Gloxy: An oxygen-sensitive coal for accurate measurement of low oxygen tensions in biological systems

This paper describes the characteristics of a new oxygen sensitive, paramagnetic material that has some significant advantages for measurements of tissue pO₂ by in vivo EPR. This paramagnetic component of Welsh coal, termed 'gloxy' was found to have valuable EPR features that allow accurate measurement of low oxygen tensions in vivo; these include large oxygen- dependent changes in linewidth, a high number of paramagnetic spin centers (resulting in high signal amplitude), and stability in tissue allowing repeated pO₂ measurements to be made in vivo with high precision. Renal pO₂ was measured deep in the medulla region of isolated perfused kidneys and found to be lower than that in the cortex (1.7 ± 0.05 and 7.1 ± 0.3 mm Hg, respectively). The quality of the EPR signal obtained from the renal outer medulla and also from tumors in mice was such that the pO₂ measurements were obtained with a precision of ±3% of the measured pO₂ (Kidney: 1.7 ± 0.05 mmHg; Tumor: 1.37 ± 0.04 mmHg). In vitro tests on the viability of cells and in vivo studies using Gloxy demonstrate the stability and inertness of this oxygen-sensitive material.