1096
Anal. Chem. 1981, 53, 1096-1099
were considered, a lifetime of 4 ps is found by taking the log of the curve and calculating the negative reciprocal of the slope. From 212 ps on, the decay is exponential, agreeing, within experimental error, with the lifetime of the exponential decay under 421-nm excitation, where no such plateau occurs. Whether or not these results are due to possible metastable states above the lowest triplet (311,) that renew the emitting electronic transitions, or whether such states are preferentially shielded by the enhancer species, is not immediately clear. However, we were able to resolve the entire enhanced decay with 296-nm excitation into two components, one corresponding to a natural lifetime (about 34 ps equal to unenhanced uranyl solutions), the other to what might be termed phosphate-enhanced decay (about 145 ps). A least-squares fit of the curves yielded coefficients of determination of 0.99 for both lifetime values.
LITERATURE CITED
ps
(1) Considlne, D. M., Ed. “Scientific Encyclopedla”;Van Nostrand Rheinhold: New York. 1976 p 2262. (2) Jablonskl, B. R.; Leyden, D. E. Anal. Chem. 1979, 51, 681. (3) Sakuraba, S.; Matsushlma, R. J . Am. Chem. SOC.1072, 94, 2662. (4) Neely, W. C.; Ellls, S. P.; Cody, R. M. Photochem. Photoblol. 1971, (5) Jorgensen, 13, 503. c, K. J . Lumln. 1979, 18, 19, 63. (6) Marcantonatos, M. D. Inofg. Chlm. Acta 1978, 26, 41. (7) Yokoyama, Y.; Moriyasu, M.; Ikeda, S.J . Inorg. Nucl. Chem. 1976,
38, 1329,
(8) Burrows, H. D.; Kemp, T. J. Chem. SOC.Rev. 1974, 3 , 139. (91 Marcantonatos, M. D. Inorg. Chlm. Acta 1977, 25, L101. ( I O ) $111, C. W.; Peterson, H. E. Anal. Chem. 1947, 19, 646. (11) Reeder, S. W.; Hitchon, B.; Levinson, A. A. Geocblm. Cosmhlm.
Acta 1972, 36,025.
RECEIVED for review November 3,1980. Accepted March 19, 1981.
Determination of Ethanol in Gasohol by Infrared Spectrometry David R. Battiste,” Slaton E. Fry, F. Tom White, M. Wllson Scogglns, and Ted B. McWllllams Phillips Petroleum Company, Research and Development, 342A-PL, Bartlesville, Oklahoma 74004
Measurement of ethanol concenttation In a serlgs of gasohol samples by Infrared (IR) spectrometry ylelded a value of 10.0 f 0.12 vol % at the 95% level of confidence. The 88O-cm-’ absorbance band of ethanol was the analytkal band of choke because of the absence of thls band In other alcohols (methyl alcohol, isopropyl alcohol, n-butyl alcohol, and fed-butyl aicohoi) which could be present In gasohol. The percent ethanol In any type gasoline can be determlned, the purlty of ethanol feed stocks can be ascertained, and the sampilng hardware can be configured for analysis of single samples or process streams.
Because of the increasing use of ethanol in gasoline and because refinery and gasoline terminal operators need an accurate, fast, easy, and relatively inexpensive method to determine the volume percent ethanol in gasoline, we have developed an infrared method for this analysis. Technical Division A of Committee D-2 of the American Society for Testing and Materials (ASTM) defines gasohol as “A motor fuel containing a nominal 10% by volume of denatured ethanol in unleaded gasoline” (1). Analytical methods described in ASTM’s “Proposed Specifications for Gasohol and Leaded Gasohol” include: (1) gas chromatography (GC) of gasohol with use of methanol as an internal standard, (2) GC of a water extract of gasohol, and (3) the volume increase on extraction of ethanol from gasohol into ethylene glycol. Franke (2) described a mass spectrometricmethod of determiningethanol in gasoline in 1961 and Aleksandrov and Tysovskii reported a microwave spectrometric method for this determination in 1966 (3). However, none of these methods meets all of the above criteria. Computerized infrared (IR) spectrometry, on the other hand, has all of the desirable characteristics listed above. One infrared method for determination of ethanol (1-20%) in gasoline has previously been reported (4). This method was developed primarily for use as an experiment in quantitative infrared spectrometry in a course on analytical in0003-2700/81/0353-1096$01.25/0
strumentation and the experimental needs and objectives differ from those of industry. In our infrared method, the spectrum of the base gasoline (Le., unleaded gasoline used to make the gasohol) was subtracted from the spectrum of the gasohol by use of a digital computer to yield the IR spectrum of ethanol. A W i h Model 12 attenuated total reflectance (ATR) accessory, equipped with a zinc selenide (ZnSe) crystal mounted in a liquid ATR cell was used to hold 1 mL of gasohol. The 1200-800-cm-’ region of the IR speCtrum of the base gasoline, standard gasohol, and unknown gasohol was scanned, the subtraction was performed, and the absorbance of the 880-cm-l band of ethanol in standard and unknown was determined. The ratio of the absorbance of the 880-cm-‘ band of the unknown to that in the standard times the volume percent ethanol present in the standard yielded the percent ethanol in the unknown. EXPERIMENTAL SECTION The Perkin-Elmer 580 and 283 infrared spectrometersequipped with Data Stations, and the Digilab FTS-15 were used in development of the infrared method (Perkin-Elmer Corp., Nonvalk, CT; Digilab Inc., Cambridge, MA). The calibration curve and statistical results presented were developed with data obtained on the Perkin-Elmer 580. Routine analyses described for commerical gasohol samples were obtained on the Perkin-Elmer 283 (see Table V). In all cases, the sample holder was a liquid attenuated total reflectance (ATR) cell equipped with a 52 X 20 X 2 mm zinc selenide crystal (45’ face angle) mounted in a Wilks Model 12 ATR accessory. About 1mL of sample was needed to fill one side of the ATR liquid cell. A freshly prepared standard of 10 vol % absolute ethanol in Phillips unleaded gasoline was run at the same time as unknowns were analyzed. Absolute ethanol, obtained from U.S.Industrial Chemicals Co., was used to make the standard gasohol samples. RESULTS AND DISCUSSION The infrared spectra of commonly available alcohols, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and tert-butyl alcohol, which could be found in motor fuels are shown in Figure 1 (I,5). The carbon oxygen stretching band of ethanol at 1050 cm-l could be used as the analytical band 0 1981 Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL.
I -A n-BUTANOIL
1800.
1467. 1300
1633
967.
1133
800
VVAVENUMBER (CM-1)
Table I. Gasohol Calibration Standards absorbances % 1050 880 1050 880 sample ETOH cm-1 d cm-1 a cm-I6 cm-' SEFOl 4.0 0.@599 0.0930 0.3068 0.1315 4.0 0.2672 0.0974 0.3149 0.1366 SEF02 8.0 0.5072 0,1878 0.5479 0.2198 SEF03 SEF04 8.0 0.5002 0.1897 0.5460 0.2207 SEFOS 10.0 0.6157 0.2347 0.6569 0.2651 SEFO6 10.0 0.6305 0.2361 0.6765 0.2635 SEFO7 12.0 0.7514 0.2896 0.7918 0.3152 SEF08 12.0 0.7362 0.2866 0.7782 0.3125 SEF09 16.0 0.9590 0.3802 1.0006 0.4087 SEFlO 16.0 0.9959 0.3855 1.0378 0.4122 a Gasoline spectrum subtracted from gasohol spectrum by use of the 965-cm-l band. Without subtraction.
*
Table 11. Linearity of Calibration Curves calibration correlation curve, cm-' coeff coeff of determn 1050'
Infrared spectra of methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, and teff-butyl alcohol. Flgure 1.
1050
0.9994 0.9997 0.9988 0.9995
880;
1050 880
0
21
53, NO. 7, JUNE 1981 1097
a
With subtraction,
0.9987 0.9994 0.9976 0.9991
Without subtraction.
Table 111. Percent Ethanol in Synthetic Gasohol Samples b
a
1050
u
Y
