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Simple digestion and visible spectrophotometry for copper determination in natural rubber latex

Supunnee Duangthong^a,*, Khwannapha Rattanadaecha^a, Wilairat Cheewasedtham^b, Puchong Wararattananurak^a, Pipat Chooto^a

 
ABSTRACT:     A simple method for determination of copper contents in natural rubber (NR) latex based on the complex formation between Cu(II) and zinc diethyldithiocarbamate (Zn(II)-DDTC) and extraction with dichloromethane followed by visible spectrophotometry at 435 nm was developed. A low-cost wet digestion system for NR latex was adopted by digesting a sample in a Pyrex tube with the a mixture of concentrated H₂SO₄ and concentrated HNO₃ at 180 °C. Under the optimum conditions, the linear range of 0.1–4.0 mg/l (R²>0.99), the limit of detection and the limit of quantification were 0.0356 and 0.1188 mg/l, respectively, the intra-day (n=10) and inter-day (n=6) relative standard deviations were 0.4–3.2 and 0.8–3.4%, respectively, and recoveries of 92–101% were obtained. Fe(III), Mn(II), and Zn(II) did not interfere with the tolerance limit of 9.0, 9.0, and more than 500 mg/l, respectively, which are higher than their usual concentrations in latex. The method was applied to copper determination in a concentrated latex sample prepared from field latex samples by centrifugation. The copper content was found to be 6.8–7.0 mg/kg (on total solids content) and copper content in the field NR latex sample was 16.6–23.8 mg/kg (on total solids content). No difference was observed between the proposed method and ICP-OES as well as between the proposed digestion and Kjeldahl digestion.

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* Corresponding author, E-mail: supunnee.d@psu.ac.th

Received 11 Aug 2017, Accepted 9 Mar 2018