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Anal. Chem. 1981, 53, 1238-1240
The surface area determination can also be examined in
terms of a hypothetical cylindrical chain model of polystyrene. The repeat distance for polystyrene is 2.5 A so that the overall chain length, I , corresponding to 1 g (0.0096 mol) can be calculated. The measured surface area, A = 1780 m2, can be equated to that of a cylinder, rD1,and this gives a chain diameter, D, of 3.9 A. This value can be compared to a value of 5.2 A based on the model compound, ethylbenzene, whose apparent size (N= 4.8) was reported by Hendrickson and Moore (17). This suggests that the apparent surface area in a PSDVB gel structure is closely related to the molecular threads that constitute the network structure.
LITERATURE CITED (1) Seidl, J.; Malinsky, J.; Dusek, K.; Heltz, W. Adv. Polym. Scl. 1967, 5 , 113-213. (2) Mlllar, J. R.; Smith, D. G.; Kressman, T. R. E. J . Chem. Soc. 1965, 304. (3) Dusek, K. J . Polym. Scl., PartCl967, 76, 1289-1299. (4) Zlablcki, A. Po/ymr 1979, 20, 1373-1381.
Halasz. I. Ber. Bunsenges. Phys. Chem. 1975, 79, 731-732. Freeman, D. H.; Poinescu, I. C. Anal. Chem. 1977, 49. 1183-1188. Halasz, I.; Martin, K. Angew. Chem., Int. Ed. Engl. 1076, 77, 901. Schram, S. B.; Freeman, D. H. J . Llq. Chromafogr. 1980, 3(3), 403-41 7. (9) Nikolov, R.; Werner, W.; Halasz, I. J . Chromafogr. Sci. 1980, 76, 207-216. (IO) Werner, W.; Halasz, I. J. Chromafogr. Scl. 1980, 78, 277-283. (11) Glddings, J. C.; Kucera, E.; Russell, C. P.; Meyers, M. N. J . Phys. Chem. 1966, 72, 4397-4408. (12) Freeman, D. H.; Patel, V. C.; Smith, M. E. J . Polym. Scl. 1965, 3, 2893-2902. (13) Schram, S. B. Ph.D. Dissertation,University of Maryland, College Park, MD. .---, 1978. (14) Scatchard, G.; Anderson, N. J . Phys. Chem. 1961, 65, 1536-1539. (15) Freeman, D. H.; Angeles, R. M.; Enagonlo, D. P.; May, W. E. Anal. Chem. 1973. 45. 788-774. (16) Freeman, D. H.; Currle, L. A.; Kuehner, E. C.; Dixon, H. D.; Paulson, R. A. Anal. Chem. 1970, 42, 203-209. (17) Hendrlckson, J. G.; Moore, J. C. J . Polym. Sci. 1966, 4 , 167-188. (5) (6) (7) (8)
RECEIVED for review January 12,1981. Accepted March 25, 1981. This research was supported by the National Science Foundation, Grant No. CHE-77-11313.
Spectrophotometric Determination of Aniline by the Diazotization-Coupling Method with N-( I-Naphthy1)ethylenediamine as the Coupling Agent George Norwitr and Peter N. Kellher" Chemistry Department, Villanova Universlty, Vlllanova, Pennsylvania 79085
The factors affecting the spectrophotometric determination of aniline by the diazotization-coupling technique using N-( 1naphthyi)ethylenediamine (also called N-( 1-naphthaieny1)1,2-ethanedlamine) (N-na) as the coupling agent in an acidic medium are investigated. The effect of nitrite concentration, effect of time for diazotization, effect of temperature for diazotization, and necessity for destroying excess nitrite (by the use of suifamic acid) are the same as for the coupling method using H-acid (8-amino-l-hydroxynaphthaiene-3,6-disuifonic acid) as the coupling agent. Acidity in the N-na method has a dual effect In that it affects the diazotization and coupling. There Is a plateau for maximum absorbance over the range of 0.5-5.0 mL of 1 N hydrochloric or sulfuric acid. The concentration of N-na has a pronounced effect on the intensity of the color and time required for development of the color. Ethanol, methanol, and acetone can cause low results.
N-(1-Naphthy1)ethylenediamine (N-(l-naphthalenyl)-l,2ethanediamine; N-na; Cl&17NHCH2CH2NH2),next to H-acid (8-amino-l-hydroxynaphthalene-3,6-disulfonic acid), is the most widely used coupling agent for the spectrophotometric determination of aniline by the diazotization-coupling technique. The conditions used previously for the N-na method vary considerably (1) and no comprehensive study has been made of the factors involved. It is the purpose of the present paper to make such a study, particularly since the N-na method has certain advantages over the recently reported (I) H-acid method. EXPERIMENTAL SECTION Apparatus and Reagents. Bausch and Lomb Model 70 spectrophotometer (1-cm cell).
All chemicals were reagent grade. Standard aniline solution no. 1 (1mL = 10.00 mg of aniline). Dissolve 1.000 g of aniline in ethanol and dilute to 100 mL in a volumetric flask with ethanol. Prepare fresh weekly. Standard aniline solution no. 2 (1mL = 1.00 mg of aniline). Dilute a 10-mL aliquot of standard aniline solution no. 2 to 100 mL in a volumetric flask with water. Prepare fresh every 3 days. Standard aniline solution no. 3 (1mL = 0,010 mg of aniline). Dilute a 5-mL aliquot of standard aniline solution no. 2 to 500 mL in a volumetric flask with water. Prepare fresh daily. Sodium nitrite solution (1%)and sulfamic acid solution (3%). Prepare fresh every 3 weeks. N-na reagent (0.75%). Add 0.375 g of N-naphthylethylenediamine dihydrochloride to about 45 mL of water while stirring and dilute to 50 mL. Prepare fresh every 4 days. Preparation of CalibrationCurve. Transfer 0.00,2.00,4.00, 5.00, and 6.00 mL of standard aniline solution no. 3 (1mL = 0,010 mg of aniline) to 50-mL volumetric flasks and dilute to about 35 mL with water. Add 2.0 mL of 1N hydrochloric or sulfuric acid. Add 1.0 mL of sodium nitrite solution (l%), swirl, and allow to stand 5 min. Add 1.0 mL of sulfamic acid solution (3%))swirl, wash down the sides of the flask, and allow to stand for 10 min. Add 2.5 mL of N-na reagent (0.75%),swirl, and dilute to the mark. Mix, remove the stopper (to permit the escape of nitrogen gas), and allow to stand 75 min or more. Measure the absorbance at 555 nm against distilled water, deduct the blank, and plot absorbance against mg of aniline per 50 mL. Procedure. Transfer an aliquot of the sample containing preferably 0.03-0.05 mg of aniline to a 50-mL volumetric flask, dilute to about 35 mL, and proceed as described in the preparation of the calibration curve.
RESULTS AND DISCUSSION Effect of Amount of Nitrite, Effect of Time for Diazotization, Effect of Temperature for Diazotization, and Necessity for Destroying the Excess Nitrite. The conditions previously established for the determination of aniline
0003-2700/81/0353-1238$01.25/00 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8 , JULY 1981
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Table I. Effect of Acid Concentration on the N-na Method (0.050 mg of Aniline and 1.0 mL of N-na Reagent (0.75%)) absorbance after different time intervals mLof mLof 1 N H C l l N H , S O , 15min 30min 1h 1.5 h 2h 2.5 h 3h 4h 24 h 0.00
0.00
0.05 0.10
0.25 0.50 1.0
2.5 5.0 12.5 25.0
0.05 0.10
0.25 0.50 1.0
2.5 5.0 12.5 25.0
0.14 0.23 0.24 0.24 0.25 0.25 0.26 0.22 0.13
0.24 0.35 0.35 0.34 0.35 0.29 0.36 0.32 0.21
0.06
0.11
0.22 0.24 0.24 0.27 0.30 0.29 0.24 0.19 0.09
0.32 0.34 0.34 0.38 0.41 0.41 0.35 0.27 0.16
0.31 0.47 0.47 0.47 0.48 0.46 0.47 0.43 0.32 0.18 0.43 0.45 0.45 0.49 0.51 0.52 0.48 0.40 0.24
by the diazotization-coupling technique using H-acid as the coupling agent (I) apply equally as well when N-na is used as the coupling agent, insofar as the effect of the amount of nitrite, effect of time for diazotization, effect of temperature for diazotization, and the necessity for destroying the excess nitrite (by use of sulfamic acid) are concerned. However, to save on the reagent (which is moderately expensive), it was decided to dilute to 50 mL in a volumetric flask rather than 100 mL as with the H-acid method. The recommended conditions for the N-na method consist, therefore, of adding 1.0 mL of sodium nitrite solution (1%)to about 35 mL of solution (containing the proper amount of acid), allowing to stand for 5 min to complete the diazotization, adding 1.0 mL of sulfamic acid solution (3%), and allowing to stand 10 min to destroy the excess nitrite. Effect of Amount of Acid. With the N-na method, the problem of acidity is quite different than with H-acid method, because the N-na is added directly to the solution after the diazotization and the coupling takes place in the acid solution. The effect of acid on the method was investigated by adding different amounts of 1 N hydrochloric or sulfuric acid to solutions containing 0.050 mg of aniline, treating with the sodium nitrite solution and sulfamic acid solution, adding the N-na, and measuring the absorbances after different time intervals. The amount of N-na reagent (0.75%) used was 1.0 mL. The absorbance was measured at 555 nm, since this was the point of maximum absorbance for the reddish purple color. The data on the effect of the amount of acid (Table I) show that acidity has a marked effect on the intensity of the color and the time required for color development. Maximum color development (after about 3 h) occurs over the range 0.5-5.0 mL of 1 N hydrochloric or sulfuric acid. Use of 2.0 mL of the acid is recommended. As can be seen from Table I, the color, once developed, is very stable and changes very little in 24 h. The high absorbance at zero acidity (Table I) was unexpected, since it was thought that no diazotization would take place in the absence of hydrochloric or sulfuric acid. The explanation for the results at zero acidity is that the acidity for the diazotization is furnished by the sulfamic acid. Apparently, diazotization is a fairly rapid reaction while the destruction of nitrite by sulfamic acid is a slower reaction. In the work with H-acid ( I ) , it was reported that no color developed at zero acidity, but this work was done in the absence of sulfamic acid. On retesting the effect of zero acidity on the H-acid method, it was found again that no color developed
0.34 0.52 0.52 0.52 0.55 0.52 0.55 0.52 0.39 0.23 0.48 0.50 0.51 0.54 0.57 0.57 0.55 0.47 0.30
0.34 0.52 0.53 0.54 0.56 0.57 0.56 0.54 0.42 0.26 0.48 0.51 0.52 0.55 0.56 0.57 0.55 0.51 0.33
0.35 0.53 0.53 0.54 0.57 0.57 0.57 0.55 0.46 0.29 0.50 0.52 0.53 0.56 0.57 0.57 0.57 0.53 0.37
0.37 0.53 0.53 0.55 0.58 0.58 0.57 0.57 0.48 0.33 0.50 0.52 0.53 0.57 0.57 0.57 0.57 0.55 0.39
0.35 0.53 0.53 0.55 0.58 0.59 0.58 0.58 0.52 0.37 0.51 0.53 0.53 0.57 0.57 0.58 0.58 0.56 0.42
0.35 0.53 0.53 0.55 0.58 0.59 0.58 0.58 0.58 0.47 0.51 0.53 0.56 0.57 0.57 0.58 0.58 0.57 0.45
without sulfamic acid (using 0.9 mL of sodium nitrite solution (2%)) but that an absorbance of 0.22 (after 15 min) was obtained in the presence of sulfamic acid. Effect of Amount of N-na. The effect of the amount of N-na was investigated by adding 2.0 mL of 1N hydrochloric acid to solutions containing 0.050 mg of aniline, treating with the sodium nitrite and sulfamic acid solutions, adding 0.1-7.5 mL of N-na reagent (0.75%), and measuring the absorbances after different time intervals. The results showed that the concentration of N-na has a pronounced effect on the time required for full color development. Complete color development could be achieved in 30 min by using 5.0 mL or more of the N-na reagent. However, since the reagent is moderately expensive, it was decided to use 2.5 mL and measure the color after 75 min. Effect of Light and Temperature on t h e Color. Light has no effect on the color or the blank. On standing for 2 days, the blank had an absorbance of only 0.01. Experiments on developing the color by heating (temperatures of 30-95 O C ) showed that heating repressed the color development. The color is not susceptible to air oxidation, as judged by the fact that the absorbance did not change when a stream of air was passed through the solution for a few minutes. Interference of Alcohol and Acetone. Alcohol did not have the effect with the N-na method of increasing the interference of undestroyed nitrite by enhancing the reaction between the nitrite and N-na (in contrast to the H-acid method in which alcohol enhances the reaction between the nitrite and H-acid ( I ) ) . The noninterference of alcohol in this respect was proved by the following experiment. Zero and 5.0 mL of ethanol were added to about 35 mL of water, followed by 2.0 mL of 1N hydrochloric acid, 0.050 mL of sodium nitrite solution (l%), and 1.0 mL of N-na solution (0.75%). The solutions without and with the ethanol both developed a deep reddish color which faded over a period of about 30 minutes to a brownish color. Both the reddish and brownish colors were of somewhat greater intensity in the solutions containing ethanol. The probable reason that alcohol does not increase the interference of undestroyed nitrite is the use of an acidic medium for the coupling. Alcohol and acetone does have the effect of repressing the development of the color in the N-na method (as was the case in the H-acid method ( I ) ) . To study this effect, solutions containing 0.050 mg of aniline, 2.0 mL of 1 N hydrochloric acid, and various amounts of ethanol, methanol, and acetone were carried through the recommended procedure. The results
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Table 11. Comparison of N-na and H-acid Methods for the Determination of Aniline property purity of commercial reagent expense of reagent stability of reagent solution medium for coupling color Amax
time for color development sensitivity to light relative sensitivity accuracy applicability to the semimicro and micro scale max permissible amt of ethanol methanol acetone toxicity of reagent
N-na
H-acid
good purity
must be purified
much more expensive than H-acid 3 days
4 days
acid reddish purple 555 nm 75 min
days. As with the N-na method, the maximum spread for the four absorbance reading was 0.015. The calibration curves followed Beer's law. Nature of the Dye. There seems to be little information concerning the nature of the dye obtained with N-na. However, it is known that in coupling reactions with 1naphthylamine the coupling occurs in the 4 position of that compound (2). Therefore, it would be expected that with N-na, the coupling would likewise take place in the 4 position. The formula of the dye would, therefore, be as follows:
AHZCH lnlni
sodium bicarbonate cherry red 526 nm 15-45 min
color and blank color is are insensitive insensitive, blank is sensitive 1.45 x the sensitivity of the H-acid methoda about the same as the H-acid method applicable applicable
2.5 mL/50 mL 5.0 mL/100 mL 0.75 mL/50 mL 3.0 mL/100 mL 5.0 mL/50 mL 5.0 mL/100 mL low toxicity, low toxicity, noncarcinononcarcinogenic ( 3 ) genic ( 4 ) a Absorbance of 0.50 on the Model 70 Bausch and Lomb spectrophotometer was equivalent to 0.88 pg/mL and 1.28 pg/mL for the N-na and H-acid methods, respectively.
showed that the maximum amounts of ethanol, methanol, and acetone that can be present without causing low results were 2.5, 0.75, and 5.0 mL, respectively. Accuracy and Precision. To check the accuracy and precision, we analyzed the four concentrations of aniline used in the preparation of the calibration curve on four successive
Comparison of N-na and H-Acid Methods. A comparison of the N-na and H-acid methods is given in Table 11. It is seen that each method has its advantages and disadvantages. Probably, the most important advantage of the N-na method is that the use of an acidic medium for the coupling may keep certain compounds (organic or inorganic) in solution. Another advantage of the N-na method is its greater sensitivity. It is believed that the N-na and H-acid methods between them will fill all of the requirements for the accurate spectrophotometric determination of aniline (and probably other aromatic amines) by the diazotization-coupling technique. The two reagents furnish an interesting contrast. N-na, which was first used as a coupling agent by Bratton and Marshall for the spectrophotometric determination of sulfanilimide derivatives (5), is primarily an analytical reagent and is not used in the dye industry. H-acid has been widely used as a coupling agent in the dye industry since about 1900. LITERATURE CITED (1) Norwitz, G.; Keliher, P. N. Anal. Cbem. 1981, 53, 56-60. (2) "Kirk-Othmer Encyclopedia of Chemical Technology", 3rd ed.; Wlley: New York, 1978; Vol. 3, pp 387-433. (3) National Cancer Institute, Carinogenesis Testing Program, Report No. 79-1 724 (PB-289733), "Bioassay of N-(l-Naphthyl) Ethylenediamine Dihydrochlorlde for Possible Carcinogenicity", Bethesda, MD, Aug 1978. (4) Armeli, G. Med. Lav. 1988, 59, 366-369. (5) Bratton, A. C.; Marshall, E. K., Jr. J . Biol. Cbem. 1939, 728, 537-550.
RECEIVED for review February 11,1981. Accepted April 10, 1981.
