Vibrating Dropping Mercury Electrode For Polarographic Analysis of Agitated Solutions DAVID A. BERMAN, PAUL R. SAUNDERS, AND RICHARD J. WINZLER School of Medicine, University of Southern Calgornia, Los Angeles, Cali$. H E dropping mercury electrode has been limited chiefly to Tsolutions that are free from agitation, for any stirring results in irregular dropping of mercury from the capillary and consequent fluctuations in current. The shielded dropping mercury electrode (8, 11) has been successfully applied to agitated solutions, but has the disadvantage of introducing a time lag in the current readings ( 7 ) . A vibrating dropping mercury electrode was developed by this laboratory to fill the need of applying the polarographic method to biological systems requiring continuous agitation. Enforced drop electrodes, which have been developed chiefly for increasing the accuracy of the current readings or for synchronizing the drop rates of multiple capillaries, have been described by several investigators. Kanner and Coleman ( 4 ) incorporated a solenoid in the design of their apparatus as a means of initiating a new mercury drop after the current measurement. Heyrovsk4. ( 3 ) used the device developed by Cermak and Hanus ( 8 ) for obtaining derivative curves. The drop rates of the electrodes in this device were synchronized by a solenoid. Skobets and KavetskiI (9) positioned a glass hoe under the dropping mercury electrode for the purpose of controlling the drop rate, and demonstrated that it was possible with this arrangement to increase the accuracy of the current readings. None of the authors describing such enforced drop electrodes indicated, however, that their devices could be applied to stirred solutions. The vibrating dropping mercury electrode described in this paper was developed specifically for systems requiring continuous agitation. Although the device was designed primarily for measuring the oxygen uptake of contracting isolated cardiac muscle preparations, it is also suited for other analytical procedures where agitation of the solution is required.
was mounted on rubber to eliminate any appreciable vibration other than that of the electrode. Only slight irregularities in current were observed (Figure 2) when the apparatus was free of secondary vibration. A comparison between polarograms of 0.001 M lead nitrate, taken with the conventional dropping mercury and the vibrating dropping mercury electrode in the absence of oxygen, is shown in Figure 2. I n the lower curve, B, taken with the vibrating dropping mercury electrode, nitrogen was continually passed through the solution. Some reduction in sensitivity is apparent with the vibrating electrode. A linear relationship between oxygen tension and current was demonstrated. Tenth molar potassium chloride containing 0.03% gelatin as a maximum suppressor was equilibrated with four gas mixtures of oxygen and nitrogen containing 99.7 * 0.2% oxygen, 49.9 * 0.2% oxygen, 20.9% oxygen (air), and 0% oxygen (nitrogen). The gas mixture was bubbled continuously into the solution during the recording of the current a t a constant voltage (-0.6 volt us. S.C.E.). The dropping mercury electrode has been successfully applied to the study of the rate of oxygen consumption of yeast by Baumberger (1) and W-inzler (10); the &02 values agreed with values obtained with conventional manometric methods. Figure 3 shows that the rate of oxygen consumption of yeast, measured with the vibrating electrode, agrees with that determined for the same yeast suspension with the conventional electrode. The readings obtained when the solution was saturated with air are indicated by A for the dropping mercury electrode and by B for the vibrating mercury electrode. The rate of oxygen utilization as determined with the vibrating and conventional elec-
APPARATUS A\D PROCEDURES
Figure 1 presents the details of construction of the vibrating dropping mercury electrode. The device is driven by a O.Oj-hp., 1800 r.p.m. synchronous motor, A , geared up through a 1 to 2.7 spur gear train, B and C, to 4860 r.p.m. Spur gear C is mounted on one end of a Bhaft, D, which passes through a brass sleeve bearing, F , and terminates with a 0.25-inch extension n i t h an eccentricity of 0.012 inch. A phosphor bronze shaft, 0.025 inch thick, G, attached to the mounting of ball bearing E, links the eccentric portion of D with a flexible phosphor bronze plate, H , 0.025 inch thick. steel shaft, I , 0.125 inch in diameter, connects H to a holder, J . The capillary, mercury reservoir, and tubing (not shown) are the types used in the conventional dropping mercury electrode ( 5 ) . The height of the mercury column was approximately 80 cm., and the drop time in the absence of vibration was 4 seconds. Sargent-Heyrovskg polarograph Models XI and XI1 were used in this study. A saturated calomel electrode served as the anode. The temperature in all experiments mas 23" * 0.1" C ill1 chemicals were reagent grade, and all solutions IT ere prepared with double-distilled water EXPERIMENTAL RESLLTS
With the rapidly vibrating electrode, the drop size and time were greatly reduced and moderate agitation of the solution under these circumstances did not affect the reproducibility of the current significantly. The vibrating assembly
V Figure 1. Diagram of Vibrating Dropping Mercury Electrode
1040
V O L U M E 23, NO. 7, J U L Y 1 9 5 1
1041
Table I. Relation between Current and Concentration of Lead Ion
Electrode Vibrating Vibrating Conventional Conventional
Current (Corrected
Pb(N0l)r Concn., Millimoles/ Liter
for Residual
1.0 0.5 1.0 0.5
3.90 1.97 6.83 3.41
Current),
pa,.
pa./hfillimole/Liter 3.90 3.94 6.83 6.82
urated calomel electrode. Sitrogen gas was passed continuously through the solution during the recording of the current with the vibrating dropping mercury electrode. The use of the dropping mercury electrode for the amperometric titration of lead has been described by Kolthoff and Pan (6).
50r
A
I I
I
I
2
3
ML. 0.05 M K 2 C ~ 2 0 7
J
e
Figure 4. Amperometric Titration with Vibrating Dropping Mercury Electrode
Figure 2. Polarograms of Oxygen-Free 0.001 M Lead Nitrate in 0.1 M Potassium Chloride and 0.0370 Gelatin A. Dropping mercury electrode B. Vibrating dropping mercury electrode
trodes was 13.5 and 13.2 cu. mm. per minute, respectively. S o time lag was observed with the vibrating elertrode. Table I shows that with both the vibrating and conventional electrodes a linear relationship betn een current and lead concentration is obtained. Two concentrations of lead nitrate in 0.1 -11 potassium chloride plus 0.03% gelatin were used. The current was measured a t a potrntial of -0.8 volt with respert to thr sat-
Titration of 50 ml. of 0.0096 M Pb(N0s)z i n 0.1 M KNOi with 0.05 M KzCrzOi at voltage u s . S.C.E. = -1.0. Nitrogen passed continuously through solution durin titration. Theoretical end point = 4.80 ml. of 0.05 M &Cr107
This titration was selected as an example of the applicability of the vibrating dropping mercury electrode to amperometric titrations performed a t voltages a t which oxygen is reduced (Figure 4). A disadvantage of the dropping mercury electrode in amperometric titrations where oxygen is an interfering substance is that, unless air-free reagents are used, an inert gas must be passed into the system after each addition of reagent, and then the solution must be allowed to come to rest before the current can be measured. With the vibrating dropping mercury electrode, amperometric titrations can be performed more rapidly because an inert gas can be passed into the system continuously without interfering with the current measurement. ACKNOWLEDGMENT
I
The study reported in this paper was supported by a grant from the Life Insurance Medical Research Fund. The authors wish to thank the Allan Hancock Foundation for the use of facilities during this investigation. LITERATURE CITED
Figure 3. Rates of Oxygen Utilization of Yeast Determined with Vibrating and Dropping Mercury Electrodes 50 m g . of yeast (Fleischmann’s) i n 10 ml. of 0.1 M phosphate buffer, PH 6.8, containing 1%glucose. Voltage US. S.C.E., -0.6
(1) Baumberger, J. P., Cold S p r i n g Harbor Symposia Quant. Bid., 7, 195 (1939). (2) Cermak, Vl., and Hanus, T I . , Czech. P a t e n t Application P 3181-48 (Oct. 22,1948). (3) Heyrovskj., J.. Ckem. Listy, 43, 149 (1949). (4) Kanner, O., and Coleman, E. D., U. S. Patent 2,361,295 (Oct. 24,1944). ( 5 ) Kolthoff, I. M., and Lingane, J. J., “Polarography,” Kew York, Interscience Publishers, 1941. (6) Kolthoff, I. M., a n d P a n , T.D., J . Am. Chem. Soc., 61, 3402 (1939). (7) Laitinen, H. A , , personal communication. (8) Laitinen, H. A , and Burdett, L. IT.,AXIL. CHEY., 22, 833 (1950). (9) Skobets, E. M.,and Kal-etskii, Ii. S., Zavodskaya Lab., 15, 1299 (1949). (10) TTinzler, E. J., .J. Cellular C o m p . PhusioZ., 17, 263 (1941). (11) !%e, I T , S., Chemistru & Iizdustrg, 1948, 37. KECEIVED August 2 1 , 1950
