Measurement of tubular fluid bicarbonate concentration by the cuvette-type glass micro pH electrode.

NIy comments will be confined to aspects of electrode construction or measuring techniquie that liffer from those originally (lescribed by Uhlich, Baldamus, and Ullriclh(l). I wislh to indlicate my deep gratittu(le to these investigators who kin(dly introduce(d me to their elegant method in 1968. The hiiglh impedlance Orion 801 amplifier witlh specially slhielded cables was used for the pH electrode portion. The multichambered Plexiglas bath (Fig. 1) differs only in small details from that built by the Frankfurt group. Our chamber is perhaps simpler to construct because it is madle of cylindrical shapes and we have not required sloping si(les to control bubble accumulation. For reasons that are not entirely clear to me we usually get very quiet records despite the fact that we do not tuse a cage set-uip. The major modifications wlhiclh we introcltdcedl involve sample handling, validation of the pCO. of the sample, an(d the question of so-called memory effects. In the following paragraplhs I will review our experience relating to these issues and then comment on some of the tlheoretical points concerned witlh the calculation of tubular fluid bicarbonate or pH tusing this type of in vitro measuring svstem. It was found that wlhen the sample is introduce(d into the electrode, movement of its meniscuts create(d botlh electronic noise andl the danger of aspirating the entire sample tlhereby lbreaking contact with the external reference electrode. A constriction well tup into the inert glass segment as slhown in Figs. 2 and 3 stabilize(l the meniscus and minimizecl these difficulties. Seconcl, in our early trials serious cliscrepancies were found between the actual bicarbonate concentration of known micro sample standards, andl the bicarbonate