Contin uo us Sa mpIing a nd UItra microdete rmination of Nitrogen Dioxide in Air MORRIS B. JACOBS and SEYMOUR HOCHHEISER Bureau of Laboratory, Departmenf o f Air Pollution Control, New York 35, New York
b Nitrogen dioxide is determined in air in the presence of much higher concentrations of sulfur dioxide on an hourly basis by using an automatic 24-hour sampler. Air is aspirated through a fritted-glass bubbler containing 0.1N alkali solution. The absorbed nitrogen dioxide is determined colorimetrically as the azo dye by using it to diazotize sulfanilamide in phosphoric acid and then coupling it with N - ( 1 -naphthyl)-ethylenediamine dihydrochloride. Nitrogen dioxide in the order of parts per hundred million of air can b e determined. The sulfur dioxide present is also absorbed, but when oxidized to sulfate with hydrogen peroxide, does not interfere with the reaction.
E
large metropolitan area, or for that matter, every urban area, every large industrial area, and even some farm areas have an air pollution problem (6). This may be a very serious one, as in Los Angeles and London (during certain times of the year), or one of a lesser degree, as in the case of New York City. To determine the extent and the severity of air pollution existing in any region, it is necessary to have objective methods for the measurement of pollutants. These methods enable a community to know whether its air-pollution problem is increasing, decreasing, or remaining the same and, therefore, to prevent disaster. Nitrogen dioxide and other nitrogen oxides are produced b y combustion processes, such as in Diesel and gasoline-powered engines, to a lesser extent (4). Estimates of the amount of nitrogen oxides, as nitrogen dioxide, arising from the burning of fuel gas, fuel oil, gasoline, and refuse from general public emissions, petroleum-industry emissions, and other industrial emissions in Los Angeles totaled 284 tons per day in 1950 (9). Emissions of nitrogen oxides of the same order of magnitude probably occur in New York. The nitrogen oxides are poisonous gases that are particularly dangerous because of their insidious character. It is desirable to have a method by which the amount of nitrogen oxides or, more specifically, nitrogen dioxide can be monitored on a 24-hour basis. VERY
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The following simple, convenient method was developed for the continuous sampling and ultramicrodetermination of nitrogen dioxide in urban atmospheres. APPARATUS AND REAGENTS
A Wilson 24-hour automatic air sampler was used (14). Its modified Greenburg-Smith impinger ('7, 8) was replaced by a bubbler of equivalent dimensions equipped with a gas disperser of coarse fritted glass (Figure 1). A filter paper trap 11 inches in diameter to retain particulate matter and a flowmeter capable of registering 1.3 liters per minute were inserted in the sampling line. A Coleman spectrophotometer Model 14 with a set of matched oblong cuvettes 20 x 40 mm. was used. The absorbing reagent is 0.1N sodium hydroxide solution with 2 ml. of butyl alcohol per liter. The coupling reagent is a 0.1% solution of N - ( I-naphthyl)-ethylenediamine dihydrochloride (1 ml. is equivalent t o 1 mg.). Prepare the diazotizing reagent by dissolving 20 grams of sulfanilamide in
A
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I
I10 VOLTS
Figure 1. Automatic sequence sampler for nitrogen dioxide A. B.
To pump Hour clock C. Dusf tllter D. To sampling point E. Reservoir F. Fritted bubbler G. 24-hour clock
1 liter of water containing- 50 ml. of phosphoric acid. Hydrogen peroxide, 1% solution. PreDare the standard sodium nit'rite solution (1 ml. = 10 7 NO2) by dissolving 150 mg. of sodium nitrite in 1 liter of water and diluting 10 ml. of this solution to 100 ml. PROCEDURE
Aspirate air a t 1.3 liters per minute through 30 to 35 ml. of absorbing reagent in the automatic air sampler apparatus. Twenty-four 40-minute samples are obtained in this manner. Transfer the samples to 50-ml. Nessler tubes, add 1 drop of hydrogen peroxide reagent, and mix to oxidize the dissolved sulfur dioxide to sulfate. Add 10 ml. of diazotizing reagent and then 1 ml. of X-(1-naphthyl)-ethylenediamine dihydrochloride reagent. Dilute to 50 ml. and mix. Allow to stand for 30 minutes and determine the absorbance in the spectrophotometer a t 550 mh using the reagent blank as the reference. To calibrate, add 0.2, 0.4, 0.6, 0.8, and 1.0 ml. of standard sodium nitrite solution to 35 ml. of absorbing reagent in five 50-ml. Nessler tubes. Add 1 drop of hydrogen peroxide solution, 10 ml. of diazotizing reagent, 1 ml. of coupling reagent, and dilute to 50 ml. Read in the spectrophotometer a t 550 mp (found t o give the maximum absorption) using the reagent blank as the reference. Calculations. Kitrogen dioxide can be expressed as parts per hundred million of the air sample. For a 52-liter air sample a t 760 mm. of mercury and 25' C., 1 7 of nitrogen dioxide is equivalent to 1 p.p.h.m. Effect of Sulfur Dioxide. I n a 52-liter air sample having a concentration of 5 p.p.h.m. of nitrogen dioxide, 1 p.p.m. of sulfur dioxide caused a 50% reduction in color after one-half hour. One drop of 1% hydrogen peroxide oxidized the sulfur dioxide t o sulfate, b u t did not interfere with the intensity of the nitrite color when determined after 30 minutes. Absorption Efficiency. To evaluate the empirical absorption efficiency of the 0.1N sodium hydroxide solution, air (1.3 liters per minute) was aspirated through the fritted-glass bubblers in series containing 35 ml. of this absorbing reagent. Although
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II I I I I I I I I I I I llllllllll 1 P 1 P 3 4 5 6 7 8 9 1 0 1 1 1 P l
Figure 2.
P 3 4 5 6 7 8 9 1 0 1 1
NOON
A. M.
P. M.
Concentration of nitrogen dioxide, January 1957 Average values for month, hourly basis
the air of Yew York City is relatively acid, 35 ml. is satisfactory for a 52liter air sample. The nitrite formed is stable in the absorbing reagent for 48 hours. The absorption efficiency which is dependent on the dimensions and the porosity of the frit ( l a ) , is better than 90% with the dispersers used (Table I). Color Production. A rapid and quantitative method of dye production is necessary (a p H of less than 2 is required for maximum color production). Because a final volume of 50 ml. is desirable and 35 ml. of absorbing reagent is used, the proper p H is not obtainable n-ith acetic acid. Hydrochloric acid does not give sufficiently rapid color development, but phosphoric acid gives both rapid and maximum color development. The diazotizing and the coupling reagents are more stable when stored separately. Results. Typical results for 24hour sets of samples (representing 711 samples) are given in Table I1 and Figure 2. Various methods, including this one, for the determination of nitrogen dioxide in New York City air show t h a t the order of magnitude of the concentration of this pollutant is in the parts per hundred million range. Table I1 also shows the marked effect of sulfur dioxide on the determination of nitrogen dioxide (their concentrations vary inversely), DISCUSSION
Thomas and his coworkers (13) used a variation (12) of the Griess-Ilosvay method for the continuous sampling and determination of nitrogen dioxide in air. The Bratton and Marshall reagent ( I ), N-( 1-naphthyl)-ethylenediamine dihydrochloride, was substituted for 1-naphthylamine [which had been used by British workers (S)],
was combined with sulfanilic and acetic acids, and mas used with a fritted bubbler. Cholak and his associates (2) and Moore, Cole, and Katz (IO) used this combination of reagents n-ith sequence samplers. Members of the staff of this laboratory encountered difficulty in determining the concentration of nitrogen dioxide in New York City air by the various methods described by Jacobs (8). d manual or “grab” sampling technique, using the mixed reagents suggested by Jacobs (8) in 1941, a fritted bubbler, and halfhour samples, was attempted on a 24hour basis with a modified Wilsonautomatic impinger. At first the method appeared adequate, because the results were of the same order of magnitude as the authors’ manual-technique results. Closer in-
Table II.
spection and comparison with the present procedure, particularly on days of high pollution when the sulfur dioxide was of the order of 1 p.p.m., showed that the nitrogen dioxide originally found was low. This apparent diminution in concentration could be reproduced by adding sulfite, which indicated that the color was reduced on standing when sulfur dioxide was absorbed along with the nitrogen dioxide. Therefore, the combined reagent was replaced by the alkaline absorption solution (containing butyl alcohol to assist in foaming and thus in trapping the nitrogen dioxide). Proper adjustment of the combined reagent and stabilization with a less volatile peroxide than hydrogen peroxide or the use of potassium chlorate mould enable it to be used directly as the sampling absorbent, but no advantage is gained if the color is to be developed subsequently and automatic recording is not being used. The nitrogen dioxide automatic analyzers and recorders now in use have not proved adequate. Among the difficulties encountered with these instruments were the damage caused by the high acidity of the mixed reagent and its lack of stability. The method described here is superior to the automatic analyzers now in use. Table I. y SO?
Absd. 1.0 1.8 2.8
45 6.4
Absorption Efficiency SO? Efficiency, C’ Carried Over 10 0.1 91 0.2 90 0.2 93 0.4 92 0.6 91
Hourly Variation in Nitrogen Dioxide Concentration (P.P.H.M.) and Apparent Variation with Sulfur Dioxide Concentration ( 1 957)
Time 12-1 A.M. 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-1 P.M. 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 Av .
Jan. 4.4 4.1 4.1 3.8 3.7
Feb. 4 2 4.0 3.9 3.7 3.8
5.2 5.2 5.5 5.6 6.3 6.4 6.1 5.9 5.6 5.2 5.3 4.5 5.1
5.5 5.4 5.0 5.2 5.8 5.8 5.8 5.7 4.8 4.8 4.4 4.4 4.9
Av. 4 3 4 1 4 0 3 8 3 8 3.9 4 4 4 7 4 7 5 7 6 4 5 8 5 4 5 .3 .5 3 5.4 6 1 6.1 6 0 5 8 5.2 5 0 4 9 4 5 5.0
so*,P.P hl
SO*, P.P.H.hf,
0 0 0 0 0 0
10 26 32 30 60 96 1 02 1.12 0 26 0 24 0 37 0 12 0 12 0 10 0 14 0 20 0 20 0 18 0 24 0 18 0 14 0 24 0 09 0 08
VOL. 30, NO. 3, MARCH 1958
2.0 2.0 2.0 2.0 1.0 1.0 1 0 1. 0 2 0 2 0 1 0 3 0 B O 3 0 3.0 2 0 2 0 2 0 2 0 3 0 3 0 3 0 3 0 3 0
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Thomas (IS) claims that as much as 5 p.p.m. of sulfur dioxide does not
interfere with the determinations of concentrations of nitrogen dioxide of the order of 0.4 to 0.7 p.p.m. with this device. Neither Cholak and his coworkers (2) nor Moore, Cole, and Katz (IO) reported this interference. The present work concludes that concentrations of sulfur dioxide of the order of 0.2 to 1.0 pap.m. and higher bleach the color of the dye formed with the mixed reagent when it is used as the trapping agent. This bleaching may not be apparent in the relatively high concentrations of nitrogen dioxide used by Thomas in his experiments (the concentrations are 5 to 10 times that normally present in New York City’s atmosphere). This method is empirical because of the dismutation of the nitrogen dioxide-nitrogen tetroxide mixture and because of the need for standardization of the absorbers. The quantitative aspects of the dismutation of nitrogen dioxide-nitrogen tetroxide absorbed in aqueous solution are not entirely known. Patty and Petty (11) found that the apparent average recovery of nitrite from nitrogen dioxide-nitrogen tetroxide mixtures (on the assumption that 1 mole of NOz gas yields 1 mole of NO2 ion) was 57 f 2.6y0. Their maximum and minimum recoveries -were 65 and
52%, respectively. Others on this basis reported nitrite recovery of the The actual order of 72% (18). amount of nitrogen dioxide in the air is probably greater than the results reported because only 60 to 70% of the nitrogen dioxide-nitrogen tetroxide mixture is converted to nitrite and only that portion is measured. If all of the nitrogen dioxide absorbed were converted to nitrate, the total amount could be determined by either the phenoldisulfonic acid or xylenol method (5, 8). Although such methods are far more tedious, the authors are investigating them. LITERATURE CITED
Bratton, A. C., Marshall, E. K., J . Biol. Chem. 128,537 (1939). Cholak, J., Schafer, L. J., Yeager, D. Younker, W. J., “Gaseous Contaminants in the Atmosphere,” 130th Meeting, ACS, Atlantic City, N. J., September 1956. Dept. Sei. Ind. Research Brit., Leaflet 5 (1939). Elliott, hl. A., Nebel, G. J., Rounds, F. G.. Air Pollution Control h S O C . ’ Annual Meeting, Paper 55-19, May 1955. ( 5 ) Goldman, F. H . , Jacobs, M. B., “Chemic$! Methods in Industrial Hvgiene, Interscience, New York, 1953. (6) Greenburg,
L., Jacobs, M. B., Znd. Eng. Chem. 48, 1517 (1956). (7) Greenburg, L., Smith, G. W., U. S.
Bur. Mines, Rept. Invest., 2392
(1922). (8) Jacobs, .M. B., “War Gases-Their
Identification and Decontamination,” Interscience, New York, 1942; “Rapid Method for Nitrogen Dioxide-Nitrogen Tetroxide in Atmosphere,” Metropolitan N, Y. Section, Am. Ind. Hyg. Assoc. meeting, May 1945; “The Analytical Chemistry of Industrial Poisons, Hazards, and Solvents,” Interscience, New York, 1949: “Chemical Analxsis of Foods and Food Products, Van Nostrand, New York, 1951. (9) Magill, P. L., Littman, F. E., Am. SOC. Mech. Engrs., Paper 53-A-163 (1953). (10) Moore, G. E., Cole, A. F. W.,
Katz, M., “Concurrent Determination of Sulfur Dioxide and Nitrogen Dioxide in the Atmosphere,” Air Pollution Control Assoc. meeting, Buffalo, N. I-., May 1956. (11) Patty, F. A., Petty, G. M., J . Znd. Hyg. Toxicol. 25, 361 (1943). (12) Saltzman, B. E., ANAL. CHEM.26, 1949 (1954). (13) Thomas, M. D., MacLeod, J. A . ,
Robbins, R. C., Goettelman, R. C., Eldridge, R. W., Rogers, L. H.,Zbid., 28,1810( 1956). (14) Wilson, W. L. “An Automatic Impinger for Air Sampling,” .Air Pollution Control Assoc. meeting, Chattanooga, Tenn., May 1954. RECEIVEDfor review March 28, 1957. Accepted September 26, 1957. Meetingin-Miniature, Metropolitan Long Island Subsection, New York Section, ACS, Brooklyn, N. Y., February 15, 1957.
Rapid Quantitative Determination of Sulfur in Organic Compounds IHOR LYSYJ and JOHN E. ZAREMBO Central Research, Chemical Divisions, Food Machinery & Chemical Corp., Princefon, ,An investigation was made to determine sulfur in organic compounds without cumbersome and expensive equipment, and to reduce the time involved in elemental analyses. The materials examined include compounds containing as much as 50% sulfur. The precision of the method is to & l % and a single analysis requires approximately 25 minutes of actual working time.
A
of time-honored and dependable methods for determination of sulfur in organic compounds are based on Carius digestion (1-5, 14, I 6 ) , Pregl combustion (3, 7, IO), Parr bomb combustion (8, 9, IS, I 6 ) , and eventual determination of sulfate by volumetric or gravimetric methods. However, these methods possess inherent diffiNUMBER
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N. J.
culties-Le., they are time-consuming, require considerable manipulation, and can be executed only with specialized and expensive equipment. T o eliminate these difficulties and to meet the ever-increasing volume of work in industrial and research analytical laboratories, a quest was made for a rapid, precise, simple, and economical method of elemental analysis. Following the techniques of Mikl and Pech (6), Schoniger (11, 18) developed a method for the combustion of organic materials in a n Erlenmeyer flask filled with oxygen. H e also suggested a n acidimetric determination of sulfur in compounds containing carbon, hydrogen, oxygen, and sulfur following such combustion. The authors investigated this type of combustion, followed by simple acidimetric titration of sulfuric acid.
The apparatus developed consists of a 500-ml. iodine or Erlenmeyer flask and a ground-glass tube, 24/40, whose lower end is closed and into which is sealed a platinum spiral. The upper portion of this tube is used as a handle and the platinum spiral serves as the sample carrier during the combustion. The sample is weighed on a small piece of filter paper or into a gelatin capsule. The paper is then folded and inserted into the platinum spiral. The gelatin capsule is simply fitted into the spiral. T o each is attached a small filter paper wick. The wick is ignited with a sma!l Bunsen burner and the whole unit IS inserted into a n iodine flask which has been flushed with oxygen and contains a solution of hydrogen peroxide. The reaction takes place in about 30 seconds:
