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 pO(2) 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 pO(2) measurements to be made in vivo with high precision, Renal pO(2) 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 pO(2) measurements were obtained with a precision of +/-3% of the measured pO(2) (Kidney: 1.7 +/- 0.05 mmHg; Tumor: 1.37 a 0.04 mmHg). In vitro tests on the viability of cells and in vivo studies using Glory demonstrate the stability and inertness of this oxygen-sensitive material.