When an extraci; of a composite 2gram sample of creeping indigo leaf meal containing approximately 0.3% of 3-nitroprop:tnoic acid (6) was polarographed in acetatt: buffer, the single well-defined wave which resulted differed from that obtained with the pure acid only in t h a t its slope was less and the half-wave potential was more negative. That ths linear relationship between concentration and diffusion current persisted in the plant extract was shown by adding increments of the acid stock solution and polarographing the resulting mixtures, which ranged to 3.5 X lO+M with from 5.4 X respect to the added acid. When an extract of alfalfa meal which did not contain any 3-nitropropanoic acid ( 5 ) was accorded the E)ame treatment, the wave resulting from the reduction of the added acid was similar to that obtained with the creeping indigo extract. Data obtained in this manner, less a blank value of 1.09 X ll)-4M, provided the standard curve used to determine the concentration of acid in creeping indigo. As may be seen in Table VI, which summarizes the results of this plant extract study, the idiffusion current resulting in these instmces was consistent with that obtained with purified acid for comparable amounts of electroactive material. The polarographic determination of 3-nitropropanoic acid in 14 samples of creeping indigo meal which had been dried for 36 hours a t 58” C. gave values ranging from 0.171 to 0.4710/,. These
Table VI. Plant Extract Study Concn. of x i t i added, id/(? x 10-4111 i d , fia. x lo4 EL,z,volt
Creeping Indigo 0.346 1.72 2.39 3.08 4.06 5.38
0.51 2.44 3.47 4.36 5.81 7.70
1.48 1.42 1.45 1.42 1.43 1.43 Av. 1.44 &
-0.86 -0.90 -0.90 -0.90 -0.91 -0.90 0.02
Alfalfa Meal 0.346 1.03 1.72 2.39 3.08 4.06 5.38
0.52 1.49 2.54 3.55 4.61 6.09 8.09
1.50 -0.97 1.45 -0.96 1.48 -0.95 1.48 -0.94 1.50 -0.94 1.50 -0.94 1.50 -0.94 Av. 1.49 f 0.01
agreed substantially with values obtained for parallel determinations carried out on the same samples according to the method of Matsumoto et al. ( 6 ) . I n this range the standard deviations found for the polarographic and spectrophotometric methods were 0.0031 and 0.0071, respectively. The standard deviation for a set of replicate polarographic analyses carried out on an alfalfa meal sample containing 0.026% of added Bnitropropanoic acid was 0.0025. The relative simplicity and rapidity of the polarographic method become apparent when one considers that the analysis can be carried out
directly on the buffered and deaerated plant extract in approximately 5 minutes. The spectrophotometric method, on the other hand, entails heating the buffered plant extract in the presence of formaldehyde for an hour to displace the nitro group of the 3nitropropanoic acid and then going through a rather involved procedure to determine the nitrite ion formed. LITERATURE CITED
( 1 ) Cooke, A. R., Arch. Biochem. Biophp. 5 5 , 114 (1955). (2) Furman, N. H., Norton, D. R., ANAL. CHEM.26, 1111 (1954). (3) Gresham, T. L., Jansen, J. E., Shaver,
F. W., Frederick, M. R., Fiedorek, F. T., Bankert, R. A., Gregory, J. T., Beears, W. L., J . Am. Chem. SOC.7 4 , 1323 (1952). (4) Kolthoff, I. ,,M., Lingane, J. J., “Polarography, 2nd ed., Vol. 11, p. 746, Interscience, New York, 1952. (5) Matsumoto, H., Unrau, A. M., Hylin, J. W., Temple, B. P., ANAL. CHEM.33, 1442 (1961). (6) .Meites, L., “Polarographic Techniques,” p. 52, Interscience, New York, 1955. (7) Ibid., p. 56. (8) Miller, E. W., Arnold, A. P., Astle, M. J., J. Am. Chem. SOC. 70, 3971 (1948). (9) Morris, M. P., Pagan, C., Warmke, H. E., Science 119, 322 (1954).
RECEIVEDfor review October 2, 1961. Resubmitted May 13, 1963. Accepted July 1, 1963. Abstracted from a dissertation presented by Lester H. Muramoto to the Graduate School of the University of Hawaii in partial fulfillment of the requirements for the degree of master of science, June 1961.
Coulometric Efficiency of Anodic Deposition and Cathodic: Stripping of Chloride at Silver Electrodes H. A. LAITINEN and
ZUI-FENG LIN1
Department of Chemistry, University of Illinois, Urbana, 111.
b Deposition at ccmstant current from relatively high (0.1 to 1 .OM) concentrations of chloride followed by cathodic stripping at constarit current gave current efficiencies (CE) of essentially zero at extremely low current densities (CD), increasing hyperbolically toward unity with increasing CD. This behavior could be attributed to the formation of AgC12- complex. At low chloride concentrations ( l o w 3tl3 lO-*M), the apparent CE increased with increasing CD, attained a maximum, and then decreased. This behavior could be attributed to dissolution of AgCl at low CD and formation cif free Ag+ at high CD. At 0.01M chloride, the low solubility and low rate of dissolution permit a CE of very nearly unity over a wide range of CD. A coulometer based on
this finding is suggested. Deposition at a constant potentiat, followed by cathodic stripping, gave roughly quantitative recovery of chloride, with a relative standard deviation of *2.5?& and a 1.6%, at chloride concentrabias of tions of 1.76 to 17.6 fig. per ml.
+
T
HE ELECTROLYTIC behavior of chloride and its application to microdeterminations have been studied by many authors. Lingane and Small (14) used a controlled anode potential of 0.25 f 0.01 volt us. SCE to determine 0.25 to 3.0 mg. of C1- coulometrically. Shain and Perone (19) made a limited study of C1- determinations in concentrations down to 4 X 10-6M in 80% ethanol by collecting C1- on a minute
Ag electrode a t 0.30 volt us. SCE followed by linear voltage scanning stripping. Several analytical methods have been proposed for the determination of traces of chloride, based on the anodic formation of films on mercury rather than on silver (1, 4, 10). As far as we can ascertain, however, none of these methods is based on the quantitative deposition of chloride and therefore the precision and accuracy are limited by the reproducibility of the deposition step. Moreover, these investigations involving mercury are not directly pertinent to the present study.
* Present address, Chemistry Department, National Taiwan University, Taipei, Taiwan (Formosa), China. VOL. 35, NO. 10, SEPTEMBER 1963
1405
EXPERIMENTAL
All chemicals used mere of C.P. grade and used without further purification except KCl, KAg(CK)2, and Hg. ICC1 was purified by threefold recrystallization from water. KL4g(CN)2was prepared from AgN03 and KCN and recrystallized twice from conductivity water. Hg was purified by vacuum distillation. A stock solution of KC1, either 1.00 or O.lOJ1, was prepared, an aliquot amount was taken by means of a calibrated buret, and diluted with supporting electrolyte whenever further dilution was necessary. Vanadous sulfate in contact with zinc amalgam in dilute H2S04 was used in deaeration of N2 according t o hleites (16). The supporting electrolytes were 0.1M KSOs in t h e constant current process, and 0.1X CH3COOH 0.1V CH3COONa in the constant potential proces. A common H-type cell mas used in the constant current process (CCP). The working electrode compartment was about 150 ml. in capacity and separated from the counter electrode portion with a coarse sintered glass. Three gas inlets nere provided, t n o of nhich nere for deaeration and one for keeping a nitrogen atmosphere over the test solution.
0.21 TI ME, S E C O N D S
Figure 2. cycle
+
'
D : H:
Aq&
SALT
-
BRIDGE
"IE
LASS
\i
5 EPARATOR
TO M* N 0 ME T E R
I M
SIDE V I E W
Figure 1 .
Electrolysis cell for CPP
The cell used in the constant potential process (CPP) is shown in Figure 1. A potentiostat, of stability better than i. 1 mv., constructed by Enke (5) was used to control the potential. The capacity mas about 10 nil. Ag-coated platinum electrodes TI ere used as the working electrodes. The apparent surface areas nere 1.5 and 8 sq. cm. in CCP and CPP, respectively. Ag-coating was carried out according t o Samson (17'). The apparent surface area
'
"
,
'
"
I
I
4
600-6
SX10-3M
-
ou
'
' ' ' ' ' ' ' ' 0.4 0.8 1.2 1.6 2.0 C U R R E N T D E N S i T Y ( X 10-2) MA&2 1
'
'
2.4
I
0.20 SILVER ELECTRODE POTENTIAL, VOLT
0.30
Figure 5.
0.10
Experimental points: for t+ = 40 to 100 seconds Smooth curves: calculated Curve 1, considering AgCl dissolution Curve 2, considering free Ag' formation Curve 1-3-4, considering both 1 and 2
Figure 4. Voltammetric curves of CI- on Ag anode in 0.1 M CH3COOH 0.1 M CH3COONa
+
zero i o - 4 ~CI5 10-4~ (4) 1 0 - 3 ~ ( 5 ) 5 X 10 3M
(1) (2) (3)
x
t/t+ has a value between 1 and 2, the plot of C E against I is nearly hyperbolic. sq. cm./second Taking D = 2 X sq. cm./ for AgCl and 1.5 X cm., second for AgC12-, 6 = 8 X A = 3 sq. cm. (roughness factor = 2), and assuming that CO is equal to solubilities of AgC1, and t h a t C b = zero, the apparent C E could be calculated for various values of I . The results for
Table 1.
Calculated Current Efficiencies
Co = 3.8 X
mole/
ml . 3 5 10 20 30 40 50 60 70 80 90 100 120 150 200 2.50 300 350 400 500
8.3 45.0 72.5 86.3 90,s 93.1 94.5 95.4 96.1 96.6 96.9 97.3 97.7 98.2 08.6 98.9
600
...
700 800 !)00 I000 2000 2300
,..
... ... ...
...
...
... ... ...
...
Co = 1.4 X lo-' mole/
ml.
lO-4iM and 1.00M C1- are presented in Table I. I n these calculations the solubility data of Pinkus and Forbes (18) were used, taking into consideration the diverse ion effect of KNO, (Y),and t/t+ was taken to be 1.5. The calculated results are in reasonable agreement with those expected for low current densities for l O - 4 M C1- (Figure 5) and at higher current densities for 1. O O M C1- (Figure 3). At high chloride concentrations (0.1 to l.OM), the low C E can be attributed t o complex formation, and a reaction rate model might be more rational. If we write the reaction scheme
...
Ka
...
AgCL- (surf) e
...
... ... ... ... ... ... 5.0
156
24.0 36.7 48.3 62.0 69.6 74.7 78 . 3 81 . 0 84.8 87.3 89.1 90.5 91 . G 92.4 96.2 96.7
K4
AgCli- (bulk) (3)
Ks a n d Kd represent mass transport of AgC12- from surface t o bulk, so K 3 = Kq. If [AgCld-Ib = a [AgCl2-Io where 0 6a 1, then the net mass transport rate of AgC12- from the surface is K3 (1 - a) [-4gCl2-l0. The net rate of formation of AgClz- is KIA [C1-Ia K B[AgClz-]a. At the steady state, [AgCL-lo
K*A[Cl-Iol[K*
ANALYTICAL
CHEMISTRY
+ K3 (I - a ) ]
(4)
and thf rate of dissolution can be written
z"(bgx?)= K,R3 (1 - a ) A dt
+ Ka(1 -
[Kz
of AgCl in excess C1- would be constant as long as A is kept constant. The quantity of electricity consumed in anodic plating was more than 2000 pC/sq. cm., and since that required for formation of one layer of 4gC1 was calculated as 193 pC/sq. cm. (a), several layers of AgCl must be formed upon anodic plating of C1- on Ageven taking 2 as the roughness factor of the electrode surface. I n a fresh solution or a solution not appreciably contaminated with AgC12-, a N 0; therefore, with constant A , the rate of solution is simply proportional to (Cl-)o, viz., -dAgCl( dt
8)
=
K[Cl-]o
(6)
This result is in good accordance with James' finding (9) in C1- concentration larger than 0.111.1. Equation 6 gives
+ c1- Kie K;
&4gCl(S)
[C1-Ia/ a)]
(5)
Accordingly, if a = 1, :drlgCl(s)/dt a = 0, the rate-of dissolution
= 0, nnd if
1408
Apparent CE's in 10-4M CI-
VS. S C E
-AgCl(s) = K[Cl-]ot
(7)
in which -AgCl(s) means loss of AgCl from the surface deposit by complex formation during time t. If the same I is adopted in both anodic and cathodic processes, the apparent CE can be expressed
+
K'([Cl-Io,t, [Cl-]o-t-} It+
(8)
where K' is a constant, equal to 9.65 X 1010K/1.5 if AgCl(s) is in gram equivalent, [ c l - ] ~ ,[C1-l0,, and [Cl-], are surface concentrations in anodic, standing, and cathodic processes. Under the experimental conditions, if [Cl-]O+ can be assumed to be constant, and [Cl-]+ [Cl-lo, = [Cl-],, then
Equation 8 reducw to Equation 9 in which C constant 5 1.
Table It. Coulometric Efficiency of 0.01 M KCI Saturated with AgClz and Ba(NO&
(1) (9)
+
Accordingly, a plot of C E us. (t, t)should be a straight line and the slope should depenc on [Cl-]b, I, and t+. With [C1-]b of 1.00, 0.10, and 0.01M, and t+ of 100 for 1.00and 0.01M, 50 for 0.1OW, the slope ratio of 1.00 to 0.10 to 0.OlM was calculated as 1: '/4 :0.0. From Equation 5 , it can be expectccl that when a becomes larger, dissolution of AgCl will be slowed down; hence, C will increase toward unity. Plots a, b, and c for 1 , O O X in Figure 6 were obtained in the sam: solution in which several anodic-cathodic cycles were carried out in the ntmed order. Since C for the first plo, was 0.4, for the second, 0.47, and foi. the third, 0.6, the increasing tendency of Cis evident. When solutions of 1.00 and 0.1OM GI- were saturated with separatelyprepared AgCl and then filtered, CE's were almost unity when t, was zero; however, CE's wei-e 1.13 in 1.00-Tf (initial concentration) when t, was 20 minutes, 1.79 in O.lOM (initial concentration) when t, was 30 minutes. Even in 0.01M C1-, a CE slightly larger than unity was observed; however, this phenomenon could be eliminated by addition of Ba(NO& This suggests t h a t on digestion of AgCl in relatively high C1- solution, some depositable species, probably a negatively-charged AgCl colloid, could be formed. With 10-3M C1-, CE's were much higher than unity if the soh tion was used in an anodic-cathodic cycle a t small 1(1 < 100) with zero t., fi it had previously been used in cycles r.t large I . CE's in Curve 2 of Figure 3 will be found to be larger in the range I = 380 to 1300 compared with those computed from the competitive electrode reaction. This result must be a t t r i h t e d to the reduction of colloidal .4gO on the Ag electrode as previously observed by several authors ( I I , l S , 80,LI). The abnormal CE's were largely depressed by gelatin, but not a t all by Ba(hTO&. The following resiilts (Table 11) obtained in 0.01M C1- saturated with AgCl and Ba(KO& show khat the Ag/AgCl/ C1- (0.OlM) electroce is promising as a coulometer electrode. I n this construction, the cell resistance was 350 ohms measured by rneans of a conductance bridge; therefore, the maximum iR drop was about 2.2 volts when I = 4107 pa./sq. em. Deposition of AgCl at Constant Potential. As mentioned previously, the anode potential should not exceed 0.269 volt if the formation of excess Bg+ is to be avoided. Nevertheless, the deposition of C1- was found to be incomplete
a
With I + = I-, t,. N 50 Z (pa./cm.2) t+ (seconds) t- (seconds) 5.5 50.0 49.8 54.0 50.0 50.0 50.0 ... 118.5 50.0 49.9 50.5 ... 234.0 50.0 50.1 50.0 ... 1132.0 50.0 50.0 50.0 50.2 50.0 ... 15-17 0 50.0 50.1 50.0 ... 2700 0 50.0 50 2 50. I 50.0 50.0 ... 50.0 50.2 3804.0 50.0 50.2 52.0 ... 4107.0 52.0 ... 50.0 49.9 50.0 50.1 50.0 49.8
CE (%) 99.6 100.0
...
t-a
CEa
... ...
... ...
50.0
100.0
50.7
100:4
...
99.8
... 50.0 ... ...
100: 2 100:o
100.4
...
50.2
100:4
...
50.3
10h:6
100.2
...
...
100:2
...
...
100.4
:
I tii) 4
50.2
100: 4
...
100.4
... ...
60.0 ... Also under stirring in cathodic stripping.
100:0
99.8 100.2 99.6
52.1 52.2 ...
100:2 100.4
59.7
99.5
... ... ...
... ...
...
(2) With I+ = I - and various t , Z = 313.0
t-
t+
15.0
15.0
20.1 24.1 45.6 49.9
20.1 24.4 45.4 50.3
...
...
..
..
Z = 1400.0
52.4 100.2 206.1
I = 3175.0
10.1
52.4
100.0
206.0 10.2 30.2 50.1
30.0
50.1
(3)
With
CE 100.0
100.0
101.2
99.6
100.8 100.0
99.8 100.0 101.0 100.7 100.0
CE
t-
tt
80.6
100.6
600.6
100.1
.. ..
...
...
... ...
... ... ...
100.0
100.1 200.0
100.1 99.5 100.0
80 .1 99 . 9 100 .3
99.6 100.1 207.8 299.8 400.3
207.9 ..
300.1 400.1 600.3
201.1 206.1
99.7 99.8 100.0 99.9
100.1
206.0
I+. # I-
I+ 7.1 14.0 70.5 153.5 1400.0
t+
I-
t-
1000.0
153.0 152.5 1400.0 310.0 1435.0 151.5
46.4 92.2 5.0 68.5 7.5.3 373.0
2000.0
500.0 300.0
700.0
40.1
CE = I- t- /XI+ t+ 100.0 99.0 100.0 100.4 100.6
100.7
(4) Summation of various I + and t+, but constant I -
I+ 1400.0 311.0 101.0 7.3 4.7 4.0 1452.5 1441.5 154.0 70.9 3405.0 1443.0 312.4 153.8 103.0 70.1 24.3 13.9 7.0 3.7
CE = I- t- /ZI+ t+
4 100.5 100.0 100.0 1300.0 4000.0
*..
...
"..
14i00.0
130.7
166:6
... ...
...
40.0
1450.0
... ... ...
160.0 ~ .. ..
...
...
-.. ".. 99.9 , ..
1x3,s ... ...
li31'.7
100.1
...
1000.0
200.0 500.0 80.0 80.0 100.0 150.0 200.0 400.0 500.0
500.0 1000.0 5000.0
1-
t-
62.3
...
...
... ...
... ... ... ... .. .. ..
143f.5
ifi.2
99.7
... ... ...
... ...
... ... ... ...
...
VOL 35, NO. 10, SEPTEMBER 1963
# . .
...
1409
Figure 6.
Effect of standing on CE
(1) 1.00M f + = 1 0 0 seconds a, b, c successive anodic-cathodic cycles (2) O.lOM, t+ = 50 seconds (3) 0.01M, t i = 100 seconds
even a t 0.28 volt as shown by the data in Table 111. Therefore, the applied controlled potential was raised little by little to determine the optimum potential for quantitative deposition. The results are shown in Figure 7 . The apparent recovery increases with increasing anodic potential, reaches a maximum, and then decreases. Although the curves take different paths at different chloride concentrations, and show different maximum depositions,
Table 111.
Deposition of CI- at E = 0.28 volt vs. SCE Deposition completeness, ICl-I 70 2.5 x 10-4 70.2 5.0x 10-4 90.8 1.0 x 10-3 94.5
027
0.28
0.29
0.30
0.31
0.32
0.33
APPLIED POTENTIAL,VOLT.S VS. SCE Figure 7.
Apparent recovery of C1- vs. applied potential Curve(1) 5 X 1 0 - 4 M C I Curve (2) 2.5 X 10-4M Curve ( 3 ) 1 O-4M Curve (4) 5 X lO-;M
the apparent recoveries a t 0.33 volt are about the Sam?, within 5% of theoretical for the four plots. Undoubtedly there is a compensation of errors, since the formation of excess Ag+ will more or less compensate for t h e incomplete deposition of AgC1. No conditions were found for accurate determination of C1- from very dilute aqueous solution. As shown in Table IV, however, the apparent recovery was fairly quantitative in the
concentration range of 5 X to 5 X 10-4111’(1.76 to 17.6 pg./ml.) at a n applied potential of 0.33 volt us. SCE. In Table IV, EA# is the applied potential, E, is the potential of the electrode immediately after the applied voltage is cut off, i is the constant current in pa. used in cathodic stripping, and R is the apparent recovery in per cent. The relative standard deviation of the apparent recovery is i2.5y0with a positive bias of l.6y0. LITERATURE CITED
Table IV.
(Cl-), N 0 0 ?, 5 5
x x x 5 x
10-5 10-5 10-6 10-5 10-4 10-4 10- 4 10-4 2.5x 10-4 2.5x 10-4 2 . 5 x 10-4 2.5x 10-4 2.5x 10-4 .i x 10-4 .j x 10-4 5 x 10-4 5 x 10-4
1410
0
volt
E~gl
0.329 0,329 0.329 0.327 0.327 0.329 0.329 0.329 0.329 0,330 0.329 0,329 0.330 0.330 0.331 0.329 0,329 0.328 0.328
ANALYTICAL CHEMISTRY
Apparent Recovery of CI-
Ea, volt 0,319 0.307 0.314 0.309 0.310 0,312 0.314 0.312 0.315 0.312 0.312 0.312 0.312 0.315 0:3i3 0,312 0.312
i, wa. 409.4 1902 409.4 1902 1902 409.4 1902 4536 1902 4536 4j36 4536 4536 4536 4536 4536 4536 4536 4536
R, % . . . (t- = 0) . . . ( t - = 0)
104.4 101.5 101.5 99.3 100.5 99.0 104.5 99.0 100.0 101.1 105.2 95.8 100.8 102.9 103.7 103.4 104.5 Av. 101.6
(1) Ball, R. G., Manning, D. L., Menis, Oscar, ANAL.CHEM.32, 621 (1960). (2) Barney, J. E., Argersinger, W. J., Jr., Reynolds, C. A., J . Am. Chem. SOC. 73, 3785 (1951). (3) Beck, W.H., Dobson, J. V., WynneJones, W. F. K., Trans. Faraday SOC. 56, 1172 (1962). (4)Brainian, Kh. Z.,Roizenblat, E. N., Zavodsk. Lab. 28, 21 (1962); C.A. 56, 14923e (1962). (5) Enke, C. G., Ph.D. Thesis, University of Illinois, Urbana, Ill., 1959. (6) Fleischmann, ?”I., Thirsk, H. R., Electrochim. Acta 1 146 (1959). (7)Harned, H.S.,dook, M. A., J . Bm. Chem.SOC.59, 1290 (1937). (8) Hodgman, C. D.. “Handbook of Chemistry and Physics,” 13th ed. D. 2414. Chemical Rubber Publishing e o . , 1955. (9) James, T. H., Vanselow, W., J . Phyls. Chem.62, 1189 (1958). (10) Kemula, W.,Kublik, Z., Taraszewska, J., Microchem,. J., Symp. Ser. 2, 865 (1962).
(11) Kolthoff, I. RI., St,ork, J. T., Analyst 80, 860 (1955).
(12) Laitinen, H. A., 'Chemical Analysis," p. 115, hlcGraw-Hill, New 170rk, 1960. (13) Laitinen, H. A,, Jerinings, W. P., Parks, T. I)., IND.E ~ GCHEV., . ANAL. En. 18, 355, 358 (1946). (14) Lingane, J. J., Smdl, L. A., ANAL. CHEM.21. 1119 (1949). (15) Rleites; L., Ibid., 2 0 , 084 (1948).
(16) Ramette, R. 37, 348 (1960).
W.,J . C h m . Educ.
(17) Samson, S., Anal. Chim. d c t a 13, 473 (1955). (18) . , Sridell. A , . "Solubilities of Inorganic and Metal (jrganic Compounds," 3rd ed., 1'01. I, pp. 34-40, Van Nostrand, New York, 1940. (19) Shain, I., Perone, S. P., 4 x a ~CHEM. . 33, 325 (1961).
(20) Stock, J. T., Turner, W.R., Chpm. Ind. (London) 1961, 1710. (21) Tsynov, G. A., Muraskina, I. I.,
Uzbeksk. Khim. Zh. 1960, 38; C . A .
56, 844% (1962). RECEIVEDfor review March 7 , 1963.
Accepted July 22, 1963. The authors express their thanks to the Fulbright Foundation for financial support of thls work in the form of a research scholarship granted to Zui-feng Lin.
Polarogralphic Monitoring of DifFerential Reaction Rates Determination of A4-3-ketosteroids in the Presence of A1l4-3ketoste roids ALAN F. KRIVIS and
GEORGE R. SUPP
Cenfral Analytical labo;atories, Olin Mathieson Chemical Corp., New Haven 4, Conn.
b Polarographic monitoring of differential reaction rate analyses has been studied. A determination of residual A4-3-ketostert3ids in A1s4-3ketosteroids has been made b y following a pseudo first-order semicarbazone reaction. A simple plct of log i for the semicarbazone as a function of time was used to obtain the current due to the reduction of the A4-3-
