The production and testing of double-barreled pH glass microelectrodes for measurement of intratubular pH.

It lhas been possible to miniatuirize the glass pH electrode to an extent tllat it can be uised to measture the intraltiminal pH of single mammalian nephrons(l). There are, however, a nutmber of problems that arise from the miniaturization process. Thlese includ(le electrode insulation, the incorporation of a suitable reference electrode witlh the pH glass electrode, an(d the ultimate achievable miniiaturization of the micro pH sensitive tip. There are certain criteria that must be satisfiedl before suichi electrodles can be used. The first arises from tlle problem of a(lequate insuilation. Instulation mtust be suclh that only a small portion of tlle tip of the electrode that is entirely witlhin the lumen of the neplhron is responsive to lhy(drogen ion activity. The reference electrode shoukl be an integral part of the pH electrocle so that the voltage reading across the reference and pH electrode will not be affecte(d by any transepithielial potentials that may exist within the neplhron. The size of the tip of the electrode slhotuld be sufficiently small so as not to cauise extensive daimage to the neplhron wlhen the ptunctture is made. It is now possible to make a miniatturized pH electrode witlh an integral reference wlhose combined tip cliameter is somewlhat less than 1 ju. Probably the most formidlable problem in making the miniaturizedl pH electrode is to obtain adlequate insulation of all but the extreme tip of tlle glass pH electrode. The types of insulating materials triedl by Us and the results obtained lhave been discussedl previously(2). All organic insulatinig materials were tunsuccessful; two metlhods of insulation proved satisfactory. Tlle first was a staining teclhnique in wlhiclh some of the sodium in the sturface of the glass pH capillary was exclhanged witlh silver ions, thus obliterating its pH sensitivity(3). Tllis metlhod, altlhouglh quite satisfactory for producing small numbers of electrodes, was