Photometric method for the determination of alkaloids in toxicological analyses with special reference to strychnine and brucine

Abstract

Alkaloids are now generally defined as basic compounds of vegetable origin. In describing all the vegetable bases as alkaloids we are therefore collecting in one class a number of substances of widely differing constitution with a correspond¬ ing variety of chemical properties. All members of this grou|>21) contain one or more nitrogen atoms. A few contain nitrogen in an open chain, but the nitrogen in general is present in a cyclic structure such as in pyridine, quinoline, isoquinoline or pyrrole. Still other alkaloids are derived from purine or from complex dicylic systems as in the second half of the chinchona alkaloids and in the tropine group. The nitrogen atom possesses basic characteristics which show in almost all members of this group of compounds. A few are soluble in water forming solutions which are alkaline to litmus, but the majority are only slightly soluble in water and only feebly basic. Morphine is the most conspicuous example of a small group of alkaloids, containing phenolic groups in the molecule which mask the basic nature of the nitrogen atom.As there is, at present, a tendency towards an increasing reliance upon colorimetrie methods, we adopted as a foundation Prudhomme's original technique with Brodie*s later work, extending this method to a large number of different alkaloids# We hoped to get ultimately an accurate and sensitive general method for the estimation of alkaloids in toxicologieal and pharmaceutical analyses#This method, which is based on the reaction between acidic dyes and basic drugs proved to be a sensitive and accurate method for the determination of minute amounts of cinchona alkaloids (Brodie et al., 1945). As it was not extensively studied, it was thought that it would be of analytical value to extend this method to a number of acidic dyes and alkaloids using different solvents. It was hoped ultimately to get an accurate and sensitive general method for the estimation of alkaloids in toxicological analysis for routine purposes. This thesis deals with the critical examination of the method, and its application to toxicological analysis.A number of acidic dyes of different chemical nature were tested for their reactivity with a variety of alkaloids. Quinine was chosen as a representative example of alkaloids for its pronounced basic character and its great sensitivity to this reaction. Preliminary experiments showed that 5 ug. gave an easily detected colour. She dyes found suitable for use were tested for their reactivity with some of the important alkaloids usually met with in toxicological analysis.She critical examination of the method was further studied for quantitative purposes. Strychnine was chosen as an example of an alkaloid. Strychnine and brueine, which are commonly present together and so closely related to be difficult to separate completely, especially in small quantities, are often required to be determined separately in naturally occurring mixture* She recovery of strychnine from aqueous solution was studied and applied to biological materials. She method was extended for the estimation of strychnine in very low concentrations by concentrating the dilute samples followed by estimating the alkaloid by the above method.Toxicological samples due to poisoning with naturally occurring mixtures of strychnine and brucine, for example tincture Nux Vomica, the powdered nux vomica seeds, or ignatus beans, are expected to contain both alkaloids. As strychnine and brueine both respond to the alkaloid dye formation method, they should "be separated before their individual estimation. For this purpose a chromatographic study of the separation of these two alkaloids was discussed in a part of this work.A technique was finally evolved for the estimation of strychnine and brucine in mixture, present in very low concentrations in aqueous and biological material.