Anal, Chem. 1904, 56, 2405-2407
experiment closely conforms to & values reported from potentiometric measurements. In summary we have shown that by use of simulations it is possible to extend CV analysis for reversibly reduced complex systems to systems with low ligand concentration. It should be noted that this approach must be applied with some caution. At very low ligand concentration the possibility is greater for complications due to complexes between the metal ion and hydroxide and/or anions of the supporting electrolyte. In the cases studied the good agreement between predicted and experimental results would indicate that this is not a serious problem. Extension to more complex systems and to other electroanalytical techniques is in progress.
LITERATURE CITED (1) Von Stackelberg, M.; Von Freyhold, H. 2.Elektrochem. 1040, 46. 120. (2) Llngane, J. J. Chem. Rev. 1941, 29, 1. (3) DeFord. D. D.; Hume, D. N. J . Am. Chem. SOC. 1051, 7 3 , 5321. (4) Schaap, W. B.; McMasters, D. L. J . Am. Chem. SOC. 1061, 83, 4699. (5) Klatt. L. N.; Rouseff, R. L. Anal. Chem. 1070, 42, 1234. (6) Irvlng, H. Adv. Polarogr. 1960, 1 , 42. (7) Leggett, D. J. Talanta 1080, 27, 767. (8) Koryta, J. Pfog. Polarogr. 1062, I , 295. (9) Buck, R. P. J. Elecfroanal. Chem. 1063, 5 , 295. (IO) Butler, C. 0.; Kaye. R. C. J. Nectroanal. Chem. 1964, 8 , 463.
2405
(11) Macovschl, M. E. J . Nectfoanfll. Chem. 1968, 16, 457. (12) Elenkova, N. 0.;Nedelcheva, T. K. J . Elecfroanal. Chem. 1976, 69, 305. (13) Spell, J. E., 11; Phllp, R. H., Jr. J. .€/ecffmnal. Chem. 1080, 712, 281. (14) Kllla, H. M.; Phllp, R. H., Jr. J . Elecfroanal. Chem., in press. (15) Bard, A. J.; Faulkner, L. R. “Electrochemlcal Methods”; Wlley: New York, 1980; Appendix B. (16) Nikolov, T.; Isolfova-Tsaneva, M.; Lyakov, N. Mefallurgiya (Lenlngrad) 1977. 23(a). ,-,. 1314. (17) Laltlnen. H. A.; Onstott, E. I.; Bailar, J. C., Jr.; Swann, S. J . Am. Chem. SOC.1940, 7 1 , 1550. (18) Spike. C. G.; Parry, R. W. J. Am. Chem. SOC. 1053, 75, 3770. (19) Basolo, F.; Murmann, R. K. J . Am. Chem. SOC. 1952, 74, 5243. (20) Cotton, F. A.; Harris, F. E. J . Phys. Chem. 1055, 59, 1203. (21) Avdee, F. A.; Zabronsky, J.; Stutlng, H. H. Anal. Chem. 1983, 55, 298. (22) Shah, S. K.; Suyan, K. M.; Gupta, C. M. Talanta 1080, 2 7 , 455. (23) Placeres, C. R.; Leon, J. J.; TruJlllo, J. P.; Monterlango, F. G. J. Inorg. Nucl. Chem. 1081, 43, 1681. (24) McMaster, D. L.; DiRalmondo, J. C.; Jones, L. H.; Lindley, R. P.; ZeRmann, E. W. J. Phys. Chem. 1062, 66, 249. (25) Clavatta, L.; Vlllafiorlta, M. Gazzerta 1055, 95, 1247. (26) Carlson, 0. A.; McReynolds, J. P.; Verhoek, F. A. J. Am. Chem. SOC. 1945, 67, 1334. (27) Gupta, K. D.; Gaghel, S. C.; Gaur, J. N. Monatsh. Chem. 1070, l l a , 657. (28) Sharma, R. S.; Gaur, J. N. J. Elecfrochem. SOC.India 1078, 2 7 , 261. (29) Maheshwarl, A. K.; Jaln, D. S.; Gaur, J. N. Monafsh. Chem. 1975, 106, 1033.
.
~
RECEIVED for review March 26,1984. Accepted June 11,1984.
Determination of Nitrite Ion and Sulfanilic and Orthanilic Acids by Differential Pulse Polarography S. T. Sulaiman Department of Chemistry, College of Science, University of Mosul, Mosul, Iraq
Nltrlte Ion can be determlned wlth a hlgh degree of accuracy and sensltlvlty by dlfferentiai pulse polarography utlilzlng the rapld and quantitative reactlon between nltrlte Ion and sulfanlllc acld or orthanlllc acid at pH 1.5. The experimental detectlon limit Is shown to be 8.6 X lo-’ M (as NO,-) In slmpie aqueous soiutlon. The method Is further used to determlne concentratlons of sulfanlllc acld down to 4 X lo-’ M and orthanlllc scld down to 1.6 X lo-’ M under optlmum condltlons.
the quantitative reaction of nitrite with diphenylamine to yield diphenylnitrosamine (DPN), with a practical working limit of 4.6 ppb. DPN is toxic, may be a carcinogen, and may act as nitrosating agent via transnitrosating (8). The purpose of this paper is to demonstrate the differential pulse polarographic behavior of diazonium salts obtained from diazotation of sulfanilic and orthanilic acids for the trace determination of nitrite. The method is simple, sensitive, and rapid.
The nitrosation of most aliphatic and aromatic amines with nitrite leads to the formation of N-nitrosamines, many of which have been shown to be potent carcinogens (1-3), and, when correlated with other nitrogen forms in water, can provide an index of organic pollution (4). Thus a sensitive and rapid method for the determination of nitrite is desirable. Numerous methods have been proposed for the determination of nitrite, among them are the spectrophotometric (4, 5), ion selective (3), and polargraphic methods (6-8). The spectrophotometric methods have limited sensitivity and dynamic range; most of them depend on unstable colors and are time-consuming. Differential pulse polarographic determinations of nitrite have been reported either by direct measurement of nitrous acid (6) (detection limit 0.5 ppm) or indirectly by the enhancement of the ytterbium peak (7). A detection limit of 46 ppb of nitrite ion was achieved under ideal conditions. Another report appeared by Harrington et al. (B), in which nitrite was determined by differentialpulse polarography using
EXPERIMENTAL SECTION Apparatus. Polarographic curves are recorded with a Metrohm Polarecord E 506 in conjunction with an E 505 polarography stand equipped with mechanical drop timer. A three-electrode system was used the working electrode was a dropping mercury electrode; the reference electrode was an Ag/AgCl, KCl with ceramic liquid junction; and the counterelectrode was a platinum wire. The differential pulse mode was used with a 100 mV pulse, a 2-5 drop time, and scan rate of 3 mV s-l, except where otherwise indicated. All polarographic measurements were performed at room temperature (20 O C ) . The solution was deareated by passing through it a slow stream of helium for 15 min. Reagents. All chemicals used were of analytical grade. M was prepared by dissolving Standard nitrite solution 2.17 X 0.1499 g of sodium nitrite in twice-distilled deionized water, followed by the addition of a pellet of sodium hydroxide and 1 mL of spectroscopic grade chloroform, and diluted to 1L. Dilute solutions were prepared from this stock solution by appropriate dilution or by direct pipetting into samples. Sulfanilic acid and orthanilic acid were obtained from BDH M) of each compound were prepared in Stock solutions deionized water. A series of the modified Britton-Robinson universal buffer (BRB) solutions (pH 1.8-2.0) were prepared as given by Britton
0003-2700/64/0356-2405$0 1.50/0 0 1984 American Chemlcal Soclety
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
Table I. Effect of pH on E, and I, of 8.6
X
10"
M DOA and DSA
DOA
a
PH
EPl, v
10-21p~, pA
1.5 2.6 3.6 4.0 3.6 5.2
-0.17 -0.17 -0.16 -0.16 -0.16
56.4 53.0 31.0 11.0 5.0
a
DSA 4 2 9
v
-0.40 -0.58 -0.71 -0.75 -0.78
10-21p~, pA 47.8 41.4 40.8 27.0 13.0
a
Epl,
v
10-2Zp1, pA
-0.11 -0.10 -0.10 -0.105 -0.12
113 113 108 83 13
a
Epzt
v
10-21p2, pA
-0.36 -0.56 -0.58 -0.64 -0.69
9.0 11.0 18.0 19.5 6.0
a
The peaks completely disappeared.
(9) and used as supporting electrolyte. Procedure. For the determination of nitrite, the differential pulse polarogram was run on a deoxygenate solution (25 mL) containing an excess of orthanilic acid or sulfanilic acid (lo-*M), BRB, and HCl(O.05 M)(pH 1.5). The background current was recorded. To this solution was added a certain amount of nitrite and the current-voltage curve recorded again. The background current was subtracted from the current observed after addition of the sample. Nitrite was then determined by the method of standard addition. For the determination of sulfanilic acid or orthanilic acid, the above procedure was followed on a solution containing the supporting electrolyte (BRB-HCl), and excess amount of nitrite M)and an appropriate aliquot of sulfanilic acid or solution orthanilic acid.
RESULTS AND DISCUSSION The preliminary investigations of the polarographic behavior of some diazonium salts have been previously studied (10, 11). Elofson et al. (10) showed that the reduction of diazotized aniline and related compounds gave two main polarographic waves. The main reduction peaks for diazotized sulfanilic acid in 0.1 N HCl appear at -0.33 and -0.56 V vs. SCE at 0 "C. In the present study, the differential polarogram of diazotized orthanilic acid (DOA) showed two well-defined peaks of almost equal height at -0.17 V and -0.40 V (Figure 1). On the other hand diazotized sulfanilic acid (DSA) showed one well-defined major peak at -0.11 V and a small peak at -0.36 V (Figure 2). The peak potentials and peak currents of these reduction peaks have been found to vary with pulse amplitude, drop time, and pH. Effect of pH. The differential pulse polarograms for DSA and DOA were investigated at various pH values. The results, shown in Table I, indicate that the peak potential E, of the first reduction peaks for both compounds are clearly pH independent. Similar observations were reported by Elofson et al. (10) for the DC polarography of DSA. On the other hand, the height I, of both the peaks and Ep of the second peak are dependent on pH. Maximum response was found at pH 1.5 (BRB HC1) which is chosen for the present study. The change of peak half-width with pH is consistent with an irreversible electrode reaction (12). Variation of I, with Pulse Amplitude and Drop Time. DP polarograms of DSA and DOA a t various drop times (Figures 1A and 2A) and various pulse amplitudes (Figures 1B and 2B) illustrate how the height of the peak increases as the pulse amplitude and drop time increased. Optimum values were obtained a t pulse amplitude 100 mV and drop time 2
-0:s -0.4 -0.3 -0.2 -0.1
Epiv
I
-0.5 -0.4 -0.3 -0.2 -0.1
Eplv
I
Figure 1. Differential pulse polarograms of 8.6 X M DOA at pH 1.5: (A) pulse amplitude 100 mV and drop tlme (1) 0.6 s, (2) 1.0 s, (3) 1.4 8, and (4) 2 s; (6) drop time 2 s and pulse amplitude (5) 40 mV, (6) 60 mV, (7) 80 mV, and (8) 100 mV. B
+
8.
It was also found that the peak half width is independent of pulse amplitude (Figures 1A and 2A). This is in agreement with the observation for the irreversible reduction system (13). Stability of the Diazonium Salts. The differential pulse polarograms for DSA and DOA are recorded at different times (Table 11). It can be seen from this table that the diazotized product is stable for about 24 h in solution containing a mixture of BRB and HC1 as supporting electrolyte.
-
P
I
1.5 -0.4 -0.5 -0.2 -0.1
-0.5 -0.4 -0.3 -0.2 -0.1
0
Ep CV)
Flgure 2. Differential pulse polarograms of 8.6 X M DSA at pH 1.5: (A) pulse amplitude 100 mV and drop tlme (1) 0.6 s, (2) 1.0 s, (3) 1.4 s,and (4) 2 s; (e) drop tlme 2 s and pulse amplkude (5) 40 mV, (6) 60 mV, (7) 80 mV, and (8) 100 mV.
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
Table 11. Effet of Time on I , of 4.0
X
M DOA and DSA
10-2Z,., uA
time, h
DOA
DSA
0.25 0.5 1.0 2.5 3.0 7.0 24.0
18.0 17.95 17.9 18.0 18.0 18.0 16.5
70.8 71.5 70.8 70.9 70.2 70.8 70.0
Table IV. Determination of Orthanilic Acid and Sulfanilic Acid sulfanilic orthanilic acid concn, M 0.04 0.08 0.12 0.16 0.32 0.48 1.28 2.00 4.00 4.48 8.48
Table 111. Nitrite Determination from Diazotization of Orthanilic Acid and Sulfanilic Acid DOA
DSA
10-2Zpz(corr), 10-21p(corr),
104[NOf],
10-zZpl(corr),
M
PA
PA
2.4 4.7 6.3 9.3 13.4
0.08 0.15 0.22 0.47 0.70 1.00 1.80 2.40 4.5 8.5 11.9 15.9 19.9
0.086 0.172 0.258 0.430 0.86 1.29 1.72 3.44 5.16 8.6 17.2 25.8 34.4 43.0
2407
10-zzpl(corr),
WZp2(corr),
acid 10-zZp(corr),
FA
PA
PA
1.32 4.25 6.75 13.75 15.0 31.25
0.83 1.80 3.08 8.03 12.00 23.70 25.5 51.5
0.65 1.41 2.18 2.95 5.75 8.52 23.25 36.75 71.25
PA 0.125 0.213 0.42 0.57 1.25 1.80 2.38 4.80 7.30 12.50 25.20
Effect of Concentration. When the DP polarograms are recorded at differnt concentrations of DOA and DSA, the results indicate that at low concentrations of DOA (less than 5 x 10" M) the peak current of the second peak only is proportional to the concentration. At higher concentrations (up to 8 x lob M) the peak currents of both peaks give a very good calibration graph. DSA, on the other hand, shows a good variation of the peak current of only the fiist major peak with concentrations up to 1.7 X M. For both diazonium salts (DSA and DOA), the E, values move to more negative values on increasing concentration. In the case of DSA, a plot of Ep vs. log [DSA] gave a straight line having a slope of 58 mV and hence the number of electrons a n, is equal to 1.0. Quantitative Trace Determination. The optimum conditions for the analytical determination of nitrite in aqueous solution were found to be a t pH 1.5 (supporting electrolyte mixture of BRB + HCI), pulse amplitude 100 mV, scan rate 3 mV 8-l and drop time 2 s, for the concentration range between 8.6 X lo-* and 1.7 X 10" M via diazotization of sulfanilic acid and for the concentration range between 1.72 X lo-' and 4.3 X 20-5 M via diazotization of orthanilic acid. Some typical results for sample aqueous solutions are shown in Table 111. This table shows the results of the DP method for a series of known nitrite solutions. These solutions are prepared by adding appropriate aliquots of nitrite stock solution to 25 mL of reagent solution containing M either sulfanilic acid or orthanilic acid and buffer solution pH 1.5 (BRB + HCl). The data appear to be quite good. Peak currents are linearly related to the concentrations (the least-squares plot gives a correlation coefficient of better than 0.999). The lowest experimental detection limit of nitrite was found to be 8.6 X lo4 M obtained from DSA with a standard
deviation of about 8% which is quite reasonable for such low concentrations. Determination of Sulfanilic Acid or Orthanilic Acid. The optimum conditions for the determination of sulfanilic acid or orthanilic acid are found to be similar to those used for nitrate determination. Some typical results for the microdetermination of sulfanilic acid or orthanilic acid are shown in Table IV. Their solutions are prepared by adding an appropriate aliquot of either sulfanilic or orthanilic acid stock solution to 25 mL of reagent solution containing 5 X lo4 M NO2- and buffer solution of pH 1.5. The result agrees well with the calibration graph construction by this technique. The lowest detection limit for the determination of sulfanilic acid and orthanilic acid was 4 X lo-' and 1.6 X 10" M with standard deviation of 2 and 1.8%, respectively. Interferences. The interfering effect of some foreign ions that may accompany nitrite was examined by carrying out determinations of 1ppm of nitrite in the presence of each of these ions. The results indicate that the following ions (represented as ppm) do not interfere and give an error of less than 1 2 % : PO-: (250), B033- (250), CH3COO- (250), NO3(68), C032-(54), CN- (42), C1- (64), F-(15), SO:- (80), NH4+ (201, Ag+ (85), C02+(32), Ni2+(381, Ca2+(36). The following ians interfere and give an error 115%: Cu2+(65), Cd2+(65), Hg2+(30), Sn2+(50),Fe3+(33),I- (801, S2-(20),and SO:- (35). Registry No. NOz-, 14797-65-0; sulfanilic acid, 121-57-3;orthanilic acid, 88-21-1; water, 7732-18-5.
LITERATURE CITED LiJinsky, W.; Epstein, S. S. Nature (London) 1970, 225, 21-23. Wolff, I. A.; Wasserman, A. E. Science 1972, 177, 15-19. Choi, K. K.; Fung, K. W. Analyst (London) 1980, 705, 241-245. Gabbay, J.; Almong, Y.; Davidson, M.; Donagi, A. E. Analyst (London) 1977, 102, 371-376. (5) Szekely, E. Talanta 1968, 75, 795-801. (6) Princeton Applied Research Application Brief N-1, Princeton, NJ, 1974. (7) Boese, S. W.; Archer, V. S.; O'Laughlin, J. W. Anal. Chem. 1977, 49, 479-484. (8) Chang, S. K.; Kozenlauskas, I?.;Harrington, G. W. AM/. Chem. 1977, 49, 2272-2275. (9) Britton, H. T. S. "Hydrogen Ions", 2nd ed.; Chapman and Hail: London, 1952; Vol. 1, p 362. (10) Elofson. R. M.; Edsberg, R. L.; Mecherly, P. A. J . Nectrochem. SOC. 1950, 9 7 , 166-177. (11) Atkinson, R. M.; Warren, H. H.; Abed, P. 1.; Wing, R. E. J . Am. Chem. Soc. 1050, 72, 915-918. (12) Parry, E. P.; Osteryoung, R. A. Anal. Chem. lB85, 37, 1634-1637. (13) Parry, E. P.; Oldham, K. E . Anal. Chem. 1968, 40, 1031-1036. (1) (2) (3) (4)
RECEIVED for review December 13,1983. Accepted April 23, 1984.
