| In the new century, the developing direction of analytical chemistry is high sensitivity and selectivity, fast analytical speed, automatic convenient and economical. And analytical instrument is deeply automatized, dgitized, computerized, which has become more intelligent,informational. Since the importance of the instrument becomes more and more visible in the field of science as well as industry.This research in view of is the water and the waste water online examination request, discussed the flowing pause to analyze the instrument the design and the development method.This analysis instrument by flows the injection analysis basic principle, the examination technology underlie, the union luminosity analysis high sensitivity, the high accuracy characteristic, through monolithic integrated circuit realization automatic control and analysis.The whole apparatus is based on the principle of flow injection and Lambert-Beer's law ,and ATMEGA128 chip microprocessor serves as operation control and data collection; 540nm light-emitting diode (referred to as LED) serves as light source, and TSL2561 illumination sensor serves as the detector; so it realizes the automation of many functions such as liquid stream driving, sampling, sample injecting, data detecting, data processing and output displaying. The instrument can be applied in both on-line monitoring and direct off-line analysis of sample testing at any moment.The principle of the experiment is that nitrite couples with hydrochloric acid N-(1-naphthyl) ethylenediamine after being diazotized by sulfanilamide to form a rose-colored dye to be determined by light-emitting diode(LED) at 540nm; as for the determination of nitrate, it is reduced to nitrite by cadmium or zinc reduction column ,and then in connection with primary nitrite in water samples couples with hydrochloric acid N-(1-naphthyl) ethylenediamine after being diazotized by sulfanilamide to form a rose-colored dye to be determined by light-emitting diode(LED) at 540nm, and the value determined subtract the content of nitrite that is detected without making water samples flow through reduction column to elicit nitrate content. When the device is applied in the determination of nitrite, its detection limit is 2.92×10-3 mg/L; standard deviation S=1.54×10-3 mg/L, relative standard deviation RSD=1.45%.Its detection limit and precision satisfies the requirement of water quality testing.
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