- Email: [email protected]
phloroglucinol for the spectrophotometric determination of nitrite
MICROCHEMICAL
JOURNAL
4,
242-245 (1989)
Some Observations on the Use of P-Rosaniline Hydrochloride/PhloroglucinoI for the Spectrophotometric Determination of Nitrite V. RAMAN' AND M. S. DABBAS* Chemistry Division,
National
Physical Laboratory,
Dr. Krishnan
Road, New Delhi 110012, India
Received April 11, 1989; accepted May 11, 1989 A new spectrophotometric method is described for the estimation of nitrite and nitrogen dioxide. Acidified p-rosaniline hydrochloride is diazotized in the presence of nitrite/nitrogen dioxide trapped in alkaline sodium arsenite and the diazo compound thus formed is coupled with phloroglucinol in alkaline medium to yield a yellow dye which absorbs at 420 nm. The interference of sulfite, sulfide, and metallic ions like Cu(II), Pb(II), Mn(II), Fe(III), V(V), and Cr(VI) is investigated. Beer’s law is obeyed in the concentration range of 0.04-0.48 &ml of nitrogen dioxide. 8 1989 Academic press, I~C.
INTRODUCTION
Nitrites/nitrogen dioxide are well-known pollutants. Nitrite consumption shows symptoms which resemble those of cyanide poisoning. Nitrogen oxides are produced as environmental contaminants when organic compounds undergo combustions; important environmental sources of these toxic oxides include automobile exhaust, incinerators, fossifuel power plants, and tobacco smoke. Since these oxides themselves are free radicals they cause biological damage by free radical mechanism. It is well known that nitrogen dioxide is more toxic than nitric oxide and produces nitrous acid by hydrogen abstraction. The nitrous acid can nitrosate amines to form nitroso amines which are extremely potent carcinogens (I). The maximum admissible concentration of nitrite is 0.1 pg/ml and the threshold limit value of nitrogen dioxide is 3 ppm (2). Chemists have postulated various methodes for the determination of nitrite/ nitrogen dioxide. Most of the methods are based on the azo dye formation (3-5) while few methods comprising reagents which do not lead to the formation of azo dyes are also reported (6-9). Spectrophotometric or calorimetric methods are simple, sensitive, and easily accessible to many scientists. Hence, the authors have developed a spectrophotometric method for the estimation of nitrite/nitrogen dioxide using acidified p-rosaniline hydrochloride and phloroglucinol as diazotizing and coupling reagents. The reagents are easily available and the color reaction is easy to follow. In the present investigation, nitrite helps in the diazotization of acidified p-rosaniline hydrochloride which is later coupled with phloroglucinol in alkaline medium to yield a yellow colored dye which absorbs at 420 nm. The ’ To whom correspondence * Deceased.
should be addressed.
242 0026-265X/89 $1.50 Copyright 0 1989 by Academic Press, Inc. All rights of reproduction in any form reserved.
SPECTROPHOTOMETRIC
DETERMINATION
OF NITRITE
243
method is sensitive and nitrite content as low as 0.04 pg/ml can be estimated. The method is applied to the estimation of nitrogen dioxide in air after fixing it in alkaline sodium arsenite. Beer’s law was obeyed in the concentration range of 2-24 p,g of nitrite in 50 ml of the solution. MATERIALS
AND METHODS
Reagents All chemicals used are of analytical grade and all dissolutions and dilutions were made with double-distilled water. Sodium nitrite (4 pg/ml of nitrite concentration): 1.5 g of sodium nitrite was dissolved in water after the addition of 10 ml of 2% sodium hydroxide and the volume was made to 1 liter. This was further diluted 250 times to get 4 pg/ml of nitrite concentration taking care to add 10 ml of 2% sodium hydroxide solution in every dilution. p-Rosaniline hydrochloride (0.04%): 100 mg of the p-rosaniline hydrochloride was dissolved in water, 15 ml of concentrated hydrochloric acid was added, and the volume was made up to 250 ml. Phloroglucinol (0.1%): 100 mg of this reagent was dissolved in water and made to 100 ml. Alkaline sodium arsenite: 1 g of arseneous oxide and 1.2 g of sodium hydroxide were dissolved in water. The volume was made to 2 liters after the addition of 4 g of sodium hydroxide. Apparatus A Perkin-Elmer Lamda 3B UVNIS used for absorbance measurements.
spectrophotometer with a l-cm cell was
Procedure Sodium nitrite solutions (4 p&ml of nitrite) of 0.5, 1, 2, 3, 4, 5, and 6 ml were taken in a series of 50-ml volumetric flasks. Two milliliters of p-rosaniline hydrochloride was added to each flask and shaken well. This was followed by the addition of 2 ml of phloroglucinol and 10 ml of 2% of sodium hydroxide solution. Yellow color developed immediately. The flasks were shaken well, made up to the volume, and absorbances were measured at 420 nm against the reagent blank. The absorbances when plotted against the nitrite concentration rendered a straight line graph. The experiment was repeated after adding 10 ml of alkaline sodium arsenite to sodium nitrite solution. It was observed that the absorbances were unaffected by the presence of alkaline sodium arsenite solution. The above experiments clearly indicate that nitrogen dioxide in air can be estimated by this method after trapping it in alkaline sodium arsenite solution. However, it is recommended that the calibration graph should be prepared with nitrite fixed in alkaline sodium arsenite solution.
244
RAMAN
AND
DABBAS
RESULTS AND DISCUSSION Nitrite ions are known to form diazo compounds with aromatic compounds containing a free primary amino group in the reactive position in the presence of acids like hydrochloric and sulfuric acids. The diazo compounds thus formed couple with compounds containing naphthyl or phenolic groups. p-Rosaniline hydrochloride is a dye having a free amino group. The acidified dye reacts with nitrite to form a diazo compound which when coupled with phloroglucinol produces a yellow dye in alkaline medium. The dye absorbs at 420 nm and is quite stable. Nitrogen dioxide is generally trapped in alkaline sodium arsenite solution (10, II). In the present investigation it was observed that the absorbances were little affected when alkaline sodium arsenite was used for fixing nitrite. Hence this method is applicable to the estimation of nitrogen dioxide in air after fixing it in alkaline sodium arsenite solution. It was also observed that nitrogen dioxide fixed in alkaline sodium arsenite is very stable. Beer’s Law, Sandell’s Sensitivity, and Reproducibility Beer’s law was obeyed in the concentration range of 2-24 pg of nitrite/50 ml of the solution. Reproducibility of the method was checked by taking several samples of the same concentration. It was observed that the standard deviation was 0.009 for 4 p,g of nitrite in 50 ml of the solution. Sandell’s sensitivity was calculated to be 0.0011 Fg/cm2. Interference The interference of sulfide, sulfite, and few metallic ions which are generally present as pollutants is investigated. Added to nitrite solutions (20 pg) were 100 p,g of Cu(II), Mn(II), Pb(II), Fe(III), Cr(VI), and V(V) and the absorbances were measured after the azo dye formation. It was observed that Mn(I1) and Fe(II1) enhanced the absorbance value by 10% and Cu(II), Cr(VI), and V(V) caused a decrease in the absorbance by 18, 13, and 4%, respectively. Sulfite ion interferes to a lesser extent. It was observed that 200 pg of sodium sulfite when added to 20 p.g of nitrite ion decreased the absorbance value by only about 6%. Sulfide interferes seriously. Added to 20 kg of nitrite solution were 20, 40, 60, and 80 ug of sulfide ion as sodium sulfide. It was observed that there is a considerable decrease in the absorbance value (Table 1). The observations are in close agreement with those of Norwitz and Keliher (12). Application of the Method to Air Samples The method was applied for the estimation of nitrogen dioxide in air by collecting air samples at the rate of 0.5, 0.75, and 1.2 liters/min for 5 h in alkaline sodium arsenite solution and later estimating aliquots by the standard as well as by the proposed method. It was observed that the concentration of nitrogen dioxide in air by both of the methods is in agreement and was found to be 0.01 ppm.
SPECTROPHOTOMETRIC
DETERMINATION
OF NITRITE
245
TABLE 1 Interference of Sulfide Ion Quantity of nitrite ion added (I&!)
Quantity of sulfide ion added (Id
Absorbance (AU)
20 20 20 20 20
20 40 60 80
0.345 0.295 0.245 0.195 0.165
ACKNOWLEDGMENT The authors are grateful to Dr. S. K. Joshi, Director, National Physical Laboratory, for his encouragement throughout this investigation.
REFERENCES 1. Pryor W. A. Mechanisms and detection of pathology caused by free radicals, tobacco smoke, nitrogen dioxide and ozone. In Environmental Health Chemistry (J. D. Mckinney, Ed.), p. 451. Ann Arbor Science, Michigan, 1981. 2. Marr, I. L.:, Cresse, D. C. Environmental Chemical Analysis, pp. 249, 251. Litho, East Kilbride, 1983. 3. Balasubramaniyan, N.; Vijanthimala, R. 2. Gesamte. Hyg. Zhre. Crenzgeb., 1987, 33, 212-213. 4. Bhatt, A.; Gupta, V. K. J. Indian Chem. Sot., 1980, 57, 1056-1058. 5. Ramkrishna, T. V.; Balasubramaniyan, N., Z. Gesamte. Hyg. Zhre. Crenzgeb., 1984,30,467468. 6. Balasubramaniyan, N.; Sivagami, M. Z. Gesamte. Hyg. Zhre. Crenzgeb., 1986, 32, 156157. 7. Jimnenez-Sanchez, J. C.; Lemus Gallego, J. M. Microchem. J., 1985, 32, 69-75. 8. Nagashima, K.; Matsumoto, M.; Suzuki, S. Anal. Chem., 1985, 57, 2065-2067. 9. Sanchez-Pedreno, C.; Sierra, M. T.; Sierra, M. I.; Sanz A. Analyst (London), 1987,112,837-840. 10. Christie, A. A.; Lidzey, R. G.; Radford, D. N. F. Analyst (London), 1970, 95, 519-524. 11. John, H. M.; Beard, M. E.; Sugges, J. C. J. Air Polk. Control Assoc., 1977, 276, 553-556. 12. Norwitz, G.; Keliher, P. N. Analyst (London), 1985, 110, 689-694.
JOURNAL
4,
242-245 (1989)
Some Observations on the Use of P-Rosaniline Hydrochloride/PhloroglucinoI for the Spectrophotometric Determination of Nitrite V. RAMAN' AND M. S. DABBAS* Chemistry Division,
National
Physical Laboratory,
Dr. Krishnan
Road, New Delhi 110012, India
Received April 11, 1989; accepted May 11, 1989 A new spectrophotometric method is described for the estimation of nitrite and nitrogen dioxide. Acidified p-rosaniline hydrochloride is diazotized in the presence of nitrite/nitrogen dioxide trapped in alkaline sodium arsenite and the diazo compound thus formed is coupled with phloroglucinol in alkaline medium to yield a yellow dye which absorbs at 420 nm. The interference of sulfite, sulfide, and metallic ions like Cu(II), Pb(II), Mn(II), Fe(III), V(V), and Cr(VI) is investigated. Beer’s law is obeyed in the concentration range of 0.04-0.48 &ml of nitrogen dioxide. 8 1989 Academic press, I~C.
INTRODUCTION
Nitrites/nitrogen dioxide are well-known pollutants. Nitrite consumption shows symptoms which resemble those of cyanide poisoning. Nitrogen oxides are produced as environmental contaminants when organic compounds undergo combustions; important environmental sources of these toxic oxides include automobile exhaust, incinerators, fossifuel power plants, and tobacco smoke. Since these oxides themselves are free radicals they cause biological damage by free radical mechanism. It is well known that nitrogen dioxide is more toxic than nitric oxide and produces nitrous acid by hydrogen abstraction. The nitrous acid can nitrosate amines to form nitroso amines which are extremely potent carcinogens (I). The maximum admissible concentration of nitrite is 0.1 pg/ml and the threshold limit value of nitrogen dioxide is 3 ppm (2). Chemists have postulated various methodes for the determination of nitrite/ nitrogen dioxide. Most of the methods are based on the azo dye formation (3-5) while few methods comprising reagents which do not lead to the formation of azo dyes are also reported (6-9). Spectrophotometric or calorimetric methods are simple, sensitive, and easily accessible to many scientists. Hence, the authors have developed a spectrophotometric method for the estimation of nitrite/nitrogen dioxide using acidified p-rosaniline hydrochloride and phloroglucinol as diazotizing and coupling reagents. The reagents are easily available and the color reaction is easy to follow. In the present investigation, nitrite helps in the diazotization of acidified p-rosaniline hydrochloride which is later coupled with phloroglucinol in alkaline medium to yield a yellow colored dye which absorbs at 420 nm. The ’ To whom correspondence * Deceased.
should be addressed.
242 0026-265X/89 $1.50 Copyright 0 1989 by Academic Press, Inc. All rights of reproduction in any form reserved.
SPECTROPHOTOMETRIC
DETERMINATION
OF NITRITE
243
method is sensitive and nitrite content as low as 0.04 pg/ml can be estimated. The method is applied to the estimation of nitrogen dioxide in air after fixing it in alkaline sodium arsenite. Beer’s law was obeyed in the concentration range of 2-24 p,g of nitrite in 50 ml of the solution. MATERIALS
AND METHODS
Reagents All chemicals used are of analytical grade and all dissolutions and dilutions were made with double-distilled water. Sodium nitrite (4 pg/ml of nitrite concentration): 1.5 g of sodium nitrite was dissolved in water after the addition of 10 ml of 2% sodium hydroxide and the volume was made to 1 liter. This was further diluted 250 times to get 4 pg/ml of nitrite concentration taking care to add 10 ml of 2% sodium hydroxide solution in every dilution. p-Rosaniline hydrochloride (0.04%): 100 mg of the p-rosaniline hydrochloride was dissolved in water, 15 ml of concentrated hydrochloric acid was added, and the volume was made up to 250 ml. Phloroglucinol (0.1%): 100 mg of this reagent was dissolved in water and made to 100 ml. Alkaline sodium arsenite: 1 g of arseneous oxide and 1.2 g of sodium hydroxide were dissolved in water. The volume was made to 2 liters after the addition of 4 g of sodium hydroxide. Apparatus A Perkin-Elmer Lamda 3B UVNIS used for absorbance measurements.
spectrophotometer with a l-cm cell was
Procedure Sodium nitrite solutions (4 p&ml of nitrite) of 0.5, 1, 2, 3, 4, 5, and 6 ml were taken in a series of 50-ml volumetric flasks. Two milliliters of p-rosaniline hydrochloride was added to each flask and shaken well. This was followed by the addition of 2 ml of phloroglucinol and 10 ml of 2% of sodium hydroxide solution. Yellow color developed immediately. The flasks were shaken well, made up to the volume, and absorbances were measured at 420 nm against the reagent blank. The absorbances when plotted against the nitrite concentration rendered a straight line graph. The experiment was repeated after adding 10 ml of alkaline sodium arsenite to sodium nitrite solution. It was observed that the absorbances were unaffected by the presence of alkaline sodium arsenite solution. The above experiments clearly indicate that nitrogen dioxide in air can be estimated by this method after trapping it in alkaline sodium arsenite solution. However, it is recommended that the calibration graph should be prepared with nitrite fixed in alkaline sodium arsenite solution.
244
RAMAN
AND
DABBAS
RESULTS AND DISCUSSION Nitrite ions are known to form diazo compounds with aromatic compounds containing a free primary amino group in the reactive position in the presence of acids like hydrochloric and sulfuric acids. The diazo compounds thus formed couple with compounds containing naphthyl or phenolic groups. p-Rosaniline hydrochloride is a dye having a free amino group. The acidified dye reacts with nitrite to form a diazo compound which when coupled with phloroglucinol produces a yellow dye in alkaline medium. The dye absorbs at 420 nm and is quite stable. Nitrogen dioxide is generally trapped in alkaline sodium arsenite solution (10, II). In the present investigation it was observed that the absorbances were little affected when alkaline sodium arsenite was used for fixing nitrite. Hence this method is applicable to the estimation of nitrogen dioxide in air after fixing it in alkaline sodium arsenite solution. It was also observed that nitrogen dioxide fixed in alkaline sodium arsenite is very stable. Beer’s Law, Sandell’s Sensitivity, and Reproducibility Beer’s law was obeyed in the concentration range of 2-24 pg of nitrite/50 ml of the solution. Reproducibility of the method was checked by taking several samples of the same concentration. It was observed that the standard deviation was 0.009 for 4 p,g of nitrite in 50 ml of the solution. Sandell’s sensitivity was calculated to be 0.0011 Fg/cm2. Interference The interference of sulfide, sulfite, and few metallic ions which are generally present as pollutants is investigated. Added to nitrite solutions (20 pg) were 100 p,g of Cu(II), Mn(II), Pb(II), Fe(III), Cr(VI), and V(V) and the absorbances were measured after the azo dye formation. It was observed that Mn(I1) and Fe(II1) enhanced the absorbance value by 10% and Cu(II), Cr(VI), and V(V) caused a decrease in the absorbance by 18, 13, and 4%, respectively. Sulfite ion interferes to a lesser extent. It was observed that 200 pg of sodium sulfite when added to 20 p.g of nitrite ion decreased the absorbance value by only about 6%. Sulfide interferes seriously. Added to 20 kg of nitrite solution were 20, 40, 60, and 80 ug of sulfide ion as sodium sulfide. It was observed that there is a considerable decrease in the absorbance value (Table 1). The observations are in close agreement with those of Norwitz and Keliher (12). Application of the Method to Air Samples The method was applied for the estimation of nitrogen dioxide in air by collecting air samples at the rate of 0.5, 0.75, and 1.2 liters/min for 5 h in alkaline sodium arsenite solution and later estimating aliquots by the standard as well as by the proposed method. It was observed that the concentration of nitrogen dioxide in air by both of the methods is in agreement and was found to be 0.01 ppm.
SPECTROPHOTOMETRIC
DETERMINATION
OF NITRITE
245
TABLE 1 Interference of Sulfide Ion Quantity of nitrite ion added (I&!)
Quantity of sulfide ion added (Id
Absorbance (AU)
20 20 20 20 20
20 40 60 80
0.345 0.295 0.245 0.195 0.165
ACKNOWLEDGMENT The authors are grateful to Dr. S. K. Joshi, Director, National Physical Laboratory, for his encouragement throughout this investigation.
REFERENCES 1. Pryor W. A. Mechanisms and detection of pathology caused by free radicals, tobacco smoke, nitrogen dioxide and ozone. In Environmental Health Chemistry (J. D. Mckinney, Ed.), p. 451. Ann Arbor Science, Michigan, 1981. 2. Marr, I. L.:, Cresse, D. C. Environmental Chemical Analysis, pp. 249, 251. Litho, East Kilbride, 1983. 3. Balasubramaniyan, N.; Vijanthimala, R. 2. Gesamte. Hyg. Zhre. Crenzgeb., 1987, 33, 212-213. 4. Bhatt, A.; Gupta, V. K. J. Indian Chem. Sot., 1980, 57, 1056-1058. 5. Ramkrishna, T. V.; Balasubramaniyan, N., Z. Gesamte. Hyg. Zhre. Crenzgeb., 1984,30,467468. 6. Balasubramaniyan, N.; Sivagami, M. Z. Gesamte. Hyg. Zhre. Crenzgeb., 1986, 32, 156157. 7. Jimnenez-Sanchez, J. C.; Lemus Gallego, J. M. Microchem. J., 1985, 32, 69-75. 8. Nagashima, K.; Matsumoto, M.; Suzuki, S. Anal. Chem., 1985, 57, 2065-2067. 9. Sanchez-Pedreno, C.; Sierra, M. T.; Sierra, M. I.; Sanz A. Analyst (London), 1987,112,837-840. 10. Christie, A. A.; Lidzey, R. G.; Radford, D. N. F. Analyst (London), 1970, 95, 519-524. 11. John, H. M.; Beard, M. E.; Sugges, J. C. J. Air Polk. Control Assoc., 1977, 276, 553-556. 12. Norwitz, G.; Keliher, P. N. Analyst (London), 1985, 110, 689-694.