Electron Donor-Acceptor Complexing Reagents in the Analysis of Pesticides

The quantitative in situ determination of pi-complexed pesticides by reflectance spectroscopy is discussed and quantitative results and stability studies obtained on cellulose and silica-gel thin-layer plates are presented. Detection limits are in the microgram region, with the linear working range for the Mobam-CNTNF complex chosen as an example being 1–10 meg on cellulose and 3–10 meg on silica gel. The complexed pesticide may be recovered following quantitative determination for mass spectral confirmation. The method shows particular utility in studying the degradation of pesticides.     

Observations on the Crystal Structures of Electron Donor-Acceptor Complexes

The theoretical interpretation of electron donor-acceptor complex formation in terms of charge transfer interactions has stimulated many structure determinations for these complexes. These fall into three classes, depending on the type of orbitals involved in charge transfer. In σ-σ complexes, intermolecular bonds become shorter and intramolecular bonds become longer as charge transfer increases. Relative orientations correspond to overlap of donor and acceptor molecules in directions of “preferred polarizability”. Intermolecular bond lengths in σ-π complexes show similar trends, and the axial orientation in the benzene-halogen complexes is probably the result of the best compromise between orbital overlap and energy factors. π-π Complexes contain stacks of alternate plane-to-plane donor and acceptor molecules, arranged in three characteristic ways. There is little correlation between interplanar spacing in these stacks and charge transfer properties. The relative orientations of donor and acceptor molecules within the stacks are determined by a combination of charge transfer interactions (maximized when aromatic rings of donor and acceptor molecules are displaced by half a ring diameter) and dipole-induced dipole interactions (maximized, for example, when a polar bond of one molecule overlaps a polarizable region of another). Crystal packing requirements and dispersion forces modify these effects, and no satisfactory theoretical treatment of this complex combination of interactions is yet available.     

A Practical Interfacing of HPLC with Electron Capture Detection (HPLC-ECD)

Abstract

Conventional HPLC can be simply, conveniently, and inexpensively interfaced to the electron capture detector within any GC. Various parameters have been evaluated to determine the suitability of this approach for the selective trace analysis of aliphatic and aromatic nitro derivatives.     

A Rapid Method for the Determination of Organochlorine, Pyrethroid Pesticides and Polychlorobiphenyls in Fatty Foods Using GC with Electron Capture Detection

A new, single-step extraction and purification method was developed for the separation of 26 organochlorine pesticides (OCPs), three pyrethroid pesticides (PPs) and six polychlorinated biphenyls (PCBs) from fatty foods of either animal or vegetable origin. The method includes homogenisation of extracted fat and diatomaceous earth. Separation was achieved using a mini Pasteur pipette where a matrix solid-phase dispersion extraction was carried out with only 5 mL of dimethyl sulphoxide as an eluting solvent. A Pasteur pipette was joined to a prepacked slurry filled Florisil column, water deactivated to 15% where a liquid–liquid extraction and adsorption chromatography successively took place. The elution of OCPs, PPs and PCBs was performed with n-hexane/diethyl ether. Recoveries for PCBs were from 81 to 86% and for OCPs 68 to 94%, except for β-HCH, which gave lower, more variable recoveries. Excellent recoveries were obtained for pyrethroid pesticides, mostly more than 80%. The method was applied to 509 fatty samples for monitoring of these compounds. GC, with two columns connected to two electron capture detectors (ECD), was used.     

Complexing Polymer Films in The Preparation of Modified Electrodes for Detection of Metal Ions

Summary: The complexing properties of poly (3-(pyrrol-1-yl)propylmalonic acid) (poly1) and poly(N,N′-ethylenebis[N-[(3-(pyrrole-1-yl)propyl) carbamoyl) methyl]-glycine (poly2) coated electrodes (C|poly1 and C|poly2) towards Cu(II), Pb(II), Hg(II) and Cd(II) cations using the open circuit chemical preconcentration-anodic stripping technique were studied. Sorption process of metal cations onto complexing surfaces was readily investigated through the combination of a chemical pre-concentration-anodic stripping technique with a Langmuir isotherm model. The modified electrodes were used for the voltammetric determination of Cu(II), Pb(II), Hg(II) and Cd(II) ions, giving low detection limits for Cu(II) (5 × 10⁻⁹ mol L⁻¹) and Pb(II) (5 × 10⁻¹⁰ mol L⁻¹). The ability of the modified electrodes to analyze Cu(II) ions in natural sample has been demonstrated by the analysis of a tap water sample. The results of the preconcentration process under competitive conditions clearly shows that the selectivity of complexing molecular electrode materials can be subtly tuned upon playing on the accumulation time, polymer thickness and/or memory effect of the binding polymers, opening up new avenues towards evolutive and efficient smart sensing materials.     

真菌毒素的液相色谱分离和检测

本文研究了一项分离棒曲霉素,青霉酸,赭曲霉素A和B,桔青霉素,玉米赤霉烯酮及柄曲霉素七种真菌毒素的高效液相色谱分离和检测方法。为实现分离,选择了反相方式。流动相为乙腈-水(55:45v/V),并添加了2.5mm草酸,pH为5.5。流量1.0ml/min。文中讨论了流动相中乙腈%、添加草酸的浓度对七种真菌毒素k’值的影响,对柱效N的影响,并从原理上讨论了保留机理。本文也综合地讨论了检测条件。也讨论了有关定量分析的参数,建立了一种较好的分析七真菌毒素的痕量定量方法。     

气相色谱电子捕获检测器检测蟑螂头部痕量章鱼胺的衍生物

章鱼胺(OA)是昆虫体内的痕量神经活性物质。本实验研究了蟑螂头部基质中OA的提取、章鱼胺与五氟丙酸酐的衍生化反应,优化了最佳衍生反应条件。建立了适合于昆虫样本中OA痕量测定的衍生化气相色谱-电子捕获检测方法。昆虫头部匀浆样本在10 ng/g OA添加浓度时回收率在89%~118%;该方法的最低检出浓度为1.7ng/g。采用GC-MS对衍生化产物进行了定性确证分析。     

A Primer on the Analytical Aspects of Silicones at Trace Levels-Challenges and Artifacts – A Review

Silicones (polydimethylsiloxanes) find use in a wide variety of industrial and consumer product applications because of their outstanding properties. Potential human exposure to silicones occurs at the work place during manufacturing and product formulation, as well as through the normal use of consumer products containing them.The entry of silicones into various environmental compartments raised health and safety concerns from potential exposure and mandated numerous environmental and toxicological studies. Such studies require qualitative and quantitative determination of silicone species at trace levels. However, the ubiquitous presence of silicones coupled with their unique chemistry renders their analysis at trace levels challenging.This paper provides a consolidated account of various aspects silicones that must be borne in mind to obtain reliable data. The following are some of topics discussed: differences in the chemistry of silicones vs carbon; precautions in sample handling to avoid losses and inadvertent chemical transformation; potential sources for artifacts and interferences that could lead to systematic errors and data misinterpretation; sources for background and the need for matrix matched blank experiments; distinguishing silicones from silicates to avoid overestimation; potential for incorrect structural assignments; preventing inadvertent contamination; questionable claims on the presence of silicones in biological matrices including that of silicone implants.     

Determination of Pesticides in the Rhizome of Traditional Chinese Medicines by Gas Chromatography with Electron Capture Detection

A simple and efficient gas chromatography method for the determination of 27 organochlorine and pyrethroid pesticides in traditional Chinese medicine was developed. Pesticide residues were extracted from the samples by oscillation and ultrasound, and purified by gel permeation chromatography and florisil solid phase extraction. The analysis was performed by gas chromatography with micro-electron capture detection. The purification conditions, such as the extraction and elution solvents, extraction methodology, and gel permeation chromatography conditions, were optimized. Traditional Chinese medicines were purified by different methods based on their composition. Under optimized conditions, the calibration graph was linear from 10 to 500 µg/L and the correlation coefficients varied from 0.9958 to 0.9997. The detection limits of these pesticides were between 0.09 and 1.82 µg/kg. The recovery of the pesticides spiked in various samples at four concentrations ranged from 73.2% to 106.4%, with relative standard deviations between 1.0% and 14.0%. This study indicates that the method is useful for determining pesticides in rhizome traditional Chinese medicines.     

Derivatizations for Improved Detection of Alcohols by Gas Chrohatography and Photoionization Detection (GC-PID)

Abstract

Pentafluorophenyldimethylsilyl chloride (flophemesyl chloride, F1) is a well known derivatization reagent for improved electron capture detection (ECD) in gas chromatography (GC)(GC-ECD), but it has never been utilized for improved detectability and sensitivity in GC-photoionization detection (GC-PID). We have now utilized a wide variety of flophemesyl alcohol derivatives in order to show a new approach for realizing greatly reduced minimum detection limits (MDL) of virtually all alcohol derivatives in GC-PID analysis. This particular derivatization approach is inexpensive and easy to apply, leading to quantitative or near 100% conversion of the starting alcohols to the expected flophemesyl ethers (silyl ethers). Detection limits can be lowered by 2–3 orders of magnitude for such derivatives when compared with the starting alcohols, along with calibration plots that are linear over 5–7 orders of magnitude. Specific GC conditions have been developed for many flophemesyl derivatives, in all cases using packed columns. Both ECD and PID relative response factors (RRFs) and normalized RRFs have been determined, and such ratios can now be used for improved analyte identification from complex sample matrices, where appropriate.

We have attempted to describe in this preliminary report some interesting results and approaches for improved GC-PID detection of a large number of alcohols and alcohol analogs. The method of derivatization is extremely simple to perform, and appears to lead to a single, well-defined product of known structure in 100% yield or thereabouts. Chromatography for typical flophemesylalcohol analytes can be excellent, as in Figure 1, with symmetrical peak shape, little or no tailing, and overall excellent MDLs. With GC-detector-computer interfacing, we are able to obtain both chromatograms and preliminary as well as calculated data within a single 5–10 minute time span²⁷ The total amount of time per analysis will obviously depend on the particular analyte derivative and the chromatography obtained. RRFs and normalized RRFs are quite easy to determine, they are fully reproducible, and can serve as good markers for a particular alcohol and its flophemesyl derivative. In view of the calibration plots possible and MDLs, these overall analytical methods for GC-ECD-PID using flophemesyl derivatization should, we hope, find widespread and ready acceptance and utility by the analytical community.     

Spray Reagents for the Visualization and Detection of Sesame Oil Unsaponifiables on Thin-Layer Chromatograms

Anisaldehyde and crotonaldehyde have been tested as spray reagents for the visualization of major components of sesame oil unsaponifiable matter. Colours produced using anisaldehyde were shades of the spectrum, which are characteristic of the lignans and sterols inherented in the Sesamum indicum in relatively higher coverage, sensitivity and selectivity. However, crotonaldehyde could detect four of the eleven unsaponifiable matters in relatively more stable and bright colour spots.     

Derivatization of Drugs and Bioorganics for Improved Detection by Gas Chromatography and Photoionization Detection (GC-PID)

Abstract

Pentafluorophenyldimethylsilylchloride (flophemesyl chloride, FICI) has recently been used for derivatizations of alcohols, leading to significant improvements in detectability by gas chromatography (GC)-photoionization detection (PID) and electron capture detection (ECD). This off-line reaction has now been applied to a number of related alcohol derivatives, naturally occurring bioorganics such as cholesterol, androsterone, and similar sterols and steroids. Standard GC-ECD-PID analytical parameters have been determined, such as detection limits, calibration plots, ECD and PID relative response factors (RRF), ECD/PID relative response factor ratios, etc. for underivatized and derivatized substrates. Packed and capillary column GC conditions have been used with a 10.2 eV PID lamp. Application of the optimized derivatization-GC-ECD-PID method is reported for bioorganics in biological media. The overall results demonstrate the immediate applicability of such an approach for a number of alcohol derivatives, especially those having biological properties.     

膜上痕量亚甲蓝样品的间接光声检测

介绍了一种新的膜上痕量样品分析方法与实验装置。利用间接光声效应对光吸收物质进行检测，全文对方法原理、实验装置以及影响因素进行了详尽讨论。膜上亚甲蓝定量线性范围１×１０＾－６￣１×１０＾－４ｍｏｌ／Ｌ，检出限为４６ｐｇ。     

Investigations for the detection of genotoxic substances on TLC plates

The present study describes modifications to an existing bioautographic method for detecting genotoxic substances on thin-layer chromatography (TLC) plates by using the umu assay. It will be shown that the complex procedure that is described in the literature can be significantly simplified. Using the modified method, it is possible to detect 0.3?ng of the genotoxic substance 4-nitroquinoline-N-oxide. With 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside (X-gal), a suitable substrate for environmental samples for the detection of the resulting β-galactosidase was found. Experiments showed, in contrast, that indirectly genotoxic substances could not thus far be identified on the TLC plate with overlayer bioautography.     

Recent Analytical Method for Detection of Chemical Adulterants in Herbal Medicine

Herbal medicine has become popular in recent years as an alternative medicine. The problem arises when herbal medicines contain an undeclared synthetic drug that is illegally added, since it is a natural product that does not contain any chemical drugs due to the potential cause of harmful effects. Supervision of herbal medicines is important to ensure that these herbal medicines are still safe to use. Thus, developing a reliable analytical technique for the determination of adulterated drugs in herbal medicine is gaining interest. This review aims to provide a recent analytical method that has been used within the past 5 years (2016–2021) for the determination of chemical adulterants in herbal medicine.     

浊点萃取-异辛烷反萃取-气相色谱测定茶叶中拟除虫菊酯农药残留

建立了浊点萃取-异辛烷反萃取-气相色谱(ECD)检测茶叶中联苯菊酯(Bifenthrin)、甲氰菊酯(Fenpropathrin)、功夫菊酯(Cyhalothrin)、氯菊酯(Permethrin)、氰戊菊酯(Fenvalerate)、溴氰菊酯(Deltamethrin)6种拟除虫菊酯农药残留的方法.对含1.2%(m/V)聚乙二醇6000(PEG6000)表面活性剂和40%(m/V)(NH4)2SO4的6种拟除虫菊酯溶液进行加热萃取,所获得的富集相用异辛烷超声反萃取,并经离心对上层异辛烷溶液进行进一步净化处理,即可获得富集倍数达75倍的6种农药.本方法的检出限(LOD)为:联苯菊酯、甲氰菊酯和功夫菊酯0.4 μg/kg;氰戊菊酯2.1 μg/kg;氯菊酯和溴氰菊酯3.0 μg/kg;用本方法测定了新鲜茶叶中6种拟除虫菊酯农药,含量分别为4.17, 4.15, 4.09, 4.01, 3.93和3.51 μg/kg.在上述茶叶样品中添加20 μg/kg 的6种农药后测定,添加回收率为72.3%～85.6%; 相对标准偏差为2.2%～5.6%.     

Efficient Separation of Ar and Kr from Environmental Samples for Trace Radioactive Noble Gas Detection

Radioactive noble-gas isotopes, ⁸⁵Kr (half-life t_1/2=10.8 y), ³⁹Ar (t_1/2=269 y), and ⁸¹Kr (t_1/2=229,000 y), are ideal tracers and can be detected by atom trap trace analysis (ATTA), a laser-based technique, from environmental samples like air and groundwater. Prior to ATTA measurements, it is necessary to efficiently extract krypton and argon gases from samples. Using a combination of cryogenic distillation, titanium chemical reaction and gas chromatography, we demonstrate that we can recover both krypton and argon gases from 1-10 L "air-like" samples with yields in excess of 90% and 98%, respectively, which meet well the requirements for ATTA measurements. A group of testing samples are analyzed to verify the performance of the system, including two groundwater samples obtained from north China plain.     

Ligand Exchange Reactions for the Fluorescent Detection of Nanogram Amounts of Metal Ions on TLC Plates

Abstract

A number of metal ions have been separated as their diethyldithiocarbamate chelates by thin-layer chromatography and detected by means of a ligand exchange reaction between a metal/calcein complex and the diethyldithiocarbamate chelate. Visual detection limits, after development, are 0.1 to 2 ng per spot for the metal ions studied. The potential of this new method for the fluorescent analysis of metal ions is discussed. It is particularly promising as a simple field method. Spiked natural water samples are analyzed to demonstrate its usefulness.     

Detection of Pesticides in the Environment Using Biosensors Based on Cholinesterases

Abstract

Amperometric biosensors based on acetylcholinesterase or butyrylcholinesterase were used for the kinetic determination of organophosphate and carbamate pesticides. The current of the biosensor I_ss was measured continuously with substrate; the addition of samples with pesticides resulted in the time decrease of the current dl/dt. The relative inhibition RI=(dl/dt)I_ss was used as the signal for evaluations. For several pesticides, different calibration curves (dependencies of RI on concentration c) were obtained depending on the affinity of the individual pesticide to the cholinesterase used. This affinity was described using the bimolecular inhibition constant k_i. The single calibration curve independent on the type of pesticide was obtained as the dependence of RI on the product k_ic, thus indicating the effects of both concentration and inhibiting properties on the response of the biosensor. The relative inhibition was used to characterise anticholinesterase toxicity of the sediments collected from the Morava River and its tributary streams. The influence of both point (large cities) and nonpoint (agriculture) sources of pollution was identified.     

全固定化试剂流动注射化学发光测定铜

采用离子交换固定法把Ｌｕｍｉｎｏｌ（Ｌｕ），ＣＮ＾－固定在阴离子交换树脂上，串入流动注射系统中，当一定量洗脱剂被注入阴离子交换柱时，洗脱下来的Ｌｕ和ＣＮ＾－与分析物Ｃｕ＾２＋发生化学反应，产生化学发光，实现对Ｃｕ＾２＋的在线检测。本法检出限为１．３×１０＾－９ｇ／ｍＬ，线性范围为４．０×１０＾－９－６．０×１０＾－６ｇ／ｍＬ，ＲＳＤ为３．４％，单次测定在１ｍｉｎ内能完成。已用于井水中铜的测定，结果