Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.     

Construction and validation of automated purge-and-trap-gas chromatography for the determination of volatile organic compounds

An automated purge-and-trap chromatographic system for the determination of dissolved volatile organic compounds in aqueous samples was built in the laboratory with minimum cost both in the construction and routine operation. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. The use of a multi-sorbent bed quantitatively trapped a wide range of volatile organic compounds at ambient temperature, including the extremely volatile ones such as dichlorofluoromethane (CFC-12). Flash heating for rapid desorption and adequate plumbing for minimizing dead volume resulted in excellent chromatographic separation at above-ambient temperatures, which eliminated the need for cryogen for cooling at the head of the column, a second refocusing stage, or entire GC oven for refocusing. This cryogen-free system was tested with standard solutions and environmental samples for determining hydrocarbons with flame ionization detection, and halogenated compounds with electron-capture detection. An innovative method was also developed for validating the system's linearity for extremely volatile compounds. By introducing ambient air, which usually contains constant levels of anthropogenic halocarbons, e.g., CFC-12 and CFC-11 (CCl3F), the need to prepare aqueous standards containing extremely volatile compounds is avoided, hence providing a convenient method for evaluating a purge-and-trap system.     

Development and validation of an automated monitoring system for oxygenated volatile organic compounds and nitrile compounds in ambient air

Few studies were conducted on oxygenated volatile organic compounds (OVOC) because of problems encountered during the sampling/analyzing steps induced by water in sampled air. Consequently, there is a lack of knowledge of their spatial and temporal trends and their origins in ambient air. In this study, an analyzer consisted of a thermal desorber (TD) interfaced with a gas chromatograph (GC) and a flame ionization detector (FID) was developed for online measurements of 18 OVOC in ambient air including 4 alcohols, 6 aldehydes, 3 ketones, 3 ethers, 2 esters and 4 nitriles. The main difficulty was to overcome the humidity effect without loss of compounds. Water amount in the sampled air was reduced by the trap composition (two hydrophobic graphitized carbons—Carbopack B:Carbopack X), the trap temperature (held at 12.5 °C), by diluting (50:50) the sample with dry air before the preconcentration step and a trap purge with helium. Humidity management allowed the use of a polar CP-Lowox column in order to separate the polar compounds from the hydrocarbon/aromatic matrix. The safe sampling volume for the dual-sorbent trap 75 mg Carbopack X:5 mg Carbopack B was found to 405 mL for ethanol by analyzing a standard mixture at a relative humidity of 80%. Detection limits ranging from 10 ppt for ETBE to 90 ppt for ethanol were obtained for 18 compounds for a sampling volume of 405 mL. Good repeatabilities were obtained at two levels of concentration (relative standard deviation <5%). The calibration (ranging from 0.5 to 10 ppb) was set up at three different levels of relative humidity to test the humidity effect on the response coefficients. Results showed that the response coefficients of all compounds were less affected by humidity except for those of ethanol and acetonitrile (decrease respectively of 30% and 20%). The target compounds analysis shows good reproducibility with response coefficient variability of less then 10% of the mean initial value of calibration for all the compounds. Hourly ambient air measurements were conducted in an urban site in order to test this method. On the basis of these measurements, ethanol, acetone and acetaldehyde have shown the highest concentration levels with an average of 2.10, 1.75 and 1.37 ppb respectively. The daily evolution of some OVOC, namely ethanol and acetaldehyde, was attributed to emissions from motor vehicles while acetone has a different temporal evolution that can be probably associated with remote sources.     

An automated instrument for human STR identification: design, characterization, and experimental validation

The microfluidic integration of an entire DNA analysis workflow on a fully integrated miniaturized instrument is reported using lab‐on‐a‐chip automation to perform DNA fingerprinting compatible with CODIS standard relevant to the forensic community. The instrument aims to improve the cost, duration, and ease of use to perform a “sample‐to‐profile” analysis with no need for human intervention. The present publication describes the operation of the three major components of the system: the electronic control components, the microfluidic cartridge and CE microchip, and the optical excitation/detection module. Experimental details are given to characterize the level of performance, stability, reliability, accuracy, and sensitivity of the prototype system. A typical temperature profile from a PCR amplification process and an electropherogram of a commercial size standard (GeneScan 500?, Applied Biosystems) separation are shown to assess the relevance of the instrument to forensic applications. Finally, we present a profile from an automated integrated run where lysed cells from a buccal swab were introduced in the system and no further human intervention was required to complete the analysis.     

Rewiring chemistry: algorithmic discovery and experimental validation of one-pot reactions in the network of organic chemistry

Computational algorithms are used to identify sequences of reactions that can be performed in one pot. These predictions are based on over 86?000 chemical criteria by which the putative sequences are evaluated. The "raw" algorithmic output is then validated experimentally by performing multiple two-, three-, and even four-step sequences. These sequences "rewire" synthetic pathways around popular and/or important small molecules.     

微扰分子轨道法在有机化学中的应用

经Dewar, Hoffmann, Epiotis, Houk, Wolfe和Kost等理论化学家的努力,PMO理论已经成为研究影响分子构型、构象和(立体专一性和区域专一性)反应产物的结构因素的一个有效的手段。Epiotis的非键轨道作用理论已经使有机化学家认识到, 一个拥挤的构象或过渡态不一定是一个能量上不利的状态。π轨道作用的分析表明, 共轭基团间的作用在本质上是相斥的, 全平面构象不是共轭效应最大的构象。WSW-like法不仅为定量PMO法提供了一组完整的、具有正确集据数的轨道基组, 而且它还成功地将轨道作用能转化为原子作用能。     

扫描隧道显微镜在有机化学中的应用

扫描隧道显微镜的最大优点是可达到原子量级的分辨率。本文综述了STM对有机分子的结构、聚集形态及其反应过程的研究。     

Optimization and validation of an automated voltammetric stripping technique for ultratrace metal analysis

A new automated batch method for the determination of ultratrace metals (nanogram per liter level) was developed and validated. Instrumental and chemical parameters affecting the performance of the method were carefully assessed and optimized. A wide range of voltammetric methods under different chemical conditions were tested. Cadmium, lead and copper were determined by anodic stripping voltammetry (ASV), while nickel, cobalt, rhodium and uranium by adsorptive cathodic stripping voltammetry (AdCSV). The figures of merit of all of these methods were determined: very good precision and accuracy were achieved, e.g. relative percentage standard deviation in the 4-13% for ASV and 2-5% for AdCSV.The stripping methods were applied to the determination of cadmium, lead, copper, nickel, cobalt, rhodium and uranium in lake water samples and the results were found to be comparable with ICP-MS data.     

Construction and calibration of an instrument for three-dimensional ion imaging

We describe a new instrument based on a delay-line detector for imaging the complete three-dimensional velocity distribution of photoionized products from photoinitiated reactions. Doppler-free [2+1] resonantly enhanced multiphoton ionization (REMPI) of H and D atoms formed upon photolysis of HBr and DBr in the range 203 nm < or = lambda photolysis < or = 243 nm yields radial speeds measured to be accurate within 1% of those calculated. The relative speed resolution is about 5% and limited by photoionization recoil broadening. A relative speed resolution of 3.4% is obtained for [3+1] REMPI, which minimizes the ionization recoil. We also determine the branching ratio between ground-state and spin-orbit-excited product channels and their associated anisotropies. We find that DBr photolysis dynamics differs slightly from its HBr counterpart.     

A microfluidic flow chemistry platform for organic synthesis: the Hofmann rearrangement

We report on the use of commercially available chemical microreactors to effect the Hofmann rearrangement of aromatic amides to the corresponding carbamates.     

高通量、自动化蛋白质结晶筛选技术以及相关仪器的研究进展

基于X射线晶体学的蛋白质结构解析主要依赖于大规模结晶条件筛选获得的高衍射分辨率的蛋白质晶体。近年来,自动化、高通量的液体操控技术和相关仪器的快速发展为蛋白质结晶筛选提供了高效、可靠的研究手段,显著推动了蛋白质结构生物学的研究。文章综述了蛋白质结晶筛选的自动化液体处理技术的发展,包括移液器、注射泵、同步纳升定量吸取注射、喷墨打印、超声喷射以及微流控等技术。文章详细介绍了各技术所对应的典型商品化仪器及其在蛋白质结晶筛选中的应用。此外,文章还介绍了集成多孔板的储存和操控、编码扫描、环境控制和软件管理等诸多功能的一体化液体操纵平台。     

Development of an automated monitoring system for various gas-phase organic carbonyls in ambient air

An automated monitoring system for various C₁ to C₅ gas-phase organic carbonyls in ambient air is described. The system consists of a parallel plate diffusion scrubber (PPDS), which is coupled with a high-performance liquid chromatography–ultraviolet (HPLC–UV) system using an automated injection valve. Compared with an annular diffusion scrubber (DS) employed so far for gas-phase carbonyl monitoring, PPDS shows an improved collection efficiency for formaldehyde, acetaldehyde, propionaldehyde, and acetone with >97% at an airflow rate of 0.5?L/min. High gas–liquid concentration ratios of PPDS and an optimised HPLC–UV system allow limits of detection (LOD) in a range of 80–500?pptv. A low liquid hold-up volume of the PPDS results in a short response time of about 10?min. Additionally, the optimised analysis time for 13 carbonyl compounds containing calibration standard enables brief measurement intervals of 25?min. The developed PPDS–HPLC system shows its reliability from urban site monitoring in Seoul, South Korea.     

Collaborative validation of the quantification method for suspected allergens and test of an automated data treatment

Previous publications investigated different data treatment strategies for quantification of volatile suspected allergens by GC/MS. This publication presents the validation results obtained on "ready to inject" samples under reproducibility conditions following inter-laboratory ring-testing. The approach is based on the monitoring of three selected ions per analyte using two different GC capillary columns. To aid the analysts a decisional tree is used for guidance during the interpretation of the analytical results. The method is evaluated using a fragrance oil concentrate spiked with all suspected allergens to mimic the difficulty of a real sample extract or perfume oil. At the concentrations of 10 and 100mg/kg, imposed by Directive 76/768/EEC for labeling of leave-on and rinse-off cosmetics, the mean bias is +14% and -4%, respectively. The method is linear for all analytes, and the prediction intervals for each analyte have been determined. To speed up the analyst's task, an automated data treatment is also proposed. The method mean bias is slightly shifted towards negative values, but the method prediction intervals are close to that resulting from the decisional tree.