A simple spectrophotometric method for the determination of copper in industrial, environmental, biological and soil samples using 2,5-dimercapto-1,3,4-thiadiazole

A simple spectrophotometric method is presented for the rapid determination of copper at a trace level using 2,5-dimercapto-1,3,4-thiadiazole (DMTD) as a new spectrophotometric reagent. The method is based on the reaction of nonabsorbent DMTD in a slightly acidic (0.002 - 0.014 mol dm(-3) sulfuric acid) aqueous solution with copper(II) to produce a highly absorbent greenish-yellow chelate product that has an absorption maximum at 390 nm. The reaction is instantaneous and the absorbance remains stable for 24 It. The average molar absorption coefficient and Sandell's sensitivity were found to be 5.65 x 10(4) dm(3) mol(-1) cm(-1) and 10 ng cm(-1) of Cu-II, respectively. Linear calibration graphs were obtained for 0.1 - 20 mug cm(-3) of Cu-II; the stoichiometric composition of the chelate is 1:2 (Cu:DMTD). A large excess of over 50 cations, anions and complexing agents (e.g. tartrate, oxalate, citrate, phosphate, thiourea, SCN-) do not interfere in the determination. The method was successfully used for the determination of copper in several Standard Reference Materials as well as in some environmental water samples, biological samples, soil samples and solutions containing both copper(l) and copper(II) and complex synthetic mixtures. The method has high precision and accuracy (s = +/- 0.01 for 0.5 mug cm(-3)).