A new process to pretreat blood samples has been developed. This process combines the Advanced Oxidation Process (AOP) treatment (using H 2 O 2 and UV irradiation) with acid deactivation of the enzyme catalase in blood. A four-cell reactor has been designed and built in house. The effect of pH on the AOP process has been investigated. The kinetics of the pretreatment process shows that at high CH 2 O 2 ,t=0 , the reaction is zeroth order with respect to CH 2 O 2 and first order with respect to C blood . The rate limiting process is photon flux from the UV lamp. Degradation of whole blood has been compared with that of pure hemoglobin samples. The AOP pretreatment of the blood samples has led to the subsequent determination of chromium and zinc concentrations in the samples using electrochemical methods.