ENVIRONMENTALLY FRIENDLY METHOD OF DETERMINING MAGNESIUM CONTENT IN NATURAL RUBBER (NR) LATEX BY COMPLEXOMETRIC TITRATION

摘要

It is well known that magnesium (Mg) is an important element that promotes natural rubber (NR) plant growth. Though essential for promoting growth, the presence of an excessive amount of Mg content has been found to give an adverse effect on the NR latex stability during processing operations as well as on the properties of the NR latex itself. Hence it is imperative to determine Mg content in NR latex and one of the most common ways of doing it is by complexometric titration method which is economical, practical and reliable. Despite its practicality, the titration method suffers from formation of more stable complexes with EDTA, during titration, in the presence of other metals such as Calcium (Ca). To encounter the problem, cyanide compound, for example potassium cyanide (KCN) is added to mask these complex metals. The only problem with KCN is with its toxicity since it has been classified as an extremely toxic chemical. When disposed this compound has detrimental effect on the environment, and very toxic to aquatic life. To avoid the risk and continuous exposure to KCN in laboratory work, a cyanide-free compound has been used to replace cyanide as a masking agent. This paper discusses on the comparison works involving complexometric titration of Mg content in field and concentrated latexes by using KCN as well as a cyanide-free compound as masking agents following two different methods. The Mg content in field latex samples was determined by direct titration of the latex, which involves diluting the latex one hundred fold, while for latex concentrate samples, the titration was done on the serum of the latex after coagulation with 25% acetic acid. The pH was adjusted to alkaline condition with ammonia/ammonium chloride buffer and masking agent was added before titrating with EDTA using Eriochrome Black as an indicator. For concentrated latex, it was observed that a comparable result was obtained from the two masking agents used following two different methods. For field latex, significant difference in the results was obtained by using the two methods for determining Mg content which was due to an introduction of an additional step in one of the methods prior to titration. Both methods demonstrated good sensitivity and accuracy. Percentage of recovery ranging from 81% to 119% was obtained with an established detection limit of 2ppm. An attempt was also made to establish the limit of quantification (LOQ) for both methods.