The phase separation and colour reaction of Cr(Ⅵ) and Cr(Ⅲ) with pheylfluorone (PF) and Triton X-100 is studied. Based on the properties of selective separtinn and enrichment of phase separation, a method for the simultaneous determination of Cr(Ⅵ) and Cr(Ⅲ) has been developed, The interference of overlapping spectra of complexes can be overcome by using the computations obtained by inverse least squares method. The method was applied to the determination of trace Cr(Ⅵ) and Cr(Ⅲ) in composite samples, tap w...