2578 Anal. Chem. 1986, 58, 2578-2581 A I I I FiBER 1 I I 5 IO 15 20 25 MiNUTES Flgure 3. zyxwvutsrqpon Pyrograms of carrot fiber and pectin derived therefrom. PY-GC. Statistically similar linear relationships between area of the methanol peak and DM were observed whether or not the mixtures were included in the data analysis. Apparently, even though the chemical environment around methoxy groups for a given DM is different within a polymer molecule than in a mixture of polymers prepared to simulate that DM, the chemistry of methoxy fragmentation is influenced mini- mally. For conditions described in the Experimental Section, a linear model % DM = 2.34 Area (MeOH) + 1.22 was derived with coefficient of determination of 95% and coefficient of variation (CV) of 11.71. zyxwvutsr Thii CV is comparable to CV reported in the literature for other methods used to determine DM (7). The amount of methanol measured in these pyrolysis ex- periments was calculated to represent 40-50% of known methylated galacturonate units. This diminished value could result from incomplete pyrolysis or from secondary reaction of methanol. The latter is more probable. Another peak eluting at 4.2 min, identified tentatively as formaldehyde, correlated negatively (correlation coefficient = -0.92) with DM but to a lesser extent than methanol. This was the last peak discarded during the regression analysis. The major source of formaldehyde likely is the unesterified carboxyl groups. Figure 3 depicts a pyrogram of carrot pectin together with one of carrot fiber. The similarities of the two profiles and to the profile of citrus pectin are evident. Nevertheless, only 35% DM was calculated from the area percent of methanol and linear model given earlier, whereas the value was known to be greater than 75%. When the three-parameter model was used, 50% DM was found. The discrepancy is likely related to matrix effects and demonstrates that models derived for pectins from one fruit source cannot be generalized to pectins from other plant sources. This observation does not detract from the method presented here but supports the concept that calibrations must be derived from similar sub- strates for acceptable quantatitive information to be generated. ACKNOWLEDGMENT The authors thank Edwin Piotrowski for performing the mass spectrometry experiments and Peter Hoagland for supplying carrot fiber and pectin. Registry No. Pectin, 9000-69-5;low-methoxyl pectin, 9049- 34-7. LITERATURE CITED (1) Fishman, M. L.; Pfeffer, P. E.; Barford, R. A,; Doner, L. W. J. Agric. FoodChem. 1984, 32, 372-378. (2) Rees, D. A.: Wight, A. W. J. Chem. Soc. zyxw B 1971, 1366-1372. (3) Fishman, M. L.; Pepper, L.; Pfeffer, P. E. Polym. Mater. Sci. Eng. (4) Kertesz, 2. I. The Pectic Substances: Interscience: New York. 1951; Chapter 111. (5) Schuitz, T. H. Methods in Carbohydrate Chemistry; Whistler, R. L., Ed., Academic Press: New York, 1954; Voi. 5, pp 189-194. (6) Waiter, R. H.; Sherrnen, R. M.: Lee, C. Y. J. Food Sci. 1983, 48, 1006-1007. (7) McFeeters, R. F.; Armstrong. S. A. Anal. Biochem. 1984, 139, 2 12-2 17. (8) Irwin, W. J. Analytical Pyrolysis; Marcel Dekker: New York, 1982; p 343. 1984, 51. 561-565. (9) Shuiten, H. R.; Bahr, V.; Giirtz. W. J. Anal. Appl. Pyrolysis l9Sll 1982. 3. 229-241. (10) Zamorani. A.; Roda, G.: Lanzarini, G. Ind. Agrar. 1971, 9, 35-40. (11) McReady, R. M. In Methods in Carbohydrate Chemistry: Whistler, R. L., Ed.: Academic Press: New York, 1965: pp 166-179. (12) Wood, P. J.; Siddiqui, I. R. Anal. Blochem. 1971, 39, 418-428. (13) Afifi, A. A.; Azen, S. P. Statistical Analysis: A Computer Oriented Approach; Academic Press: New York, 1972: pp 252-259. (14) Draper, N. R. and Smith, H. In Applied Regression Analysis, 2nd ed.; Why: New York, 1981; pp 294-352. RECEIVED for review January 7, 1986. Resubmitted June 4, 1986. Accepted June 9, 1986. Capillary Gas Chromatography/Fourler Transform Infrared Spectroscopy Using an I njector/Trap Allen J. Fehl* and Curtis Marcott zyxwvutsr The Procter & Gamble Company, Miami Valley Laboratories, Cincinnati, Ohio zyxwvu 45247 Capillary gas chromatography/Fourier transform infrared (GC/FT-IR) spectroscopy can be a very useful tool in mo- lecular analysis, especially regarding isomer identification (I). The technique has, however, suffered classically from a lack of sensitivity. Recent attempts have been directed at in- creasing overall sensitivity by reducing system noise through the use of small-area detectors and optical revisions that preclude lightpipe emission from reaching the detector (2). Another option for bettering sensitivity is to increase signal by injecting more sample. This is, however, not easily done because of chromatographic restrictions. Samples concen- trated in solvent or collected from headspace over materials of interest are not readily introduced zyx to a capillary GC because of the large volumes of solvent (or air) present with the sample. 0003-2700/86/0358-2578$01.50/0 0 1986 American Chemical Society