Identification of pesticide residues in real matrices by combining retention indices and specific multidetection responses

A previous paper reported the possibility of using the ratio between the responses of two different specific detectors to a single compound (detector response ratio, DRR) as an identification criterion for that compound, in combination with its retention index. This article gives some applications of DRR in the identification of some pesticides in four different fruits (apples, apricots, strawberries, and peaches) in a range varying from 0.02 to 1.3 ppm, by means of their ECD/FPD DRRs. After clean-up GC analyses were performed on a single column with dual parallel detection; a personal computer system was used for data analysis.     

Effect of ammonia on the response of the electron capture detector (ECD)

The effect of ammonia on the electron capture detector (ECD) response has been investigated. Nitrogen with different ammonia concentrations (5–20%) was used as make-up gas. Compared to pure nitrogen, the ECD response decreased when the ammonia concentration in the make-up gas was 5%. However, the response increased when the ammonia concentration was 20%. The response factor of 4-chlorophenol increased 4 fold when ammonia was 20%. Also, di- and tri-chlorophenols increased by 30–50%. The nitroaromatic compounds responses increased by about 2–3.7 times with 20% ammonia in the make-up gas. The signal-to-noise (S/N) increased when 20% ammonia in nitrogen was used as make-up gas compared to pure nitrogen. Also, the detector linearity increased by 50% with ammonia.     

Characterization of Semtex by supercritical fluid extraction and off-line GC-ECD and GC-MS

Researchers using electron capture for the detection of explosive vapors currently claim the ability to detect the presence of RDX in Semtex – a plastic explosive comprising hexahydro-1,3,5-trinitro-1,3,5-triazane (RDX) in a matrix of styrene-butadiene copolymer and hydrocarbon oil. The vapor pressure of RDX at room temperature is 0.006 ppb, and therefore well below the detection limit of electron capture detection (ECD). The positive response generated by ECD is, consequently, not from the presence of RDX, but from some other component. This paper describes the extraction and identification of several compounds in Semtex, along with the determination of which is responsible for the positive response of an ECD-based detector. From the results of supercritical fluid extraction and off-line gas chromatography combined with electron capture and mass spectrometric detection, it has been concluded that ethylene glycol dinitrate is the component responsible for the positive ECD response. This conclusion is based on the requirements necessary for ECD detection, i.e. electronegativity, and a sufficient vapor pressure. The other compounds present were eliminated as possible choices because they either can not be detected by an ECD or do not have sufficient vapor pressure under ambient conditions.     

Electron capture detector performance parameters in view of the response presentation forms

Summary Four most frequently used presentation forms of the ECD response are described. Equations describing the dependence of the sensitivity, linearity and minimum detectable concentration of the ECD working under constant frequency mode of operation on the pulse period are derived from Wenthworth’s kinetic model for all four forms mentioned above. The forms presented are compared on the basis of equations derived. Results of the calculations are given and some predictions are experimentally tested for sulphur hexafluoride. Good agreement was found between the predicted and observed relationships. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Analysis of polynuclear aromatic hydrocarbons by glass capillary gas chromatography using simultaneous flame ionization and electron capture detection

The possibility of simultaneous application of an electron capture (ECD) and a flame ionization detector (FID) connected to a glass capillary column for analyzing polynuclear aromatic hydrocarbons (PNA) has been investigated. The ECD/FID ratio is determined for 46 PNA compounds. The ratios vary from 0.02 to 117 with relative standard deviations better than 20 percent determined from 10 replicate analyses. The results suggest that the method may be used for obtaining additional evidence in identifying PNA in environmental samples. Impurities and transformation products in the standard were identified by computerized glass capillary gas chromatography/mass spectrometry. Quinones and diones are responsible for the high EC-response determined in some trace components in the standard. An application of the method is shown for PNA from particulates in urban atmospheres.     

高效液相色谱-喷壁/薄层安培检测器用于同时测定5种环境优先污染酚

结合传统的喷壁式和薄层式安培检测器,制备了一种新型的喷壁/薄层安培检测器。 联合高效液相色谱（HPLC）同时对5种环境优先污染酚进行了检测。 实验发现,安培检测工作电极面积的增大会导致响应电流的增大,但同时也会增大噪声,因此,基于信噪比优化电极面积是重要的。 选用色谱柱SHIM-PACK VP-ODS（150 mm×4.6 mm）,流动相V（甲醇）∶V（0.1 mol/L PBS,pH=7.5）=40∶60,柱温40 ℃,流速1 mL/min,进样量20 μL,安培检测电位为1.0 V,紫外检测波长为220 nm,喷壁-薄层安培检测器不经富集对对硝基酚、苯酚、间甲酚、2,4-二氯苯酚和2,4,6-三氯苯酚共5种酚类物质的检测下限均低于1 μg/L(S/N=3),优于相同条件下的紫外检测器和商品电化学检测器。 用于实际水样分析亦获满意结果。     

气相色谱/电子捕获检测法测定键合态糖苷的研究

该文建立了GC/ECD法测定键合态糖苷的分析方法,采用N-甲基-双(三氟乙酰胺)(MBTFA)对目标物进行衍生,并优化了反应温度和时间.结果表明在60℃下反应50 min时,衍生效果最好.该衍生反应在产物中引入氟元素,可用GC/JECD法进行测定.以苯氧基葡萄糖苷为典型目标物进行线性研究,方法在0.05～200 mg/...     

Electron capture detector response to low electron affinity aromatic hydrocarbons using positive ion stabilization and alkyl chloride sensitization

The electron capture detector (ECD) response to numerous aromatic hydrocarbons of low electron affinity (EA) is shown to be detrimentally affected by two processes which compete with and typically overwhelm the electron capture reactions of these molecules. It is shown that the effects of these two undesired reactions can be eliminated by the permanent addition of trimethylamine and one of several alkyl monochlorides to the detector make-up gas. These modifications of the detector gas result in greatly increased sensitivity, increased linearity, and increased reproducibility of response. A kinetic model for the ECD responses of low EA resonance capture molecules is developed which appears to explain these improvements.     

Detection of the reduced forms of radical adducts on the ESR trace using HPLC‐electrochemical detector‐ultraviolet absorption detector‐electron spin resonance‐MS

To detect and identify the electron spin resonance (ESR) silent forms of the α‐(4‐pyridyl‐1‐oxide)‐N‐tert‐butylnitrone (4‐POBN) radical adducts, an electrochemical detector (ECD) was employed as a reactor in the HPLC‐ECD‐UV absorption detector‐ESR‐MS (HPLC‐ECD‐UV‐ESR‐MS). The ECD was employed to regenerate the radical forms from the reduced forms. The reduced forms of the 4‐POBN/pentyl radical adducts were analyzed using the HPLC‐ECD‐UV‐ESR‐MS. On addition of the ECD applied potential of +0.3 V, a peak appeared on the ESR trace of the HPLC‐ECD‐UV‐ESR‐MS analyses, indicating that the radical forms are regenerated from the reduced forms. The HPLC‐ECD‐UV‐ESR‐MS analyses were also performed for the reaction mixtures of phenylhydrazine with CuCl₂. Two peaks (peaks I and II) were detected on the UV trace (300 nm) of the HPLC‐ECD‐UV‐ESR‐MS. The mass spectra showed that the peak I and peak II compounds are radical and reduced forms of the 4‐POBN/phenyl radical adducts under the ECD applied potential of 0.0 V. Peak I was only detected on the ESR trace under the ECD applied potential of 0.0 V. In addition to peak I, peak II appeared on the ESR trace under the ECD applied potential of +0.3 V, indicating that the reduced forms are oxidized to the corresponding radical forms.     

Single‐step modified QuEChERS for determination of chlorothalonil in shallot (Allium ascalonicum) using GC‐μECD and confirmation via mass spectrometry

A single extraction method was developed for chlorothalonil in shallot using gas chromatography with an electron capture detector (GC‐μECD). Samples were extracted with single‐step modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method using ethyl acetate as an extraction solvent. Significant matrix effects were observed, and the calibration curve was constructed from the matrix. The linearity of the analytical response across the studied range of concentrations (0.01–1.00 mg/L) was excellent, obtaining a correlation coefficient (r²) of 0.996. >0.996. Recovery studies were carried out on spiked shallot blank samples, at two concentration levels (0.4 and 2.0 mg/kg) with three replicates performed at each level. Mean recoveries of 97.2–104.9% with RSDs of 1.3–2.7% were obtained. The method is demonstrated to be suitable for the determination of chlorothalonil in shallot. The dissipation rates of chlorothalonil were described using first‐order kinetics, and its half‐life was 2.8 days. Based on the dissipation pattern of the pesticide residues, the pre‐harvest residue limit (PHRL) was also calculated. Residues were confirmed via mass spectrometry. Copyright © 2012 John Wiley & Sons, Ltd.     

Polymer analysis using pyrolysis-GC-FTIR-MS and GC-AED

Volatile pyrolysates of a methyl methacrylate-butadiene-styrene copolymer (MBS) have been analyzed using a capillary gas chromatograph equipped with a Fourier transform infrared detector in tandem with a mass selective detector, and a gas chromatograph-atomic emission detector system. Among the volatile compounds observed were monomers used for synthesis of the polymer. Numerous oligomers of higher boiling point were also found; identification of these could be used to give structural information about the parent polymer. Combining information from these techniques was found to be extremely useful for the analysis of polymer pyrolysis products. In characterizing each compound it was found particularly helpful to juxtapose feature-specific chromatograms (e.g., single ion monitoring from the mass-selective detector and the selected wavelength chromatography from the infrared detector).     

Analysis by electron oscillation in a conventional GC detector

The oscillation of electrons—as driven by AC polarization—can be used to extract a high-sensitivity signal from a conventional electron capture detector. For example, hexachloroethane was detected at a hypercoulometric ratio of 2.0 F/mol, down to ca. 60 fg/s (S/N=3) and with a linear range in excess of two orders of magnitude. The change in carrier gas from nitrogen to argon-methane produced the expected order-of-magnitude increase in optimum oscillation frequency. Anab initio simulation of potentials and ion populations in a heterogeneous electron capture system under a high-frequency AC regime provided further insight into the detector's mechanism: Hypercoulometric response is mainly caused by increased cation-electron recombination in the plasma region, owing to a decreased field gradient and an increased cation concentration.Material taken from doctoral thesis (Dalhousie University, 1987)     

Electrochemical,fluorescence, and UV detection for HPLC analysis of various cysteine derivatives

Electrochemical (ECD), fluorescence (FLD), and UV spectrophotometric (UVD) detection were used to monitor various S-alk(en)yl-L -cysteines and their corresponding sulfoxide isomers following pre-column derivatization with o-phthaldialdehyde-tert-butylthiol and separation by reversed-phase HPLC. Recording of hydrodynamic voltammograms, FLD stop-flow scanning, and on-line captured UV spectra were methods used for establishing optimal detector settings which were defined as a compromise between favorable selectivity and high sensitivity. Optimal detector settings were found at: (A) 750 mV vs. Ag/AgCl for ECD; (B) excitation at 230 nm and emission at 420 nm for FLD; and (C) 337 nm for UVD. Various aspects of detector practicability such as selectivity, baseline disturbances due to excessive reagent, scanning possibilities, as well as detection limits were evaluated and compared. Minimal detectable amounts of the compounds were in the range of 130-160 fmol for ECD, and 2.5-3.5 pmol and 13-16 pmol for FLD and UVD. In addition, the possibilities and benefits of detector coupling were examined.     

Irigermanone,a Noriridal with Unprecedented Methylketone Function,from Iris germanica

A new iridal, irigermanone ( 1 ) and nine known congeners, 2 – 10 , respectively, have been isolated from the dried rhizomes of German iris (Iris germanica). The structure of 1 was established by spectroscopic methods including HR‐ESI‐MS, 1D‐ and 2D‐NMR, and electronic circular dichroism (ECD) spectroscopy. Compound 1 is a structurally unique noriridal, and it possesses an unprecedented methylcarbonyl group instead of the α,β‐unsaturated aldehyde function typical for this group of triterpenes.     

气相色谱-微池电子捕获检测法同时检测饮用水中多种有机污染物

本文建立了气相色谱-微池电子捕获检测法(GC-μECD),同时测定生活饮用水中百菌清、七氯、滴滴涕、六六六、林丹、六氯丁二烯、溴氰菊酯、1,1-二-氯苯、1,2-二氯苯、三氯苯、六氯苯11种有机氯,马拉硫磷、对硫磷、甲基对硫磷、毒死蜱、乐果、敌敌畏6种有机磷,以及硝基苯、2,4,6-三硝基甲苯、1,3-二硝基苯、邻,间,对硝基氯苯、2,4-二硝基氯苯,2,4-二硝基甲苯6种硝基苯类有机物的分析方法.样品经萃取后,采用OV-1701色谱柱(30 m×0.25 mm×0.25μtm)程序升温进行分离,用微池电子捕获检测器(μECD)进行检测,通过保留时间定性,外标法定量.结果表明该方法分离效果好,灵敏度高,选择性强,简便、快速、准确,能够满足同时测定生活饮用水中上述23种有机化合物的需要.     

A theoretical model of the electron capture detector

Summary This paper reports a theoretical model of the ECD detector. The model presented here can be used to examine the influence of pulse parameters on the current and signal characteristics of the detector. On the basis of this model it was found that a space charge is created in the detector when it is supplied with pulse voltage. Due to the electric potential generated by the space charge, in the time between the pulses the electrons and negative ions move towards the detector electrodes. The ionization current of the detector is the sum of the electron current flowing to the anode under the influence of the supplied pulse voltage and the current flowing under the space charge potential in the time between the pulses. It was also found that the detector signal is the sum of the differences between those two currents caused by introducing the sample molecules to the detector. The model was tested for a detector with different electrode configurations which worked at temperature of 300 K or 573 K and which was supplied with nitrogen or Ar+10% CH₄ as the carrier gas.     

Analysis of sludge extracts by high resolution GC with selective detectors

Combination of various GC detectors by using a Varian effluent splitter with glass capillary columns has been found to be a rapid procedure for profiling organics extracted from sludges and river sediments. The selectivity and the increased sensitivity of the thermionic nitrogen-phosphorus detector (TSD), the electron capture detector (ECD), and the flame photometric detector (FPD) over the flame ionization detectors (FID) or mass spectrometers allow the detection of compounds present at trace levels without need for extensive sample cleanup. Furthermore, the combination of two selective detectors may supplement the information with regard to the chemical functionalities required for structure elucidation.     

Simultaneous determination of cypermethrin and fenvalerate residues in tomato by gas chromatography and their applications to kinetic studies after field treatment

In this study simultaneous determination of cypermethrin and fenvalerate residues in tomato fruit (Lycopesicon esculentum) grown in Khartoum, Sudan, was carried out using gas chromatography with electron capture detector (GC‐ECD). The method was linear in the ranges of 0.075–0.009 and 0.75–0.037 mg/mL for cypermethrin and fenvalerate, respectively. The limits of detection and quantification were found to be 0.003 and 0.01 mg/mL and 0.014, 0. 047 mg/mL for cypermethrin and fenvalerate, respectively. The recoveries of cypermethrin and fenvalerate spiked in tomato were 97 ± 7.5 and 99.5 ± 1.8%, respectively. The kinetic study of the degradation of both pesticides was performed and the ultimate evaluation of the kinetic data revealed a first‐order kinetics with respect to the tomato fruit; an explanation was put forward to account for the results. Copyright © 2011 John Wiley & Sons, Ltd.     

气质联用法分析氘代医药中间体

探讨用HP-5毛细管色谱柱,MSD作检测器,以质荷比相对丰度的面积归一方法,定量测定质子泵合成中间体氘代产物的纯度．用此方法测定标准品及氘代苯、氘代蒽结果误差小于2％．实验表明,质荷比相对丰度归一方法简单、快速、灵敏度高,可用于定性、定量监控反应的进行,适用于氘代化合物纯度的测定．     

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.