Measurements of absorbance at 565 nm were carried out with a spectrophotometer (USB 4000 UV–vis, Ocean Optics) coupled via optical fibers (600 μm diameter) to aliquid waveguide capillarycell (LWCC, World Precision Instruments) with a flow path of 100 cm (inner volume 250 μL) and to a light source (Model LS-1-LL halogenlamp, Ocean Optics).