Characterisation of the adsorbate-adsorbent interaction between drugs or pesticides and carbon/silica compounds
Van Eeden, Charlotte May
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Administering adsorbates such as activated charcoal can treat acute poisoning from chemicals and pesticides. It has been suggested that activated charcoal is an effective antidote for virtually all organic and inorganic compounds. The aim of this study was to characterise the adsorbate-adsorbent interactions. Adsorbents used were chitosan, activated charcoal, silica and humic acids. Adsorbates used were paracetamol, prazosin hydrochloride, cimetidine, fluoxetine hydrochloride, conjugated estrogens and amitraz. Amitraz is widely used in South Africa and amitraz adsorption studies were performed to gain an insight into effective pesticide waste and dip vat management. This study used different solution properties to determine their influence on the hydrolysis of amitraz. Amitraz hydrolysis could be described as a pseudo-first order rate process and a type ABCD pH rate profile. Hydrolysis increased with temperature and was fastest at low pH, slowest at neutral to slightly alkaline pH, and slightly increased above pH 10. Hydrolysis was fastest in water, slower in propylene glycol and ethanol solutions and slowest in DMSO mixtures. In surfactant solutions, anionic micelles enhanced and cationic micelles retarded the hydrolysis rate. The half-live of amitraz was reduced from 27 days for the aqueous suspension in buffer pH 5.8 containing 0.5 % sodium lauryl sulphate to 8 hours and 12 hours when 1 % potassium oxihumate was added. Adsorbents were mixed with amitraz solution for 24 hours at 31°C. Study results proved that coarse activated charcoal powder adsorbed more than the other adsorbents used and can be used to treat amitraz poisoning or to manage spills. A study was also done to investigate amitraz adsorption on pears and oranges. Fruit soaked in amitraz solution for 5 minutes and left to dry for 24 hours, were washed in solutions of distilled water, sodium lauryl sulphate, cetrimide and Tween 80. Four crystal forms of amitraz were identified by their crystal morphology, XRPD patterns, aqueous solubility and thermal properties. Form C was the most stable with t½ of 136 days. Forms B and D were least stable with t½ of 28 days. Stability correlated with solubility differences. The addition of sodium lauryl sulphate increased hydrolysis (t½ = 17 hours) and no difference in stability of crystal forms in anionic surfactant solutions occurred. Adsorption activity of activated charcoal and chitosan were done on OTC drugs. The official dissolution media, simulated gastric and intestinal fluids were used. Cimetidine did not adsorb onto activated charcoal or chitosan tablets. Adsorption of paracetamol was minimal. Prazosin hydrochloride and fluoxetine hydrochloride were strongly adsorbed by activated charcoal with no adsorption onto chitosan. Conjugated estrogens were adsorbed by chitosan and not by activated charcoal. Anionic surfactants such as sodium lauryl sulphate can potentially be used for cleaning up amitraz, as it demonstrated increased solubilisation and hydrolysis of amitraz. Activated charcoal can be used to treat many drug poisonings and overdoses.
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