dry residue was redissolved in chloro form and analyzed by IR spectrosco py. T h e carboxyl peak at 1750 c m - 1 was also taken as a measure of appar ent tallow concentration. For the GC confirmation, molasses was extracted with p e n t a n e , and fatty acid esters in the extract were saponi fied with base (7). Methyl esters were prepared by refluxing with boron trifluoride esterification reagent. E s t e r s were analyzed on a polyethylene glycol succinate column by use of a flame ionization detector. T h e GC column separates the fat and oil esters accord ing to the sum of carbons and double bonds in the acid and alcohol moieties. Methyl ester extracts of t h e uncont a m i n a t e d molasses (I), uncontaminated molasses plus tallow spikes (II), contaminated molasses (III), and s t a n d a r d tallow (IV) were prepared and assayed by GC. Order of testing was randomized to avoid systematic errors. Reference methyl ester mix tures simulating most fats and oils were injected into the GC. Relative peak areas and retention times of the fat and oil reference (F&OR) mixture made u p of lard, beef, tallow, and palm oil closely matched those of (II), (III), and (IV); similar peaks were absent or of low relative intensity for (I). T h e s e data strongly indicated t h a t residual tallow
adhering to the metal surfaces of the ship's holds had c o n t a m i n a t e d the molasses. T a b l e II compares t h e m e t h yl ester composition of the tallow of unknown origin with F&OR mixtures and library data. A simple b u t effec tive algorithm was developed to iden tify the origin of the tallow based on the fraction of u n m a t c h e d methyl ester composition of a library a n d un known composition. An algorithm was constructed from the methyl ester composition of the seven esters shown in Table II. Slots which were empty, i.e., where the ester was not reported, were filled with zeros to enhance computational effi ciency. Methyl ester compositions were compared on the basis of a dissi milarity index (DI) computed as fol lows. T h e sum of the ester composi tion of each fat a n d oil listed in t h e table equaled 100%. F a t s and oils con taining additional esters were exclud ed in compiling the library. S u m m e d differences (ΣΩ) between the methyl ester composition of the tallow con t a m i n a n t and each library entry were computed. T h e s u m m e d composition of each library entry and the unknown of any two listings (Ct ) equaled 200%. Therefore, DI equaled ΣΩ/Ο,. Note t h a t DI is bounded below by 0 (a per fect match), and above by 1 (a com plete mismatch).
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T h e smallest DI was obtained with the first F&OR mixture shown in the table; the composition of the tallow c o n t a m i n a n t more closely approached this reference mixture t h a n the other five available s t a n d a r d s . For compari son, the next closest reference compo sition is shown in the table. T h e "sen sitivity" of the algorithm to predicting t h e origin of the unknown tallow is striking. T h e algorithm predicts t h a t the tallow is of animal origin, probably N o r t h American beef (DI = 0.10). Quantitative GC analysis of the tal low c o n t a m i n a n t in the molasses, based on the methyl stéarate peak areas, indicated c o n t a m i n a n t levels from 0.4 to 6.6 ppm. T h e confirmed shipboard contamination of the molasses had a profound effect in the sett l e m e n t of this dispute over product liability.
Acknowledgment T h e analytical contributions of coworkers C. Eyer, I. Cabasso, K. L. Crochet, H. Hidalgo, C. G. Lee, L. Truxillo, R. Wawro, and D. Brady are gratefully acknowledged.
References (1) "Official Methods of Analysis (1970) 11th éd.," f) 454, AOAC. Washington, D.C.. 1970.
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1336 A · ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
