Continuous monitoring method of trace silicon in industrial water using continuous micro flow analysis

A continuous monitoring method was developed for the automatic determination of trace silicon in industrial water, based on the molybdenum blue absorption spectrophotometry. A sample, a molybdic acid reagent and a reducing reagent are continuously pumped with a peristaltic pump at a flow rate of ca. 75μl/min. The sample is mixed with the molybdic acid reagent in a mixing joint and then introduced into a reaction tube made of Teflon tubing (0.5mm inner diameter, 8m length) in an aluminium block bath at 23°C, in which the molybdosilicic acid is formed. A platinum wire with a diameter of 0.2mm is inserted into the reaction tube to assist the mixing of sample with reagent. The stream from the reaction tube is mixed with a stream of the reducing reaget to form the molybdenum blue, which is then introduced into a flow cell (10mm light pass length, 8μl volume) of a spectrophotometer. The absorbance at 815nm based on the molybdenum blue is continuously recorded to measure the trace silicon in samples. The method was successfully applied to the determination of trace silicon in commercial pure waters and to the continuous monitoring of trace silicon (22000ppb) in water.