DETERMINATION OF DISSOLVED SILICA IN WATERS BY A FLOW-BASED ANALYSIS SYSTEM COMPOSED OF A LASER-DIODE AND A THIN LONG FLOW-THROUGH CELL

A highly sensitive detection system composed of a laser diode (LD) and a thin long flow-through cell (TLFTC) for flow-injection analysis (FI A) has been studied. The new detection system was mainly composed of a GaAlAs LD emitting at 780 Mn (5 mW) as a light source and a polytetra fluoroethylene rod having a thin long hole (100 X 1.4 mm i.d.) as the light path. The sensitivity was enhanced about 10 times compared with a normal 10 mm now cell. For the determination of dissolved silica in waters using the molybdenum blue method, the relative standard deviati on, detection limit(3 sigma) and linear range were 0.6%, 0.0019 and 0. 02-0.3 mg Si l(-1), respectively. This detection system may also be us eful for other flow-based analytical techniques such as liquid chromat ography.