1810
ANALYTICAL CHEMISTRY
ment with provision for blocking all ions below 44. Thus all of the principal components of the atmosphere-nitrogen, oxygen, carbon dioxide, water, and argon-would not be recorded. Carbon monoxide, hydrogen sulfide, and nitric oxide would also be eliminated. All of the ions above mass 44 could be collected together and correlated with the total ionization above mass 44 from organic compounds. A disadvantage of this instrument would be the loss of the intense organic peak at mass 43. Another possible mass apparatus could utilize differences in ionization potential between organic compounds and the major components of air. Operation at an ionizing voltage below 12.2 volts xould ionize all organic compounds except methane and would not ionize nitrogen, oxygen, carbon dioxide, water, argon, carbon monoxide, or sulfur dioxide. -4disadvantage of such an instrument would be its low sensitivity. ACKNOW LEDGMEKT
The cooperation of A. J. Haagen-Smit, 4.G. Sharkey, Jr., Janet L. Shultz, J. A. Queiser, and Harold Watson is gratefully acknowledged. LITERATURE CITED (1) Air Pollution Control District, County of Los Angeles, “Air Pollution Control in Los dngeles County.” 2nd Report, 19501951. (2) Air Pollution Foundation, Rept. 4 , 81 (1955). (3) Beynon, J. H., S u t u r e 174, 735 (1954). (4) Brady, L. J., in “Analytical Absorption Spectroscopy,” ed. by LI,G. hIellon, p. 497, Wiley, Sew York, 1950. (5) Chandler, J. M,, Cannon, K. A,, Xeerman. J. C., Rudolph, A , , J . A i r Pollution Control dssoc. 5, 65 (1955). (6) Coggeshall, N. D., Saier, E. L.. J . A p p l . Phys. 17, 450 (1946). (7) Elliott, bl. A , , Davis, R. F., Friedel. R.-A,, Proc. Third World Petroleum Congress, Sect. 7, A-0. 25, 1951. (8) Elliott, hl. A , , Kobel, G . J..Rounds, F. G., J . A i r Pollution Control Assoc. 5, 103 (1955). (9) Epstein, Samuel, Air Pollution Foundation, Rept. 4 , 78 (1955).
(10) Friedel, R. A . , in “Air Pollution.” p. 222, LIcGraw-Hill, h’ew York, 1952; U. S. Tech. Conf. on Air Pollution, Washington, D . C.. hlav 3. 1950. (11) Friedel, R. A:, Sharkey, 4.G., Jr., Shultz, J. L . , Humbert, C. R., ANAL.CHEM.25, 1314 (1953). (12) Gates, D. M., Third National Air Pollution Symposium, p. 56, 1955. (13) Gutowsky, H. S., J . A m . Chem. SOC.75, 4567 (1953). (14) Haagen-Smit, .4.H., I n d . Eng. Chem. 44, 1342 (1952). (15) Hanst, P. L., Stephens, E. R., Scott, W. E.. J . A i r Pollution Control Assoc. 5, 219 (1956). (16) Happ, G. P., Stewart, D . W., Brockmyre, H. F., -&NAL. CHEY. 22, 1224 (1950). (17) Hastings, 8. H., Watson, A . T., Williams, R. B., Anderson, J. A , , Jr., Ibid., 24, 612 (1952). (18) Hutchison, D. H., Holden, F. R . , J . S i r Pollution Confrol Assoc. 5, 71 (1955). (19) Keeling, C. D., private communication. (20) Lee, J. H., IND. ENG.CHEM., ASAL. E D . 18, 659 (1946). (21) Littman, F. E., Denton, J. Q., A . v . 4 ~ .CHEM.28, 945 (1956). (22) Littman, F. E., Narynowski, C. W., Ibid.. 28, 819 (1956). (23) JfcGovern. J. J., private communication. (24) &fader, P. P., Heddon, 11.W., Lofberg, R. T., Koehler, R . H., ANAL. CHEY.24, 1899 (1952). (25) Martin, A. J. P., private communication. (26) Pfund, A . H., Science 90, 326 (1939). (27) Renzetti, N.A,, J . Chem. P h y s . 24, 909 (1956). (28) Saier, E. L., Coggeshall, N.D., BNAL.C H E M20, . 812 (1948). (29) Shepherd, AI., Rock, S. M., Howard. R.. Storms, J., Ibid.,23, 1431 (1951). (30) Stair, Ralph, Third National Air Pollution Symposium, p. 48, 1955. (31) Troy, D. J., ANAL.CHEY.27, 1217 (1955). (32) Twiss,S. B., Teague, D. 31.. Bozek, J. W., Sink, 11. V., J.Air Pollution Control Assoc. 5, 75 (1955). (33) Walker, J. K., O’Hara, C. L., A s . 4 ~ CHEM. . 27, 825 (1955). (34) Washburn, H. W., Proc. 1st National Air Pollution Symposium, Los dngeles, p. 69. 1949. (35) ’C7Teaver,E. R., Gunther. Shirley, Third Sational Air Pollution Symposium, p. 86, 1955. (36) Weaver, H. E., private communication. R E C E I V Efor D review
.lugust 20. 1956.
.iccelited October 12. 1956.
Ninth Annual Summer Symposium-Analysis of Industrial W’astes
Automatic Apparatus for Determination of Nitric Oxide and Nitrogen Dioxide in the Atmosphere M.
D. THOMAS, J.
A. MAcLEOD, R. C. ROBBINS, R. C. GOETTELMAN, and R. W. ELDRIDGE
Stanford Research lnstitute, M e n l o Park, Calif.
L.
H. ROGERS
Air Pollution Foundation, Los Angeles, Calif.
Nitric oxide and nitrogen dioxide in the atmosphere can be determined continuously with automatic sampling and recording apparatus. Tw-o special absorbers are employed for absorption of nitrogen dioxide in a modified Griess reagent followed b>-colorimetric recording. One absorber measures the nitrogen dioxide alone; the other measures nitrogen dioxide plus nitric oxide after the latter has been oxidized by ozone, permanganate, or chlorine dioxide. Concentration limits of the instrument range up to about 1 p.p.m., but they can be considerably extended or reduced. Standard error is about &594..
T
H E oxides of nitrogen, in the concentration range of parts per 10,000,000, play an important role in the photochemical reactions which are primarily responsible for Los Angeles smog ( 5 ) . Nitrogen dioxide appears to be the principal acceptor of the radiant energy, and nitric oxide is involved in the chain reactions that follow. Xitrogen pentoxide or the equivalent nitric acid, both free and combined with organic radicals, is one of the products of the reactions. Aerosol samples collected in Los Angeles (3)contain about 10 times as much nitrate as similar samples collected in other cities. There is no evidence that nitrous oxide enters into either these reactions or the analytical procedures described later, even though it is probably present in appreciable amount. Nitrogen dioxide is the logical member of this group to select for initial study. I t s absorption in various reagents, though difficult, is practicable, and the highly specific and sensitive diazo reaction with one of the modified Griess reagents ( 1 , 4,
1811
V O L U M E 28, NO. 12, D E C E M B E R 1 9 5 6 7 , 9, 11) is available for its estimation. Jacobs ( 7 ) has reviewed the literature on this useful reagent. Sitric oxide is not significantly absorbed when aspirated through a solution that takes up nitrogen dioxide, but apparently passes through the system unchanged. Sitrogen pentoxide and nitric acid in comparable concentrations are also without effect on t'he Griess reagent, but excessive amounts change the red azo compound to a yellow color. Sitric oxide is rapidly oxidized to nitrogen dioxide by ozone. The half-life of this reaction a t 1 p,p.m. ( 2 ) is 1.8 seconds and at 0.1 p,p.m., 18 seconds. Further oxidation of nitrogen dioxide by ozone to the pentavalent state is much slower. The half-lives of the reactions a t 1.0 and 0.1 p.p.m. are listed as 13 and 130 minutes, respectively. Evidently, ozone can be used as an oxidizing agent for nitric oxide if the concentration is controlled m-ithin comparatively narrow limits. Other oxidizing agents for nitric oxide are being studied. Chlorine dioxide and acid permanganate solution are promising and are discwssed below. n'itrogen pentoxide gave only 10 to 2057 oxidation of nitric oxide in preliminary tests and further I\-ork does not seem justified. The pentoxide is largely converted into nitric arid by the moisture in the air sample. AIethods of analysis for the oxides of nitrogen are g e n e d l y laborious. The sample is usually taken into an evacuated bottle where the oxides are absorbed in a basic solution or the Griess reagent. With agitation, nitrogen dioxide and nitrates can be absorbed in 15 minutes to 1 hour, and nitric oxide is absorbed about as quickly if peroxide is present. Oxidation of nitric oxide in the part per million range by oxygen is very slow. Results by the bottle method appear to be reliable if sufficient time is allowed for the absorption of nitric oxide. The lower oxides are determined colorimetrically by diazotization, total nitrogen and nitrate by phenoldisulforiic acid. Saltzman ( 9 ) developed an aspirating procedure for nitrogen dioxide which avoids much of the labor of the bottle method. Shaw (IO)determined nitric oxide in coke oven gas by adding air, allowing a residence time of 3 minutes, then absorbing the nitrogen dioxide in a solution containing 0.5%; m-phenylenediamine and 2.57; acetic acid. The color is compared with that produced by known amounts of sodium nitrite. Use of a factor of 2 givcs results comparable to those obtained for knonn nitric oxide-gas mixtures. Hollings 16) determines nitric oxide in coal gas by oxidizing with a solution containing 2.57, each of potassium permanganate and sulfuric acid, followed by absorption arid colorimetric analysis in Griess reagent. A commercial instrument based on this method is available in England. The Rubicon Co. of Philadelphia also makes an analyzer for nitric oxide in coal gas based on oxidation by oxygen after standing in the presence of butadiene, follom-ed by colorimetric analysis with Griess reagent. Stanford Research Institute was unable to make this instrument operate satisfactorily with atmospheric samples. I n all these methods ivith coal gas, the nitrogen dioxide is removed before the nitric oxide treatment is applied. Commercial instruments for the oxides of nitrogen in air based on part of the n-ork reported here have been made by the Borman Engineering Co. and by Harold Kruger Instruments, Inc., of Los Angeles. INSTRUMENT
Figure 1 is a diagram and Figure 2, a photograph, of the apparatus in which nitrogen dioxide and nitric oxide plus nitrogen dioxide are determined continuously and automatically. Xitric oxide can then be found by difference. The absorbing solution consists of 0.5y0 sulfanilic acid and 20 p,p.m. of, ,V-(l-naphthyl)ethylenediamine dihydrochloride in 14y0 acetic acid. This formula is recommended by Saltzman (9)., who tested various compounds suggested in the literature. It IS drawn by means of two small glass metering pumps a t a rate of 2.5 to 3.0 ml. per minute from a supply bottle, through the zero cell of the colorimeter, and allowed to drip on the top of a pair of absorber columns, where it contacts the air streams either roncurrently or countercurrently. The liquid streams then
pass by gravity, after a delay of about 8 minutes, through a pair of colorimeter cells, before uniting and flowing through a charcoal filter to a storage reservoir. The metering pumps consist. of 2-ml. glass syringes operated by eccentrics on small 20-r.p.m. motors between two stainless steel ball check valves. Delivery is excellent. By turning the three-n-ay stopcocks the liquid can be draa.n from or returned to either supply bottle. Simultaneously the air sample is split into two portions, one going directly to one absorber while the other passes throiigh a 250-ml. ozonizing flask on the 13-ay to the other absorber. Zenith gear pumps (Zenith Products Co., West Se-ivton, Mass.) are used t o draw the gas samples. Their operat'ion is very uniform. Only minor modifications of the system will be necessary if another oxidizing agent is selected instead of ozone. Figure 3 is a wiring diagram of the analyzer. By a simple rearrangement of the connections, the nitrogen dioxide cell can be read against, the nitrogen dioxide-nitric oxide cell to give nitric oxide directly. GAS ABSORPTIOR:
Sitrogen dioxide, like carbon dioxide (12)>requires a contact time of several seconds with the absorbing solution for complete absorption. Evidently, slow cheniicnl reactions such as hydration must precede the more rapid fixing reactions. This is indicated by the fact that absorption efficiency increases with increasing temperature. Good absorption can be obtained in an alkaline solution, using a fritted glass bubbler of medium porosity and butyl alcohol to induce frothing. Saltzman (9) found that his modification of the Griess diazotizing reagent was an excellent adsorbent for nitrogen dioxide under these conditions. No additive was needed to induce frothing. This t'ype of absorber would give an average concentration over a definite period of timefor example, 10 niinut>es or longer-with intermittent nieasurement of the color.
OZONIZER
250-111 F L A S K
L I O U j D FLOW
f.i4
ZERO C E L L
COLOR I M E T E R , , GE 5 - 4 L A M P
PUMP
7
Z E N I T H AIR PUMP -STORAGE B O T T L E SELECTORS
R E A G E N T STORAGE BOTTLES
Figure 1. Gas and liquid flow systems in the nitrogen dioxide-nitric oxide analyzer
Quantitative absorption of the gas is also possible in continuously floning gas and liquid streams. Three types of absorbers have been used A glass tube of 3-mm. inside diameter, about 10 meters long and coiled into a 5-cm. diameter spiral, placed horizontally, is one of the best absorbers. Flow of gas and liquid are concurrent. Convenient volumes are about 250 ml. of gas and 2.5 ml. of liquid per minute. Suction of about 12 cm. of mercury is required t o draw the fluids through the tube.
A N A L Y T I C A L CHEMISTRY
1812
A second ahsorber is a 20-mm. glass tube, 60 cm. long, filled with 3/*~-inchglass helices and mounted vertically. A 15-mm. tube is too smdl. Gas and liquid flow is countercurrent, and resistance to flow is very small. Response to changing concentrations of the gas is fairly rapid, but de6nite channelling occw in the bed, which makes the washing out of the tube slower and more uncertain than with the otherabsorhers.
between the zero cell and each of the others is recorded on a twopoint recorder. The solution 6naUy passes through a charcoal filter t o a storage bottle. The charcoal removes the dye and also the coupling compound b u t does not signiiicantntly affect the sulfmilic acid or the acetic acid. Therefore, the solution can he m u s e d b y adding another portion of coupling compound. With repeated use the solution develops a brown or green tinge, but this does not affect the calibration appreciahly. The useful life of the solution has not been determined b u t it is a t least 1month. Ozonizer. Ozone is supplied continuously by irradiating a stream of oxygen flowing a t 10 ml. per minute with a 794H lamp and mixing the gas with the air sample for nitric oxide just before i t enters the 250-ml. residence flask (Figure 1). The lamp is mounted in a 45/50 taper joint, the leads being sealed through the glass. If the lamp is operated at the minimum voltage t h a t will keep i t glowing, the output is sufficient to add 0.3 to 0.4 p.p.m. of oaone to the air sample of 240 ml. per minute. This concentration oan readily he increased up t o more than tenfold by raising the voltage. A 250-ml. flask, providing a residence time of 1 minute, Seems to be adequate. A larger flask sometimes gave a slightly higher value with the same gas mixture, or sometimes lower, depending presumably on the excess of ozone. A study WBS made of the oxidation of nitrogen dioxide by oeone. I n carrying out these experiments the ozone stream was diverted intermittently through a pohssium iodide-starch solution for onone analysis. Later a stream of ozonated oxygen at 20 ml. per minute was divided into two equal portions by means of flowmeters, and one portion was analyeed while the other went into the residence flaak
BROWN RECORDER
Figure2.
N'itrogen dioxid-itrie
oxide
analyzer
A third absorber appttars to hzve fewer shortcomings than the others. It is the same size as the second, and has a Nichrome wire spiral mounted snugly between the inside surface of the larger tube and the outriide surface of a concentric smaller tube. The wire consists of twtD pieces of No. 20 or 22 B. and S. gage, twisted together with a, spacing of about 6 to 7 mm. between nodes, and wrapped in a seven-pitch spiral. Care is taken to select tubing of uniform bore or very slight uniform taper, so that the wire will engage ba8th glass surface$ over its whole length. The 22-gage assembly heoxides with air. A small blower is used, capable of moving 1000 to 3000 liters per minute. I n Los Angeles the air was taken in through activated carbon filters. I n Menlo Park outside air is generally of satisfactory purity and filtration is omitted. Air volunie is measured v i t h a calibrated 4-inch Biram anemometer. If the outlet pipe from the blower is constricted so that all the air goes through t,he instrument, it, has been found empirically that the corrected velocity in feet per minute multiplied by 1.64 gives liters per rninut,e. Similarly, the average velocity in an 8-inch pipe multiplied by 8.6 gives liters per minute. The nitrogen dioxide is added to the intake of the blower from a small bubbler provided v i t h stopcocks on the intake and outlet tubes. The stopcock plugs are held n i t h rather strong springs. The vessel is filled about one third full with nitrogen dioxide, cooled in an ice bath, and aspirated with a slow stream of nitrogen. Then the stopcocks are closed and the vessel is weighed a t room temperature as quickly as possible. I t is returned to the ice bath for use. Sitrogen is aspirated at a definite rate controlled by an overflov through a n-ater column and measured by a capillary flowneter. After a k n o m time, aspiration is stopped and the vessel is weighed again. The loss of weight (in milligrams per cubic meter of air through the blower X 0.54) gives parts per million of nitrogen dioxide.
68
100
o
P
4 6 a TIME, MINUTES
I
O
I
P
Figure 4. Effect of time on development of Griess-Saltzman color at 20" C.
I
~ E X C E S S OZONE
Figure 5.
- p.pm
Oxidation of nitrogen dioxide with excess ozone
ANALYTICAL CHEMISTRY
1814 Nitric oxide is dispensed from a tank of compressed gas, through an Ascarite tube and a fine capillary flowmeter. It is then swept into the blower intake by a stream of nitrogen. Satisfactory precision can be obtained if the flowmeter delivers 1 ml. per minute nith a head of 10 to 15 cm. Even after it is passed through the Ascarite, a fen percent of nitrogen dioxide may be present in the gas. This is readily detected by a recorder response before the ozone is turned on. I n earlier work the nitric oxide was displaced from a mercury pipet by adding mercury a t a known rate. I n this case the mercury removed the nitrogen dioxide chemically. Data obtained for nitrogen dioxide and nitric oxide plus ozone, as well as for sodium nitrite solutions, are presented in Figure 6. Curves I and I1 represent calibrations with sodium nitrite calculated as nitrogen dioxide on May 8 and August 13 to 21, respectively. The displacement of the curve is small but definite. Slight changes in the optical system and some replacement of tubes in the recorder occurred during this time. Much larger and more inexplicable changes occurred in curves 111, IV, and V. which represent the recorder responses to known concentrations of nitrogen dioxide (circles) and nitric oxide (squares).
1001
, ,
,
,
,
tube and avoid illuminating the walls. Again there was a displacement of the calibration curve, this time to a nitrite yield of 91%. Sodium nitrite values on August 8, 13, 15, 16, and 21 all fell on or very near curve 11. It is not clear why changes in the optical system should change the relations between the nitrogen dioxide and sodium nitrite curves. So far as is known, the absorption system was not changed except for the substitution of a nickel-chromium-ironaluminum (Alloy K ) mire for glass in the absorbers, near the end of the first period. Possibly the wire modified the reaction as its surface became cleaner and more active with continued use.
I
'9
0200
0400
0600
OB00
I000
1200
1400
I600
ME (*OUR1
Figure 7.
800
2 2200 2400
2000
PST
Sample record of nitric oxide from nitrogen dioxide recorder Oct. 7 , 1955, Pasadena, Calli.
90 92 RECORDER
Figure 6.
91
96
READING
Calibration of nitrogen dioxide-nitric oxide analyzer
I. 11.
111. IV. V.
+
1
dioxide
Curve V covers a period from May 8 to August 1. Most of the data were obtained with the columns containing glass helices, and only a few Kith the wire spirals. Toward the end of this period recorder operation was improved, but the last experimental results were not appreciably different from the others. It is unfortunate that a second calibration n i t h sodium nitrite v a s not made during this period. Comparison of curves I and V indicates that the yield of nitrite from nitrogen dioxide is 577, instead of the 50y0that is expected from a simple dismutation. Curve IF' covers the period from -4ugust 2 to 13. On August 2, two photocells were exchanged, and a slightly dirty light filter was cleaned. A definite displacement of the calibration curve occurred. The whole optical system, including one rather dirty filter, was cleaned on August 8, but this caused no change. The yield of nitrite from nitrogen dioxide, calculated from curves I1 and IV, is 757,. Curve I11 gives data after Bugust 13. A zero flow cell was installed and a light shield q-as placed a t the end of each absorption cell to confine the light to the center of the
I n an attempt to clarify these relationships, the calibrations were repeated with and without the zero flov cell and the colorimeter light shields. Again the sodium nitrite response was affected only slightly by these changes. When the zero flow cells, the shields, and wire-packed absorbers were used, the nitrogen dioxide values fell on curve 111, Figure 6, or even somewhat beyond it, indicating a close approach to 100% conversion to nitrous acid. On removal of the shields, there was a sharp drop in the nitrogen dioxide response amounting to 12 to 30% in different cells. Removal of the flow cell did not cause further change in these relationships. A ne\q wire-packed absorber gave nitrogen dioxide values as low as 50 to 65% in initial tests. After continued use the response approached that of the older absorbers. Response of an absorber packed with glass helices varied from 78 to 100%. This was obviously due to channelling as indicated by the pink color of the helices, and the time required to wash out the dye after addition of nitrogen dioxide was stopped. Evidently the combined effects of variability in the absorbers and the influence of the colorimeter light shield serve to explain the shifting of the curves in Figure 6. These circumstances point to the necessity for occasional calibration with nitric oxide or nitrogen dioxide. J t must be emphasized that the calibration is empirical and that no reliance can be placed on calibration x i t h sodium nitrite. Under conditions of steady use, hon-ever, the calibration remains quite constant. This is shonn by the relatively small scatter of the points about the different curves in Figure 6. The data of curve VI which had the most dispersion, n-ere analyzed statistically and the standard deviation of the points from the straight line
V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6 mas found to be 5%. The 95% confidence level \\auld therefore be about &1070. One erratic source of error is the collection of tiny bubbles of air along the upper surfaces of the inclined colorimeter tubes. These tubes should be examined occasionally and the bubbles removed. Response Time. Response of the instrument is necessarily rather slow on account of the time required to permit full color development before the solution enters the colorimeter cell and the time to replace the solution in the cell. The former should be 8 to 10 minutes a t room temperature. This reaction could be speeded up a great deal by heating the solution to 50" to 70" C., as suggested by Morriss and coworkers (8). However, for most purposes this delay would be relatively unimportant if a long tube of small bore n-ere used, xhich mould prevent appreciable turbulent mixing of the liquid column as it flowed to the colorimeter cell. The latter presents the principal difficulty, because a fairly large cell is necessary to attain the required sensitivity. Using a cell of 15-cm. length and 15-ml. capacity, a t least 6 minutes would be needed to replace the solution completely at 2.5 ml. per minute. I n practice, the displacement is 90y0 complete in 10 minutes after the initial recorder response to a change of gas concentration, and nearly 100% complete in 20 minutes. If more rapid response were needed, the cell could be reduced iu length to 8 to 10 cm. without too much sacrifice of sensitivity. Possibly the diameter could also be reduced, which would reduce the mixing as well as the volume. Increased liquid flow could also be used.
1815 dioxide alone or to a mixture of nitrogen dioxide and ozone, the analyses were not significantly aBected. RESULTS
Comparative Analyses. A program was instituted to compare the results of analyses of samples taken simultaneously and analyzed by various methods employed in three different laboratories. Table I11 gives the results of a series of analyses of mixtures with known concentrations of nitrogen dioxide. If any nitric oxide were present in carbon-filtered air, it would react slowly in the bottles to give nitrogen dioxide. This reaction does not occur in the scrubber or recorder. Therefore, the evacuated bottle samples should yield high results whenever nitric oxide is present.
Table 11. Analysis of Alkyl Nitrite-.4ir RIixtures NO2 Concn., P.P.M. Calcd. NOS Compound concn. recorder Ethyl nitrite 0.25 0.24 0.16 0.15 0.14 0.13 Butyl nitrite 0.14 0.08 0.41 0.32 Amyl nitrite 0.07 0.04 0.15 0.29
INTERFERENCES
Several organic compounds were tested to see if they interfered nith color development in Griess-Saltzman reagent. They were added to the reagent along with sodium nitrite and the resultant color was measured in a colorimeter. Quantities employed varied between 5 and 50 y per ml. of organic compound n4th or without 0.015 y per ml. of sodium nitrite. KO significant differences in color development were noted as a result of addition of the following: Aldehydes and ketones: Butyraldehyde, heptaldehyde, cyclohexanone Peroxides: Primary, secondary, and tertiary butyl hydroperoxide, a-decyl hydroperoxide Bases: Picolines, quinoline, isoquinoline, quinaldine Some color destruction occurred upon the addition of the following: Bases: Acridine Aromatic nitroso compounds: ,V-N-dimethyl-p-nitrosoaniline, p-nitrosodiphenylaniline, p-nitrosophenol (sodium salt) Slight color reinforcement occurred upon addition of nitrosopiperidine. Three alkyl nitrites, ethyl, a-butyl, and isoamyl, were tested by introducing weighed amounts into the high volume stream of carbon-filtered air, in the same x a y as that employed x i t h nitrogen dioxide. The bulb containing the liquid nitrite was maintained a t constant temperature, the ethyl nitrite a t 20" C., nbutyl nitrite a t 30" C., and the isoamyl nitrite a t 35" C. Nitrogen was bubbled through the bulb a t a constant rate. The nitrite-air mixtures were then fed into the instrument. The data thus obtained (Table 11) indicate that, if present in the atmosphere, alkyl nitrites will be recorded as nitrogen dioxide, but only for ethyl nitrite are the results quantitative. Nitrous oxide was added to the mixture of nitrogen dioxide and ozone with and without a 21/2-minute residence time. There was no change in the nitrogen dioxide level, showing that nitrous oxide does not interfere JTith the analysis of nitrogen dioxide in the recorder. When 5 p.p.m. of sulfur dioxide mas added either to nitrogen
Table 111. Comparative Analyses of Known Kitrogen Dioxide-Air Mixtures Labora- Laboratory B tory C Laboratory A NOz Calcd., Recorder, Scrubber, 500-ml. 2-liter 12-liter P.P.M. P.P.M. p.p.m. bottles bottles bottles 0.70 0.70 0.80 0.96 0.99 0.64 0.27 0.28 0.30 0.40 0.41 0 30 0.13 0.12 0.14 0.18 0.19 0.16 0.35 0.40 0.38 0.46 0.34 0.41 0.40 0.46 0.45 0.70 0.43 0.64 0.40" 0.35 0.35 0.44 0.35 0.43 a 0.40 p.p.m. NOz and 5 p.p.m. SO2 added.
Sample Record. A sample record for nitric oxide and nitrogen dioxide for outside air in Pasadena on October 7 , 1955, appears in Figure 7 . It is interesting to note that both nitric oxide and nitrogen dioxide showed early morning maxima around 7 A . M . , decreasing to a minimum during the day, and increasing again after 5 P.M. I n Menlo Park, concentrations of nitric oxide up to 0.1 p.p.m. have frequently been observed a t night or from 6 to 8 A.M., but not during the rest of the day. Nitrogen dioxide values have been consistently zero or very low. However, regular monitoring has not yet been carried out. SUM.IRIARY
With the apparatus described atmospheric nitrogen dioxide is determined by absorbing the gas in a modified Griess reagent recommended by Saltzman, containing 0.5% sulfanilic acid and 20 p.p.m. of N - (1-naphthyl) ethylenediamine dihydrochloride in 14% acetic acid. A continuous concurrent-flow absorber is employed with metered gas and liquid volumes in a ratio 80 to 1 up to 100 to 1. The red color produced by the action of nitrous acid on the reagents is measured in a 15-cm. cell of a recording colorimeter. The intensity of the color for a given amount of nitrogen dioxide is not stoichiometric, but depends on reactions that are not understood. Empirical calibration is, therefore,
ANALYTICAL CHEMISTRY
1816 essential. ru'itric oxide is oxidized to nitrogen dioxide by ozone, permanganate, or chlorine dioxide, and determined along with preformed nitrogen dioxide in a duplicate absorber and colorimeter system. Nitric oxide can then be found by difference. The method is highly specific for compounds that can yield nitrite in solution. The only likely interfering substances are alkyl or other organic nitrites. Care must be taken to avoid oxidation of nitrogen peroxide by an excess of ozone. The other oxidants appear to be less critical in this respect. Comparison with other methods gave satisfactory agreement on Los Sngeles air samples to which known amounts of nitrogen dioxide were added. LITERATURE CITED
(1) Bratton, A . C., Narshall, E. K., Jr., Babbitt, D., Hendrickson, -4.R., J . B i d . Chem. 128,537-50 (1939). (2) Cadle, R . D., Johnston, H. S., Proc. Xatl. Air Pollution Symposium, Second Symposium, pp. 28-34, Stanford Research Institute, Menlo Park, Calif., 1952.
Chambers, L. d.,Foter, M. J . , Cholak, J., I b i d . , Third Symnosium. nn. 24-32. =~ ~~~~~, r r . ~ 1955. ~.~~ , ~~
Greiss, P., Ber. 12,427 (1879). Haagen-Smit, -4.J., Fox, I f . M., Ind. E ~ i g .C'hem. 48, 1484-7 (1956).
Hollings, H., Inst. Gas Engrs., Commun. No. 154,6 pp. (1937). Jacobs, AI. B., "The -1nalytical Chemistry of Industrial Poisons, Hazards, and Solvents," pp. 355-9, Interscience, Sew York, 1949.
Morriss, F. Y.,Boise, C., King, F., Division of .\nalytical Chemistry, Symposium on Air Pollution, 130th Meeting, ACS, Atlantic City, S . J., September 1956. Salteman, B. E., ANAL.CHEY.26, 1949-55 (1954). Shaw, J . A , , IND.ENG.CHEM.,Ah-AL.ED.8, 162-7 (1936). Shinn, AI. B., Ibid. 13, 33-5 (1941). Thomas, h1. D., Hill, G. R., "Photosynthesis in Plants," J. Franck, W. E. Loomis, eds., pp. 20-25, Iowa State College Press, Ames, Ion-a, 1949. RECEIVED for rei-iew June 1 1 , 19.56. Accepted October 3 , 1956. Supported by the Air Pollution Foundation, Los Angeles, Calif., the ilrnerican Petroleum Institute, and Stanford Research Institute. Presented in part, Division of Analytical Chemistry, Symposium on Air Pollution, 130th Meeting, .iCS. Atlantic City, S . J . , September 1956.
Ninth Annual Summer Symposinm-Analysis of Industrial Wastes
Fixation of Sulfur Dioxide as DisuIfitomercurate(I1) and Subsequent Colorimetric Estimation PHILIP W. WEST
and
G. C. GAEKE
Coates Chemical Laboratories, Louisiana State University, Baton Rouge, La.
Sulfur dioxide in the atmosphere is removed and concentrated by scrubbing through 0.l.M sodium tetrachloromercurate(I1). Stable, nonvolatile disulfitomercurate(I1) is formed. The subsequent determination of the isolated sulfur dioxide is based on the redviolet color produced when p-rosaniline hydrochloridehydrochloric acid mixture (0.04q~dye670 concentrated acid) and formaldehyde (0.27") are added to the sampling solution. The absorption maximum is at 560 m p and the color is temperature-independent and stable for several hours. The method is sensitive (0.005 to 0.2 p.p.m. with a 38.2-liter air sample scrubbed through 10.0 ml. of sampling solution) and should be useful in the absolute determination of sulfur dioxide in air pollution surveys. R'itrogen dioxide is the only common interference.
S
ULFUR dioxide is almost without question the most impor-
tant of all air pollutants. I t is an irritant gas that affects the upper rePpiratory tract, causing physical discomfort and even death. Four parts per million can readily be detected by odor; but as the nose becomes accustomed to it, the concentration necessary to produce a response increases. Eight to 12 p.p.m. will cause coughing and 20 p.p.m. will lead to eye irritation (4). The toxicity of sulfur dioxide to man varies, apparently depending on the physical condition of the individual and on other factors. It has been considered a contributory cause of death in disasters such as those a t London and Donora, Pa. The maximum allowable concentration is generally accepted as 10 p.p.m. However, sulfur dioxide may be toxic to vegetation in concentrations in the order of 2 or 3 p.p.m. and i t is corrosive to metallic construction materials in concentrations of less than 1 p.p.m. Therefore, concentrations smaller than the stated maximum
alloviable concenti ation may be highly objectionable and, under some circumstances, even dangerous. The occurrence of sulfur dioxide in air is general. This results from its uses in bleaching, fumigation, refrigeration, manufacture of sulfuric acid, etc. Of special significance is the release of this gas as a by-product in the burning of sulfur-containing coals and oils and in the smelting of many ores. It is also released during the manufacture of paper by the sulfite process and in such chemical operations as the synthesis of phenol. I n spite of its significance, methods for the determination of sulfur dioxide in air are generally not too satisfactory, especially if complex industrial atmospheres are to be analyzed. The methods used may be divided into two main groups: based on its reducing properties, or on its acidic character or the acidic nature of its oxidation product. One of the methods used in early pollution surveys was that of the Selby Smelter Smoke Commission ( 4 ) . A sample of the atmosphere TI as drawn into a partially evacuated 20-liter bottle containing a feiy milliliters of a standard solution of iodine. The sulfur dioxide in the sample was absorbed by the iodine n hen the bottle was shaken vigorously. The excess iodine was determined by thiosulfate titration. The main method in use today is based on a similar procedure, in which the air sample is scrubbed through a standard solution of iodine and potassium iodide; and the excess iodine is determined by titration with standard thiosulfate ( 3 . 5 ) . Many variations of this method have been proposed. However, there are several disadvantages in the use of iodine as an absorber. During the collection of the sample some iodine may volatilize; other reducing agents present in the air, such as hydrogen sulfide, react with iodine, and some iodide is oxidized to iodine by the air bubbling through the solution or by oxidants that may be present in the atmosphere. Hydrogen peroxide has also been suggested as an absorber for sulfur dioxide ( 7 ) . The reaction produces sulfate and hydrogen ions, and several methods are available for the determination of
