ANALYTICAL
662
found to be convenient. For some applications (3) elution with ether followed by chloroform-butanol mixtures was sometimes advantageous. Table I summarizes recoveries obtained for various known acids from both ether and chloroform-butanol chromatograms. The data indicate that the recoveries from Celite columns may be somewhat smaller than those obtained with silica gel (5). Moreover, because acids appearing late on the chromatogram, such as citric (Figure 1, A), are released in increasingly larger effluent volumes, the magnitude of the blank can approach that of the measurement—for example, when 0.1 millimole of citric acid is chromatographed the volume of blank (in ml. of 0.1 N sodium hydroxide) is 12% of the total titration. These methods have been applied in this laboratory in numerous carbon isotope studies of intermediary metabolism (ß, 9, 10). Under the experimental conditions employed, chemically and isotopically pure acids were isolated from a number of biological
CHEMISTRY
(2) Carson, S. F., Mosbach, E. H., and Phares, E. F., J.
Bad.,62,235
(1951). (3) Denison, F. W., Jr., Ph.D. dissertation, University of Texas, 1951. (4) Dische, Z., Biochem. Z„ 189, 77 (1927). (5) Isherwood, F. A., Biochem. J., 40, 688 (1946). (6) Long, C„ Ibid., 36, 807 (1942). (7) Lugg, J. W. H., and Overell, B. T., Australian J. Set. Research, 1, 98 (1948). (8) Marvel, C. S., and Rands, R. D., Jr., J. Am. Chem. Soc., 72, 2642
(1950). (9) Mosbach, E. H., Phares, E. F., and Carson, S. F., Arch. Biochem. Biophys., 33, 179 (1951). (10) Mosbach, E. H., Phares, E. F., and Long, . V., Federation Proc., 10, 226 (1950); Arch. Biochem. Biophys. (1951). (11) Peterson, . H., and Johnson, M. J., J. Biol. Chem., 174, 775 (1948). Í12) Umbreit, W. W., Burris, R. H., and Stauffer, J. F., ‘‘Manometric Techniques and Related Methods for the Study of Tissue Metabolism,” Minneapolis, Burgess Publishing Co., 1946.
systems. LITERATURE
CITED
(1) Anthony, D. S., Mosbach, E. H., and Long, . results.
V.. unpublished
Received for review June 30, 1901. Accepted October 2, 1951. Work performed at the Oak Ridge National Lat^iratory under Contract W-7405-Eng26 for the Atomic Energy Commission.
Iodometric Determination of Ozone Linde
C. M. BIRDSALL, A. C. JENKINS, and EDWARD SPADINGER Air Products Co., Division of Union Carbide and Carbon Corp., Tonauanda, .
V.
for the past 50 years discloses man) contraozone determination. This work was undertaken to clarify the situation and establish a reliable method. A chemical method is described, which proved suitable for ozoneA physical method has been oxygen mixtures containing up to 25% ozone. devised for use as a standard of comparison in testing this chemical method. Comparisons have been made with other chemical analytical methods for ozone. This work should clarify the present unsatisfactory situation regarding the chemical analysis of ozone-oxygen mixtures. As the uses for ozone increase, these methods should be of increasing importance. A survey of the literature
dictory and confusing
on
ozone
statements
concerning methods of
have long been hampered by of analysis. A survey of the literature reveals a host of claims and counterclaims for various methods, mainly modifications of the iodometric method; man\" of these contentions have little experimental basis. The neutral potassium iodide method has been shown to give correct results by Ladenburg and Quasig (4) and Treadwell and Anneler (10). Riesenfeld and Bencker (6) also concluded that neutral potassium iodide gave correct results up to 20% ozone, although they present data only up to 8%. Much of the controversy has been brought about by Riesenfeld’s (5, 7) proposal that the potassium iodide solution be buffered with boric acid. The apparent check (within 2%) of this method with a gas density method is probably fortuitous, for the molecular weight of ozone as determined by the two methods was not run on the same sample of ozone and one analytical result out of three recorded gave an ozone percentage of 107.7 (7). Ruyssen (8, 9) found that boric acid-buffered potassium iodide gave high results, and Krais and Markert (3) questioned Riesenfeld’s contention (5) that the use of a boric acid buffer was necessary. To help clarify the situation, it was decided to study various methods for the determination of ozone in ozone-oxygen mixtures. The methods tested were the neutral and boric acid-buffered potassium iodide and the arsenious acid procedures. Acidified potassium iodide was not considered, because results nearly 50% too high have been repeatedly obtained by this method. A preliminary experimental survey of these procedures using ozone concentrations up to 5 mole % showed that the accuracy of the on
ozone
the lack of a standardized method INVESTIGATIONS
neutral potassium iodide method surpassed that of the boric acid-buffered method. This conclusion was based on a comparison of the chemical analyses with analyses by a physical method similar to that described below. The results obtained in this preliminary survey are given in Table I. In addition, a series of tests was made to determine the effect of the amount of potassium iodide reacted upon the accuracy of the method. An ozonizer with an output of 1.3 mole % ozone was used in these tests and six series of three analyses were made, in which the first and last were on low volumes of the ozone-oxygen mixture and the middle one on increasingly larger volumes. It was found that up to 67% of potassium iodide consumed, the amount used up had no effect upon the result. The pH of several
Table I.
_Mole Pressure change
3.37
4.29
4.28
. 13
4.13
4.21 4.48 4.38 u
6
Results of Preliminary Survey Per
Cent_
Corrected Neutral0 for compressi- iodometric method bility 3,36 3.40 4.39 4.27 4.26 4.33 5.11 4.11 4.19 4.46 4.56
5.23
Absolute Buffered6 iodometric difference, method mole % Oa + 0 04 +0.12 1-0.07 +0.12 4.86 +0.75 4.83 + 0.64 5. 16
+0.70
5.33 +0.77 2% unbuffered aqueous KI solution. 7% aqueous KI solution, saturated with boric acid.
Relative
Error, % + 1.2 + 2,8 + 1.6
-2.4
+ 18. —
2
15.3
+ 15.7
+ 16.9
VOLUME
2 4,
NO.
4,
APRIL
1952
of the potassium iodide solutions was determined after their reaction with ozone. In the range of 12 to 67% potassium iodide consumption the pH ranged from 10.9 to 11.2. The pH of the unreacted potassium iodide solution was 6.59. The arsenious acid method showed some promise, but was not as easily adapted to large ranges of ozone concentration as was the use of potassium iodide solution.
663
of the sensitive sulfuric acid manometer indicated that any change in pressure caused by decomposition was too small to introduce significant errors in the composition. The composition of ozone was computed as follows: P'2> L
X 100
mole % 03
=
2
final pressure. initial pressure and P2 where P¡ Corrections were applied in a few cases where the initial and final temperatures differed slightly. A correction was also applied for deviations from the perfect gas laws for ozone-oxygen has been found to be 0.996 to mixtures. The ratio caled. % 03 After recording the 0.995 over the range 0.1 to 25% ozone. final pressure and temperature, the ozone-oxygen mixture was immediately swept from A through C and through the absorption vessel by oxygen admitted at D. Oxygen was allowed to flow through the apparatus at a slow rate for 15 minutes in order to purge it completely of ozone. =
=
CHEMICAL
The chemical analysis
ANALYSIS
standardized
was
as
follows:
The gas was allowed to pass slowly through a spiral absorption vessel containing 100 ml. of an aqueous 2% potassium iodide
solution. After complete purging of the ozonizer, the solution was acidified with 10 ml. of 1 M sulfuric acid and titrated with 0.1 N sodium thiosulfate. This sodium thiosulfate solution was standardized frequently against a Bureau of Standards sample of potassium dichromate. The composition of the ozone-oxygen mixture was computed as follows:
It was decided, therefore, to make an extensive study of a standardized neutral potassium iodide procedure, in the belief that this would give most quickly the desired result—namely, an analytical method of known accuracy and precision over a specified range. PHYSICAL
METHOD
In order to test the accuracy of any analytical method for ozone it is necessary to establish the concentration of ozone in various ozone-oxygen mixtures by some reliable physical method. Such a method should permit the immediate chemical analysis of the mixture after its concentration has been determined; otherwise decomposition occurring between measurements made by the physical and chemical methods might lead to erroneous conclusions. The physical method used in this investigation is believed to fulfill this requirement. The general method has been described by Warburg {11). The compositions of the mixtures used were determined by the pressure change at constant volume and temperature when part of a known volume of oxygen was converted to ozone in a calibrated ozonizing vessel with a volume of 300 cc. This vessel, shown in Figure 1, was filled with dry high purity oxygen at atmospheric pressure and with stopcocks C and D closed. [This oxygen contained less than 0.1% nitrogen. Oxides of nitrogen present after ozonizing (6% ozone) were less than 5 p.p.m.] After thermal equilibrium had been established', the absolute pressure in the vessel was determined by means of a barometer and the open-end sulfuric acid manometer, E, was observed with a eathetometer. Ozone production was then started. At room temperature the maximum ozone concentration that could be obtained was about 5 mole %. When higher concentrations were desired bulb F was filled with liquid nitrogen and the lower tip of A was immersed in liquid oxygen. Under these conditions, liquid ozone condensed on the surface of F and dripped to the bottom of A, where it was maintained by the low temperature of the liquid oxygen. By this method it was possible to build up the concentration of ozone to about 25 mole %. When enough ozone had been accumulated the high voltage was turned off, the flask of liquid oxygen removed, and the vessel allowed to warm up to room temperature. With liquid ozone evaporating from the bottom of the ozonizer there was always a possibility of explosion and one apparatus was thus destroyed at this point in the procedure. After the vessel and its contents had come to equilibrium at room temperature, the temperature and pressure were again measured. Observations
, ryf ,-a Mole % 03 A
=
11.2 X A -5--svww-— t-
vA
t h iO
v
760
X -U A h í
O
z‘0·10
273.15 +
fiiA X ,100 w
t·,
where V is the volume of the ozone-containing vessel referred to in the description of the physical method, P·; is the final pressure in that vessel, and i2 is the corresponding temperature in degrees
c.
RESULTS
A comparison of the mole per cent of ozone in the various mixtures as determined by the physical and chemical methods is given in Table II. As is apparent from these data, the method may have a small positive bias.
Ozone in Mixtures
Table II.
Ozone, Mole %
By pressure
change 3.33 3.39 3.51 11.72 12,25 12,84 17.42 17.63 20.07 24.27
By neutral iodometric for method compressibility Corrected 3.32
3.38 3.50 11.67 12.20 12.79 17.33 17.54
19.97 24.15
3.31 3.51
3.56
•
11.91
12.76 12.96 17.54 18.11 20.69 23.80
_
Absolute
Difference -0.01
+0. 13 +0.06
+ 0.24
+0.56
+0.17 +0.21 + 0.57 +0.72 -0.29
Relativ
Error,
1
-0.3 + 3.8 -1.7
-2. 1 ++< > + 1.3 + 1.2 + 3.2 + 3.6
A positive bias is also indicated by the data of Treadwell and Anneler {10, page 89) in their investigation of the neutral potassium iodide method. Using the method of assigning rank numbers {12) to the absolute differences, it is found that there is a 95% chance that the data in the second and third columns of Table II are statistically different. If the bias as well as all random error is assigned to the chemical results, it amounts ro a relative correction of —2.0%. Applying this correction, the standard deviation of the relative error is 1.4%. DISCUSSION
After the experimental work described in this paper had been completed, an article on the same subject was published by
ANALYTICAL
664
Boelter, Putnam, and Lash {2). The conclusion of these authors with respect to the neutral potassium iodide method is the same as that reached in the present paper. However, there is considerable difference with respect to the findings when boric acid is used as a buffer; they found no error, whereas the figures in Table I show a considerable difference between results obtained with and without boric acid. Boelter (1) has suggested that this discrepancy mat" be explained by the difference in the war- the was absorbed by the iodide solution. Ir the work of Boelter et al. (ß) the ozone was absorbed directly from the gas phase into the iodide solution in a modified Hempel bulb without much agitation of the solution. When ozone reacts with potassium iodide, potassium hydroxide is a product of the reaction, and as the reaction of ozone with potassium iodide is fast and the diffusion of potassium hydroxide is slow, the liquid surface where the ozone reacted mat' well have been at a higher pH than the bulk of the solution. On the other hand, in the work summarized in Table I of this paper the ozone was swept through a bubbler containing the boric acid-buffered iodide solution. The solution was strongly agitated by the bubbling and the pH at which the ozone was absorbed was therefore1 more nearly that produced by the boric acid—i.e., about 4.6. It is this low pH which brings about the erroneously high results.
ozone
CONCLUSION
In the concentration range investigated (1 to 25 mole %) the of a 2% unbuffered aqueous solution of potassium iodide for the analytical determination of ozone gives precise results which use
CHEMISTRY
accurate to 2cj when compared with a physical method use of boric acid as a buffer is unnecessary and can lead to erroneous results. are
The
ACKNOWLEDGMENT
The assistance of J. A. Beattie of the Massachusetts Institute of Technology in the computation of the deviation from the perfect gas laws for ozone-oxygen mixtures is greatly appreciated. A considerable portion of this work was performed under contract for the Bureau of Aeronautics, United States Xavv. LITERATURE
CITED
(1) Bucher, E. D., private communication. (2) Boelter, E. D., Putnam. G. I... and Lash. E. L, Anal. Chem.. 22, 1533 (1950). (3) Krais, P.. and Markert, H., Angeie. Chem.. 45, 309 (1932). (4) Ladenburg, A., and Quasig, R.. Ber.. 34, 1184 (1901). (5) Riesenfeld, E. H.. Angeu·. Chem.. 45, 309 (1932). (6) Riesenfeld, E. H,, and Beneker, F.. Z. nnorg. Chem.. 98, 167
(1916). Riesenfeld, E. H., and Schwab, G.. Ber.. 55, 2092 (1922). Ruyssen, R., Xatuune. Tijdschr.. 14, 245 ¡1932). Ihid., 15, 6-13 (1933). Treadwell, F. P., and Anneler, K.. Z. nnorg. Chem., 48, 86 (1906). (11) Warburg, E., Ann. Phijsik.. (IV) 9, 1286 (1902). (12) Wllcoxon, Frank, American Cyanamid Co., “Some Rapid Approximate Statistical Procedures," 1949.
(7) (8) (9) (10)
Received
for review July 27,
19.11.
Accepted .January 24. J952.
Ultraviolet Spectrophotometric Study of Eugenol-lsoeugenol System V. C. VESPE AND D. F. BOLTZ, Wayne University,
spectrophotometric study of eugenol to ascertain the and isoeugenol was undertaken effect of position of the double bond in the side chain on the ultraviolet absorption spectra and to devise a spectrophotometric method for determinEuing these compounds in synthetic mixtures. genol and isoeugenol have characteristic ultraviolet absorption spectra amenable to the spectrophotometric analysis of a two-component system. The optimum wave lengths fór absorbancy measureAn ultraviolet
l-hydroxy-2-methoxy-4-allylbenzene, and isoEUGENOL, eugenol, l-hydrox3"-2-methoxy-4-propenylbenzene, are two constituents found in many essential oils and synthetics. The purpose of this investigation was to compare the ultraviolet absorption spectra of these isomers and to explore the possibility of a simultaneous ultraviolet spectrophotometric determination of these two constituents in synthetic mixtures. A survey of the literature showed that the spectrophotometric method had not been applied to this problem (8-6), although the ultraviolet absorption spectra of cis- and irans-isoeugenol and eugenol have been determined (9). GENERAL
EXPERIMENTAL
WORK
Apparatus. The absorbancy measurements were made with a Beckman Model DLT spectrophotometer and 1.000-cm. quartz cells. Reagents. Eugenol and isoeugenol, USP XIII grade, Fritzsche Bros., were distilled at reduced pressure until samples gave the
Detroit, Mich.
and molar absorbancy indexes were deterThe double bond in conjugation with the benzene ring in the case of isoeugenol resulted in the existence of an absorbancy maximum at a lower wave length than for eugenol and a much larger molar absorbancy index. Simultaneous spectroof eugenol and isophotometric determination eugenol was possible in solutions in which the eugenol-isoeugenol ratio varied from about 0.5 to 50, concentration of eugenol being 10-4 to I0-i molar. merits
mined.
required refractive index values. Ethyl alcohol and water were used as solvents. General Procedure. A definite amount of each liquid was weighed in a weighing bottle and transferred by washing with ethyl alcohol to a 100-ml. volumetric flask and the volume was adjusted to the mark with ethyl alcohol. Aliquots of this solution were then transferred to a 1-liter volumetric flask and diluted to the mark with distilled water. Absorbancy measurements were taken from 220 to 350 mg at 2-mg intervals. Distilled water was used in the reference cell. RESULTS
AND DISCUSSIONS
Ultraviolet Absorption Spectrum of Eugenol. Curve 1 in Figure 1 shows the ultraviolet absorption spectrum of eugenol. The curve is characterized by an absorbancy maximum at 279 mg. Beer’s law was found to apply at wave lengths 254 and 282 mg for concentrations ranging from 0 to 60 p.p.m. of eugenol. The reason for selecting these wave lengths for testing for con-
