Application Of Sequential Injection Technique Coupled With Spectrophotometer In Element Speciation Analysis

In this dissertation, the sequential injection coupled with spectrophotometer technique was proposed and applied to the speciation of iron and phosphorus.The first section of the dissertation is a review on importance and recent advances of element speciation. Extraction of phosphorus and analytical methods of element speciation were introduced. The methods mainly include atomic spectrometry, molecular spectrometry, chromatography, capillary electrophoresis, electrochemistry, mass spectrometry and the flow injection analysis.The second section described a sequential injection spectrophotometric method for determination of iron speciation. Tiron was used as the chromogenic reagent in acid medium for Fe (Ⅲ) and total iron after Fe (Ⅱ) was on-line oxidized to Fe (III) by H2O2. The loading sequence, the concentration and volume of reagents, and flow rate were optimized by univariate method. Middle-carrier method was proposed for baseline separation of the response signals of Fe (III) and total iron. On-line oxidation and determination of iron speciation by same calibration curve were achieved. The linear range was0.1-25mg/L and detection limit(3a) was0.08mg/L, for both Fe (Ⅲ) and Fe (II). The%R.S.D. was1.7%and1.1%for Fe (III) and Fe (II), respectively. A throughput of10samples (20peaks)/h can be achieved. The proposed method was successfully applied to determination of iron speciation in soil and medication with a recovery between93%and105%.In the third section, an automated flow-through microcolumn fractionation system was proposed for monitoring phosphorus in soils. This system includes dynamic extraction and on-line determination of phosphorus. H2SO4(0.25mol/L) was used as an extractant for fractionation of phosphorus in soil samples. The determination was based on Molybdenum Blue(MB) reaction. The proposed flow assembly implies several advantages as compared to fractionation analysis in the batch mode in terms of saving of extractant and other reaction reagents, shortening the operational times from hours to minutes. The linear range was0.1-5mg/L and detection limit(3a) was0.03mg/L. The relative standard deviation for thirteen repeated measurements is2.2%for4mg/L phosphorus. The proposed method was successfully applied to extraction and determination of phosphorus in different soil samples with a recovery between90%and114%.In the last section, characteristics of the experiments were summarized, and the prospect of application of SI coupled with spectrophotometer in element speciation was described.