A highly sensitive detection system, which was composed of a thin, long, flow-through cell (TLFTC) and a semiconductor laser (SCL), for flow injection analysis (FIA) spectrophotometry has been developed. The new detection system was mainly composed of a thin, long, light path (100 mm x 1.4 mm i.d.), which was made of a polytetrafluoroethylene rod as an absorption cell, along with a GaAIAs semiconductor laser emitting at 780 nm (5 mW) as a light source. With the use of the detection system, the detection sensitivity was improved by about 10 times in comparison to FIA spectrophotometry with a normal flow cell. The detection system can be useful for determinations of many trace components in samples. The determination of total phosphorus in water, with the use of molybdenum-blue photometry, was one of its applications, and the relative standard deviation, detection limit (3σ), and linear range were 1.0%, 0.6, and 1.0-50 μg P/L, respectively. The determined results for the total phosphorus in the water samples by this method were almost coincident with those obtained by the official method. The detection system may also be useful for other flow-based analytical techniques such as liquid chromatography.
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