Monitoring of Polychlorinated Biphenyls in Surface Water Using Liquid Extraction,GC/MS,and GC/ECD

Abstract

A rapid and reliable analytical method, at trace level concentration was developed and validated for monitoring polychlorinated biphenyls (PCBs) in Jordanian surface water. The method combines the advantage of liquid extraction together with gas chromatography‐mass spectrometry (GC/MS) and gas chromatography‐electron capture detector (GC/ECD). The performance of the method was evaluated by analyzing certified reference material (CRM) of the analytes and applied on real water samples collected from different sites in Jordan. A mixture of 60∶40 dichloromethan‐petroleum ether was chosen as a convenient binary solvent for liquid–liquid extraction. The GC conditions for GC/MS were optimized using He as a carrier gas, temperature programming, and chlorpropham as an internal standard (IS).

The conditions for GC/ECD were performed using N₂ gas and a temperature program from 160 to 280°C with different increasing rates. The method of GC/MS in the selective ion mode (SIM) gave linear relationships for all PCBs tested between 0.60–6.0 µg/l with R ²=0.9934 (n=7×18). Recoveries from spiked water samples ranged between 87.6 and 91.4%. The mean accuracy and precision obtained were 4.9% and 2.16%, respectively. The mean of detection limit was 0.14±0.04 µg/l. In GC/ECD, linear relationships for all PCBs examined over the range of 0.3–2.4 µg/l was verified as characterized by a linear regression equation and correlation coefficient, R ²=0.9915 (n=12). The average precision and accuracy were 4.86% and 5.21%, respectively. Analyses results clarified that none of the examined Jordanian water samples contained any of the searched for PCBs within the detection limit achieved.     

Quantitation Of The Local Anesthetic Dibucaine With Gas Chromatography / Mass Spectrometry

Abstract

A chemical ionization and an electron impact GC/MS assaying approach is presented for determining dibucaine concentrations in biological fluids. Both use deuterium-labeled drug as the internal standard and rely on the same sample extraction and sample preparation procedure. Under chemical ionization conditions (CH₄), the assaying limits are in the range of 1–80 ng/ml of serum. Under electron impact conditions, the analytical range is 20–800 ng/ml. The chemical ionization procedure has been found suitable for monitoring drug levels in man. One volunteer, who received a single 5-mg oral dose, showed peak serum drug concentrations of 23 ng/ml attained 2 hr after drug administration. The biologic half-life (ß phase) was 11 hr.     

New Approaches to Chemical Sensing‐Sensors Based on Polymer Swelling

Abstract

Although there is an extensive literature on polymer swelling, only in recent years has work been performed to exploit this phenomenon for chemical sensing. The lifetime of most sensors based on polymer swelling is limited by delamination of the polymer film. Swelling and shrinking introduce a shear force at the sensor/polymer interface that eventually severs the covalent bonds holding the polymer layer onto the substrate. This is a problem for any sensor configuration that involves immobilization of a swellable layer on a rigid substrate. Recently, sensor platforms have been developed to address this problem. Furthermore, coupling polymer swelling to optical, magneto, and electrochemical transduction technologies has greatly increased the scope of applications for sensors based on swellable polymers.     

SEC‐MR‐NMR: Online Coupling of Size Exclusion Chromatography and Medium Resolution NMR Spectroscopy

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC‐MR‐NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table‐top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online ¹H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. ¹H NMR spectra of PMMA and PS homopolymers as well as PS‐PMMA block copolymers were of sufficient quality to enable detection and de‐formulation of unknown polymer compounds. ¹H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC‐MR‐NMR combination.

     

相位敏感光时域反射分布式光纤传感技术

由于散射光的相位变化对外部扰动极其敏感,相位敏感光时域反射(Φ-OTDR)技术具有高响应速度、超高灵敏等特点。相比现有的其他分布式光纤传感技术,Φ-OTDR技术在环境适应性与光缆布设的便捷性方面有明显的优势。本文介绍Φ-OTDR系统的原理、结构、性能及应用情况,并对其发展趋势进行展望。     

基于在线评论和前景效用的商品等级评价及选择方法

商品属性或特征的在线评论对消费者选择商品产生重要影响,现有方法尚未关注商品级别和消费者的有限理性问题。为此,本文提出在线评论中基于前景理论的商品选择方法。首先,描述了依据在线评论的商品选择问题;然后,定义商品关于属性值级别隶属度,进而计算级别正理想点和负理想点;其次,以正理想点和负理想点为参考点,计算各个商品的前景综合级别特征值,据此提出基于二元语义的商品等级评价与选择方法。最后,通过一个商品选择案例说明该方法的有效性和合理性。     

Ammonia monitoring at trace level using photoacoustic spectroscopy in industrial and environmental applications

An ammonia traces analyser based on photoacoustic spectroscopy is described. The system uses a CO(2) laser and a properly designed resonant photoacoustic cell to achieve ammonia detection at sub-parts-per-billion (ppb) level. The instrument features unattended automatic on-line monitoring of ammonia with a detection limit of 0.1 ppb. Interferences from atmospheric CO(2) and H(2)O are efficiently suppressed by a careful selection of the laser wavelength and a compensation of the water vapour signal made with a high-precision hygrometer. The cell design enables continuous measurement at high flow rates (up to 5 l/min), which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces. Various examples of applications of the instrument in the semiconductor industry and for atmospheric pollution monitoring are presented. They demonstrate the excellent performances of the system and its suitability for these applications.     

Online Copper Removal for Selenium Determination by Hydride Generation–Inductively Coupled Plasma Optical Emission Spectrometry

Abstract

Selenium determination in samples with a high copper content by hydride generation–inductively coupled plasma optical emission spectrometry (HG‐ICP‐OES) after online copper removal and selenium (VI) reduction is described. An activated carbon minicolumn was used for the retention of copper and its subsequent separation of Se. Se(VI) was then online reduced by heating into a PTFE coiled reactor with 12 M HCl. The analyte was introduced into a water stream containing sodium tetrahydroborate (NaBH₄) in order to generate selenium hydride (H₂Se). The detection limit (DL) obtained was 0.8 µg L^?1, and the precision, expressed by the relative standard deviation (RSD), was 2.5% (n=10; 10 µg L^?1 selenium level). The current method was applied to the Se determination in two copper reference materials, MBH‐39DK 3601 (with a Se content of 90 mg kg^?1) and MBH‐39 DK 3604 (with a Se content of 15 mg kg^?1).     

In situ monitoring of styrene polymerization using Raman spectroscopy. Multi‐scale approach of homogeneous and heterogeneous polymerization processes

Free radical polymerization of styrene was monitored in situ by combining Raman spectroscopy to other experimental techniques (gravimetry and rheology). Three different processes were investigated: bulk, emulsion and miniemulsion polymerization. A complete analysis of the evolution of Raman spectrum during the course of reaction showed that a lot of information about molecular dynamics could be extracted and related to chemical phenomena. In addition, we report for the first time the coupling of Raman spectroscopy to a rheometer in order to monitor styrene bulk polymerization both at the scale of chemical bonds and at the scale of macroscopic phenomena (viscosity variation). Copyright © 2013 John Wiley & Sons, Ltd.     

Preproduction prediction of the optical normalized reflectance transient of MOVPE-grown AlGaAs films using transfer matrix method

This paper reported on the prediction and analysis of the optical normalized reflectance (NR) transient of AlGaAs multi layers and Distributed Bragg Reflector (DBR) using transfer matrix method (TMM). The simulation result correlated well with the measured NR transient of grown samples. Deviations of Al_xGa_1?xAs composition between the expected and real grown sample were predicted successfully. Smaller optical oscillation amplitude in the first DBR layer was predicted and could be used as an indication of Al composition. Special characteristics of NR transient within the first three pairs of DBR were also clarified using the calculated transmissivity changing with the growth thickness. TMM simulation of NR transient was thus shown to be a convenient and reliable pre-production technique, also not restricted to the AlGaAs material.