Rapid Colorimetric Determination of Benzidine RIP G. RICE' and EARL J. KOHN N a v a l Research Laboratory, Washington,
D. C.
A rapid colorimetric procedure for the determination of benzidine by oxidation with permanganate in the presence of nitric acid is presented. The reproducibility of results is unaffected by small amounts of hydrochloric acid; however, the quantity of permanganate solution required is critical. The average deviation between this method and a gravimetricprocedure is 3~0.19 gram per lite1 for solutions containing 19 to 25 grams per liter of benzidine dihydrochloride. Results mal he duplicated on the same sample with a precision average of f 0 . 1 3 gram per liter.
A
R A P I D procdure for the quantita,tive determination of benzidine in the presence of excess hydrochloric acid w:i* required for process control in the course of the development of a riew electrochemical recorder paper (9). Gravimetric ( 6 , 6, 16 I, volumetric (13, 1.4, 1 7 ) , colorimetric (4,8),and electrometrir ( I 11 ) methods were too lengthy for this process or required t h r :thsence of excew halogen ( 7 ) . The oxidation of benzidine in acid medium produces a greenish ~.ellorvcolor ( 2 , 12), the intensity of which conforms with Beer's h \ v on dilution. The new met,hod is a modification of the photornrtric procedure for the determination of permanganate using and is hnsed upon the light absorption chimeterheiizidine (I,?), iptirs of an aliquot sample of the benzidine solution which is osidizrd with potassium permxngannte in the prewnce of niti,ict avid. ~
benzidine dihydrochloride of known concentration. The time required for a single analysis is about 10 minutes. The absorption cell containing the benzidine solution must he cleaned frequently with cleaning solution. Otherwise a film, which is not removed by rinsing with water, eventually forms on the glass and significantly changes the light transmittance. PREPARATION O F CALIBRATION CURVE
Solutions were made up containing 19, 21, 23, and 25 grams of benzidine dihydrochloride, and 3 ml. of concentrated hydrochloric acid in 1 liter of 'water. These four solutions were analyzed gravimetrically in triplicate by modification of the method of Marsden and Pollard (10)as follows: A 20-ml. aliquot of the benzidine solution was pipetted into a 5O-ml. beaker containing 5 ml. of sodium sulfate solution (6.4 grams per 100 ml. of distilled water). The mixture was stirred, allowed to stand 15 to 30 minutes in a n ice-water bath, then filtered through a fine porosity sintered-glass filter crucible \I hich had been previously brought to constant weight by washing with cold 80% ethyl alcohol and drying at, 75" C. The white precipitate of benzidine sulfate was washed free of salts with cold 80% ethyl alcohol, and the crucible F a s dried for 1 hour a t 75' C., cooled for 0.5 hour in a desiccator. and n-eighed. The washing, drying, and cooling were repeat'ed until the crucible reached constant \wight. From the weight of benzidine sulfate found in the aliqiiot. the concentration of benzidine dihydrochloride in the original solution was calculated. The four standardized solutions were then analyzed for benzidine by the colorimetric procedure given above. The per cent light transmittance was plotted on semilogarithm graph paper against the grams per liter of benzidine dihydrochloride in the solution from xhich the 0.20-ml. aliquot was taken (FigiirP 1 ) .
.-\PP.\RATL'S
Photelometer, Cenco-Sheard-Sanford, equipped with a 410- to 190-mp filter and two I-em. absorption cells. Volumetric flask, 1 liter. Two pipets, 1.0 ml., 1IohI type. graduated in 0.1-ml. units. Calihrated medicine dropper. REAGENTS
Benzidine dihydrochloride, c.P., obtained from Mathrson. Coleman and Bell, Inc. Sitric acid, specific gravity 1.42. Tlydrochloric acid, specific gravity 1.18. Potassium permanganate solution, 0.40070, prepared according to Fales and Kenny ( 3 ) , except that a sintered-glass filter rru(+)le was used in place of a Gooch asbestos mat.
3o16
I 7 I8 19 20 21 22 23 24 25 26 27 25 CONCENTRAXIH O F B E ' d D I Y E . 2HSL M i l ) IFi S3LUTIOV SAMPLE0
Figure 1.
Calibration curve
PROCEDURE
h sample of benzidine solution containing about 4.6 mg. uf benzidine dihvdrochloride (0.20 ml. for a 2.3% solution), and containing 3 ml. of hydrochloric acid per liter of solution, is pipetted into the 1-liter volumetric flask which contains 900 to 950 ml. of distilled water. Four drops (0.11 to 0.16 ml.) of nitric acid are added from a calibrated medicine dropper and the sides of the flask are -sashed down with distilled water. T h e flask is then swirled to mix the acid and the benzidine solution. By means of the second pipet, 1.00 ml. of 0.400% potassiupi permanganate solution is added to the flask, the sides are again washed down, and the flask is swirled. The flask is then filled to the mark with distilled water and the contents are mixed well. A 1-cni. absorption cell is filled with the greenish yellow solution and placed in the photelometer. Exactly 8 minutes aftcr the addition of the permanganate solution the per cent light transmittance of the colored solution is read against the light transmittance of distilled water. The concentration of benzidine dihydrochloride in grams per liter is read directly from a Calibration curve (Figure 1 ) prepared from a series of solutions of
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1 Present address, Chemistry Division, Naval Ordnance Laboratory, White Oak,Silver Spring. Md.
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2
! 4
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l 1 , , , l , , l l 8 IC ' 2 I4 I6 I8 20 22 24 26 T I M E AFTER ADDITION Of PERMANGANATE SOLUTION ( W I N )
Figure 2.
1630
l
I
6
Stability of colored solution
!e
l 3C
,
32
V O L U M E 27, NO. 10, O C T O B E R 1 9 5 5
1631
This serves as the working curve. T h e authors did not find i t necessary to construct a new calibration curve each time a new permanganate solution was prepared. DISCUSSION
The effects of several variables were investigated for their influence upon the color formation and quantitative application of the procedure. These factors included the stability of the colored solution, concentration of nitric and hydrochloric acids. and the concentration of the permanganate solution. Stability of Colored Solution. The per cent transmittance of the pieenish yellow solution varies with time, as shown in Figure 2 . For this reason it is essential t h a t all photelometer reading. be made a t exactly the same time after addition of the pernianganate aolution. Consideration of the curve indicates t h a t t h e time of photelometei reading may be arbitraily chosen. T h e authors considerecl 8 minutes as the minimum period of time required for the performance of the necessary manipulations.
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Table I. uo
1;\pt 1
2 3
.; 4
7 8
10
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chloride, and the average differenre was 2Z0.19 gram per liter. These analyses were performed a t intervals over a n extended period of time, during which the temperature varied between 20" and 35' C., indicating t h a t normal variations in room temperature have no apparent effect upon the reproducibility of results. The precision of the method is shown in Table 111. T h e a v w age deviation from the mean values ranged from 4~0.07to f0.23 gram per liter. Results may be duplicated on the same sample with a precision average of 2~0.13gram per liter.
Table 11. Comparison of Colorimetric and Gravimetric Benzidine. Expt. KO. Grar. 1 22.4 2 13.1 20.3 3 4 22.4 5 21.5 6 21.9 7 22.0 8 22.3 9 21.9 10 20.9 11 19.9 12 22.9 22.1 13 14 22.8 4 r . diirerence
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Effect of Nitric Acid
HNOa Added, XI1 0 03 0 05 0 08 11 13 16 18 0 21 0 26 0 40
0 0 0 0
Transmittance, 43 6 43 9 44 8 45 7 45 7 45 7 46 3 46 8 46 8 47 0
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Acid Concentration. Hydrochloric acid, in concentratioria of 0.1 to 0.670, has no appreciable effect upon the per cent traiismittance of the colored solution. The optimum concentration of added nitric acid is 0.11 to 0.16 ml. per liter; the per cent trailsmittanre is eonstant over this range as shown in Table I.
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Methods 2HC1. G./L. Difference, G./L.
Color. 22.9 13.1 20.5 22.0 21.7 22.0 22.2 22.2 21.9 21.1 19.8 22.9 22 5 22 5
L0.5 0.0 +0.2 -0.4 f0.2 f0.1 t0.2 -0.1 0.0 +0.2 -0.1 0.0 t0.4 -0 3
+ 0 1'3 -
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Table 111. Precision of Method AT. Benzidine Dihydrochloride Found, G./I.. 22 4 19 5 19 7 20 9 21 8 2.7 2 24 0 24 9 25 5 Total av. deviation, g. 4.
Sample
No.
No. of Detns.
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Range, Nin. 22.3 19.1 19.8 20.0 21.G 22.9 24 0 24.8 23 4
G./L. Max. 22.6 19.7 19.9 21.2 21.9 23.5 24.0 25.0 25.7
AT. Deviation from Mean,
G./L.
jzo.12 10.23 10.10 zt0.23 zto.10 zt0.23 0.00 z t 0 . 07 10.10 i0.13
~ _ _ _ _ ~ _ _ _ ~ -
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ACKYOWLEDGMENT
T h e authors are indebted t o Curtis R. Singleterry for many helpful comments and suggestions. LITERATURE CITED
.itanash, I. A , , and Velculescu, .i.I., B e r . deut. chem. Ges.. 6 5 H , 1080-2 (1932). Belcher, R., and Kutten, A. J., J . Chem. Soc., 1951, 546-7. Fales, F. A , , and Kenny, F., "Inorganic Quantitative Analysis." new ed., p. 408, D. Appleton Century, Xew York, 1939. Glassman, J. ll.,and lleigs, J. IT7., Arch. I n d . Hug. Occupational Med., 4,519-32 (1951). Hereog, W.,Chem. Rundschau Mitteleuropu u . Balkan, 7, No. 15,17-19 (1930). Hereoe. IT.., Chem.-Zto.. 50.642-3 (1928). liainz, G., and Pohm, M., Mikmchemie v e r . Mikrochirri. Acta, 35, 189-93 (1950). Klein, B., ~ X D ENG. . CHEM.,ANAL.ED.,16, 536-7 (1944). Kohn, E. J., Venezky, D. L., Rice, R. G., Ross, F. J., and Xsbury, G. F., Sr., Saval Research Laboratory, NRL Ilept. 4001 (Unclassified), July 11, 1952. JIarsden, A. W,, and Pollard, A. G.. J . Soc. Chem. I n d . ( L o n d o n ) , 56,464 (1937). Llatrka, YI., Chemie (Prague), 8 , 13-4 (1952). I'iccard, J., Ber. deut. chem. Ges., 44, 959-60 (1911); 46, 1848-60. 1860-2 (1913). Roesler, A., and Glassmann, B., Chem-Ztg., 27, 986 (1903) Simon, A , , and Reetz, Th., Z . anorg. u . allgem. Chem., 194, 89 112 (1930). Wiese, A . C., and Johnson, B. C., J . B i d . C'hem.. 127, 203 9 (1939). van Loon, J. P., Proc. Koninkl. A k a d . Wetenschap. Amsterdam. 5,377-8 (1903). Vaubel, W., Z . anal. Chem., 35, 163-4 (1896) LI
Figure 3.
Effect of concentration of permanganate
Concentration of Permanganate. The variation of per cent transmittance of a solution containing 22.8 grams per liter of 1)enzidine dihydrochloride with increasing amounts of a d d e I 0.4ooyOpermanganate solution is shown in Figure 3. It can bc seen t h a t the validity of the method is dependent upon the a?curate addition of a critical amount of permanganate solution. Comparison of Results. Comparative data obtained from the colorimetric method and the modified procedure of Rlarsden and Pollard (10) are presented in Table 11. The greatest difference between procedures was 0.5 gram per liter of benzidine dihydro-
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RECEIVED for review October 5 , 193.1.
Accepted hIay 5. 19.55.
