(2)、N_(2)O和SF_(6)仪器响应值与标称摩尔分数的线性拟合相关系数(R2)均为0.9999,线性拟合残差和准确度基本达到WMO/GAW拓展质控目标。该系统对杭州城区大气温室气体在线连续监测结果显示,2021年5~7月期间大气CH_(4)、CO、CO_(2)和N_(2)O呈明显的日变化特征,主要受人为活动影响。综合测试和试运行结果表明,该研发系统具备良好的精密度、准确度、线性和稳定性,与目前国内广泛进口的仪器相比,具有技术自主可控、运行成本更低、自动化水平更高等优势,能满足多种温室气体在线监测研究的需求。     

Ionization potential of clusters in liquids

Time-resolved observations of the fast electron transfer from an electron donor to metal ions adsorbed on metal clusters in solution have shown that a critical size of the cluster is required to make it capable of accepting electrons. The threshold is attributed to a size dependent redox potential of the cluster, increasing with the nuclearity (in contrast with the ionization potential in the gas phase which decreases when n increases): it corresponds to the nuclearity for which the cluster redox potential becomes more positive than the potential of the electron donor acting as a monitor.New data of redox potentials (or IP) of Ag_n clusters (hydroquinone as monitor) and Cu_n cluster (sulfonatopropylviologen anion as monitor) are derived. The influence of n and of the solvation or the ligand is discussed.     

On-line monitoring of traces of aromatic-, phenolic- and chlorinated components in flue gases of industrial scale incinerators and cigarette smoke by direct-inlet laser ionization-mass spectrometry (REMPI-TOFMS)

The combination of laser induced resonance-enhanced multiphoton ionization (REMPI) and time-of-flight mass spectrometry (TOFMS) represents a highly selective as well as sensitive analytical technique, well suited for species selective real-time, on-line monitoring of trace-gases. Results presented are obtained with a newly designed, mobile REMPI-TOFMS instrument, optimized for field applications. The mobile REMPI-TOFMS device either is equipped with a compact excimer laser (KrF, λ = 248 nm) or a small Nd:YAG laser (forth harmonic frequency, λ = 266 nm). A special effusive molecular beam inlet system was used, which allows direct inlet of flue gases from e.g. waste incinerators without memory effects for compounds of a molecular weight of up to 260–280 amu. Detection sensitivities in the sub-ppb region are achieved under field measurement conditions. Applications concerning on-line monitoring of combustion byproducts and fuel components are presented. This includes on-line analysis of polycyclic aromatic hydrocarbons (PAH) in the flue gas of a 0.5 MW waste incineration pilot plant, headspace analysis of wood gasification products and crude oil composition (fuel analysis) as well as highly time resolved (single puff resolution) on-line analysis of cigarette smoke. The application of the on-line REMPI-TOFMS monitor for continuous analysis of dioxin indicators in the flue gas of e.g. hazardous waste incinerators is discussed. Received: 25 September 1998 / Revised: 7 December 1998 / Accepted: 10 December 1998     

X-ray Peltier cooled detectors for X-ray fluorescence analysis

The recent results on development of X-ray Si(Li), Si-planar and CdTe p-i-n detectors cooled by Peltier coolers for fabrication of laboratory and portable XRF analysers for different applications are discussed.

Low detection limits of XRF analysers are provided by increasing of detectors sensitive surface; improvement of their spectrometrical characteristics; decreasing of front-end-electronics noise level; Peltier coolers and vacuum chambers cooling modes optimization.

Solution of all mentioned tasks allowed to develop Peltier cooled detectors with the following performances:

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Advantages and disadvantages of all types of detectors for X-ray fluorescence analysis are compared. Spectra are presented. Application of different XRF analysers based on developed detectors in medicine, environmental science, industry, cryminalistics and history of art are demonstrated.     

Mass Transport of β-Diketonate Precursors for MOCVD of YBa_2Cu_3O_(7-δ) High T_c Superconducting Thin Films

IntroductionSoonafterthediscoveryofhighT.supercoducting(HTSC)oxides,metalor-ganicchemicalvapourdeposition(MOCVD)wasproposedforpreparingtheirthinfilms[1j.Asgenerallyacceptedtoday['J,thistechniquehasdemonstrateditssuperioradvantagesinmakinglargeareahighqualityHTSCthinfilmsandwillplayamajorroleintheadvanceofdeviceapplicationofHTSCthinfilmsoverthenextfewyears.TheprecursorsusedinMOCVDforpreparinghighT.superconductingthinfilmsaremostlymetalbeta-diketonates.Theyaresolidsatroomtemperatureand…     

Application of a system suitability test for quality assurance and performance optimisation of a gas chromatographic system for pesticide residue analysis

In pesticide residue analysis, screening for over 150 compounds has to be performed on a daily basis. As part of the quality control measures it is crucial to verify that the chromatographic system fits the purpose, or if any deterioration occurred during its previous use. The operation conditions of the chromatographic system can be best monitored with properly selected system suitability test (SST) mixtures, which provide information with one injection on the characteristic performance parameters of the whole system from the injector to the detectors. We developed SST mixtures that are also suitable for use with electron-capture, nitrogen-phosphorus and pulse flame photometric detectors. These SST mixtures were applied over 3 years to monitor the system performance parameters, such as the number of effective theoretical plates, resolution, asymmetry, detection limit and selectivity. The applicability and advantages of these tests are illustrated and discussed.     

Polar solvents for the desorption of a liquid chromatographic precolumn coupled on-line with a capillary gas chromatograph

Coupling column liquid chromatography and gas chromatography on-line is becoming more important in analytical chemistry. Especially when large amounts of polar solvents can be introduced into the gas chromatograph without any problem, the technique will offer new possibilities. With a DPTMDS retention gap, evaporation rates and flooded zones of some solvents have been determined. Two modes of operation using partially concurrent solvent evaporation conditions are discussed: (1) injecting a sample via a loop of an LC valve followed by introduction into the gas chromatograph with an LC pump; (2) trace enrichment on a precolumn followed by on-line desorption with n-propanol into the gas chromatograph. Preliminary results for a splitter system, inserted between the retention gap and the analytical column which allows a considerable increase of the evaporation rate are also presented.