A Multiple Electrode Selector Used with pH Meter. Gregory S.Duboff and G. Henry Pratt, Biochemical Research Laboratory and Physics Research Laboratory, Emery Tumor Group, Los .Ingeles, Calif.
the reinvestigation of a procedure [Duboff, G. S., and Hirshfeld, S., Cancer Research, 6 , 57 (1846)] estimation of the oxidation of tyrosine induced by tyrosinase by electropotential measurements involved the selection of a suitable set of ~lectrodes. The difficulties that arose in measuring and recording potentials and pH indicated the need for an instrument t'hat could eliminate the necessity of separate determinations in a closed, air-tight vessel, con1aining a conlplicated system of enzyme, substrate, and serum. URING
Figure 2 is a diagram of the arrangement of the apparatus, as used in obtaining potentiometric measurements of tyrosine oxidation. K i t h this setup it ivas possible t o secure continuous estimations of enzyme activity, without changing and cleaning each metal electrode with hot chromic acid between measurements, I n fact, it is possible to measure the pH a t any point of t,he reaction, without interfering with the osidation. The apparatus consists of a heavy-walled glass jar, into which is inserted a rubber stopper through which are thrust the various e!ectrodes and glass tubes for introducing the reagents and gassing. The electrode cables are led upward and grouped together with a clamp and finally to their respective receptors in the switch box. This permits the occasional gentle shaking of the contents, thus eliminating a stirrer. AIDEDin part h y a g r a n t from the Emery Cancer Re-;cilirL F u n d .
Simple Calomel Electrode and Cell for Polarographic Analysis. A. H. Brunner, Jr., and P. B. hleans, Jr., Ansco Division, General Aniline and Film Corp., Binghamton, 9.Y.
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and Laitinen [IND.Esc. CHEII., .l?;a~.ED., 11, 504
IXGASE:
Figure 1.
L (1938)] pointed out the disadvantages of using the quiet mercury pool as the nonpolarizable electrode in polarographic
Wiring Diagram
Pin jacks Plug to pH meter Shielding connected to metal box T. Shielded jack
.V.
P. S.
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Figure 1 &QW a wiring diagram of the circuit for an inexpensive multielectrode selector. The box is metal, with crackled finish, and flanged on one side to accommodate the Lucite and metal plate. The box is 4 inches high, 5 inches wide, and 6 inches long. The three pin jacks are KO.8789 for the metal electrodes; the one shielded jack is Becknian No. 8660 for the glass electrode; and the shielded cable, with plug, for connecting the box to the p H meter is S o . 1880-1.
P
work and described an H-type electrolysis vessel which contains a standard reference electrodc as an integral part. This (bell has low internal resistance Ivhich makes potential correction for iR drop unnecessary, but it requires a special filling when chloride ions cannot be tolerated, and it cannot be used at higher temperatures. Although calomel electrodes commercially available for use with potentiometers have too high resistance for polarography, their general design can be utilized to make a compact half-cell of low resistance which, rvhen combined with a simple cuplike electrolysis vessel, permits msembly of an ewily made, compact unit. The conat1Uctional details of the calomel electrode and salt bridge are shown in the accompanying sketch. The electrode is %PM ENT made from soft elass t,ubing 8 mm. in-0u.tside diameter, in one end of which a short piece of platinum wire has been sealed. It may be packed in inverted position, first with sufficient metallic mercury to cover 3 the wire, then with mercury - mercuric chloride paste in saturated potassium chloride made stiff with Celite analytiHOSE TO cal grade filter aid, DRAIN and, finally, plugged fairly tightly n-ith glass wool. The bridge is made from borosilicate glass tubing; the uiper portion is 13 nim. and the lower portion 8 mm. in outside diameter. The bridge is packed tightly a t the narrow end with filter paper pulp which has been wetted with the bridge solution (Kolthoff, I. AI., and Furman, N H., "Potentiometric Titrations," p. 139, New Pork, John Wiley & Sons, 1926). If the plug is packed tightly enough, there will be practically no flox of solution from
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1
R
M
E
Figure 2. -4rrangement of Apparatus E.
Glass electrode
P.
pH meter Reference electrodc Switch box
M. Metal electrodes
R. S.
The selector switch should be chosen with care, so that leakage between electrodes at this oint will be eliminated. The insulating material of the switch scould be of steatite or an equally good ceramic. The switch points and arm should be silver plated. Finally, the arm should be adjusted so that changes from electrode t o electrode can be made as quickly as possible. The reference (calomel) electrode is connected directly to the pH meter. Holes ale cut in the metal plate which does the shielding. At no time is there any contact between the metal plate and any part of the circuit. The entire circuit is mounted on the Lucite for insulation. The aluminum plate measures 0.5 X 125 X 150 mm., and the Lucite measures 4 X 125 X 150 mm. The metal plate is placed under the Lucite. No ground is necessary. The device may be obtained assembled from the .ldolf Frese Corp , 116 Wwt 17th St., Los AngeleP 62, Calif.
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