HIGHLY SENSITIVE DETECTION SYSTEM COMPOSED OF A THIN, LONG, FLOW-THROUGH CELL AND A SEMICONDUCTOR-LASER FOR FIA SPECTROPHOTOMETRY AND ITS APPLICATION TO THE DETERMINATION OF TOTAL PHOSPHORUS IN WATER

A highly sensitive detection system, which was composed of a thin, lon g, flow-through cell (TLFTC) and a semiconductor laser (SCL), for flow injection analysis (FIA) spectrophotometry has been developed, The ne w detection system was mainly composed of a thin, long, light path (10 0 mm x 1.4 mm i.d.), which was made of a polytetrafluoroethylene rod a s an absorption cell, along with a GaAlAs semiconductor laser emitting at 780 nm (5 mW) as a light source. With the use of the detection sys tem, the detection sensitivity was improved by about 10 times in compa rison to FIA spectrophotometry with a normal flow cell, The detection system can be useful for determinations of many trace components in sa mples. The determination of total phosphorus in water, with the use of molybdenum-blue photometry, was one of its applications, and the rela tive standard deviation, detection limit (3 sigma), and linear range w ere 1.0%, 0.6, and 1.0-50 mu g P/L, respectively. The determined resul ts for the total phosphorus in the water samples by this method were a lmost coincident with those obtained by the official method. The detec tion system may also be useful for other flow-based analytical techniq ues such as liquid chromatography.