HIGH-SENSITIVITY FLOW-BASED ANALYSIS SYSTEM USING A SEMICONDUCTOR-LASER AND THIN LONG FLOW-THROUGH CELL FOR THE DETERMINATION OF TOTAL PHOSPHORUS IN WATER

A highly sensitive detection system using a semiconductor laser (SCL) and a thin long flow-through cell (TLFCT) to match flow-based analysis , such as how injection analysis (FIA), has been developed. The SCL wa s a GaAlAs semiconductor laser emitting at 780 nm (5 mW), and the TLFT C, which has a 100 mm thin long light path, was made of a poly(tetrafl uoroethylene) (PTFE) rod. The sensitivity was essentially improved abo ut 10-fold in comparison to usual FIA-spectrophotometry using a 10 mm conventional flow cell. When this detection system was applied to the determination of total phosphorus (P) in water by molybdenum-blue spec trophotometry, the relative standard deviation, detection limit and li near range were 1.0% (n = 10 at 20 mu g P l(-1)), 0.6 (3 sigma) and 1. 0-50 mu g P l(-1), respectively, and the results for the samples were fairly consistent with those by the official method. It may also be po ssible to apply the present detection system to other flow-based analy tical methods such as the liquid chromatography family.