An Ultramicro Oxygen Electrode.

326-pg. 1964.-The advantages of a ~-p-diameter platinum cathode in the Clark-type o:xygen electrode are shown to be freedom from effects due to flow, stirring, or mechanical pressure. When used with a .5-mil polyethylene membrane the I-P electrode shows only a 2 ts difference between a vigorously stirred solution and the unstirred solution. A mechanical pressure of 200 psi on the I-P covered electrode caused only a 20% reduction in current. The use of a 1-p covered electrode as an implant is suggested. electrode implant Clark-type oxygen electrode modification polarographic electrode oxygen measurement platinum electrode S TAUB (7) HAS SHOWN that several important advantages are gained by reduction of the diameter of the platinum cathode in the Clark-type polarographic oxygen electrode (2). I will show here that a reduction of cathode diameter to I /5oth of that used by Staub leads to further advantages. The gas-permeable, membrane-covered oxygen electrode introduced by Clark had a platinum cathode of about 2,000-p diameter. This electrode was sensitive to pressure on the membrane and showed changes in output when the fluid under test was stirred or flowed past at different velocities. A reduction of cathode diameter to 50 p, as reported by Staub, or to 25 1-1, as in the B'eckman-Spinco modified Clark macroelectrode (part no. I 6 I-340, reduced the effect of flow or stirring but did not entirely eliminate it. Rice (5) has prepared I o-p-diameter electrodes but used them uncovered. He did not investigate the effect on output current of flow or pressure on his uncovered electrodes. Charlton's (I) study of a I 00-p membrane-covered electrode did include flow and pressure effects but he did not distinguish between the influence of electrode diameter and membrane thickness. I have prepared electrodes with a platinum cathode diameter of I p which are almost insensitive to flow, stirring, or mechanical pressure when used with a 12-p-thick poly-ethylene membrane. These electrodes have very fast response times, giving a ggyO reading in 30 set in water and in 5 set in gas. The alternative methods of reducing sensitivity to flow rate and pressure when using larger diameter electrodes are to use thicker or less permeable membranes. Both of these alternatives increase the response time and therefore are not as satisfactory as reducing the electrode diameter and using a very thin, highly permeable membrane. Several methods are available for making polarographic oxygen electrodes with a cathode less than …