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MATERIALS AND METHODS Reagents and apparatus.Copper standard solution, 1.01 x M. MEDTA solution, 1.83 x lo-' M. MEDTA standard solution, 1.10 x M. Hydrochloric acid, solutions 0.1 and 1 M. Sodium hydroxide, solutions 0.1 and 1 M.Spectrophotometer "Lambda-1". Perkin-Elmer equipped with a quartz cell, 10 mm optical path and "Tacussel U8N" pH meter with glass and calomel electrodes (sensitivity f 0.02 pH) was used. Procedure.To d series of 10 ml volumetric flask transfer aliquots of a standard copper(I1) solution, add 2 m l of MEDTA solution 1.83 x M and the necessary drops of HC1 or NaOH solution to pH 8, diluting to the mark with distilled water. The absorbance measurements are carried out at 265 run using 10 mm quartz cells and distilled water as a blank. RESULTS AND DISCUSSIONAbsorption spectra.The spectral characteristics of Cu(I1)-MEDTA system at various pH values were studied, with a concentration of 6.42 vg Cu(I1) ml-l, and the wavelength of the absorption maximum depends on the pH. Effects of pH, reagent amount, time and temperature.With a copper(I1) concentration of 6.42 ug ml-l, a linear behaviour was obtained over the pH range 3.5-11.4. Further measurements were made at pH 8; 0.6 ml of MEDTA solution 1.83 x M was enough to form the complex and further addition of reagent did not appreciably affect the absorbance system; Copper(I1) reacts instantly with MEDTA.The absorbance of the complex solutions formed was unchanged for 24 h and up to 100°C. Beer's law, Ringbom's interval and molar absorptivity.To verify Beer's law a series of solutions was prepared following the usual procedure.In the absence of interfering ions, the copper(I1) concentration is proportional to the radiant energy absorbed between 0.51-35.30 pg Cu(I1) ml-' at 265 nm. From these results, the molar absorptivity of the system was calculated as 3.34 x lo3 1 mol-l cm-l; the sensibility was 0.019 vg c N 2 and Ringbom's optimum interval is between 4.49 and 19.25 pg Cu(I1) ml-l. Minimum photometric error is 3.1%. Reproducibility and precision.The results By three different methods ( (a) "molar ratio" of Yoe and Jones7; (b) "continuous variations" of Jobe; and (c) "slope ratio" of Harvey and Manning-), the composition of the complex was found to be Cu(II)/MEDTA 1:l.