S o appreciable loss of amino acids was observed b y visual inspection, but the chromatograms were greatly improved after the desalting procedure. ACKNOWLEDGMENT
The microdesalter TT-as constructed by Earl W. Winter and Albert Emanuel, m-hose efforts are gratefully acknowledged.
Kolthoff, I. M., Lingane, J. J., “Polarography,” 2nd ed., vol. 11, pp. 552-4, Interscience, New York, 1952. Simmonds, D. H., ANAL.CHEY. 26, 1253-4 (1954). Stein, W. H., Moore, S., J. Biol. Chem. 190, 103-6 (1951). Turba, F., “Chromatographische Methoden in der Protein Chemie,” p. 95, Springer Verlag, Berlin, 1954.
LITERATURE CITED
(1) Astrup, T., Stage, A., Olsen, E., Acta Chem. Scand. 5 , 1343-8 (1951).
(2) Block, R. J., Durrum, E. L., Zweig, G., “Paper Chromatography and Paper Electrophoresis,” pp. 84-7, 139-140, Academic Press. New York, 1955. (3) Consden, R., Gordon, A. H., Martin, A. J. P., Biochem. J. (London) 41, 590-6 (1947). (4) Decker, P., Chem. Ztg. 74, 268 (1950). ( 5 ) Hulme, A. C , S u t u r e 171, 610-11 (1953).
RECEIVED for review February 17, 1956. Accepted September 18, 1956.
Determination of O z o n e and Other Oxidants in Air COE W. WADELIN Research Division, Goodyear Tire and Rubber
Ehmert modified the method of Crabtree and Kemp for the determination of ozone in air to eliminate the need for a correction factor for the volatilization of iodine. The ozone was absorbed in a potassium iodide solution containing a measured excess of sodium thiosulfate, which was backtitrated with iodine. A further modification is now made by titrating with 0.001N potassium iodate to an amperometric end point. The apparatus for detection of the end point consists of a calomel electrode, a platinum electrode, and a sensitive galvanometer. N o batteries or resistors are required. On triplicate analyses of eight samples ranging from 15 to 25 parts of ozone per hundred million parts of air, by volume, a standard deviation of 1.45 was found. By varying the concentrations of the solutions, samples containing from 2 to 10,000 p.p.h.m. of ozone can be analyzed.
Co.,Akron 76, Ohio
Effenberger stated that 80% of the oxidant in air is ozone ( 2 ) . Crabtree and Kemp stated t h a t three to four times as much nitrogen dioxide as is normally found in air will not interfere in the determination of ozone ( 1 ) . I n studying the aging of rubber, many of the ozone determinations are made on the contents of test chambers containing artificially produced ozone concentrations of 25 to 50 p.p.h.m., where the interference of other oxidants is probably small. Crabtree and Kemp absorbed ozone in 20y0potassium iodide solution, where i t forms iodine.
NO2
+ 2H+ + 21-+
I2
+ H20 + NO (1)
403
1
I
TO VACUUM PUMP
+ 1OKI + 10H+ + 4HzO + 302 +
+ 2Na2S203
+
+ 2NaI
NazS40e
+ SKI + 6Ht 312
(7)
(3)
(4)
The iodine reacts as soon as it is formed and no volatility correction is needed. As potassium iodate is sufficiently pure to be used as a primary standard and its solutions are stable, it was proposed to use the technique of Ehmert. then to acidify the solution and backtitrate with 0,OOLV potassium iodate solution. XI08
Figure 1. Assembly of glassware for sampling, originally used b y Crabtree and Kemp
+ HzOz
512 10K+
+
They found that bubbling a large sample of air through the solution resulted in the loss of some iodine b y volatilization, and applied a 10% correction factor. -4s this correction factor is dependent on the rate of flow and the volume of the solution, i t is desirable to use a method that does not require correction. Ehmert used a potassium iodide solution containing a measured excess of sodium thiosulfate and then backtitrated the excess (3). 12
T
HE TERM “OSIDAST” is used here to mean anything t h a t will oxidize potassium iodide in aqueous solution buffered a t p H 7 . This definition was used b y Littnian and Benoliel, who pointed out that the oxidation of potassium iodide under these conditions is not specific for ozone but also responds t o oxides of nitrogen and some organic hydroperoxides ( 6 ) . Ozonides and free halogens also liberate iodine in the solution. The amount of iodine formed b y oxides of nitrogen has been stated to range from 2y0 ( 4 ) t o 80% ( 7 ) of the amount expected from Reaction 1.
The solution must be buffered a t p H 7 or higher to prevent the formation of more than 1 mole of iodine per mole of ozone (8).
+
+ 3Hz0 + 6Kf
(5)
I h o w l e s and Lowden described a circuit for amperometric end point detection, n-hich requires simpler apparatus and is more sensitive than the dead-stop end point (b). The amperometric circuit was therefore adopted. The starch end point is not sensitive enough for titrations with 0.001N solutions. VOL. 29, NO. 3, MARCH 1957
441
EXPERIMENTAL W O R K
Apparatus- The flask was the same as that used b y Crabtree and Kemp, except that the Woulff bottle was replaced by a l-liter round-bottamed flask ( ~1). The i design ~ of the~ spray jet is critical and is described in detail by Crabtree and Kemp ( I ) .
B
T o test the stability of sodium thiosulfate during sampling, 70 ml. of buffer solution and 5 ml. of sodium thiosulfate solution Jvere placed in the sampling flask and 125 liters of air were drawn through ~ ~the solution. Titration showed that no decomposition had occurred. The galvanometer and electrodes were connected in series through a double-pole double-throw switch as shown in Figure 2.
N 2'
F t
P Z
ml. of potassium iodate solution required t o titrate the solution after sampling = normality of potasRium iodate solution = temperature, degrees Kelvin = sample flow rate, liters per minute = sampling time, minutes = atmospheric pressure, mm. = oxidant concentration, parts of ozone per hundred million parts of air by volume. =
RECOMMENDED PROCEDURE
PLATINUM CALOMEL ELECTRODE ELECTRODE
Figure 2. Circuit for amperometric end point detection
Rotameter-type flowmeter such as Fischer and Porter No. 2-F-1/4-16-5, having a range of 3 to 7 liters of air per minute, Source of vacuum capable of maintaining a sampling flow rate of 5 liters per minute. A water aspirator will serve. Ten-milliliter buret., graduated to 0.05 ml. Calomel reference electrode, Beckman No. 1170. Platinum thimble indicator electrode, Beckman KO.1271. It is important that the platinum electrode have a surface area of a t least 1.5 sq. em. If a small area such as a short platinum wire is used, the circuit will lack sensitivity. Galvanometer with sensitivity of a t least 0.05 fia. per mm. LIngnetic stirrer. Reagents. To prepare the buffer solution, dissolve 1.8 grams of disodium hydrogen phosphate and 1.7 grams of potassium dihydrogen phosphate in 1 liter of water. Potassium iodate standard solution, 0.00100N. Dissolve 0.0357 gram of potassium iodate in 1 liter of water. Sodium thiosulfate solution, 0.001N. Dissolve 0.25 gram of sodium thiosulfate decahydrate and 0.1 gram of sodium carbonate in 1 liter of water. Sulfuric acid, 2 N Potassium iodide. The sampling flask and all tubing for conducting the sample to the flask were made of glass. Ground joints without lubrication were used wherever possible. Khere this was impractical, joints were made by butting glass tubing together and covering the joint with a sleeve of plastic tubing. Contact of the sample with rubber or other organic material should be avoided, to prevent consumption of ozone. 442
ANALYTICAL CHEMISTRY
Place 70 ml. of buffer solution, 1 gram of potassium iodide, 5 ml. of sodium thiosulfate solution measured with a pipet, and 10 ml. of 2N sulfuric acid in a beaker. The galvanometer will settle down to a steady reading within a few seconds after the reagents are mixed. The speed of stirring should be constant during a titration but need not be duplicated from one titration t o another. Titrate with potassium iodate solution until a permanent galvanometer deflection of 5 mm. is obtained. This is taken as the end point. Repeat the titration and average the values. As the sodium thiosulfate solution changes strength, a new blank value must be established each day. Place in the sampling flask 70 ml. of buffer solution, 1 gram of potassium iodide, and 5 ml. of sodium thiosulfate solution. Draw about 125 liters of sample through the flask at a rate of about 5 liters per minute, adjusting the rate with the pinch clamp, and note the exact flow rate and time. Empty the solution into a beaker, add 10 ml. of 2N sulfuric acid, and titrate. The flow rate must be great enough to keep the flask filled with a fine mist. The sample should be large enough so that the blank and sample titrations differ b y a t least 1 ml. If the sampling is continued so long or the ozone content of the sample is so high that the thiosulfate is exhausted, the determination must be repeated. I n sampling a chamber with an ozone concentration of 10,000 p.p.h.m., this difficulty was overcome by using 0.1N sodium thiosulfate and potassium iodate solutions. The other reagents were used without modification. CALCULATIONS
From Reaction 2 it can be seen that 1 mole of ozone forms 2 equivalents of iodine. Z = (A
- B ) X A'
where A
X 11.21 X 760 X 2' X 105 t P 273
F x
=
x
x
ml. of potassium iodate solution required t o titrate the blank
Table I.
Sample No. 1
2 3 4 5 6
-k
Analysis of Ozone Samples
Ozone Found, P.P.H.M. 15.5, 15.3, 18.6, 20.5, 19.2, 17.5, 24 6. 23.6, 18 3; 18.7; 20 9. 20.1. 18 8; 21.3: 25.2, 23.9,
14.7 21.5 13.8 23.2 16.5 19.4 22.4 23.2
Average 15.2 20.2 16.8 23.8 17.8 20.1 20 8 24.1
RESULTS
Triplicate analyses of air in a n ozone test chamber on eight different days are shown in Table I. The standard deviation is 1.45 p.p.h.m.
ACKNOWLEDGMENT
The author wishes to thank the Goodyear Tire and Rubber Co. for permission to publish this paper.
LITERATURE CITED
(1) Crabtree, J., Kemp., A. R., IND. ESG. CHEY.,ANAL.ED.18, 769 (1946). (2) Effenberger, E., 2. anal. Chem. 34, 106 (1951). (3) Ehmert, A., J . Atm. and Terrest Phys. 2, 189 (1952). (4) Gluckauf, E., Heal, H. G., Martin, G. R., Paneth, F. A,, J. Chem. SOC. 1944, 1. (5) Knomles, G., LonTden, G. F., AnaIysf 78, 159 (1953). (6) Littman, F. E., Benoliel, R. W., ANAL. CHEM.25, 1480 (1953). (7) Littman, F. E., Marynowski, C. W., Ibid., 28, 819 (1956). (8) Treadwell, F. P., Anneler, E., Z. anorg. Chem. 48, 86 (1905).
RECEIVEDfor review May 23, 1956. Accepted October 24, 1956. Rubber Division, ACS, Cleveland, May 17! 1956. Contribution 219, Research Division, Goodyear Tire and'Rubber Co.
