Studies On Spectrophotometry For The Determination Of Hydroxyl Radical And Tea Polyphenols

In this dissertation, a new spectrophotometric method for the determination of hydroxyl radical and a sequential injection analysis (SIA) coupled with spectrophotometric method for determining tea polyphenols in tea samples were developed with satisfactory results.The first section of the dissertation concerned the review on the physiological effects and damage of some radicals including hydroxyl radical, the development of analytical methods for the determination of hydroxyl radical, and sequential injection analysis technique was also introduced.For the second section, a novel spectrophotometric method for assessment of hydroxyl radical based on Rhodamine6G (Rh6G)-Co2+-KI-H2O2system in the medium of HAc-NaAc buffer solution was proposed. The possible mechanism of the reaction was discussed, and the experimental parameters including concentration and volume of the reagent and sample, acidity, temperature and other experimental factors were optimized by univariate approach. The antioxidant ability of several antioxidants including L-ascorbic acid, thiourea, and gallic acid were evaluated. The experimental result shows the scavenging activity of antioxidants is gallic acid> thiourea> L-ascorbic acid. The catalytic ability of Co2+is the highest compared with Mn2+and Fe2+. The hydroxyl radical scavenging activity of apple and celery are the highest with scavenging efficiency of78.2%and73.2%, respectively.In the third section, the SIA technique coupled with spectroptometric detection was developed to determine tea polyphenols in tea samples. It is based on a blue-violet complex formed by ferrous tartrate reacted with tea polyphenols in the medium of phosphate buffer solution (pH=7.50), and the reaction product was measured at wavelength540nm. The calibration curve was linear over5.0～100μg/mL with the correlation coefficient of0.9998, a precision (RSD) of0.68%(n=11), a detection limit (3σ) of0.8μg/mL and throughout of36samples/h. Good recoveries were obtained from92.1%to104.0%. The determined results for tea samples by proposed method were in good agreement with that of standard reference method (GB8317-87).In the last section, the characteristics of the two methods were summered.