Abstract The overall work presented in this thesis can be summarized as follow: - The anions fluoride, chloride, nitrate, phosphate and sulfate in the twelve selected green tea samples are present at acceptable concentration. The average concentration of the investigated anions at five min contact time in boiled water followed the sequence: F- > PO43- > SO42- > Cl- > NO3- - The mean distribution of the tested free ions in the twenty nine green tea leaves followed the order: K >P > Mg > Mn > Ca > Al > Si > Zn > Ni > Cu > Ba > Fe > Sr > Na > Mo > V - The total content and the chemical speciation (labile free ion and complex species of the element) of some selected metal ions (Al, Ca, Mg, Mn, Fe) and P in the tea sample was also performed. The results revealed that, the amount of complexed metal ions in particular Al is much higher than that present labile on boiled water. - The average concentration of caffeine, catechin, epicatechin, epigallocatechin, epicatechin 3- gallate and epigallocatechin 3- gallate in the infusion tea leaves in boiled water for five min employing HPLC at 205 nm were found in the range 0.086 - 2.23, 0.113 - 2.94, 0.58 - 10.22, 0.19 - 24.91, 0.22 - 13.88 and 1.01 - 43.34 mg g-1, respectively. The content of caffeine and catechins in the tested tea samples followed the sequence: EGCG > EGC > ECG > EC > C > Caffeine - The performance of the employed HPLC method was determined from the calculated values of the number (N) and the height equivalent to the theoretical plates (HETP) and the separation factor (Rs). The average values of N, HETP from the chromatograms at 10 µg mL-1 for the four catechins: EC, EGC, EGCG and ECG were found in the range 2.6×10⁴ ± 1.2×103 and1.7×10-3 ± 4.7×10-4 cm, respectively. The value of Rs calculated from the chromatogram for EGCG and EC was found equal 1.7 ± 5.53×10-2. The asymmetry (As) and capacity (k`) factors for the four catechins were found equal 1.0 and 2.97, respectively. The lower limit of detection (LOD) of the employed HPLC procedure for some catechins were found in the range 0.004 – 0.05 µg mL-1 and the values of lower limit of quantification (LOQ) were found in the range 0.01 – 0.17 g mL-1. The method was applied successfully for the determination of (+)-catechin even at trace and ultra trace concentration. The method was found rapid, ideal for routine analysis, reproducible, precise and accurate.