The conventional heating system was very similar to the microwave continuous-flow equipment but the heating section was a coil of stainless steel tubing with 0.45 cm i.d. and 246 cm length (with the same internal volume as the Teflon TM coil) and 0.93 mm of wall thickness, immersed in a temperature-controlled water bath. The temperature of the water bath was adjusted to provide the same temperature as the microwave oven under the same flow rate conditions, thus ensuring the same heating rate (Lo pez-FandinÄ o et al., 1996).