chloric acid, made basic with excess ammonium hydroxide, and reprecipitated with sodium carbonate. The precipitate was collected, washed, and dried. Thirty milliliters of concentrated nitric acid were added and the mixture was digested warm for 10 to 15 minutes; then it was cooled in an ice bath to just below room temperature. The precipitated strontium nitrate was collected by centrifugation and Tvashed b y treatment with 30 ml. of concentrated nitric acid as above. The strontium nitrate was dissolved in 1%-ater, and made basic with ammonium liydroxide, and the strontium was reprecipitated as carbonate by adding 10 nil. of 3N sodium carbonate. The carbonate precipitate was transferred to a suitable counting dish, dried, and betacounted for total alkaline earth activity. Cesium was precipitated from the first carbonate filtrate with silicotungstic acid. After concentration, the filtrate
was made 3N in hydrochloric acid, after which 0.125M silicotungstic acid, 2 ml. per 100 ml., was added. The precipitate was collected and purified in the standard manner (a), after which it was counted by gamma scintillation or in a beta-counter. By precipitation of basic sulfide, folloTved by carbonate and cesium precipitation steps, most isotopes of interest in sea water can be separated. If other elements are to be determined, separate portions must be taken for the analysis. The sulfide precipitate contains more than 95y0 of the activity due to rare earths (including yttrium), ruthenium, chromium, zinc, cobalt, and similar metals. The alkaline earth precipitate contains 90% of the strontium and presumably a similar amount of the barium-radium. The cesium
precipitate contains about 95% of the cesium. LITERATURE CITED
(1) Goldin, A. S., Velten, R.J., Frishkorn, G. W., ANAL.CHEIII.31, 1490 (1959). 1 2 ) Kahn. B.. Smith. D. K.. Straub.
Straub, (1958). N. IT., " PrenI
,
",
Water
Supply Paper 6 5 i (1952). (6) University of Washington Applied Fisheries Laboratory, AEC Doc. UWFL-42 ( h g . 15, 1955). ( 7 ) Zbid., UWFL-43 (Dee. 30, 1955). RECEIVED for review June 29, 1959. rlccepted October 16, 1959. Work supported in part by the -4tomic Energy Commission under Contract Yo. AT(495)-1288.
Cathodic Action of the Phenylenediamine Dihydrochlorides at the Dropping Mercury Electrode STEWART
R. COOPER
and OSCAR
F.
FOWLKES'
Howard University, Washington, D. C.
b The purpose of this investigation was to work out a method whereby the phenylenediamine dihydrochlorides could b e determined by reduction at a dropping mercury electrode. The ortho, meta, and para dihydrochlorides dissolved in tetramethylammonium bromide, with gelatin as a maximum suppressor, gave well defined waves in the 10-3M range. A plot of idvs. C gave a reasonably straight line. These compounds give waves that are easier to interpret than previous methods that have been proposed.
T
cathodic action of the phenylenediamine dihydrochlorides a t a dropping mercury electrode has been studied. The i d measurenents were made in the 10-3dI range and were read a t an E value of approximately -1.9 volts us. the saturated calomel electrode. A plot of i d 0s. C showed that it is possible to use such a graph in the estimation of these salts. Julian and Ruby (2) determined the oxidation-reduction potential of some substituted phenylenediamines polarographically using a platinum electrode. Bogdanov and Sukhobokova ( 1 ) determined p-phenylenediamine by titraHE
1 Present address, Riker Pharmaceutical Co., Northridge, Calif.
26
ANALYTICAL CHEMISTRY
€de
VS. S.C.E., VOLTS
Figure 1 . Current-voltage curves for o-phenylenediamine dihydrochloride in 0.1 M tetramethylammonium bromide and 0.01% gelatin 1 . 0.1M tetramethylammonium bromide o-Phenylenediamine dihydrochloride, X 10 - 3
2.
3. 4.
0.5 1.0 2.0
tion with ceric ion using a rotating platinum electrode. Lord and Rogers (3) analyzed the diamines by the anodic voltage scan method. Parker and Adams (4) determined the 0- and p-phenylenediamines b y anodic oxidation using a rotating platinum electrode and the current scanning technique.
5.
4.0 6. 6.0
This investigation is concerned with the possibility of determining the three phenylenediamine dihydrochlorides through the use of a dropping mercury electrode acting as cathode. The limiting currents obtained appear to be more linear than those obtained by the voltage scan or current scan technique.
Edc
VS. S.C.E., VOLTS
Figure 2. Current-voltage curves for p-phenylenediamine dihydrochloride in 0.1 M tetramethylammonium bromide and 0.01% gelatin C, MOLES/LX 10'
0.1M tetramethylammonium bromide p-Phenylenediamine dihydrochloride, X 1 0 - 3 2. 0.5 4. 4.0 3. 2.0 5. 6.0 1.
EXPERIMENTAL
Reagents. T h e samples of 0-, m-, and p-phenylenediamine dihydrochlorides and tetramethylammonium bromide were C.P. chemicals. Because aqueous solutions of t'he diamine salts are not stable in storage, they were prepared just before use. A saturated solution of potassium chloride, a 1% solution of agar in saturated potassium chloride, and O.lyosolution of gelatin were prepared. Apparatus. A Sargent XI1 polarograph was used t o record t h e waves: and a Sargent oxygen-removing furnace and tube were used t o purify t h e tank nitrogen t h a t was used for deaerating the solut'ioiis. An H cell t h a t contained a plug consisting of 1% agar in saturat,ed potassium chloride was used to hold t h e solutions to be elect'rolyzed. The anode TT-asa saturated calomel, and. the dropping mercury electrode was a Sargent 4to 7-second drop-time capillary connected to the usual tyFle of adjustable mercury reservoir. Polarogram Recordings. A solution that n-as 10--3Xin o-phenylenediamine dihydrochloride, 10-1M in tetramet'hylammonium bromide, and 0.017, in gelatin was placed in the appropriate arm of the H cell. The other arm of this cell was partially filled n-ith saturated potassium chloride and the arm of the anode vias inserted. This assembly n-as placed in a thermostat kept at 25" i. 0.02" C.. After cooling a short time the solution was deaerated for 10 minutes by passing through it. purified nitrogen that had been bubbled through 0.1X supporting electrolyte. The voltage span n-as set at 2.5 volts, the shunt ratio a t 100, and the drop tinie a t 6 seconds; then the polarogram was recorded. Solutions t h a t contained several other concentrations of this compound were treated in the same manner. I n all cases the concentrations of the gelatin :ind supporting
Figure 3. Plot of i d vs. C for 0 - , m - , and p-phenylenediamine dihydrochlorides
electrolyte n ere the same as given above. The meta and para salts were treated in the same way. Figures 1 and 2 give the characteristic curves for the ortho and para compounds. Table I gives some of the data that was obtained. A plot of ij z's. C is given in Figure 3. The vP3 t"* for the dropping electrode was calculated to be 1.55 nig.*/3set.-"? DISCUSSION
The ortho compound gave a single wave, while the para compound gave two Tvaves. This tendency t o give two rvaves increased with increasing concentration of the salt. As it was rather difficult to measure the first wave accurately, the total wave height was used in the case of the latter salt. The wave for the meta conipound [vas very similar to that for the ortho compound, although at higher concentrations it gave a double wave. I n all cases, the id values were measured at approximately 1.9 volts with a correction being made for the residual current. Preliminary experiments showed that a maximum was produced R hic!i could be suppressed by making tlle solution O . O l ~ o in gelatin. The halfwave potentials varied b e h e e n - 1.43 and - 1.52 volts. The diamines do not give a cathodic wave at a dropping mercury electrode. However, upon the addition of enough hydrochloric acid to change them to dihydrochlorides, the wave appears. Apparently the wave is due to the discharge of hydrogen from the protonated base. The i d to C values were fairly constant in all three cases, and a plot of i d 1's. C gave a straight line in the cases of the ortho and meta compounds and not
Table I. Diffusion Currents for Phenylenediamine Dihydrochlorides Molarity, X 10-3 i d , pa, Ortho, E = -1.86 Volts US. S.C.E. 0.5 3.99 9.24 1.0 19.11 2.0 4.0 39,07 6.0 59,64 Meta, E = -1.93 Volts us. S.C.E. 4.20 0 .5 7.98 1 .o 2.0 15.75 4.0 30.66 6.0 45.15 Para, E = -1.90 Volts us. S.C.E. 0.5 3.36 1 .o
6.72 13.44 26.04 40.74
2.0
4.0
6.0
much deviation in the case of the para compound. Therefore, i t is possible to read concentrations in the range studied from such a calibration curve without introducing a large error. LITERATURE CITED
(1) Bogdnnov, S. G., Sukhobokova, N. S., Zhur. Anal. Khim. 6 , 276 (1951). ( 2 ) Julian, D. B., Ruby, W. R., J. Am Chem,. SOC.72. 4719 ~- (1950). I
(33 Lord, S. S., Jr., Rogers, B., ANAL. CHEW 26, 284 (1954). (4) Parker, R. E., Adams, R. N., Ibid., 28, 828 (1956).
RECEIVED for review April 28, 1959. Accepted October 5, 1959. Abstracted from a thesis presented by Oscar F. Fowlkes in Dartial fulfillment of the requirements Tor the degree of master of science, Howard University, Washington, D.C., 1956.
VOL. 32, NO. 1, JANUARY 1960
27
