Table 1. Validity of a Single Conversion Factor
NomiMixture Conversion nal CoplPosition, Mg, Factor, C.p.M./M Samplc Polyprop I- poly- Polypropyf Wt., ene-C" Mg. ene-&( ethylene 500 45.7 453.2 580 45.1 447.8 569 10.4 490.6 562 10.8 495.1 553 lW 100 5 .., 560 101 2 ... 557 100 z5 ... 564 109.2a .., 562 Avo 561 & 2 4 Liquid.
14 copolymers were prepared in our laboratory from high-purity ethylene and propylene. All labeled polymers were prepared from the same propylene feed tagged with pr0py1ene-l-C~~. The validity of the method rests upon the reasonable assumption that conversion factors obtained from mixtures of polypropylene and polyethyleneeither one labdcd-can be used with copolymers of thcm. Our conversion factors were the propylene-CI4 specific activities in such mixtures; they were determincd by using the new method to obtain the activities of mixtures of the polypropylene-CI4 and the polyethylene, and dividing thr activities by the respective known wcights of the polypro-
p ~ 1 e n e - Cin ~ ~these mixtures. These conversion factors are shown in Table I, along with values for the polypropylene-C" alone. The two liquid samples were prepared like the solid mixtures, except that no heating was necessary. Inasmuch as the conversion factors did not vary, within experimental error, with sample size, composition, or physical form, an average factor proved valid over the composition range studied. Because their propylene-C'd specific activities were the same, all samplea had the same absolute counting efficiency. By comparison with a benzoie-C*4 acid standard, this efficiency was found to be 70%. The propylene contents of the 14 different copolymers were determined in duplicate and are shown in Table 11. Counting times of 2 to 4 minutes and 6 to 12 minutes were used with the 0.5- and 0.1-gram samples, respectively. The differences in the duplicate determinations are small, and most of them can be attributed to statistical counting errors. CONCLUSION
The new method gives the precision of the previous method but saves either carbon-I4 or counting time because larger samples can be counted with much higher efficiency. It can be applied to other copolymers prepared from monomers, one of which is labeled with a
Table It.
Precision of Copolymer Analyses
( % propylene) 0.5-G. Samples 0.14.Samples 1.99,' 1.99 1.89. 1.86 2.05; 2.09 2.0s; 2.07 3.23,3.24 3.11, 3.09 3.42,3.46 3.13, 3.10 4.48,4.31 4.33, 4.32 8 . 7 3 . 8.74 7.89.8.26 10.48;10.62 9.42; 9.41
suitable beta emitter. With distinctive labeling, more than one component could be so determined. For polymers that will not dissolve in o-xylene at temperatures below the boiling point, suitable scintillators could be prepared from higher-boiling .solvents, such as mesitylene or triethylbenzene. LITERATURE CITED
(1) Bua, iF., Manaresi, P., ANAL. CHEW 31,2022 (1959). (2) Danusso, F.,Pajaro, G., Sianesi, D., J . Polymer Sci. 22, 179 (1956). (3) Natta, G.,Mazxanti, G . , Valvaasori, A., Pajaro, G., Chdm. e ind. 39, 733 (1957). (4) Wagner, C. D., Guinn, V. P., 1vucleonics 13, No. 10,56 (1955). (* -5, ) Wei. P. E.. ANAL. CHEM. 33. 216 (1961j. (6) White, C. G.,Helf, S., Nucleonics 14,No. IO, 46 (1956). RECEIVED for review January 9, 1961. Accepted May 8,1961.
Absorptivities for the Infrared Determination of Trace Amounts of Ozone PHILIP L. HANST,' EDGAR R. STEPHENSI2 WILLIAM E. SCOTT,2 and ROBERT C. DOERR laborafories for Research and Development, Franklin Insfitufe, Philadelphia, Pa.
b The infrared absorptivity of gaseous ozone was determined for use in the analysis of polluted air. Absorption ce1l.s of various lengths were charged with ozone, which was measured by two physical methods. The absorptivity determined at 9.48 microns in the infrared is 3.74 X lo-,* p.p.m.-' meter-' for 1 atm. total pressure over a wide range of concentration and path length. Results obtained by the long-path infrared instrument agreed with those found with an ultraviolet ozone photometer when synthetic ozone was determined in air at parts per million concentrations.
* Present address, Avco Research and
Advanced Development Division, Wilmington, Mass. * Present address, Scott Research Laboratories, Inc., Perkasie, Pa. ~
T
HE measurement of ozone concentrations of less than 1 p.p.m. in air became important in studies of chemical reactions of air pollutants, when this substance was discovered in polluted air. Long-path infrared spectrophotometry provides the most specific method available for this measurement, although it is neither as sensitive nor as simple as the chemical methods. The instrument used for this work haa been described ( 4 ) . When the long-path infrared technique was first applied to air pollution analysis, i t was necessary to determine the absorptivity of ozone. Since there was some doubt as to the reliability of the usual potassium iodide methods (3) when applied to these very dilute mixtures, two methods based on the physical measurement of known quantities of ozone were adapted. The
first of these methods waa based on the one described by Birdsall, Jenkins, and Spadinger (1) and used the change in pressure and volume produced by the ozonization of a known volume of oxygen, In the second method, liquid ozone was vaporized into a known volume and its pressure measured. The first of these methods was used to determine the absorptivity of o9ione at concentrations in the parts per million range (in air), while the second waa used in the range of millimeters of Hg pressure. The absorptivity was virtually the same in the two c w s . MEASUREMENTS AT
P.P.M. CONCENTRATIONS
An apparatus (Figure l), patterned after one described previously (I), was used to prepare ozone samples of known volume. VOL. 33, NO. 8, JULY 1961
1113
ion!
tube (volume 125 ml.) was Theflushe with cylinder oxygen at atmospheric pressure; then a volume of oxygen was trapped by closing both stopcocks. The silicone oil manometer was checked to make sure that the pressure was constant. The voltage, 7000 to 10,OOO volta a.c., wm then applied to the tube for about 0.50 minute to generate ozone in the trapped oxygen. After turning off the volta e, the decrease in pressure as indicated the silicone oil manometer was r e a i This represents both a volume decrease and a pressure decrease caused by the formation of ozone:
SILICONE 0 OM TEMPERATURE TER JACKET
THKRMOMETER
- ro
%
LONG-PATH CELL
30,- 20s
Figure 1 . Electric discharge apparatus for preparing ozone from known volume of oxygen
The amount of ozone formed was ceIculated from this decrease in pressure
Table 1. Absorptivity of Ozone at P.P.M. Concentrations (Total pressure at 1 atm.; Perkin-Elmer Model 99, NaCl prism, 500-micron slit) Absorptivity, a, P.P.M. -1 M. -1, 0: Path, Time,e at 9.48 p, X lo-' Trial P.P.h, Meters Min. Mean Mean dev.
72
a
3.75 3.75
Table
II.
Concn., Mm. Hg' Mean 4.00-8.22 3.77 x 10-4 3.85 x 10-4 3.10-6.95 Over-all mean 3.80 X lo-' To convert mm. of Hg to p.p.m., multiply by 1.32 X lo*.
Table 111. Comparison of Infrared and Ultraviolet Measurement of Ozone Concentration (P.p.m.)
Infrared, Franklin Institute (120-M. Path) 1.3 2.4 3.8 0.7
0.0 0.0
1114
0
3.77
0 .O7
3.71
0.09
3.74
0.03
3.76
0.00
Absorptivity for Ozone at Mm. of Hg Concentrations R~~~~of o8 Absorptivity, a, P.P.M.-' at 9.48p
N ~ of. Trials 8 0
500 120
0.09
(last three) 3.78 0.00 3.74 0.05
Over-all mean From introduction of ozone.
Slit Width, Microns
a
28 31
3.70
Ultraviolet, Kruger Photometer 1.2 2.4 3.7 0.64 0.58 0.59
ANALYTKAL CHEMISTRY
Mean dev. 0.16 x lo-' 0.12x 10-4 0.14 X lo-&
and volume using the perfect gas law. During the short time interval required to prepare and measure a sample of ozone, the water jacket was able to maintain the temperature of the ozonizer sufficiently constant. Meanwhile a blank spectrum was run on the ambient air present in the cell. This measured amount of ozone was then swe t into the long-path cell with adlitional oxygen and was allowed to mix by natural turbulence. This mixing required from 0.25 t o 0.50 hour. The principal ozone absorption in the rock salt region is centered a t 9.6
microns, as shown in the typical tracing in Figure 2. The units for the ordinate are arbitrary, since the quantity measured, Io/Z, is dimensionless. The data obtained by this method are summarirced in Table I. The average absorptivity was found t o be 3.74 0.03 X lo-' p.p.m.-' meter-' a t 9.48 microns, the wave length of maximum absorption. Trial 13 also showed that it is independent of path length. MEASUREMENTS AT MM. OF HG
*
CONCENTRATIONS
An independent series of measurements was made by using liquid nitrogen to liquefy small samples of ozone from a stream of ozonized oxy en. T h e condensed oxygen was pumpecfoff while the trap was maintained a t liquid nitrogen temperature. At this temperature the vapor pressure of li uid oxygen is about 162 mm. of IIg, w h e that of ozone is 0.015 mm. of Hg. Each ozone sample was evaporated into an evacuated 10-cm. absorption cell and the resultant ozone pressure determined with a silicone oil manometer, After pressurizing the cell to 1 atm. with cylinder oxygen, the ozone band wm scanned with a Perkin-Elmer Model 99 monochromator equipped with an NaCl prism. The results of 14 such measurements of the absorptivity are summarized in Table 11. Since the absor tivity varies with resolution or slit wi&h for some bands, two slit widths were used for the meaauremenh. This result agrees well with that obtained by the pressure-volume technique at concentrations about 1000-fold smaller. The reliability of the liquefaction method was verified by measuring the ultraviolet absorption of gaseous samples prepared in the =me way, and measured into a specially constructed ultraviolet absorption cell (sodium chloride windows; path length 9.8 cm.).
The absorptivity a t 2550 A. was then measured using a Beckman ultraviolet spectrophotometcr. The value obtained was 16.8 mm.-l meter-' which agrces adcquntcly with the value of 16.7 mm.-l metcr-1 obtained by Inn and Tan:tka (S). In each of these ultrrtviolet determinntions, the ozone WRR introduced simultaneously into the infrarcd ccll and in each case the infrared absorptivity agreed with that listed in Table 11. COMPARISON WITH ULTRAVIOLET PHOTOMETER
The ozone calibration was also compared with the values indicated by an ultraviolet ozone photometer made by Harold Kruger Instruments Co., San Gabriel, Calif. For this comparison, air was continuously passed through the long-path cell a t several hundred liters per minute along with a flow of ozonized oxygen sufficient to maintain a steady concentration of ozone. The ultraviolet photometer was used to monitor the effluent, so that simul-
taneous readings could be obtained by the two methods on the same gaa mixture. The ultraviolet instrument had previously been calibrated by the builder, using an ozone stream whose concentration was measured with potassium iodide. The ozone concentrations indicated by the two instruments were in good agreement, as indicated by the data in Table 111. This implies that the particular potassium iodide method used to calibrate the ultraviolet photometer was valid. AIR ANALYSIS
The long-path method described here was used to measure the ozone concentrations found in so-called photochemical air pollution. Such concentrations are typically in the range of a few tenths of 1 p.p.m. (v./v.) and can be readily identified and measured with the long-path technique. These results are reported in detail elsewhere ( 4 ) . From the shape of the ozone band observed for the atmospheric samples it WLM~concluded that there were no important interferences from other compounds in
these samples. If methanol were present in appreciable concentration, for example, it would overlap the 9.6-micron ozone band but would be readily identifiable by the chracteristic Q branch of this band. ACKNOWLEDGMENT
The authors are grateful to the Smoke and Fumes Committee, Division of Refining, American Petroleum Institute, for its generous support and to the members of Project Advisory Committee VI for valuable advice and encouragement. LITERATURE CITED
(I) Birdsall, C. M., Jenkins, A. D.,
Spadinger, E., ANAL. CHEM.24, 662 (19.52'). \ - - - -
(2) Inn,'.E. C. Y.,Tanaka, Y., J. O p t . SOC.Am. 93,870(1953). (3) Renzetti, .N. A., Advances in Chem. Ser., No.21,230 (1959). (41 Scott. W.E..Steuhens. E. R.. He.nEt,. P. L., Doerr, k. Prbc. Am: Petrol: Znst. 37, Sect. 111, 171 (1957). \
,
e.,
RECEIVEDfor review Soptember 12, 1960. Accepted April 17, 1961.
Sodium Diphenylaminesulfonate as an Analytical Reagent for Ozone H. H. BOVEE' and REX J. ROBINSON Department o f Chemistry, University o f Washington, Seattle 5, Wash.
b Sodium diphenylaminesulfonate, selected as an analytical reagent for the determination of ozone, reacts with ozone to form a turquoise blue product with an absorption maximum at 593 mp. The reagent has been tested under various conditions to determine the effects of pH, temperature, concentration, type of sampling equipment, and rate of sample flow on its. reaction efficiency. The effects of nitrogen dioxide, chlorine, hydrogen peroxide, and other interferences have been investigated. An analytical procedure using 1% sodium diphenylaminesulfonate in 0.02% perchloric acid solution has been developed and tested for precision. It gave satisfactory results when. fleld tested with ozone formed by inert gas-shielded welding arcs and by an electrostatic &precipitator.
T
HE determination of trace concentrations of ozone in air in the presence of the oxidizing gases has long been recognized as difficult. The ozone analytical methods in general use today are nonspecific and
often of insufficient sensitivity for work in the industrial hygiene and air pollution fields. Potassium iodide reagents, although widely used for ozone determination, have been especially vulnerable to the effects of interferences. Neutral, buffered, and alkaline potassium iodide are the preferred absorption reagents, but when the released iodine is measured by a titrimetric procedure, the sensitivity is relatively low. With measurement of the released iodine by colorimetric procedures, sensitivity is increased to a satisfactory level. The use of traps to remove potential interferences has not been very successful. None of the traps tested was 100% efficient in removing the interference and all absorbed a t least a part of the ozone. Since the amount of ozone available for measurement is normally very small, even partial absorbance in a trap could critically affect the result. For this reason traps should be avoided whenever possible. Many other chemical and physical methods for ozone measurement have been proposed but have not gained wide acceptance. Thorp (IO), in his ozone
bibliography, gives an excellent summary of ozone methods prior to 1954. Since 1954 several papers have proposed new approaches to the ozone determination problem. Among these is the phenolphthalin oxidation reaction described by HaagenSmit and Brunelle (6), the long-path ultraviolet absorption equipment of Renzetti (6), and the nitrogen dioxide equivalent method of Saltzman and Gilbert (7). I n the research reported here sodium diphenylaminesulfonate (NaDS) was chosen for investigation as an analytical reagent for ozone, after a number of organic compounds were screened for optimum analytical properties. Because its oxidation potential (- 0.85 volt) is appreciably more negative than iodide's (-0.69 volt), i t is less susceptible to oxidative interference than iodide. Further, when interfering reactions do take place, specific colors are formed which differ from the color obtained with ozone. This not only enables the analyst to recogI Present address, Boeing Airplane Co., Seattle 24, Wash.
VOL. 33, NO. 8, JULY 1961
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