Studies on sequential injection spectrophotometric system using a reflective flow cell for process analysis

A reflective flow cell was developed and coupled to a sequential injection system and optical fiber photometric detection system based on emitting diode light source. A multistrand bifurcated optical fiber was coupled with incident light,detector and flow cell. Optical fibers were used to carry light from the electronics unit to a reflective flow-through cell and back. The liquid flow path through the cell is linear with a large exit aperture such that bubbles are not trapped in the optical path. The optical arrangement is such that the incident light crosses the liquid flow orthogonally and is reflected back to the receiver fiber. This arrangement reduces the reflective index sensitivity by an order of magnitude relative to a conventional flow cell. The cell showed good immunity to refractive index and air bubble effects. The chromog enic reaction of chloride ion with mercury thiocyanate-iron(Ⅲ) was used as a m odel reaction to optimize the experiment system and check the optical system. The reflectance of the reaction was monitored with blue emitting diode. The linear range was 0-100 mg·L~-1 Cl~-. A detection limit (3 σ ) of 1.2 mg·L ~-1 ,precision of 1.5% ( n =11),and a throughput of 30 samples per hour were achieved.