Studies On Sequential Injection Coupled With Chemiluminescence For The Determination Of Trace Chromium And Arsenic

In this dissertation, the sequential injection method combined with chemiluminescence detection technique was proposed and applied for the determination of trace trivalent chromium in the environmental water, urine samples, trivalent arsenic in water samples and satisfactory results were obtained.The first section of the dissertation concerned the review on the progress of analytical methods for the determination of trivalent chromium in recent years. The methods including atomic spectrometry, spectrophotometry, electrochemistry, molecular luminescence, and the flow injection analysis were introduced and their analytical performance was evaluated briefly.The experiment in the second section of the dissertation described sequential injection combined with chemiluminescence detection for the determination trivalent chromium, which is based on trivalent chromium catalysis to chemiluminescence produced by luminol hydrogen peroxide system under alkaline condition, and the CL intensity is proportional to the concentration of trivalent chromium in a certain range of concentration. Sodium bromide was used in the experiment as the reaction sensitizer, EDTA as a masking agent to improve the sensitivity and selectivity of the reaction. Under the optimum condition, the linear response range is1.0×10-9-1.0×10-7mol/L. The detection limit (3σ) is3.2×10-10mol/L. The relative standard deviation (rsd) is0.74%for eleven repeated measurements at5.0×10-8mol/L levels. The method was applied to the determination of chromium in both the environmental water samples and urine samples, and the recoveries are over93.7%-108.5and91.9%-107.5%respectively. The determination result of the national standard material (GSB07-1187-2000) was in agreement with the certified value.In the third section, a simple, fast sequential injection system with chemilumine-scence detection for the determination of arsenic in water samples was proposed, based on arsenic oxidized by potassium permanganate in acidic medium. Using formaldehyde and sodium hexametaphosphate could significantly enhance the CL intensity of the system. CL intensity is linear response in a certain range of content of As(Ⅲ). A univariate approach was adopted for the optimization of experimental parameters, and the possible reaction mechanism was also discussed. With sequential injection sample controlled by software, the volume of sample and reagents were reduced greatly and the efficiency had been improved apparently. The CL intensity is proportional to the concentration of arsenic in the range1.0-20.0μg/L and20.0-400.0μg/L, respectively. The detection limit (3σ) is0.44μg/L. The relative standard deviation for eleven repeated measurements at10μg/L levels is1.7%, and the relative standard deviation for thirteen repeated measurements for100μg/L arsenic is0.89%. The method was applied to the determination of arsenic in freshwater samples and obtained satisfactory results.In the last section, a summary for the characteristic of SI-CL system was described.