Chromatographic identification of pesticides

The chromatographic properties of 51 common pesticides have been measured using seven different chromatographic systems involving gas-liquid chromatography (GLC), high-performance liquid chromatography (HPLC) with diode-array spectrophotometric detection and thin-layer chromatography (TLC) with different spray reagents. Correlation coefficients were calculated for combinations of all systems. The best combination of the chromatographic systems examined for the identification of an unknown compound is GLC on OV-17, HPLC on ODS-Hypersil with acetonitrile-water as eluent and TLC using an isooctane-ethyl acetate solvent system.     

Physico-Chemical Properties of the Most Suitable Spray Reagent for Fluorescence Enhancement in Thin-Layer Chromatography

Abstract

In a fluorescence-enhancing method by spraying with a viscous organic solvent in thin-layer chromatography(TLC), the relationship between fluorescence enhancement and the properties of spray reagents was investigated, using 5-dimethylamino-1-naphthalene-sulfondimethylamide(DNS-DMA) as a fluorescent compound. A stuitable reagent should have two properties of giving high fluorescence intensity to a fluorescent compound and good transmigration from an adsorbent to the reagent medium, i.e., having the large product of relative fluorescence quantum number(RFQN) in the reagent solution and Rf value of the fluorescnet compound in TLC using the reagent as a developing solvent.

A mixture of Triton X-100 and chlofoform(2:8) showed the largest product for DNS-DMA, so that the mixture was expected to be the most suitable reagent, and DNS-amine fluorescences on a plate were enhanced about 100-fold practically. Standard curves for DNS-amines were linear in the range of 1 to 20 pmole per spot. The Triton X-100 mixture also was useful to other DNS-derivatives such as DNS-amino acids and DNS-peptides.

This selection of a suitable spray reagent was also discussed on other fluorescent compounds.     

Benzil and Benzoin: General Spray Reagents for the Visualization of Organic Compounds on Thin Layer Chromatograms

Benzil and Benzoin spray reagents have been adopted to detect some organic compounds on thin layer chromatograms (TLC). These reagents were found to visualize sugars, amino acids, dicarboxylic acids and some natural products on thin layer plates. Colors produced with these reagents were shades of the spectrum and characteristic of individual or class of the organic and natural products.     

Plates for thin-layer chromatography with adsorption-immobilized reagents in chemical test analysis methods

The use of plates for thin-layer chromatography (TLC) with adsorption-immobilized organic reagents in chemical test methods for analysis is considered. Triarylmethane, triazine, eirodine, acridine, and rhodamine dyes are used for immobilization. The degree of retention of the reagents is 52–98%. It is found that the absorption spectra of these reagents on TLC plates exhibit a hypsochromic shift of absorption bands by 8–30 nm in comparison with their absorption spectra in solutions. The retention is higher for the reagents that exhibit a hypsochromic shift of absorption bands on TLC plates. The sorption isotherms of the reagents on TLC plates are obtained and analyzed. Test methods have been developed for the determination of 1–200 mg/L Au(III) and 0.1–5 M acids and alkalies with the use of reagent TLC plates. The relative standard deviation of the results of analysis is no larger than 10%; the time of analysis is 3–7 min.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 291–296.Original Russian Text Copyright © 2005 by Amelin, Tretyakov.     

Impregnated silica-based layers in thin layer chromatography

Abstract

Impregnated thin-layer chromatography (TLC) layers based on silica gel are presented. Impregnating agents such as metal cations, inorganic ions, chelating agents, chiral selectors, surfactants, ion-pairing reagents, and ionic liquids are discussed. The role of impregnated TLC layers in medicinal chemistry is highlighted. The historical overview of TLC separations on physically coated layers is given and some future prospects ahead of this technique are discussed.     

Effects of Different Stationary Phases and Surfactant or Cyclodextrin Spray Reagents on the Fluorescence Densitometry of Polycyclic Aromatic Hydrocarbons and Dansylated Amino Acids

Abstract

The detectable luminescence of twelve dansy1 amino acids and four polycyclic aromatic hydrocarbons (PAH's) spotted on five common TLC stationary phases was evaluated. The detectable luminescence varied appreciable for compounds associated with different stationary phases. The use of surfactant and cyclodextrin spray reagents caused luminescence enhancements on some stationary phases but not others. The reagents did not affect all compounds to the same degree indicating that qualitative information could be obtained in some cases. The largest luminescence increase for a compound spotted on silica gel was for pyrene (i.e., 47-fold) sprayed with sodium cholate. The degree to which the plates were dried also affected the luminescence intensity. Possible reasons for the observed effects are discussed.     

New chromogenic reagents for labelling amino groups in peptides. Chromatographic and preparatives aspects

Summary A new type of chromogenic reagent for labelling the amino groups of peptides or amino acids, 5-substituted 2,4-dinitrofluorobenzenes, is presented. These reagents are characterized by a polarity determined by the function included in the substituent in the 5-position and by the nature of this substituent. Preparation and chromatographic behaviour of these reagents, of eventual by-products of reactions and of some N-(2,4-dinitro-5-diethylaminophenyl)-peptides or amino acids are described.Proportions in solvent mixtures are v/v except otherwise indicated. Abbreviations: lit=literature, TLC=thin-layer chromatography, TLE=TL electrophoresis, see also: Figs. 2, 3, 5.     

无机离子交换剂的研究（Ⅳ）：偏磷酸铈的薄层色谱应用

本文系统研究了10种金属离子（其中8种为贵金属离子）在偏磷酸铈薄板上的色谱行为，考察了各种洗脱体系、展开温度以及薄层厚度对金属离子比移值的影响，找出了最佳分离体系，成功地实现了一系列混合离子的分离与分析。     

Stationary phases for thin-layer chromatography

This paper presents a review of the literature concerning development of the stationary phases for thin-layer chromatography (TLC) in the last ten years. The silica gel remains the most important adsorbent for TLC separation. The kinetic properties of the silica-gel thin layer and the new TLC plates have been presented. Other materials used as stationary phase were alumina, zirconium oxide, Florisil, and ion-exchanger. Chemically new bonded stationary phase development is also discussed. The improvement of the separations of some organic mixtures by impregnation of silica gel, cellulose, or polyamide plates (with transition metal ions and silver salts) and their applications is presented. The impregnation of the thin layer with organic stationary phase and inclusion complexes is another method used for the enhancement of the separation efficiences. Another modality to improve the selectivity in TLC using ion-pairing as reagent of impregnation is described as well. The actual state of chiral separation by TLC is discussed with concrete references to recent advances in chiral stationary phases. The use of nonpolar chemically bonded stationary phases impregnated with transitional metal ions is presented as chiral stationary phases. The cellulose, modified cellulose, chitin, chitosan, and their derivatives are presented and their potential for the analysis of the racemates is discussed. The cyclodextrines and macrocyclic antibiotics were used with very good results for enantiomeric separation by TLC. A new separation approach with molecular imprinting polymers was reported as a chiral stationary phase in TLC. The examples provide a wide range of structural types that can be readily resolved enantiomerically by TLC.     

4-PICOLINE-o-DINITROBENZENE; A GENERAL CHROMOGENIC REAGENT FOR LOCATION OF ORGANOPHOSPHORUS PESTICIDES ON THIN-LAYER CHROMATOGRAMS

Abstract

A new general chromogenic reagent for location of organophosphorus pesticides and some of their breakdown products on thin-layer chromatograms has been developed. Chromatoplates are sprayed with 4-picoline and heated for 20 minutes at 100°C in an oven. After cooling, they are sprayed first with o-dinitrobenzene then with alkali. Pesticide spots appear blue in color.     

Ultrathin-Layer Chromatography (UTLC)

Ultrathin-layer chromatography (UTLC) differs from high-performance thin-layer chromatography (HPTLC) and from thin-layer chromatography (TLC) in two basis things: the layer thickness, and the migration distances of the analytes. UTLC has a monolithic or a nanostructured stationary silica gel phase bound directly to the glass plates. Layer thickness in UTLC is 10 μm, instead of 100–250 μm in HPTLC. Migration distances are in the range of 1–3 cm for UTLC, instead of 8–10 cm for HPTLC. Therefore, the major advantages of UTLC over HPTLC and TLC are the shorter development times and higher separation efficiency and sensitivity. Moreover, separations on UTLC plates require smaller reagent and sample volumes. However, the UTLC plates are very difficult to manage with the TLC and HPTLC equipment currently available. Therefore, the next challenge in this area is the development of an inexpensive solution with appropriate instrumentation (sensitive optical scanners and sample application systems). UTLC had been used for separations of many compounds, e.g., pharmaceutically active ingredients, pesticides, plasticisers, natural products, and other chemical substances.     

The Application of Cross-Scanning to Conventional Thin-Layer Chromatography

Abstract

The technique of cross-scanning, the scanning of thin-layer chromatographic (TLC) plates perpendicular to the direction of development, is applicable to conventional quantitative TLC where significant advantages over normal scanning are realized by its use. Several factors are discussed which influence the ability to cross-scan, such as application of the sample, solvent development and instrumentation.     

Spray reagents for the detection of amino-acids on thin-layer plates

Three spray reagents for the detection of amino-acids on silica-gel thin-layer chromatography plates are reported. The reagents produce various colours, which may be used to identify some of the amino-acids directly, and assist in their detection.     

On-Plate Electrochemical Detection for Thin-Layer Chromatography

Abstract

Voltammetric electrochemical detection (ECD) coupled with thin-layer chromatography (TLC) was demonstrated for the quantification of trace organic compounds directly on a TLC plate. the electrochemical detection solvent was a thin layer of aqueous potassium chloride. For undeveloped plates, detection limits for p-anisidine and p-phenetidine were 10 ng and 13 ng, respectively. Linearity was demonstrated over nearly 2 orders of magnitude. After development, detection limits increased by approximately a factor of ten. Advantages of this method over other quantitative TLC methods include sensitivity, speed, simplicity, and cost. in addition, this method is selective for electrochemically active compounds. Major sources of experimental error include spot size reproducibility, working electrode placement, and supporting electrolyte film thickness.     

Comparison of Normal and Reversed-Phase TLC for Separation of Selected Pesticides

JPC – Journal of Planar Chromatography – Modern TLC - Fifteen urea pesticides have been separated on RP-18WF254 plates with methanol-water and mixed organic (acetonitrile-methanol, 1:1...     

Thin-layer chromatography of endotoxins, their derivatives and contaminants

Thin-layer chromatographic (TLC) separation techniques were used to analyze the heterogeneity of various preparations which included smooth and rough endotoxins (ET), Lipid A precipitates and synthetic Lipid A samples and a novel cytotoxic bacterial lipid. Furthermore, carbohydrate-rich split products (PS) of ET were also separated on commercial silica-coated plates. Satisfactory results were obtained by two-dimensional TLC or by the combination of chromatography followed by high-voltage electrophoresis in the separation of PS of ET cleaved by mild acetic hydrolysis. Several spray reagents were found which were eminently suitable to detect carbohydrate containing compounds. Less specific but generally useful spray reagents were also developed which gave strong color reactions with lipids, proteinaceous and carbohydrate containing split products of the ET preparations. Improved chromatographic resolution has also revealed substantial heterogeneity in both rough and smooth ET samples. Three biological activities of the separated components could be determined. These were antigenicity detected by reactivity with monoclonal antibodies on the TLC plates, endotoxicity, determined by the Limulus amoebocyte lysate (LAL) test and direct cytotoxicity of P815 cells in vitro. Considerable amounts of non-endotoxic and non-antigenic contaminants could be detected in all preparations tested. Significant amounts of free Lipid A were also found in smooth ETs. Thus a new level of complexity is recognized by TLC within these preparations.     

Transfer of silica gel TLC screening methods for clarithromycin,azithromycin, and amodiaquine + artesunate to HPTLC–densitometry with detection by reagentless thermochemical activation of fluorescence quenching

ABSTRACT

A previously published model process was used for the transfer of silica gel thin-layer chromatography (TLC) screening methods for clarithromycin, azithromycin, and amodiaquine?+?artesunate pharmaceutical formulations published in the Global Pharma Health Fund E.V. Minilab manual for the identification of counterfeit drugs to high-performance TLC–densitometry quantitative methods that can be used in support of regulatory compliance actions. In these new methods, detection of clarithromycin, azithromycin, and artesunate was achieved by thermochemical activation involving simple reagent-free heating of the layer to produce derivatives of the drugs that quench fluorescence under 254?nm ultraviolet light. Additional drugs with TLC screening methods published in the Minilab manual and/or Compendium of Unofficial Methods for Rapid Screening of Pharmaceuticals by Thin Layer Chromatography that do not naturally quench fluorescence were studied and also found to be detectable by thermochemical activation on silica gel layers. The conditions of the thermochemical activation were studied, and in situ spectra of drug zones before and after heating were obtained. Heat activation of fluorescence quenching seems to be a widely applicable detection method that is safer and more convenient than the use of chemical spray, dip, or vapor phase reagents.     

Thin-layer chromatographic analysis of cocaine and benzoylecgonine in urine.

The sensitivity achieved by the described thin-layer chromatographic (TLC) method greatly exceeds that of previously published TLC methods for the determination of cocaine and its principal metabolite, benzoylecgonine, in urine. Sensitivity for cocaine and benzoylecgonine approaches 0.1 and 0.25 mug/ml, respectively, for a 5.0-ml specimen. A simple extraction with a mixed organic solvent provides the basic mechanism for isolating the drugs from biologic specimens. Cocaine and its metabolites are stable in sulfuric acid solutions but labile in aqueous media containing certain other inorganic and organic acids; therefore, an emphasis on the utilization of sulfuric acid solutions is employed throughout the procedure. An evaluation of sensitivities achieved for cocaine and benzoylecgonine by various detection reagents is presented. The technique is applicable to drug screening programs.     

Enzyme Inhibition and Chromatographic Techniques: Comparative Studies and Application to Pesticide Residue Analysis

Abstract

The development of enzyme inhibition techniques in relation to pesticide analysis is discussed, along with discussion of (a) principles of thin-layer chromatograph-enzyme inhibition (TLC-EI) technique, (b) general procedures of the technique, (c) the use of enzymes in combination with TLC and colorimetry, and (d) merits and limitations of the techniques. TLC-EI techniques and gas-liquid chromatography are compared based on sensitivity of detection, selectivity, and applicability to pesticide analysis.

The TLC-EI technique is being used and developed further in the Research Laboratories, Health Protection Branch, Ottawa for determination and confirmation of some organophosphorus and carbamate pesticides. Recently, it has been developed to detect methomyl (Lannate^(R)) residues in rapeseeds, oils, and meals.     

Recent advances in thin-layer chromatography of pesticides

Advances in the applications of thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) for the separation, detection, and qualitative and quantitative determination of pesticides, other agrochemicals, and related compounds are reviewed for the period 1998-2000. Analyses are covered for a variety of samples, such as food, biological, and environmental, and for residues of pesticides of various types, including insecticides, herbicides, and fungicides, belonging to different chemical classes. References on formulation analysis, hydrophobicity studies, and the use of TLC and thin-layer radiochromatography (TLRC) for studies of pesticide metabolism, degradation, uptake, and related studies are also included.