[Direct determination of trace copper in dry tea by spectrophotometry with Naph]

In the ethanol/water medium containing 0.1 mol.L-1 ammonium acetate (NH4Ac) and 1.5% (w/v) sodium dodecyl sulfate (SDS), the complex chromogenic reaction of trace Cu (II) with 5, 8-dihydroxy-1, 4-naphthoquinone (Naph) has been studied. Based on this study, a novel spectrophotometric method for determining trace Cu (II) has been developed. The results show that the maximum absorption of the colored complex is at 330 nm, the molar absorptivity is 1.8 x 10(4) L.mol-1.cm-1, the detection limit of the method is 0.3 mg.L-1 for Cu (II) and Beer's law is obeyed for Cu (II) in the range of 0.0-4.5 mg.L-1. The linear regress equation of A is 0.290 CCu(II) (mg.L-1) +0.015, the correlation coefficient is 0.9981, the standard recovery of Cu (II) is in the range of 97.9%-104.1% (n = 6) and the relative standard deviation (RSD) is in range of 1.6%-5.1% (n = 6). Both of the precision and accuracy are suitable to microanalysis. The method was applied to trace copper determination in dry tea samples with satisfactory results.