CHROMATOGRAPHIC BEHAVIOUR OF PESTICIDES AND COMPOUNDS OF PHARMACEUTICAL IMPORTANCE

Abstract

Since 1956, when thin layer chromatography was first introduced by Stahi as a procedure for analytical adsorption chromatography, large amount of work has been done on development of suitable systems for the separation of various classes of compounds. Although a large amount of work on TLC separation of various classes of organic compounds has been done and suitable separation schemes for plant materials like glycosides, alkaloids, sugars, anthraquinones, phenols and many materials of biological and biochemical importance e.g. amines, steroids, lipids have been worked out,the problem of overlapping and tailing hinders efficient separation. To resolve this problem the use of mixed adsorbents in chromatography was first tried by Morris in 1962, Carton and Bradbury in 1965 and then by Cheng Hesia in 1968. Thus reagents which will complex or chelate to a lesser or greater extent with the substance to be separated have been tried as additives to the main adsorbent material. Since then many attempts have been made for the separa tion and identification of many classes of compounds. The important work in this field has been done by Bark and co workers in 1967 for the separation of phenols using polyamide and different amides as impregnants. Later on Yasuda in 1971 used different metal salts as impregnant for improving the separation of aromatic amines. 11 In spite of a large amount of work done on the TLC separation of various classes of organic compounds, little work has been done on the TLC separation of pesticides and many of the compounds of pharmaceutical importance. Hence it was considered necessary to extend TLC method for devising suitable systems for working out separation schemes for pesti cides and some compounds of pharmaceutical importance and to investigate the use of impregnants for improving such separations schemes. Thus the present thesis is concerned with the TLC studies on Organo-phosphorus pesticides, Organo-chlorine pesticides, Carbamates, , Antihistamines, Sulfa drugs, Barbiturates and Amino sugars, and the use of metal salts as well as phenols and amines as impregnants. The eleven organo-phosphorus pesticides taken were - Malathion, Phorate, Trichlorfon, Vamidothion, Monitor, Orthene, Diazinon, Ro-nnel, Phosalone, Methyl azinphos and Dimethoate. The different metal salts used as impregnants were - Cadmium acetate, Zinc acetate, Manganese acetate,ZnSO^. and it was found that silica gel G impregnated with 2,0£ zinc acetate acted as the best adsorbent system. The best solvent system was found to be n-hexane-xylene-ethyl acetate-acetone (50:15:5:18). The spots were visualized by iodine vapours. The impregnation by phenols was also tried for these eleven organo phosphorus pesticides. Eor this o-cresol, p-cresol and m-cresol was tried as impregnants. The solvent system was the same as in metal iii salt impregnation and the best impregnant found was 0.5$ p-cresol on silica gel G. Correlation between chromatographic behaviour and hydrogen bonding between organo-phosphorus pesticides and p-cresol used as impregnants was worked out on Beckmann IR 20 spectrophotometer on sodium chloride plates at different concentrations of each pesticides and mixture with p-cresol (Chapter II). The different nine carbamates studied for separation were : Carbaryl, Bendiocarb, Carbafuran, Baygon, Ziram, Zineb, Aldicarb, MIPC and BPMC. .The different metal salts used as impregnant were zinc acetate, zinc sulphate, cadmium acetate and manganese acetate. The most suitable solvent system was benzene: ethyl acetate (50:10) and the best impregnant found was 0.1$ zinc acetate on silica gel G. Carbaryl, Bendiocarb, Carbafuran and Baygon were detected with a freshly prepared solution of eerie sulphate while others were visualized by iodine vapours (Chapter III). TLC separation of seven antihistamines on phenol as well as different metal salts impregnated plates were tried. The antihistamines were - Diphenhydramine HCl, Bromodiphenhydramine, HCl, Chlorpheniramine malate,Carbinoxamine,Mepyramine, Antistine and Actidil. Phenols tried as impregnants were - phenol, o-cresol, m-cresol and p-crcsol end different metal salts tried were - zinc acetate, manganese acetate, cadmium acetate, zinc sulphate and zinc chloride. In phenol iv impregnation 0.75$ m-cresol used as impregnant gave the most satisfactory results and best solvent system found was n-butanol-ethylacetate - ammonia (30:30:0.5). Whereas on metal salt impregnation 1$ zinc acetate gave the best results and solvent system was found to be ethanol -BMP - ammonia (32:10:0.2). The plain silica gel G plates as well as impregnated plates were detected by Dragendorff reagent (Chapter IV), The separation of ten closely related sulfa drugs were worked out. The sulfa drugs were - Sulfaphenazol, Sulfaguanidine, Sulfamethizole, Sulfadiazine, Sulfadimidine, Sulfasomidine, Sulfathiazole, Sulfapyridine, Sulfacetamide and Sulfanilamide^ Copper salts - copper sulphate, copper acetate and copper chloride were taken as impregnants. The most suitable solvent system was ethyl acetate : benzene (40:20) and silica gel G impregnated with 0.1$ copper sulphate acted as the best adsorbent system. The plain silica gel Gplates were sprayed by Dragendorff reagent while the impregnated plates were self visualized because of copper sulphate impregnation (Chapter V). The separation of seven barbiturates -Phenobarbita* , Barbituric acid, 1:3 dimethyl barbituric acid, Di sodium barbital, Diethyl barbituric acid, thio barbituric acid and Pentobarbital were studied on silica gel Gplates impreg nated with different copper salts as well as with different amines. In case of copper salts impregnation 0,2$ copper sulphate impregnated plates gave the best possible results by employing benzene methanol (40:8) as the best solvent system. In both the cases the spots were visualized by spraying with 1$ aq. solution of mercurous nitrate. In case of impregnation by amines, 2$ ethylenediamine gave the best results using benzene:ace tone (40:12) as best solvent system. Correlation between chromatographic behaviour and hydrogen bonding between barbiturates and amines used as impregnants was worked out by using the spectroscopic method of Baba and Suzuki (1961). (Chapter VI). TLC studies of four closely related amino sugars were carried out on metal salts impregnated plates. The amino sugars were- Glucose amine, Mannose amine, Galactose amine, and N-acetyl Glucose amine. The metal salts as impregnant were - Cadmium sulphate, Cadmium acetate, Cadmium nitrate, Zinc sulphate and Manganese sulphate. The amino aigars were visualized by spraying with 0.25$ ninhydrin in 1-butanol. In this separation silica gel impregnated with 1$ cadmium sulphate gave the best results with methanol:acetone (50:10) as solvent system. (Chapter VII). Eight organo-chloro pesticides were separated on silica gel G plates - Methoxychlor, Endosulfan A, Endosulfan B, P, P'-DDT, Aldriri, Dieldrin, Lindane, Endrin, since no suitable solvent system has been reported so far for the simultaneous TLC separation of Endosulfan A and B alongwith other pesticides, investigation were carried out to evolve a suitable solvent system for this purpose. The solvent system cyclohexane:chloroform (50:5) was found to be suitable for this separation.