Copper is a nutritionally essential metal and is widely distributed in nature. 1 Hence, there is a great need to develop, simple, sensitive, selective and inexpensive methods for the determination of copper in environmental, biological and soil samples for continuous monitoring to establish the levels of Cu in environmental and biological matrices.Spectrophotometry is essentially a trace-analysis technique and is one of the most powerful tools in chemical analysis. Although 2,5-dimercapto-1,3,4-thiadiazole (DMTD) has been reported as a spectrophotometric reagent for lead, 2 it has not previously been used for the spectrophotometric determination of copper. This paper reports on its use in a very sensitive, highly specific spectrophotometric method for the trace determination of copper. The method is based on the reaction of non-absorbent DMTD in a slightly acidic solution (0.002 -0.014 mol dm -3 H2SO4) with copper(II) to produce a highly absorbent greenish-yellow chelate product followed by a direct measurement of the absorbance in an aqueous solution. With suitable masking, the reaction can be made highly selective and the reagent blank solutions do not show any absorbance. Experimental ApparatusA Shimadzu (Kyoto, Japan) (Model-160) double beam UV/VIS the recording spectrophotometer and Jenway (England, UK) (Model-3010) pH-meter with a combination of electrodes were used for the measurements of absorbance and pH, respectively. A Varian (Model-Spectr AA-400 plus) atomic absorption spectrometer equipped with a microcomputercontrolled air-acetylene flame at 324.8 nm was used for comparing the results. Reagents and solutionsAll of the chemicals used were of analytical-reagent grade or the highest purity available. Doubly distilled deionized water, which is a non-absorbent under ultraviolet radiation, was used throughout.Glass vessels were cleaned by soaking in acidified solutions of KMnO4 or K2Cr2O7, followed by washing with concentrated HNO3 and rinsed several times with deionized water. Stock solutions and environmental water samples (1000 cm 3 each) were kept in polypropylene bottles containing 1 cm 3 of concentrated HNO3. More rigorous contamination control was applied when the copper levels in the specimens were low. DMTD solution, 4.42 × 10 -3 mol dm -3This solution was prepared by dissolving the requisite amount of 2,5-dimercapto-1,3,4-thiadiazole dipotassium salt (DMTD) (Aldrich A.C.S. grade) in a known volume of distilled deionized water. More dilute solutions of the reagent were prepared as required. Copper(II) standard solution, 1.57 × 10 -3 mol dm -3A 100 cm 3 amount of stock solution (1 mg cm -3 ) of copper was prepared by dissolving 392.9 mg of copper sulfate pentahydrate (CuSO4·5H2O) in doubly distilled deionized water 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 -...
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