| Total nitrogen and total phosphor are two important indicators of sea environmental monitoring, high concentration of phosphate and nitride can cause seawater eutrophication, finally lead to russet tide. So, accurate determination of the total nitrogen and total phosphor in seawater is very important. At Present, our country has mostly adopted national standard traditional off-line analysis to determine total nitrogen and total phosphorus. The traditional laboratory analysis has many abuses, such as complex operation,and the long measurement cycle. And not answered needs of preventing calamity,monitoring seawater situation and researching scientific. Style of monitoring based on automation, intelligent and network will replace style of measuring manually in the laboratory in process. There are some modern equipments of monitoring nitrogen or phosphorus all over the world, but the existing monitoring instruments for nitrogen or phosphorus is not adapted to the determination of total nitrogen and total phosphorus united in seawater.This research work is to manufacture a set of on-line automatic analytical methods and devices to monitor total nitrogen and total phosphorus in seawater. It makes great sense to improve the monitoring level of China's seawater quality.This paper studies the reduction and diazotization and azo-dye method of total nitrogen after digestion, and determines the best determination conditions of reduction and coloration. Establish a set of on-line automatic analytical devices to monitor total nitrogen and total phosphorus after digestion, selected the method of flow injection-cadmium column reduction, diazotization and azo-dye spectrophotometric as the on-line automatic determination method of total nitrogen and total phosphorus in seawater after digestion. The method of molybdate determination of total phosphorus in seawater after digestion.On the basis of a series of single element test, determine the best working parameter of each flow path.1. The conditions of reduction are:pump speed of reduction is 20rmin-1, the diameter of cadmium particles is 0.3-0.8 mm, and the length of the cadmium column is 8cm, range of pH is 8.0 to 9.0. The reduction efficiency can be stabilized at more than 98%. The chromogenic conditions are:concentration of sulfanilic acid solution is 0.16g·L-1,reacting for 0.5 min, concentration of hydrochloric acid naphthyl ethylenediamine solution is 0.12 g·L-1,the chromogenic time is 5 min. Under optimum working conditions, this method can get the good liner range, precision, detection limit, percent recorvery.2. The chromogenic conditions of tatal phosphor are:chromogenic agent A: concentration of ammonium molybdate is 0.24g·L-1, chromogenic agent B:concentration of antimony potassium tartrate is 0.04g·L-1, sodium sulfate is 4g·L-1,antiscorbutic vitamin is 4 g·L-1. This method can get the good liner range, precision, detection limit, percent recorvery.3. The error cause by differ salinity can rectify by the carrying current and standard curve of corresponding salinity. This method has very strong power of anti-interference, in the range of error permissible, major element of seawater have no impact on determining.4. The optimum working conditions of flow injection analysis system of total nitrogen after digestion are:sample volume is 20mL, length of reaction coil L1 is 0.4m, length of reaction coil L2 is 2m, rate of flow of sample is 4mL·min-1, concentration of sulfanilic acid solution is 0.64g·L-1, reacting for 0.5 min, concentration of hydrochloric acid naphthyl ethylenediamine solution is 0.48g·L-1。5. The optimum working conditions of flow injection analysis system of total phosphorus after digestion are:sample volume is 20mL, length of reaction coil L1 is 2m, length of reaction coil L2 is 2m, rate of flow of sample is 4mL·min-1. Chromogenic agent A:concentration of ammonium molybdate is 0.8g·L-1,chromogenic agent B: concentration of antimony potassium tartrate is 0.16g·L-1, sodium sulfate is 16g·L-1 antiscorbutic vitamin is 16 g·L-1.Test method is reliable and stable,high speed of analysis, instrument and reagent are all stable, convenient for maintaining.
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