وجود آلکالوئید در نمونه‌های گیاهی: روش معرف‌های آلکالوئیدی در مقایسه با بروموکرزول‌گرین

Background: Alkaloids are a group of nitrogenous compounds with potential effects on the physiological behavior of human and animals. Some of these compounds are considered important drugs in modern medicine, such as atropine and morphine. Plants are considered the most important source of alkaloids. Therefore, investigating the presence of alkaloids in different plants is very important. Usually, alkaloids in plants are identified by methods such as those of Dragendorf, Wagner and Meyer, among others, which require milligrams of alkaloids for identification. In the present study, a fast and sensitive procedure for detecting of alkaloids in plants is presented.Methods: Twelve dried plants samples were investigated for the presence alkaloids. After extracting the total alkaloid into methanol using a Soxhlet extractor, a few milligrams of the extract was transferred to a separatory funnel, buffered to pH 4.7, the bromocresol green (BCG) solution (10-4 M) was added, mixed and extracted with CHCl3 until a yellow color was observed in the CHCl3 layer, indicating the presence of the alkaloid. The crude extracts were also investigated by the standard methods of Dragendorf, Wagner and Meyer for the presence of alkaloids. Results: Investigation of the 12 plant samples for the presence of alkaloids by the standard reagents of Dragendorf, Wagner, and Meyer showed that only Camelia sinensis (flowers), Echium amoenum Fisch & Mey (flowers), and Stachys (aerial parts) are devoid of alkaloids, with all other samples positive for alkaloids. By the BCG procedure, similar results were obtained, except for the E. amoenum flower, which was positive. The minimum detectable limit for alkaloids by the BCG method is the equivalent of approximately 40μg atropine. Conclusions: According to previous reports, only one of these plants does not contain alkaloids. All studied plants positive for alkaloids by standard reagents were positive by the BCG procedure. Stachys was negative for alkaloids by both the standard reagents and the BCG method, in agreement with previous reports. However, black tea, reported to contain xanthine alkaloids, was negative for alkaloids by both the standard reagents and the BCG method. Therefore, the BCG method is not suitable for the detection of xanthine alkaloids. Nevertheless, the microgram detectable limit for alkaloids indicates that the BCG method is very sensitive.