Iron (III) carboxymethylcellulose as swellable credible matrix for the controlled release of a mosquito larvicide

Abstract

Controlled release formulations of a mosquito iarvicide Fenthion® as monolithic slabs were made by insolubilizing sodium carboxymethylcellulose by the ionotropic cross-linking with ferric chloride under ambient conditions of temperature and pH. Slabs containing 20% and 10% larvicide concentrations and three different extents of cross-linking were made. Evaluation of these formulations under static conditions in water has been continued till the formulations started extensive erosion. The release profile and stability of the formulations varied depending on the larvicide loads and cross-linking periods. Formulations with 48.0 h of cross-linking with 20% and 10% larvicide (FeF3 and FeF6) were evaluated for 21 and 27 weeks with the respective average release rates of 6.4766 × 10 -7 and 2.5094 × 10 −7 mg cm −2 s −1. Among these formulations, FeF2 exhibited maximum closeness to zeroorder release behaviour compared to the rest. Constant rate of release was observed, after an initial high rate of release, due to the swelling and gradual hydrolytic erosion of the ionic cross-links of Fe(III) carboxymethylcellulose matrix. Erosion rate constants were calculated by assuming that the release of fenthion from these formulations is due to the erosion of the entrapping matrix.