selection valve[33]. All of these components are able to be operated in either manual or automatic mode by a built-in programmable logic controller. A Shimaden (Tokyo) SR91 proportionalintegral-derivative (PID) digital controller was used to control two
cartridge heaters (C3JX4A, Watlow Japan, Tokyo) and a thermocouple (type K chromel-alumel, Sakaguchi E.H VOC, Tokyo). In
order to assemble a heater device, each cartridge heater was installed into a tubular brass on which Teflon tubing was coiled to
make a heated loop. Spectrophotometric measurements were
made using a Soma (Tokyo) visible detector (S-3250) equipped
with aflow-through cell (8mL volume, 10 mm path length). Absorbance was measured at 510 nm for both analytes. The detector
output signal was recorded with a FIA monitor (Ogawa & Co.)
controlled by a PC. Theflow line was built using 0.5 mm inner
diameter Teflon tube, and only the back pressure coil was of
0.25 mm inner diameter Teflon tube (3 m long).