ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
nology. However, the ultimate utility of these procedures will depend on whether or not correlations between the average molecular structure parameters and process conditions can be found. Studies to determine such correlations are in progress.
ACKNOWLEDGMENT The author expresses his appreciation to R. H. Pahl for preparing the samples and to Carol Collier for obtaining the proton NMR spectra. LITERATURE CITED (1) H. C. Anderson and W. R. K. Wu, Bull. U.S. Bur. Mines, No. 66 (1963). (2) A. G.Sharkey, Jr., J. L. Shultz, and R. A. Frledel, Fuel, 41,359 (1962).
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(3) D. L. Wooton, H. C. Dorn, L. T. Taylor, and W. M. Coleman, Fuel, 55, 224 (1976). (4) H. C.Dorn and D. L. Wooton, Anal. Chem., 48, 2146 (1976). (5) H. L. Retcofsky and R. A. Friedel, "Spectrometry of Fuels", R. A. Friedel, Ed., Plenum Press, New York, N.Y., 1970,p 70, p 99. (6) F. K. Schweighardt, H. L. Retcofsky, and R. A. Friedel, Fuel, 55, 313 (1976). (7) R. J. Pugmire, D. M. Grant, K. W. Zilm, L. L. Anderson, A. G. Oblad, and R. E. Wood, Fuel, 56,295 (1977). ( 8 ) R. B. Williams, "Symposium on Composition of Petroleum Oils, Determination and Evaluation", ASTM Spec. Tech. Pub/., 224, 168 (1958). (9) S.A. Knight, Chem. Ind., 1967,1920. (10) D. R. Clutter, L. Petrakls, R. L. Stenger, Jr., and R. K. Jensen, Anal. Chsm., 44, 1395 (1972).
RECEIVED for review January 23, 1978. Accepted April 28, 1978.
Analysis of Commercial Chloroform for Chloromethyl Methyl Ether by Fourier Transform Infrared Spectrometry S. R. Lowry" and J. D. Banzer T. R. Evans Research Center, Diamond Shamrock Corporation, Painesvllle, Ohio 44077
Chloroform solutions have been analyzed for trace amounts of chloromethyl methyl ether (CME) using Fourier transform Infrared (FTIR) spectrometry. The signal averaging Capability and high sensitivity of the FTIR system were essentlal in overcoming the strong absorbance of the chloroform. CME was detected In standard solutions contalnlng as little as 1 ppm of CME. NOCME could be detected in samples of cornmerclal chloroform.
amounts of commercial CME (Eastman Organic Chemicals). Solutions in the low ppm region were obtained by diluting diquots from a 2000-ppmstock The were run in a sealed liquid cell with a -2-mm path length. All the infrared spectral data described in this study were obtained with a Nicolet 7199 FTIR system; 4096 data points were acquired for each interferogram, and an 8192 point transform was calculated utilizing the Happ-Geyzel apodization function shown below.
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There is evidence in the literature ( I ) that chloromethyl methyl ether (CME) is carcinogenic. This is of concern because CME could possibly be formed in the production of methyl chloride by chlorination of dimethyl ether, a byproduct. When methyl chloride is subsequently chlorinated to produce chloroform, CME will codistill and contaminate the finished chloroform. A method was needed for the detection and measurement of possible trace levels of CME in chloroform. Although chromatographic procedures have been reported for determining CME ( 2 , 3 ) ,major instrument modifications would be required to prevent interference from the chlorinated solvent. In order to avoid these difficulties, other methods of analysis were sought. Because of the high sensitivity and spectral subtraction capability of Fourier transform infrared spectrometry (FTIR),a simple method utilizing this technique appeared feasible ( 4 , 5 ) . A study of this nature also offered an opportunity to determine the limitations of the instrument in the detection of trace components. This paper discusses the results of the analysis of CME in chloroform by FTIR spectrometry.
where D(i)is the ith value of the difference spectrum, A,(i) and A,(i) are the ith values of the sample and reference spectra in absorbance units, and x, is a scaling factor. For the work reported here, x , was always close to 1 because the small amounts of CME in the solutions produced a negligible concentration effect. However, small adjustments in x, frequently improved the baseline in the region of interest. The criteria for subtraction were a flat baseline and the disappearance of the peaks around 2000 cm-'.
EXPERIMENTAL Reference chloroform was prepared by washing propellant-grade chloroform (inhibited with 300 ppm 2-pentene) with dilute KOH solution, drying with anhydrous sodium sulfate, and storing over a molecular sieve. This procedure will hydrolyze any CME which might be present and will remove residual water. Standard solutions were prepared with this reference chloroform and known
RESULTS AND DISCUSSION Spectra were obtained from a sample of reference chloroform and from a 2000-ppm solution of CME in chloroform. Although the spectra are dominated by peaks corresponding to the chloroform vibrational modes, measurable differences can be seen in the two spectra. Figure 1 shows these two spectra and the difference spectrum that resulted from
0003-2700/78/0350-1187$01 .OO/O
where ni is the ith data point from the zero path difference point and N is the total number of data points after the one at zero path difference. This apodization function yields a final spectrum with smaller side bands than the boxcar function and narrower peak widths than the triangular apodization function. The signal-to-noise ratio was improved in the spectra by co-adding 400 interferograms before performing the Fourier transform. In order to eliminate any discrepancies due t o a mismatch of sample and reference cells, all spectra were obtained with a single cell. A spectrum of the reference chloroform was subtracted from each sample spectrum using the software supplied with the system. This difference mectrum is calculated as shown below.
0 1976 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
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Flgure 1. (A) Spectrum of 2000 ppm CME in chloroform. (B) Spectrum of reference chloroform. (C) Difference spectrum showing CME
spectral subtraction. A minor problem of computerized data manipulation is revealed in Figure 1C. When mathematical operations are performed on spectral data with totally absorbing regions, several forbidden processes may occur (division by zero, log 0, and word overflow). While the computer attempts to compensate for these operations, artifacts frequently appear in those spectral regions of the difference spectra where the initial spectra had no transmittance. However, no mathematical manipulation of the spectra can create meaningful information in those regions where total absorbance occurs. When those regions of the spectrum were ignored, the difference spectrum in Figure 1compared favorably with the Coblentz reference spectrum of CME (6). The peak at 1115 cm-l was chosen for the analysis of CME in chloroform based on the data in Figure 1. This peak corresponds to the C-0 stretching mode of the ether. Even though the large chloroform peaks a t 1220 cm-l and 1030 cm-' contributed significantly to the absorbance in this region, the FTIR instrumentation was sufficiently accurate that spectral subtraction produced adequate compensation at 1115 cm-l. This is demonstrated in Figure 2, where the absorbance spectrum of chloroform is subtracted from the spectrum of a 20-ppm solution of CME. While the original difference spectrum (C) appears featureless, a scale expansion of 100 reveals the 1115 cm-I peak quite clearly. A series of spectra were obtained from solutions containing measured amounts of CME (20,15,10, 5 , 2, 1 ppm). These spectra were acquired for the purposes of developing a calibration curve and determining detection limits. Figure 3 shows the spectra from these solutions in the region from 1150 cm-' to 1050 cm-'. Although the large scale expansion required in this figure did reveal a noticeable amount of noise, the peak at 1115 cm-l was detectable even in the spectrum from the 1-ppm solution. A calibration curve was developed from the data shown in Figure 3. A baseline was obtained for each spectrum by visually estimating the points where the peak ended, and subtracting this line from the spectra utilizing the FTIR software. The absorbance data were linear in the concentration range from 1-20 ppm. Least squares analysis indicated that the data fit a straight line with a residual variance of 0.113 X absorbance unit for the six measurements. While the choice of baseline may be somewhat ambiguous because of
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Flgure 2. (A) Absorbance spectrum of 20 ppm CME. (B) Spectrum from reference chloroform. (C) Dlfference spectrum. (D) Dlfference spectrum scale expanded 100 tlmes
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Figure 3. Absorbance at 1115 cm-' for standard solutions
the presence of noise, the linearity of the calibration curve indicated that even in the 1-ppm case, a reasonable baseline can be determined. Spectra were obtained from a number of samples of production chloroform, and from samples of the reference chloroform. The top trace in Figure 4 is the difference spectrum from two samples of the reference chloroform. Any fluctuations from a totally flat line can be attributed to noise inherent in the experiment. The magnitude of this noise determines the detection limits of the method. The second trace in Figure 4 is the difference spectrum of production chloroform and a sample of the reference chloroform. Any peaks in this spectrum are caused by differences in the two chloroform samples, or by experimental noise. The important observation is the lack of any peak a t 1115 cm-l. While most of the spectra in this study were obtained by co-adding 400 interferograms and then performing the Fourier transform, the actual spectra can also be combined to further reduce the noise. Since four separate spectra were obtained from both production chloroform and the reference chloroform, coaddition can be utilized to produce two spectra which are equivalent to signal averaging 1600 times. If the noise is assumed to decrease as the square root of the number of scans, the signal-to-noise ratio should improve by a factor of 2 in the
ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
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Flgure 4. (A) Dlfference spectrum from two samples of reference chloroform. (B) Dlfference spectrum from a spectrum of technlcal chloroform and the reference spectra. (C) Dlfference spectrum after co-addition of four spectra
final difference spectrum. These results are shown in the bottom trace of Figure 4. Once again, no peak corresponding to the presence of CME is seen. One important factor which has not been discussed is the observation that the CME standards decompose on standing. Work which hm been reported in the literature (7,8) indicated that CME was rapidly hydrolyzed by water. The presence of small amounts of water in the reference chloroform or even water adsorbed on the windows of the cell may explain the
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decomposition of the CME. Because of this decomposition, a fresh 2000-ppm solution was made for each series of standards, and the final standard solutions were each run immediately after preparation. Decomposition was particularly significant for the low concentration standards, where the large amount of co-addition required to reduce noise took sufficiently long (- 10 min) that the already small peak was reduced further. Thus, decomposition of the sample nullified any improvement gained by reducing the noise, Four hundred co-addition spectra appeared to give a reasonable trade-off between decomposition and noise reduction, Further reduction in noise level would require co-adding spectra from several freshly prepared solutions in a fashion similar to that described for the samples in Figure 4. This work has clearly demonstrated that chloromethyl methyl ether can be detected in standard solutions at the 1-ppm level. Examination of technical grade chloroform by FTIR spectrometry gave no evidence that CME was present. Although the CME solutions do degrade with time, the linearity of the calibration curve demonstrates that this problem can be solved by rapid analysis of the solutions.
LITERATURE CITED (1) S. Laskln, R. T. Drew, V. Capplello, M. Kuschner, and N. Nelson, Arch. Envlfon. Health, 30, 70 (1975). (2) R. A. Solomon and G. J. Kallos, Anal. Chem., 47, 955 (1975). (3) G.J. Kallos, W. R. Albe, and R. A. Solomon, Anal. Chem., 49, 1817 (1977). (4) P. V. Allen and A. J. Vanderwlelen, Anal, Chem., 49, 1602 (1977). (5) P. R. Grifflths, "Chemlcal Infrared Fourler Transform Spectroscopy", John Wlley and Sons, New York, N.Y., 1975. (6) Coblentz Soclety Spectra, Spectrum No. 6530, 1970. (7) T. C. Jones and E. R. Thornton, J . Am. Chem. SOC.,89,4883 (1987). (8) J. C. Tou and G. J. Kallos, Anal. Chem., 46, 1866 (1974).
RECEIVED for review January 19,1978. Accepted May 1,1978.
Analysis of the Isomeric Methylchrysenes by Matrix Isolation Fluorescence and Fourier Transform Infrared Spectrometry P. Tokousbalides, E. Ray Hinton, Jr., Richard B. Dickinson, Jr., Paul V. Bilotta, E. L. Wehry," and Gleb Mamantov* Department of Chemistry, University of Tennessee, Knoxville, Tennessee 379 16
The matrix isolation ( M I ) Fourler transform infrared and molecular fluorescence spectra of the six isomeric monomethylchrysenes are compared. Each one of the six isomers can be identified, in mixtures containing all six compounds, by M I fluorescence spectrometry. Unambiguous identification of four of the six isomers can be achieved in six-component mixtures by M I Fourier transform infrared spectrometry. Quantltatlon of the methylchrysenes, individually and in mixtures, by M I spectrometry is described. The M I spectra of the methylchrysenes are compared with those of other polycyclic aromatlc hydrocarbons which are not readily separated from the methylchrysenes.
Structural isomers of polycyclic aromatic hydrocarbons (PAHs) often exhibit strikingly different levels of carcinogenic potential. For example, benzo[a]pyrene is a notoriously hazardous compound, whereas its structural isomer, benzo-
[elpyrene, is comparatively innocuous ( I ) . The position of substitution in alkylated PAHs can also have drastic effects upon tumor-initiating ability and carcinogenicity. For example, there are six isomeric monomethylchrysenes (molecular formula CI9Hl4);these compounds have been reported to be present in coal liquefaction products (2)and cigarette smoke condensate ( 3 ) . Of these six isomeric compounds, 5methylchrysene is among the most actively carcinogenic PAHs yet identified (almost identical in potency as a complete carcinogen to benzo[a]pyrene), while the remaining five methylchrysenes and the parent PAH are much less strongly carcinogenic ( 4 , 5). Assessment of the potential health hazard associated with mixtures of isomeric PAHs thus frequently requires identification and quantitation of individual compounds; "class analyses" of groups of isomeric compounds, while valuable, may lead to overestimates of the carcinogenic potential or toxicity of a given sample. Identification and quantitation of individual methylchrysenes in mixtures containing all six
0003-2700/78/0350-1189$01.00/0@ 1978 American Chemical Society
