Spectrophotometric Determination of Copper in Alkaline Solution of EDTA-Copper:Studies on Electroless Plating of Copper (Part 2)

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EDTA was added to an electroless copper plating bath as a complexing agent for the copper ion. The absorbance of the alkaline solution of EDTA-copper complex was investigated by spectrophotometric determination to estimate the copper ion in the solution.The wave-length at the maximum absorption of the solution was approximately 740mμ. The absorbance at 740mμ was greatly affected by pH of above 10.5, but little affected by buffer solutions and co-existing substances such as excess of EDTA, HCHO, HCO2-, CH3OH, and SO42-. Accordingly, it was known that copper ion concentration in the solution can be estimated by spectrophotometry by adjusting pH of the solution.In addition, the depedence of absorbance on pH was varied according to the sort of buffer solutions added to the solution. The absorbance was decreased with the increase of pH above 10.5 by the addition of Kolthoff or Universal buffer solution. While, the absorbance was decreased with the increase of pH above 8.0 or 7.5 by the addition of Sorensen or Michaelis buffer solution, respectively.The difference of the dependence of absorbance on pH between these buffer solutions was supposed to be due to the change in the structure of complex salt affected by ammonia or glycine in the latter buffers.
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