Studies And Applications Of Catalytic Spectrophotometry For Determination Of Traces Formaldehyde And Nitrite

Formaldehyde and nitrite are both poisonous and supposed to cause cancer. Therefore, their determination is not only an important aspect in food and water quality control, but also meaningful for the development of biological science. Small amount of formaldehyde and nitrite are commonly analyzed by spectrophotometric method for it is simple and efficient, but the problem is that the detection limit is not low enough and the reagents used for detection is toxic. Thus, it is inevitable to find new analytical techniques which are safer and more sensitive. Catalytic spectrophotometry is a branch of kinetic spectrophotometry. It is considered to be one of the most sensitive methods. So it is meaningful to find new methods which are stable, selective and with good reproducibility.After reading a lot of relative documents and information, some new catalytic kinetic spectrophotometric methods were studied. Based on the catalytic effect of formaldehyde and nitrite on the O-R reaction, we choose potassium bromate as oxidant while quinionimine-dye as reducing-agent. The reaction temperature, time, medium and reagent concentration were optimized. In addition, the reaction mechanism has been researched. These spectrophotometric methods are simple, stable, selective and with good reproducibility. They have been applied for the determination of trace formaldehyde and nitrite in the food and water samples with satisfactory results.This paper is divided into five chapters.In the first chapter, we summarized the theory and the development of catalytic kinetic spectrophotometry, analytical techniques of formaldehyde and nitrite, and the application of catalytic kinetic spectrophotometry on the detection of formaldehyde and nitrite.In the second chapter, we studied a new catalytic spectrophotometric method which was based on the catalytic effect of formaldehyde on the reaction between potassium bromate and Azur A. Absorbance change was measured at 610nm. The detection limit was 0.016mg/L with linear range of 0.035～0.66 mg/L, the linear equation wasΔA=0.074 CHCHO (mg/L) +0.351(R=0.9991). It has been also applied for the detection of trace formaldehyde in throw-away paper cups for the first time. The results showed that the content was little and those paper cups could be used safely.In the third chapter, another new catalytic spectrophotometric method for the determination of formaldehyde has been proposed. The method is based on the catalytic effect of formaldehyde on the oxidation reaction of Azur B by bromate ion in sulphuric acid medium. Absorbance change was measured at 590nm. The calibration curve showed the linear range was 0.096～0.24 mg/L, the linear equation wasΔA=3.752CHCHO (mg/L)-0.341(R=0.9998). The detection limit was 1.3×10^-3mg/L. The method has been applied to the determination of trace formaldehyde in rice flour and vermicelli. The recovery is between 98.5% and 101.2%.In the forth chapter, we studied a new catalytic kinetic spectrophotometric method to detect the amount of nitrite. It was based on the catalytic effect of nitrite on the reaction between potassium bromate and brilliant cresol blue. Experimental conditions, such as reaction temperature, time, and the concentration of reagents were optimized by measuring the absorbance change at 630nm. Under the best condition, the detection limit was 2.9×10^-3 mg/L with linear range of 4×10^-3～0.200mg/L. The linear equation wasΔA=0.645C_NO2^-(mg/L)+0.279(R=0.9944). This method is quick, stable and with little interferences. It has been applied for the detection of nitrite in water. The recovery was between 97.5 % and 102.5%.In the fifth chapter, a new catalytic spectrophotometric method for the determination of nitrite has been devised. It is based on the catalytic effect of nitrite on the discoloring reaction of Nile blue sulphate oxidized by potassium bromate in acetic acid medium. Absorbance change was measured at 640nm. There was a linear relationship between the decrease of the absorbance and the concentration of nitrite in the range of 4×10^-3～0.240mg/L, the linear equation wasΔA=0.850C_NO2^-(mg/L) +0.0268(R=0.9997), the detection limit was 3.5×10^-3 mg/L. This method has been used directly to measure the content of nitrite in the water. The results were quite satisfactory. The recovery was between 95.0% and 100.0%.