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Spectrophotometric determination of NO2 in the working atmosphere
Talanta, Vol. 30, No. 3, PP. 185-186, 1983 Printed in Great Britain. All rights reserved
0039-9140/83/030185-02%03.00/O Copyright 0 1983Pergamon Press Ltd
SHORT COMMUNICATIONS SPECTROPHOTOMETRIC DETERMINATION IN THE WORKING ATMOSPHERE
OF NO,
B. G. ZHELYAZKOVA,* Department of Chemistry, Sofia University, 1126 Sofia, Bulgaria P. B. VARDEV Institute of Hygiene and Professional Diseases, Medical Academy, 1431 Sofia, Bulgaria and N. D. YORDANOV Institute of Orgamc Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria (Received 15 April 1982. Revised 20 September
1982. Accepted 4 October 1982)
Summary-A method is described for determining NO, in workplace atmospheres, based on its reaction with bis(diethyldithiocarbamato)copper(II) in toluene. NO, is absorbed from an air sample by a toluene solution of Cu(dtc), and the decrease in the initial absorbance at 437 nm is measured. The method has been compared with the Saltzman method. The interference of NO, Cl,, O,, SO, and other gases has been studied. The NO, concentration range of the method is I-500 mg/m3.
In an earlier paper’ we reported studies on the reaction of nitrogen dioxide with bis(diethyldithiocarbamato)copper(II), Cu(dtc),, in toluene. We found that Cu(dtc), is destroyed as a result of stoichiometric reaction of NOz with the ligand. The main product yielded at an NO,:Cu(dtc), ratio of 2: 1 was found to be the mixed-ligand complex Cu(N0,) (dtc), which has an absorption maximum at 400 nm. The final reaction products were, Cu(N0J2 and thiuramdisulphide, obtained at an NO*: Cu(dtc), ratio of 4: 1.’ EXPERIMENTAL Reagents
Copper(H) diethyldithiocarbamate was prepared by mixing equimolar aqueous solutions of sodium diethyldithiocarbamate and cupric chloride in 2:1 ratio. The precipitate was washed with water and dried at 60”. The crude product was recrystallized twice from chloroform.* Toluene was purified and dried before use. Toluene solutions of Cu(dtc), were found to be stable for several months. Nitrogen dioxide was obtained by thermal decomposition of dried reagent grade lead nitrate in a flow of 0xygen.j A Teflon permeation tube was filled with liquefied NO,. The permeation rate of the tube was determined gravimetrically and the tube was used to provide a working standard. Sal&man absorption solution was prepared and stored according to the procedure described by NIOSH.4.5 Solutions of sodium mtrite for the static calibration of the *Author to whom correspondence
should be addressed.
Saltzman method were prepared according to the same procedure.4.5 Apparatus
A dynamic mixing system6 was used to obtain an air flow with a known NO, concentration. A stream of dry cylinder air, brought to 3 1.5 + 0. lo and passed at a flow-rate of 82.5 ml/min over the NO, permeation tube was diluted with a stream of dried purified air, regulated with a needle valve and measured with a glass rotameter. Both streams were thoroughly mixed, and two glass T-pieces downstream of the mixer served as sampling ports. Various concentrations of NO, in air (in the mg/m’ range) were obtained by varying the flow of dilution air. The system was kept running for about 20 hr before calibration, to achieve equilibration between adsorption and desorption of the contaminant on the walls of the system. The humidity of the air was changed by mixing the dilution air with an air-stream saturated with water vapour. Relative humidities of 40% and 60% were produced by varymg the flow-rates of both streams and were continuously monitored with a wet/dry psychrometer. Procedure
Two all-glass fritted bubblers, each containing 10.0 ml of the Saltzman absorption solution, were attached in series to one of the ports. A second pair of all-glass fritted bubblers, each containing 5.0 ml of the toluene solution of Cu(dtc),, was attached to the other sampling port. The split gas stream was passed through both pairs of bubblers at a constant flow-rate of 150 ml/min, obtained by use of a critical orifice. Sampling times were arranged so that the absorbance of the Saltzman solutions was not more than 0.7 (m a 0.5-cm cell). The volume shrinkage caused by the volatility of toluene during the collection of the sample was corrected by addition of more toluene. 185
186
SHORT
COMMUNICATIONS
The absorbance of the Saltzman solutions was measured at 550 nm, 15 min after collection of the sample. Calibration with mtrate solution was used.4 The absorbance of the Cu(dtc), toluene solution was measured at 437 nm before and after collection of the sample, and the difference AA was used in the calculations. Calculations
Table 1. Determination
Present method
Cu (dtc)? concentration It was found that the concentration of the Cu(dtc), solution in toluene must be at least 1 x 10m4M to provide 2: 1 stoichiometry of the reaction, but must not exceed 6 x 10m4M or the initial absorbance of the Cu(dtc), solution measured in a O.l-cm optical cell will be more than 0.7.
Saltzman method, mglm’
3.9 8.7 11.5 27.2 33.9 86.9 159.3
14.3 13.5 11.4 7.1 8.2 5.0 6.2
3.2 7.9 12.5 29.0 35.9 -
Value,*
3.5 8.3 12.1 28.2 35.1 88.7 155.2
Nitrogen dioxide, mg/m3 = 0.092 x lo6 u AA/&IV
RESULTS AND DISCUSSION
mg/m’
Coefficient of variation, y0
Actual concentration of NO,, mg/m’
The concentration of nitrogen dioxide in the sample is calculated as follows: where AA is the difference in absorbance at 437 nm of the C~(dtc)~ solution before and after sampling, L’the volume of Cu(dtc)z solution in the bubbler (ml), E the molar absorptivity of Cu(dtc), at 437 nm (1.30 x lo4 I.mole ’ .cm- ‘), I the optical path-length (cm), V the volume of air sample, at 25” and 760 mmHg (litres).
of nitrogen dioxide
Nitrogen dioxide found
*Average of six determinations. Saltzman
method
and with the permeation
rate of the
NO* tube used as a standard. The results are shown in Table 1. The absence of a systematic error was proved by a t-test. Sensitivity and analysis range
The method is suitable for the determination of nitrogen dioxide in the range l-500 mg/m3. It is suitable for monitoring industrial atmospheres (the American and British TLV is 9 mg/m’).
Collection ejicieny
Interferences
The collection efficiency experiments were performed to determine the amount of nitrogen dioxide absorbed in a single bubbler in a 15-min sampling period at a flow-rate of 150 ml/min. The experiment was performed over the NO2 concentration range of 3-160 mg/m-’ and with the Cu(dtc)z concentration in the range l-6 x 10-4M. The nitrogen dioxide not collected in the first bubbler was trapped in the second. Collection efficiencies of 93-99x were found, suggesting that no recovery correction is necessary.
Strong oxidizing agents such as ozone and chlorine produce a similar effect. The interferences from NO, Sot, CO*, 0, and air humidity (up to 60%) are negligible.
REFERENCES
1.
N. D. Yordanov, B. G. Zhelyazkova and V. Terziev, Inorg. Chim. Acta, 1982, 58, 213.
2. N. D. Yordanov and D. Shopov, Compt. Rend. Acad. Sci. Bulg., 1970, 23, 1239.
Precision
and accuracy
The reproducibility of the method (sampling and analysis) was determined by measuring the amount of NO, in 40 samples, over the range l-500 mg/m3. The mean relative standard deviation was found to be 14%. The overall accuracy of the sampling procedure and analysis was determined by comparison with the
3. G. Brauer, Handbook of Preparative Inorganic Chemistry, 2nd Ed., Vol. 1, p. 488. Academic Press, New York, 1963. 4. NIOSH Manual of Analytical Methodr, 2nd Ed., Method No. P&CAM 108. NIOSH, Ohio, 1977. 5. M. Katz, Methodr of Air Sampling and Analysis, 2nd Ed. American Public Health Association, Washington, 1977. 6. F. P. Scaringelli, E. Rosenberg and K. A. Rehme, Environ. Sci. Technol., 1970, 4, 924.
0039-9140/83/030185-02%03.00/O Copyright 0 1983Pergamon Press Ltd
SHORT COMMUNICATIONS SPECTROPHOTOMETRIC DETERMINATION IN THE WORKING ATMOSPHERE
OF NO,
B. G. ZHELYAZKOVA,* Department of Chemistry, Sofia University, 1126 Sofia, Bulgaria P. B. VARDEV Institute of Hygiene and Professional Diseases, Medical Academy, 1431 Sofia, Bulgaria and N. D. YORDANOV Institute of Orgamc Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria (Received 15 April 1982. Revised 20 September
1982. Accepted 4 October 1982)
Summary-A method is described for determining NO, in workplace atmospheres, based on its reaction with bis(diethyldithiocarbamato)copper(II) in toluene. NO, is absorbed from an air sample by a toluene solution of Cu(dtc), and the decrease in the initial absorbance at 437 nm is measured. The method has been compared with the Saltzman method. The interference of NO, Cl,, O,, SO, and other gases has been studied. The NO, concentration range of the method is I-500 mg/m3.
In an earlier paper’ we reported studies on the reaction of nitrogen dioxide with bis(diethyldithiocarbamato)copper(II), Cu(dtc),, in toluene. We found that Cu(dtc), is destroyed as a result of stoichiometric reaction of NOz with the ligand. The main product yielded at an NO,:Cu(dtc), ratio of 2: 1 was found to be the mixed-ligand complex Cu(N0,) (dtc), which has an absorption maximum at 400 nm. The final reaction products were, Cu(N0J2 and thiuramdisulphide, obtained at an NO*: Cu(dtc), ratio of 4: 1.’ EXPERIMENTAL Reagents
Copper(H) diethyldithiocarbamate was prepared by mixing equimolar aqueous solutions of sodium diethyldithiocarbamate and cupric chloride in 2:1 ratio. The precipitate was washed with water and dried at 60”. The crude product was recrystallized twice from chloroform.* Toluene was purified and dried before use. Toluene solutions of Cu(dtc), were found to be stable for several months. Nitrogen dioxide was obtained by thermal decomposition of dried reagent grade lead nitrate in a flow of 0xygen.j A Teflon permeation tube was filled with liquefied NO,. The permeation rate of the tube was determined gravimetrically and the tube was used to provide a working standard. Sal&man absorption solution was prepared and stored according to the procedure described by NIOSH.4.5 Solutions of sodium mtrite for the static calibration of the *Author to whom correspondence
should be addressed.
Saltzman method were prepared according to the same procedure.4.5 Apparatus
A dynamic mixing system6 was used to obtain an air flow with a known NO, concentration. A stream of dry cylinder air, brought to 3 1.5 + 0. lo and passed at a flow-rate of 82.5 ml/min over the NO, permeation tube was diluted with a stream of dried purified air, regulated with a needle valve and measured with a glass rotameter. Both streams were thoroughly mixed, and two glass T-pieces downstream of the mixer served as sampling ports. Various concentrations of NO, in air (in the mg/m’ range) were obtained by varying the flow of dilution air. The system was kept running for about 20 hr before calibration, to achieve equilibration between adsorption and desorption of the contaminant on the walls of the system. The humidity of the air was changed by mixing the dilution air with an air-stream saturated with water vapour. Relative humidities of 40% and 60% were produced by varymg the flow-rates of both streams and were continuously monitored with a wet/dry psychrometer. Procedure
Two all-glass fritted bubblers, each containing 10.0 ml of the Saltzman absorption solution, were attached in series to one of the ports. A second pair of all-glass fritted bubblers, each containing 5.0 ml of the toluene solution of Cu(dtc),, was attached to the other sampling port. The split gas stream was passed through both pairs of bubblers at a constant flow-rate of 150 ml/min, obtained by use of a critical orifice. Sampling times were arranged so that the absorbance of the Saltzman solutions was not more than 0.7 (m a 0.5-cm cell). The volume shrinkage caused by the volatility of toluene during the collection of the sample was corrected by addition of more toluene. 185
186
SHORT
COMMUNICATIONS
The absorbance of the Saltzman solutions was measured at 550 nm, 15 min after collection of the sample. Calibration with mtrate solution was used.4 The absorbance of the Cu(dtc), toluene solution was measured at 437 nm before and after collection of the sample, and the difference AA was used in the calculations. Calculations
Table 1. Determination
Present method
Cu (dtc)? concentration It was found that the concentration of the Cu(dtc), solution in toluene must be at least 1 x 10m4M to provide 2: 1 stoichiometry of the reaction, but must not exceed 6 x 10m4M or the initial absorbance of the Cu(dtc), solution measured in a O.l-cm optical cell will be more than 0.7.
Saltzman method, mglm’
3.9 8.7 11.5 27.2 33.9 86.9 159.3
14.3 13.5 11.4 7.1 8.2 5.0 6.2
3.2 7.9 12.5 29.0 35.9 -
Value,*
3.5 8.3 12.1 28.2 35.1 88.7 155.2
Nitrogen dioxide, mg/m3 = 0.092 x lo6 u AA/&IV
RESULTS AND DISCUSSION
mg/m’
Coefficient of variation, y0
Actual concentration of NO,, mg/m’
The concentration of nitrogen dioxide in the sample is calculated as follows: where AA is the difference in absorbance at 437 nm of the C~(dtc)~ solution before and after sampling, L’the volume of Cu(dtc)z solution in the bubbler (ml), E the molar absorptivity of Cu(dtc), at 437 nm (1.30 x lo4 I.mole ’ .cm- ‘), I the optical path-length (cm), V the volume of air sample, at 25” and 760 mmHg (litres).
of nitrogen dioxide
Nitrogen dioxide found
*Average of six determinations. Saltzman
method
and with the permeation
rate of the
NO* tube used as a standard. The results are shown in Table 1. The absence of a systematic error was proved by a t-test. Sensitivity and analysis range
The method is suitable for the determination of nitrogen dioxide in the range l-500 mg/m3. It is suitable for monitoring industrial atmospheres (the American and British TLV is 9 mg/m’).
Collection ejicieny
Interferences
The collection efficiency experiments were performed to determine the amount of nitrogen dioxide absorbed in a single bubbler in a 15-min sampling period at a flow-rate of 150 ml/min. The experiment was performed over the NO2 concentration range of 3-160 mg/m-’ and with the Cu(dtc)z concentration in the range l-6 x 10-4M. The nitrogen dioxide not collected in the first bubbler was trapped in the second. Collection efficiencies of 93-99x were found, suggesting that no recovery correction is necessary.
Strong oxidizing agents such as ozone and chlorine produce a similar effect. The interferences from NO, Sot, CO*, 0, and air humidity (up to 60%) are negligible.
REFERENCES
1.
N. D. Yordanov, B. G. Zhelyazkova and V. Terziev, Inorg. Chim. Acta, 1982, 58, 213.
2. N. D. Yordanov and D. Shopov, Compt. Rend. Acad. Sci. Bulg., 1970, 23, 1239.
Precision
and accuracy
The reproducibility of the method (sampling and analysis) was determined by measuring the amount of NO, in 40 samples, over the range l-500 mg/m3. The mean relative standard deviation was found to be 14%. The overall accuracy of the sampling procedure and analysis was determined by comparison with the
3. G. Brauer, Handbook of Preparative Inorganic Chemistry, 2nd Ed., Vol. 1, p. 488. Academic Press, New York, 1963. 4. NIOSH Manual of Analytical Methodr, 2nd Ed., Method No. P&CAM 108. NIOSH, Ohio, 1977. 5. M. Katz, Methodr of Air Sampling and Analysis, 2nd Ed. American Public Health Association, Washington, 1977. 6. F. P. Scaringelli, E. Rosenberg and K. A. Rehme, Environ. Sci. Technol., 1970, 4, 924.