all constants must await the attainment of chemically pure pRA. As previous workers have noted (5) pRA samples may vary widely in their degree of impurity. Because the same specimen was used throughout these experiments the degree of impurity error will be constant, but the presence of amounts of rosaniline, for example, would have a decided effect on the specific values of constants.
LITERATURE CITED
(1) Atkin,
(1950).
S., ANAL. CHEM. 22, 947
M..Ibid.. 19. 345 11947). (3) Hormann, H.,’ Grassmann, I$.> Fries, G., A n n . 616, 125 (1958). (4) Nauman, R. V.) West, P. W., Tron, F., Gaeke, G. C., Jr., ANAL. CHEY. 32, 1307 (1960). 1 5 ) Pate. J. R.. Lodee. J. P.. Jr.. Wartburg, A. F., Ibid., fi,’1660 (1962). (6) Rumpf, R., Bull. SOC.Chim. (France) 11, 422 (1944). 12’1 Grant. W.
~
(7) Steigmann, A., J . SOC.Chem. I n d . 61, 18 (1942). ( 8 ) Crone, P. F., Boggs, W. E., ANAL. CHEM.23, 1517 (1951). (9) West, P. W., Gaeke, G. C., Jr., Ibid., 28, 1816 (1956). (10) Yarbo, C . L., Miller, B., Anderson, C. E., Stain Technol. 29,299 (1954). RECEIVED for review January 16, 1964. hccepted March 11, 1964. Division of Water and Waste Chemistry, 145th Meeting, ACS, New York, N. Y., September 1963.
Spectrophotometric Determination of Sulfur Dioxide Suitable for Atmospheric Analysis B. G. STEPHENS and FREDERICK LINDSTROM Clemson College, Clemson, S. C.
b Sulfur dioxide can b e determined by passing samples of the gas through a solution of ferric iron and 1,lOphenanthroline. It reduces the ferric iron to ferrous iron which reacts with 1,lO-phenanthroline to form the orange tris( 1,lO phenanthroline) iron(l1) complex. The interfering green-orange color of excess hydrolyzed ferric iron is conveniently masked with fluoride. Nitrogen dioxide does not interfere and ozone does not interfere at levels possible in industrial or urban atmospheres. The color forms immediately in the capturing solution and is stable for several days.
-
T
HE
METHODS USUALLY EMPLOYED
for sulfur dioxide are the iodine method, the hydrogen peroxide method, and the fuchsin method. I n the iodine method, the sample is scrubbed through a base solution, the solution acidified, and the sulfurous acid titrated with standard iodine solution (4). The sulfite solutions must be analyzed within several hours or a large error will result caused by the air oxidation of the sulfite. In a 24-hour period, 54% of the trapped sulfur dioxide will be oxidized (10). I n the iodine-thiosulfate method, sulfur dioxide is drawn through a standard iodine-potassium iodide solution with the subsequent titration of excess iodine by standard sodium thiosulfate ( 4 ) . I n the hydrogen peroxide method, other acids and acidic gases are counted as sulfur dioxide when a titration of hydrogen ion is made. When sulfate is determined, sulfuric acid and sulfur trioxide are counted along with sulfur dioxide. In the fuchsin method, the sulfur Present address, Wofford College, Spartanburg, S.C.
1308
ANALYTICAL CHEMISTRY
dioxide is trapped in a 0.121 sodium hydroxide solution, an aliquot is taken, and i t b sulfur d oxide content determined using the iodine method. Once the range of sulfur dioxide content is known, an appropriate aliquot of the trapping solution is added to a decolorized fuchsin-formaldehyde reagent and the color developed is read at 580 mp (4). West and Gaeke ( I 1 ) proposed the use of sodium tetrachloromercurate(I1) for trapping sulfur dioxide prior to its colorimetric determination with fuchsin. The sulfur dioxide reacts with the mercury complex to form the dichlorosulfitomercurate(I1) complex ( 7 ) . The sulfur dioxide complex is nonvolatile and stable enough to allow the samples to be collected and analyzed within a working day with no loss of sulfur dioxide through oxidation or volatilization ( 4 ) . The fuchsin method has been accepted by those working in the air pollution field although it is beset by several difficulties. Consistent results are not obtained from one dye-batch to another (8). Also, it is necessary to allow the sulfur dioxide-fuchsin solution to stand 20 to 30 minutes for full color development (11). The preliminary iodine measurement of the sulfur dioxide level is required because the color formation is slow. The method has one great advantage-it is much more specific for sulfur dioxide than are the other methods. I t has been shown by Hocheiser, Braverman, and Jacobs (4) that the iodin-, peroxide, and fuchsin methods can usually be used interchangeably because sulfur dioxide is by far the most common gaseous air pollutant. 1,lO-Phenanthroline has been used for years for the colorimetric determination of small amounts of iron (9).
Iron(II1) is reduced to iron(I1) with a reducing agent such a. hydroxylammonium chloride, and 1,lO-phenanchroline is added to form the colored complex. The tris(1,lO-phenanthroline) iron(I1) complex is intensely colored and stable indefinitely. Sulfur dioxide is a well known reducing agent and has been used for reduction of iron to the ferrous state prior to permanganate or dichromat2 titrations when high precision and accuracy are desired (3). It seemed obvious that these two widely different but related chemical principles could be combined in a spectrophotometric method for sulfur dioxide. EXPERIMENTAL
Apparatus. A Bausch and Lomb Spectronic 20 spectrophotometer was used t o measure the absorbance of the solutions. T h e amplifier stability of the instrument was improved as suggested by Creamer ( 2 ) . p H measurements were made with a Beckman Model H-2 p H meter with standard electrodes. Prior to each of several measurements, the meter was standardized against National Bureau of Standards standard p H 4.01 potassium acid phthalate and p H 9.18 borax buffers. For early tests of the method, 100-ml. Nessler tubes were used. Sulfur dioxide volumes were measured with a Hamilton No. 710, 100-pl., gas-tight syringe. The syringe could be read to approximately 0.2 pi.; the dead space was 37 PI.
A gas absorption train was assembled as shown in Figure 1. The wet test meter was a Precision Scientific Co. model accurate to 0.5%. The first two bubblers in the train were 250-ml. gas washing bottles fitted with frittedglass disks, Corning KO.31760. The first contained 0.1V sodium tetrachloromercurate(I1) solution, prepared by the method of West and Gaeke (11) to
with the base using a pH meter. .An additional milliliter of the 0.1M base control was required to reach pH 6.0 and 1 ml. valve of the 0 . 1 N acid brought the p H back X vacuum to 5.0. For further work, fresh solutions of silica ' sample gel ln]ection 0.001M ferric ammonium sulfate and air water b a t h port 0.00331 1 10-phenanthroline were prepared; 1 ml. of sulfuric acid was wet te1t added to t,he iron solution to suppress meter NOeHgC14 HsSO, bubbler hydrolysis. Both solutions were color0.1 M conc, less. Appropriate amounts of ferric alum and l,lO-phenant,hrolinc solutions Figure 1. Gas absorption train for standard curve preparation were placed in a 200- x 25-mm. test tube; the volume was adjusted to 15 ml. with water, 15 drops of octyl titration lamp. The blank was light, remove any sulfur dior.ide and hydrogen alcohol were added, the p H was adjusted the test solugreenish-yellow in color; sulfide from the incorning laboratory to 5.5 with 0.l.U sodium hydroxide, tion became orange. air. 'The second bubbler contained and 30 pl. of sulfur dioxide was injected To obtain a colorless blank, fluoride concentrated sulfuric acid to remove into t,he system with a flow rate of as ammonium bifluoride was added to moisture from the air. Following the about 1 cubic foot per hour. After The orange color both Nessler tubes. second bubbler was a drying tube with capture, 1 ml. of 5% ammonium biof the test solution became more apsilica gel. Following the silica gel tube fluoride was added, the volume was adparent with the removal of the partially was a glass T fitted wit,h a small serum justed to 25 ml. with water, and the hydrolyzed iron(II1). bottle stopper for sulfur dioxide sample absorbance read in 1-inch and also A sulfur dioxide sample was run as injections. The third bubbler was to 1,:2-inch cells. The concentration of above using phosphoric acid to dehold the capturing solution. It. was a the 1,lO-phenant'hroline was increased colorize the solution. Phosphoric acid 250-ml. gas n-ashing bottle fitted with a to 0.03-11 during the experiment (Table proved to be inferior to fluoride in its 40- to 60-micron porosity, fritted-glass 111). The blank for this test mixture bleaching action. T o suppress frot'hing cylinder, Corning Y c . 31770. Sarwas 0.02 absorbance unit. in the scrubber, n-octyl alcohol was gent thermostated wat.er bath was used EFFECT O F TEMPERATURE. Sulfur used as antifoaming agent'. to control the temperature of the capdioxide \vas scrubbed through test This procedure was not sufficiently turing solution to *0.25" C. % . glass solutions a t temperatures ranging from sensitive to employ the commonly used T fitted with rubber tubing was placed 0" to 100" C. by cooling or heating the 1-cm. to 1-inch spectrophotometer cells. in the tube leading :'rom the bubbler capturing test tube in a water bath -2 series of experiments were carried out t,o the vacuuni pumli. The flow rate at the desired temperature. Caing the to improve the sensitivity. of air through the tem was controlled EFFECT OF IROS(III) CONCENTRA- same procedure used in the previous by an adjustable scmv clamp on the section, except that the solutions were TION. First, the gas absorption train rubber tubing leading from the T-valve. diluted to 50 ml. aft'er capture instead shown in Figure 1 was used to deA mechanical vacuuni ~ ~ u mwas p used of 25 ml., the solutions were allowed to termine the effect of iron(II1) conrather than an aspirator to obtain come to room temperature and the abcentration. Ten milliliters of ferric greater Iiumping speed and not. higher sorbance rvas measured in 1'2-inch cells ammonium sulfate solution, 10 ml. of vacuum. -111 tubing: was polyvinyl (Figure 2). 0.157'c 1,lO-phenanthroline solution, and chloritle; polyethylen? joints were pro15 drops of octyl alcohol were placed vided a t 1)oints .I, B , 2nd 9. in a large test tube and the flow rate Sulfur dioxide sam1:les were obtained adjusted to about 1 cubic foot per from a rubber bag fit.:ed with a rubber hour. Fifty microliters of sulfur distopper and short pie-e of glass tubing Table I. Effect of Iron(lll) oxide were introduced, 1 ml. of 5% capped with a snxtll serum bottle Concentration ammonium bifluoride was added, and sto1J]Jer. 1 liter/min., room temp., 50 p l . SOP the volume was adjusted to 25 ml. The Reagents. Matheson anhydrous syringe dead space in 25 ml., 1-inch cells absorbance was determined in 1-inch grade 99.9870 minimum purity sulfur cells a t 510 mk (Table I). dioxide, G. F. Smith 1,lO-phenant'hroPer cent Ahsorhance EFFECTOF PH. Exactly the same line, and I h k c r ;\nalyzed reagent ferric 2 n 0 022 procedure was used as that for the ammonium sulfate and technical am0 2 0 215 above study except that 30 p l . inst'ead monium hifluoride were used. Fluo0 1 0 455 of 50 p l . of sulfur dioxide was injected 0 456 ride solutions were kept in poly0 02 tem each time. For this 0 00a 0 631 ethylene bottles. Distilled water was st,udy, 10 ml. of 0.0270 ferric alum used in all experimeritu. was used in the capturing solution. 0.02y0iron(II1) added afterward. Procedures. --Is,-ock solution of The pH of each solution wa5 adjusted ferric ammonium sulfate was prepared to the depired value with 0.1JI sodium by dissolving 8.6 grams of the crystalhydroxide or 0.1M perchloric acid. The line material in water and diluting to pH was varied over the range used for 1000 ml. A solutior. of 1,lO-phenanTable II. Effect of pH colorimetric iron with 1,lO-phenanthrothroline in water was prepared by line, 2 to 9 (9) (Table 11). The optidissolving 0.4 gram of the material 1 liter/min., room temp., 30 pl, SO2 + mum pH range for d f u r dioxide desyringe dead spare in 25 ml., 1-inch cells in just enough alcohol and diluting terminations was 5 to 6. Two buffer to 250 ml. -4 trapping solution was PH Absorbancen systems were investigated t o dctermiiie prepared bj. pipetting 0.5 ml. of the 0 209 2.0 the feasibility of buffering the capturing ferric ammonium sulfite stock solution 0 181 3 0 solution a t pH 5.5. Thirt>--microlit'er and 10 ml. of the 1,lO-phenanthroline 0 195 4.0 portions of sulfur dioxide were run into solution into a Nessler tube and diluting 0 255 4.5 solutions containing the usual reagent to apl)roximately 60 rnl. -410-pI. por0 344 5.0 mixture buffered with either potassium tion of sulfur dioxide was injected a t a 0 344 5.5 acid phthalate and sodium hydroxide 0 344 very low flow rate into t'he bubbler 6.0 or sodium acetate and acetic acid. 0 227 7.0 through the rubber tubing provided. 0 1x0 8,0 These buffer reagents interfered with The Sessler tube was filled to the mark 0 133 9.0 the color forming reaction. A mixture with distilled water. -4blank was preof 10 ml. of 0,0270 ferric ammonium pared in the same manner. The a Less blank of 0.013. sulfate and 10 ml. of 0.08% 1,lOSessler tubes were placed in a viewing phenanthroline was adjusted to p H 5 rack and observed with the aid of a A
8
flow r a t e
-
-
~
+
VOL. 36, NO. 7 , JUNE 1964
1309
o'80
t
0.301
0.25
;0.20
0. I O
0.05
0.00 Temperature
I
0
*C.
2
3
4
5
6
Flow R a t e (L./min3
Figure 2. 30
PI.
502 f
Effect of temperature
syringe d e a d space in 5 0 ml., '/*-inch cells
EFFECTOF FLOW RATE. The maximum allowable flow rate was determined a t 50" C. by capturing the sulfur dioxide in a 250-ml. gas washing bottle that had been fitted with a coarse-glass gas dispersion tube. The solution make-up
Table 111. Effect of Iron(lll) and 1 , l O Phenanthroline Concentration 1 liter/min., room temp., 30 pi. SO2
syringe dead space in 25 nil. Ferric ammon1,10ium Phenansulfate throline Absorbance
1x
3x
10 - a M ,
10 - 3 M ,
ml. 1 2 3 1
ml.
1 1 1 1
3 4 5 10 5 10
1 1
1 2
2
2 3
10 3x
1-inch cells 0.280 0.208 0.174 0.372 0,398 0 415 0.415 0.415 0.415 0.462 0.552
10-2M, ml. 4
1 1
5
4 4
2 3
4 4 5
5 6 5
6
5
6
6
1 3 10
0
0.523 0 552 0 602 0 638 '/*-inch cells 0 367 0 357 0 387 0 357 0 382
ANALYTICAL CHEMISTRY
+
Figure 3. 5OoC.,
30 PI. SO2
remained the same except that, the solution volume was 75 ml. for the sulfur dioxide capture and after capture the solution was diluted to 100 ml. For these studies the flow rate control valve shown in Figure 1 was adjusted until the desired rate was obtained. Thirty microliters of sulfur dioxide was injected into the system and the absorbance of the resulting solutions was measured a t 510 mp in 1;2-inch cells (Figure 3). To see if any sulfur dioxide was passing through the test solution, two bubblers, each containing 75 ml. of capturing solution, were placed in series in the constant' temperature bath a t 50" C. Suction was applied and 30 p l . of sulfur dioxide was introduced into the first bubbler. The capturing solution in the second bubbler was diluted to 100 ml. and its absorbance measured in a 1/2-inch cell. I t was the same as the absorbance of the blank. kt this point the reagent concentrations were increased to see if sensitivity would increase. Ten milliliters each of 0.001.11 ferric alum and 0.0334 1,lOphenanthroline solutibns were used instead of 5 ml. With the new formulation, 30 pi of sulfur dioxide gave an absorbance of 0.305 in a 1,/2-inch cell compared to 0.220 of the above flow rate st,udy (Figure 3). .In increase of the reagent volumes to 15 ml. did not further increase the sensitivity. It was not,ed at this point that the low pressure of the system was drawing some of the sulfur dioxide from the microliter syringe. So the gas could be injected when the system was a t atmospheric pressure, the following procedure was adopted for injecting t'he samples. The train shown in Figure 1 was disconnected a t point A , then
Effect of flow rate
+ syringe d e a d space in 100 mLP '/*-inch
cells
point B was disconnected a t the same time the flow rate control valve was opened to relieve the vacuum. Points A and B were reconnected, the sample was injected into the sample port, and the flow rate control valve adjusted to give the proper flow rate. Using this technique no sulfur dioxide was drawn from the 37-pI. dead space. T o see if the blank of the reagent solution would increase if the solutions were left a t 50' C. up to 1 hour, 30 p1. of sulfur dioxide was injected and the capturing solutions were left a t 50' C. for 15, 30, 45, and 60 minutes. The absorbance in each case mas 0.155 Zt 0.006. The absorbance of the blanks waq 0.027. PREPARATION OF A STANDARD CURVE. A gas absorption train was assembled as indicated in Figure 1. Sodium tetrachloromercurate(II), O.lM, was placed in bubbler 1, concentrated sulfuric acid in bubbler 2, and the capturing solution in bubbler 3 fitted with a coarse-glass gas dispersion tube. Ten niilliliters of 0.001 .I1 ferric ammonium sulfate, 10 ml. of 0.03.1f 1,lO-phenanthroline, and just enough 0 . l X sodium hydroxide to give a pH of 5 to 6 were placed in bubbler 3. The solution 5% as diluted to approximately 7 5 ml., 1.0 ml. of n-octyl alcohol was added, and the bubbler was placed in a water bath at 50" C. A rubber gas sampling bag was filled with sulfur dioxide and appropriate portions were injected into the system a i t h the syringe, the suction was started, and the flow rate adjusted to 2000 ml per minute. After 5 minutes, the train was disconnected at points A and B and the suction removed. The gas dispersion tube was washed inside and out with distilled nater and the solution
transferred to a 100-ml. volumetric flask. Two milliliters of 5y0ammonium bifluoride was added and the solution cooled to room tempmature. The volume was adjusted tc 100 ml. and the absorbance measured a t 510 mp in 1-inch or 1/2-inch cl:lls after mixing. Standard curves are shown in Figure 4. Sulfur dioxide volumes were corrected to standard conditions of temperature and pressure before the plots were constructed. REPRODUCIBILITY. Five runs of 30 p1. each of sulfur dioxide were made to determine the reproducibility of the method. The absortiances were measured in 1l2-inch cells (Table IV). COLOR STABILITY To determine how long a sample could be stored before its absorbante was measured, 0 and 60 pl. of sulfur dioxide were introduced into the capturing solution, the solution was diluted to 100 ml. and the abborbance \\as read in 1/2-inch cells a t intervals up i o 15 days (Figure 5). INTERFERESCES. 'The apparatus for studying interferenc1.s was the same as that shown in Figure 1 except a 125x 25-mm. test tube was inserted in the train a t point X when gases had to be generated by treatment of some chemical compound. Tvro runs were made for each substaiice; the substance was introduced befcre and after the sulfur dioxide. T h ? volume of the capturing solution W : ~ Sadjusted to 100 ml. and the absorbmce was read in ,-inch cells. Thir -y microliters of sulfur dioxide was injected in each case. Ozone was generated by passing pure tank oxygen through a silent electric discharge. The effluent ozone plus
oxygen was passed through a neutral solution of potassium iodide ( I ) for a definite time interval, the solution was acidified with sulfuric acid, and the resulting iodine solution was titrated with standard thiosulfate using starch as the indicator. The thiosulfate solution was standardized against acidified iodate-iodide using magnesium iodate tetrahydrate (6) as primary standard. Ozone was produced a t a rate of 1.7 pl. per second. The ozone was passed into the test system for sufficient time to build up the desired ozone level. Nitrogen dioxide was generated by heating 10 mg. of lead nitrate in the gas generation test tube a t X in Figure 1 and the 1300 pl. of nitrogen dioxide was led into the system. For sulfide interference study, a 0 004-If solution of sodium sulfide was prepared; each milliliter of the solution was equivalent to 100 pl. of hydrogen sulfide gas. Hydrogen sulfide was also generated by heating a mixture of sulfur and paraffin. I n an attempt to eliminate sulfide interference. 10 ml. of 0.004M cadmium sulfate was added to the capturing solution with no effect. Formaldehyde was generated by heating paraformaldehyde. Carbon monoxide was generated by heating enough calcium oxalate to give 1000 pl. of the gas. Acetylene was generated by treating 1 gram of calcium carbide in the test tube with water. Ammonia, butadiene, carbon dioxide, and hydrogen chloride were obtained from cylinders and 1-ml. portions a t atmospheric pressure were injected into the system. h formic acid solution was prepared such that 1 n-11. was equivalent to 1000 pl.
Table IV.
Reproducibility
2 liters/min., 50" C., 27 pl. SO,at S.T.P. in 100 ml., '/*-inch cells
Run
Absorbance" 0.128 0.133
1
2 3 4
0.125
0.133
5
0.137
Mean Std. dev a
0.132 0.005
Less blank of 0.027
RESULTS AND DISCUSSION
The absorption train shown in Figure 1 proved to be suitable for the evaluation and study of the method in the laboratory. Samples for analysis would naturally be run directly into bubbler No. 3 of Figure 1 and the preceding items of the train could be omitted. Adjustment of the p H of the solution to near 5.5 was necessary but buffering was not needed for the optimum p H range in Table I1 was broad, and it was not likely that a sample would contain enough acidic or basic compoilents to alter the pH of the capturing solution. In addition, the capturing solution tended to resist p H changes. The preparation of the reagent solutions was rapid and simple; the ferric ammonium sulfate and 1,lO-phenanthroline solutions were stable for a t least several months and a capturing
0.70
0.50
b\onk
O aooo
3 .
6
I
9
0
12
l15
T i m e (days)
Figure 4.
Standard curves
2 liters/min., 50°C., SO2 valumes injected a t atmospheric pressure a n d corrected to s t a r d a r d condition in 100 ml.
Figure 5.
Effect of time
2 liters /min., 5OoC.a t capture-stored a t S.T.P. in 100 ml., '/*-inch cells
a t room temp., 54 PI. SO2
VOL. 36, NO. 7, JUNE 1964
131 1
solution prepared from these reagents remained colorless for a t least one week. The reagent concentrations were not critical but Table I11 shons that the optimum amounts of 0.001.11 ferric ammonium sulfate and 0.03J1 1,10phenanthroline were 5 ml. each for a 15-ml. capturing solution. Although the sensitivity as shown in Figure 2 increased with temperature, a temperature of 50” C. was selected as the warmest temperature which could be comfortably handled for the sensitivity increase obtained. Lower temperatures could be used with a decrease in seniitivity. Control of temperature within 0.5” C. was sufficient. It is evident from Figure 3 that the maximum allowable flow rate was 3000 inl. per minute. For safety, a 2000 ml.per-minute flow rate was selected; this was equivalent to 4.3 cubic feet per hour. Having two bubblers arranged in series at this flow rate demonstrated that no sulfur dioxide was lost from the first bubbler since no color developed in the second. The standard curve shown in Figure 4 demonstrated that the method obeys 13eer’s law from 0 to 75 pi. of sulfur dioxide. When quantities of sulfur dioxide are injected into the train qhown in Figure 1 for the purpose of preparing a standard curve, care must be taken that the syringe and the system are a t the same pressure or the volume indicated on the syringe may not be delivered. The conditions mentioned for the preparation of the standard curve are the same recommended for sulfur dioxide analyses.
Table V.
Interferences
2 liters/min., 50” C., 27 pl. SO, at, S.T.P.in 100 ml., ‘/*-inch cells
Tolerated amount, p l . Formaldehyde& 60 Hydrogen sulfideh 1 Ozonec 60 Acetylened Over 1000 Ammoniae Over 1000 Butadienee Over 1000 Carbon dioxidee Over 1000 Carbon monoxide/ Over 1000 Formic acid0 Over 1000 Hydrogen chloride? Over 1000 Nitrogen dioxideh Over 1000 Pyrolysis of paraformaldehyde. * Pyrolysis of sulfur paraffin and sulfide solution. c Silent electric discharge with oxygen. Hydrolysis of ralcium carbide. e Tank. Pyrolysis of calcium oxalate. Aqueous solution Pyrolysis of lead nitrate.
+
f
1312
ANALYTICAL CHEMISTRY
The reproducibility shown in Table
IV was expected and seems entirely adequate for most trace analytical purposes. The stability of the color is indicated in Figure 5. After a day the absorbance of the solutions began to increase gradually. If blank corrections were made, the solutions could be kept a t least one week after sulfur dioxide capture before the absorbance was measured with negligible error. Up to 60 p l . of ozone caused no interference. When over 100 p l . of ozone was introduced, the absorbance of the capturing solution increased. Ozone can be tolerated up to 0.6 p.p.m. in a 100-liter sample. Nitrogen dioxide did not interfere; 2000 pg. could be tolerated nith no difficulty a t all. Hydrogen sulfide interfered quantitatively. Fortunately, the concentration of hydrogen sulfide in most samples for sulfur dioxide measurement, such as stack gaqes and industrial and urban atmospheres, is usually two hundred times lower than the sulfur dioxide level (4). These and seven other common gases which caused no interference are listed in Table V. The gases tested were tested as gases and not as derived compounds. For example. potassium nitrite solution was not used as a substitute for nitrogen dioxide. Obviously, nitrogen and oxygen did not interfere.
I t is believed that the method could be readily applied to any area of t’echnology needing a method for sulfur dioxide. The applicat,ion of the method to air pollutiori control analysis was obvious and this study was oriented in that direction. Good results could be expected even in t’he hands of unskilled personnel because there are no mystifying steps in the chemistry and all operations are straightforward. Other areas in which the method would prove valuable could include the determination of sulfur dioxide in beverages. The sulfur dioxide could be transferred from t,he sample to the test solution by passing a current of air through the sample and into the capturing solution (6). Analysis of sulfur in steels by combustion of the sample and conduct’ing the sulfur dioxide through the test solution also seems feasible. Determination of sulfur dioxide in industrial stack gases would be especially simple as would the determination of sulfur dioxide levels in automobile exhaust gases. Ko difficulty should be encountered in adapting the method to aut’omatic control of industrial processes or pollution alarm systems. LITERATURE CITED
(1) Birdsall, C. M., Jenkins, -4.C., Spadinger, E., A N . ~ LCHEM. . 24, 662 (1952). ( 2 ) Creamer, R., Ibid., 29, 1722 (1957).
( 3 ) Hillebrand, W.F., Lundell, G. E. F., Bright, H. A . , Hoffman, J. I., “Applied
CONCLUSIONS
The method described is recommended for routine sulfur dioxide determination and possesses numerous advantages over t,he methods in current, use. The color is formed as the samples are taken so the operator can judge when to st,op the sampling operation and prepare the solution for measurement. This is unlike the fuchsin method where an initial estimat,ion of the sulfur dioxide level should be made before applying the fuchsin t’est’. The sampling rate can be as high as 3 liters a minute wit.h no loss of sulfur dioxide. The sensitivity compares favorably with the more awkward colorimetric method for sulfur dioxide. For example, 0.05 to 0.7 p.p.m. sulfur dioxide can be determined in a 100-lit,er sample collected in 50 minutes at, a flow rate of 2 lit’ers per minute. The method work.; over a practical range of 0.05 to 2600 p.p.m. for convenient size samples. For these saml)les, 100-liter and 25-ml. volumes would he required, respectively.
Inorganic hnalysis,” 2nd ed., John Wiley, S e w York, 1953. (4) Jacobs, hl. B., “The Chemical Analysis of Air Pollutants,” Interscience, S e w York, 1960. (5)yIkdst,rom,F., Stephens, B. G., ANAL. CHEW34. 993 I 1962). (6) Lloyd, L?. J., kowle, B. C., dnalyst 88, 394 (1963). ( i ) Naurnan, R. V., West,, P. W., Tron, F., Gaeke, G. C., Jr., ANAL.CHEM.32, 1307 (1960).
( 8 ) Pate, J. B., Lodge, J. P., Jr., Wartbure. A. F.. Ibid.. 34. 1660 11962). (9) Smit,h, G’. F., ‘Richter, F. P , j ’“Phe-
nanthroline and Substituted Phenanthroline Indicators,” G. Frederick Smith Chemical Co., Columbus, Ohio, 1944. (10) I’rone, P. F., Boggs, W. E., AXAL. CHEM.23, 1517 (1951). (11) West, P. W., Gaeke, G. C.) Ibid.,28, 1816 (1956).
RECEIVED for review January 31, 1964. Accept,ed April 8, 1964. Southeastern Regional ACS Meeting, Charlotte, S . C., November 1963. From the dissertat’ion subniitt,ed by B. G. Stephens to the Graduate School of Clemson College in partial fulfillment of the requirements for the degree of doctor of philosophy, January 1964. U‘ork support,ed in part by Sational Defense Education Act Fellowship.
