| In this dissertation, an intelligent on-line dilution system based on micro-sampling using sequential injection analysis technique was developed and used for spectrophotometric determining of nitrite and phosphate in environmental water samples.The dissertation is divided into three parts.In chapter 1, the sequence injection analysis (SIA) technique is reviewed with the emphasis on its application in automatic dilution and environmental analysis.In chapter 2, a sequence injection analysis on-line intelligent dilution system is described that was based on micro-sampling. The spectrophotometric determination of nitrite in environmental water samples is chosen as an example to study the system. The analog voltage signals from the spectrophotometer are fed back to the sequential injection analyzer and used to judge whether dilution is needed. All the procedures, with or without dilution, are carried automatically. The calibration curve is linear over the range of 1 to 50μmol/L without dilution and 50 to 500μmol/L with dilution. The system shows good stability with the relative standard deviation less than 1% (n=11). It is characterized by simple operation, good stability.In chapter 3, a sequence injection analysis method for the direct determination of phosphate in environmental samples with on-line intelligent dilution and photometric detection is described. Phosphate was performed by the molybdenum blue method with detection at 720nm.Under the optimized conditions, the calibration graph is linear in range of 1-6mg/L and 6-50mg/L PO43-. The relative standard deviation is 1.4 % for the determination of 2 mg/L PO43- (n=11) and 1.6% for the determination of 20 mg/L PO43- (n=11) with on-line dilution. The system is characterized by high automation and wide analytical working range, which meet the requirements of automatic analysis and on-line monitoring.
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