Absorbance of Liquid Water and Deuterium Oxide between 0.6 and 1.8 Microns Comparison of Absorbance and Effect of Temperature W. C. WAGGENER Oak Ridge National Laboratory, Oak Ridge, Tenn.
This study was made in connection with the development of an cptical cell for measurement of spectra of ions in aqueous solutions a t elevated temperatures and pressures. The 10cm. absorbances of water and deuterium oxide were compared as a function of temperature from 0.6 to 1.8 microns. The results indicate that measurements of aqueous absorption spectra of metallic ions may b e extended into the infrared by a factor of 1.4 in wave length b y changing from light to heavy water media.
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region available to spectral study in aqueous media may be extended significantly into the near infrared by changing from light to heavy water solvent. The absorption bands observed in liquid water in this region arise from perturbed overtone and combination frequencies, involving stretching and deformation of the 0-H groups (9). Because the frequency of a vibrational system of atoms varies inversely as the square root of its reduced mass, the substitution of 0-D for 0-H shifts the spectrum of deuterium oxide corresponding to that of water by a factor of roughly .\/z towards longer wave lengths (6). Gore, Barnes, and Petersen (5) have compared the transmittance of water and deuterium oxide qualitatively in the infrared range from 2.5 to 15 microns, and, more recently, Evstigneev (4) has done the same in the range from 1.1 to 1.8 microns. Yet the fact that heavy water is much more transparent than ordinary water to radiation in the near infrared has not been widely exploited. This study gives a quantitative picture of the 10-em. absorbance of water and deuterium oxide from 0.6 to 1.8 microns. HE
EXPERIMENTAL
The absorption data were taken with a Cary Model 14111 recording spectrophotometer, provided with its regular thermostated cell compartment (25' C,), and separately thermostated sample cell holder (-So to 85" C.), Two
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Figure 1.
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Absorbance measurements
Sample cell containing HzO or -99.0% - - - - Sample cell containing HzO or -99.0%
. . . . Sample cell containing 99.8%
standard IO-em. fused quartz cells were equipped with long necks, and a No. 30 iron constantan thermocouple junction was mounted in each cell by a small platinum well extending through a Teflon stopper. The entire optical system was purged continuously with dry nitrogen during measurements. Cndispersed radiation was passed through the cells, and the slits were operated automatically t o provide a
DzO at 27-26' C. DzO at 82-63' C. D z 0 at 27-26' C.
constant power signal from the reference beam to the lead sulfide detector. Distilled water and 2 samples of deuterium oxide of nominal 99.8% purity were used without further purification except for removal of dissolved gas by heating the cells a t the boiling point. The older of the two deuterium oxide samples was used in making the first measurements. The newer sample had a mass-spectrographic assay of 99.78 VOL. 30, NO. 9, SEPTEMBER 1958
1569
mole % ' deuterium oxide. By comparing the absorbances of the two a t 1.667 microns and at 1.41 microns (7) a figure of 99.0 mole % ' was estimated for the older. Two types of absorption measurement are illustrated in Figure 1. The A curves represent conventional technique, the absorbance of water being against a nonabsorbing gas, nitrogen, and corrected for surface reflections in the cell. The energy response of the instrument in the near infrared is 3 to 4 absorbance units with slits operating from 0.05 to 3.0 mm.; the span of the measurement scale is 2 absorbance units. By interposing a neutral filter having an absorbance of approximately 2 in the reference beam, the high absorbance portions of the A curves of Figure 1 were measured. The data for water ( A curves) are in good agreement with those of Collins, ( I ) and later work by Curcio and Petty ( 2 ) . No quantitative data for deuterium oxide mere found in the literature. The B curves represent differential temperature absorbance of the sample cell a t a series of temperatures (2 shown) 2's. a reference cell of identical geometry and filling. Resolution data above each set of B curves were estimated from observed slit widths and the dispersion curve for the instrument. DISCUSSION AND RESULTS
This study pertains to the development of an optical absorption cell for measurement of spectra of metallic ions in aqueous solutions a t elevated temperatures. Ordinary water begins to absorb appreciably a t about 0.7 micron (7000 A,) in just the region of occurrence of many of the sharpest absorption bands of ions of the lanthanide and actinide elements. For example, the
strongest bands for neptunium(IV), (V) (a), and (VI) (IO),in 1M perchloric acid occur a t 0.96,0.98, and 1.22 microns, respectively; the first prominent water band maximum occurs at 0.96 to 0.97 micron. More important, the temperature coefficient of the band is strongly positive. Measurements are seriously complicated when a hightemperature absorption cell which has a path length of the order of 5 to 10 cm. is compared t o a solvent reference cell of identical geometry maintained a t room temperature. Because this arrangement of cells is to be used in studies of aqueous metallic ions at 250" C., the A and B curves have been compared over the region of the first prominent absorbance maximum and minimum for water. The corresponding shaded areas were carefully measured n-ith a planimeter, and the areas of the B curves relative to unit area of the A curve are given in Figure 1. These areas are equal within the probable error of measurement, though the small differences in the figures are in the direction expected from a downward shift in wave length of the maximum and minimum absorbance with increasing temperature. Using the B method, families of curves are obtained similar to the two shown in Figure 1. In these, respective envelopes of maxima and minima appear above or below zero absorbance as the sample cell temperature is greater or less than the temperature of the reference cell. The position of the differential temperature maximum lies between the respective absorption maxima US. dry nitrogen a t the two temperatures. The separation of band maxima for n-ater
and deuterium oxide are roughly 1600 and 1200 cm.-l, respectively, which is suggestive of overtones of the symmetrical deformation or bending modes given as 1615 and 1220 cm.-' for water and deuterium oxide ( 3 ) . The 10-cm. absorbance of water and deuterium oxide reach the practical energy limit for the instrument used (A 3) a t 1.14 and 1.77 microns, respectively. Above 0.7 micron for water and 1.2 microns for deuterium oxide, measurements are complicated by differential temperature absorption of the solvent. For study of aqueous solutions a t elevated temperatures in the range 0.7 to 1.14 microns for water, and 1.22 to 1.77 microns for deuterium oxide, it appears necessary to thermostat both sample and reference cell a t the temperature of measurement.
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LITERATURE CITED
(1) Collins, J. R., Phys. Ref). 26, 771 (1925). J. .4., Petty, C. C., J. Opt. (2)- Curcio, . - - - (1951). SOC.Am. 41, 3UL (3) Ellis, J. W., Sorge, B. W., J. Chem. Phus. 2. 559 119kt. ,"\
(4) gvstigneev, ' V. 'B., Doklady Akad. N a u k S.S.S.R. 89, 105 (1935). (5) Gore, R. C., Barnes, R. B., Petersen, E., AKAL.CHEM.21, 382 (1949). (6) Halverson, F., Reus. Modern Phys.
19.87 11947). (7) Lecomte, J.> Ceccaldi, M., Roth, E., J . chim. phys. 50, 1669 (1953).
(8) Sjoblom, R., Hindman, J. C., J. Am. Chem. SOC.73, 174%(1951). (9) . , Sutherland, G. B. B. M., Discussions Faraday SOC.9, 274 (1950). (10) Waggener, W.C., J . Phys. Chem. 62, 382 (1958).
RECEIVED for review November 27, 1957. Accepted May 6, 1958.
Micromethods for Analysis of Petroleum A. R. JAVES and CHRISTIAN LIDDELL Research Station, The British Petroleum Co., Ltd., Sonbury-on-Thames, Middlesex, England
b Geological prospecting for oil frequently produces small samples of oil on which as complete an analysis as possible is required. A scheme of analysis has been devised whereby many of the data given b y a large scale crude oil assay can b e obtained on a 5-ml. sample. Methods for carrying out a number of tests on very small petroleum samples include procedures for specific gravity, aniline point, aromatic content, asphaltene content, bromine number, pour point, setting point, and viscosity. These tests are also suitable for petroleum products other than crude oil. 1570
e
ANALYTICAL CHEMISTRY
I
course of geological prospecting, many small samples of oil are obtained, either from small surface seepages, when the sample may be skimmed from the surface of water pools, swamps, or rivers, or from the extraction of core samples, oil-stained surface rocks, or sands. As complete an analysis as possible is required to determine the origin of the seepage and to correlate with known reservoirs. Some knowledge of the commercial possibilities-i.e., the yields and properties of conventional distillates and rePidues-may also be of value. Frequently the amount of sample available N THE
may only be a few milliliters. Methods have been published (5) for the distillation of these small samples. This paper gives a scheme of analysis in which a number of fractions and residues are obtained by these distillation methods, and describes methods for obtaining inspection data on them. These methods are also suit,able for the analysis of small amounts of other petroleum products. SCHEME OF ANALYSIS
A conventional method for the assay of medium-sized samples of crude oil-
