Direct determination of oxygen by HPLC. 1. Basic principles of a sensitive and selective oxygen sensor

The basic principles of a novel, versatile, sensitive, and selective oxygen-sensing assay are presented in this paper. For the first time, liquid chromatography with electrochemical detection (at the hmde) has been used for the determination of oxygen. All factors concerning optimization of the chromatographic separation conditions and electrochemical detection with respect to direct determination of oxygen even in complex biological samples are discussed. Due to the combination of a chromatographic technique with amperometric detection, a high selectivity can be achieved. A direct and linear relationship between the oxygen concentration in the sample and the reduction current was verified in a large concentration range from saturation down to trace level oxygen concentrations. The novel oxygen-sensing assay provides a much higher sensitivity compared to conventional oxygen sensors. In principle, O(2) concentrations down to 4.5 × 10(-)(9) mol L(-)(1) O(2) (corresponding to a signal-to-noise ratio of 3) can be detected. Precision was determined by repeated measurements (n = 6) of air-saturated solutions (2.5 × 10(-)(4) mol L(-)(1) O(2), 20 °C, 920 mbar) which yielded relative standard deviations of lower than 0.2%.