ods (9) as well as adsorbing agents, such as alumina (IO, 1 1 ) and silica gel (2), are useful for removal of ethanol from chloroform, we found that simple overnight standing of commercial chloroform over Type 4A molecular sieve was extremely effective for this purpose. This was shown by comparing infrared spectra of the commercial, ethanol-stabilized CHC13 measured vs. itself and vs. the sieve-treated CHC13 as reference. Whereas in the former case a well compensated straight line was obtained, in the latter case the spectrum of a dilute solution of ethanol was recorded (e.g., bands a t 3630, 2980, 2900, 1050, and 880 cm-'), indicating successful removal of ethanol from the CHC13 in the reference cell by the molecular sieve treatment. Indeed, when the infrared spectrum of the sample of Nd- +caprolactam was remeasured in the ethanol-free chloroform (vs. the same chloroform as reference) no evidence for deuterium-hydrogen exchange was discerned (absence of U N H absorption a t 3420 cm-l), and the spectrum was that for the pure N-d-lactam (Figure 1C). (The U N D region differs from that observed in CC14 solution, Figure l A , because of the difference in the degree of hydrogen-bonded self-association of the lactam in the two solvents.) This result (cf. Figures 1B and 1C) clearly confirms the interference from ethanol in the obtaining of spectra of the N-dlactam in commercial chloroform solution. We have noted this interference further with other N-d-lactams and also with N-deuterio open-chain primary and secondary amides as well. Presumably such D-H exchange would also be a problem with any compound having readily exchangeable deuterium atoms, such as 0-d-carboxylic acids and alcohols, although an investigation of the full extent of the problem has not been undertaken. In any case, as a precaution the admonition to remove ethanol from commercial chloroform prior to using it as a solvent for deuterated compounds should be heeded.
CONCLUSIONS When commercial reagent or spectrophotometric grade chloroform is used as a solvent in infrared spectrophotometry, failure to remove the ethanol used as stabilizer therein can cause loss of the isotopic label of certain deuterated compounds via deuterium-hydrogen exchange involving the alcohol. Since the procedure for removing the ethanol can be as simple as allowing the solvent to stand over molecular sieve for a time, this operation could well be made a matter of routine practice generally whenever chloroform is used as a solvent for infrared spectrometric work. However,
3500
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1000
8lm-1,
Figure 1. Partial infrared spectra of 0.10 Msolutions of N-d-c-caprolactam
(0.I - m m pathlength cell).
(A) in CCI4, ( B ) in commercial reagent-grade CHC13 containing 0.5% ethanol as stabilizer, ( C ) in ethanol-free CHC13
the purified chloroform should be protected from bright illumination and used immediately, since HC1 (as well as phosgene) is generated upon exposure of the unstabilized solvent to light and air (9). This precaution is especially important in the spectrometric determination of basic compounds, whose infrared spectra may be affected by protonation by dissolved HC1.
LITERATURE CITED (1) F. Halverson, Rev. Mod. Phys.. 19, 87 (1947). (2) A. R. H. Cole in Technique of Organic Chemistry", Vol. Xi, Part 1, A. Weissberger, Ed., Interscience Publishers, New York, N.Y., 1963, p 137. (3) R . T. Conley, "Infrared Spectroscopy", Aiiyn and Bacon, Boston, Mass.; 1966, p 64. (4) L. F. Fieser and M. Fieser, "Reagents for Organic Synthesis", John Wiley and Sons, New York, N.Y.. 1967, p 703. (5) A. Koshimo, J. Appl. Po/ym. Sci., 9, 55 (1965). (6) S. E. Krikorian, T. A. Andrea, and M. Mahpour. submitted for publication in Spectrochim. Acta. (7) A . V. logansen and M. Sh. Rozenberg, Zh. Prikl. Spektrosk.. 9, 1027 (1968). (8) U. Liddel, Ann. N.Y. Acad. Sci., 69, 70 (1957). (9) J. A. Riddick and W. B. Bunger. in "Techniques of Chemistry", Vol. 11, 3rd ed., A. Weissberger, Ed., Wiley-lnterscience, New York. N.Y., 1970, p 771. (10) G. Wohlleben, Angew. Chem., 66, 752 (1956). (1 I)K.B. Whetsel and J. H. Lady, J. Phys. Chem., 68, 1010 (1964). "
RECEIVEDfor review August 7, 1975. Accepted October 1, 1975.
Infrared Analysis of Weathered Petroleum Using Vacuum Techniques Chris W. Brown* and Patricia F. Lynch Department of Chemistry, University of Rhode Island, Kingston, R.I. 0288 7
Treatment of unweathered oils with warm salt water and subsequent evacuation of the dried sample, was found to simulate the natural weathering of oils which had been in the marine environment for 2-7 days. This treatment provides a quick, accurate method for correctly matching the fingerprint of a spill sample to the source. Furthermore, It
gives Insight into the Initial changes of an oll during weathering.
The identification of the source of weathered oil presents a problem to investigators in the environmental-analytical field. It is a problem because the chemical components of ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
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Figure 1. infrared spectra in the 6 5 0 - 1 2 0 0 cm-' region of (a) unweathered crude (172), ( b ) crude (172) weathered 7 days, ( c )unweathC and 5 X Torr for ered crude (172) which had been evacuated at 35 ' 1 hr, (U) unweathered crude (172) which had been treated with warm (35 "C) NaCI/H20 prior to evacuation at 35 "C and 5 X Torr for 1 hr
petroleum are altered on exposure to the marine environment, changing the identity of the sample to some degree. Therefore, the success of any analytical fingerprinting technique must depend on its ability to accommodate these changes and yet retain its ability to discern enough unique characteristics in the weathered sample to make correct source identification possible. Over the past three years, we have developed an infrared fingerprinting method for the identification of crude and refined petroleum, and subsequently have studied the effect of weathering on over 60 different oils (1-7). The information obtained from these studies has led to the refinements in the infrared identification method. Herein, we report on the feasibility of using vacuum treatment to improve the identification method. Others (8-11) have explored the use of infrared spectrometry to identify petroleum but, to our knowledge, the effects of vacuum on petroleum have not been investigated.
EXPERIMENTAL Infrared spectra of the samples were measured on a PerkinElmer Model 521 infrared spectrophotometer. The spectral slitwidth of the instrument was
