Abstract: A portable apparatus for measuring the electrochemical characteristics of a sample is disclosed. A disposable cartridge, including a plurality of interconnected flow chambers, houses a printed circuit board substrate upon which reference and indicating electrodes are formed. The electrodes are employed in the presence of chemical reagents to aid in the electrochemical determination of a sample undergoing analysis. A thermal sensing element is in close proximity to the electrodes to permit the correction of the measurement for variations in temperature. After a pH value has been determined, the used cartridge can be mechanically ejected thus eliminating user exposure to the blood sample being measured. In this way, the pH of a blood sample can be determined quickly, effectively, inexpensively and with a minimum amount of sample and reagent preparation.