by ASTM D 3326-74T? If so, how did they make the a priori decision that these two were crudes? Were the other two unknowns subjected to distillation; if not, why not? The ASTM procedure does not provide for any such flexibility.
pendent distillation is the desirable procedure. However, by not following independent distillation, this procedure produced a larger sample size (for the same amount of time and effort), which is important for better calibration of the
LDF's.
LITERATURE CITED (1) F. K. Kawahara and Y. Y. Yang, Anal. Chem., 48, 651 (1976).
(2) W. J. Dlxon, "Biochemical Computer Programs", University of California Press, 1973. (3) C. W. Brown, M. AhmadJian, and P. F. Lynch, "Weathered PetroleumProbabilityof identification by Infrared Spectroscopy", Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1-5. 1976, Abstract 322.
James S. Mattson Center for Experimental Design and Data Analysis U.S. Department of Commerce National Oceanic and Atmospheric Administration Environmental Data Service Washington, D.C. 20235
RECEIVEDfor review, April 23, 1976. Accepted August 13, 1976.
Sir: The twofold objectives of our study were to characterize correctly an unknown sample from among several known groups of the products studied and subsequently identify correctly that unknown to a specific source. In step one ( I ) , the unknown is characterized by one of the three LDFA (1'inear discriminant function analysis). These three LDF's were calibrated with known No. 6 oils, asphalts, or crude oil resi, dues. In step two, the characterized unknown is finally identified to a source by using the appropriate set of LDF's for one of these three groups selected in step one. For example, assume that the unknown was initially characterized in step one as an asphalt. In step two the 19 LDF's for asphalt alone were used to identify which one of the 19 asphalts matched the characterized unknown. The one-step LDFA procedure was tried and failed as stated in reference (2). If via a one-step process the unknown were identified to a source without characterization, then we agree with Dr. Mattson that this one-rltep procedure would place more emphasis on precision. The sequential two-step LDFA procedure places less emphasis on laboratory precision. Independent distilltion for each subsample (aliquot) was not carried out because of lack of time. We agree that inde-
Information regarding the preparation of samples for analysis follows: The sixteen unknowns (subsamples) of Table I1 are taken from four independent samples. Two crude oil samples (unknowns) comprised of eight subsamples were fiist subjected to distillation required by ASTM D3326-74T (3), which requires that residues are analyzed after removal of volatiles boiling below 280 "C. These crude oil unknowns were designated as such when the samples were sent by the oil testing coordinator (an employee of a large petroleum company). The other two unknowns (river samples) designated as being asphalt and No. 6 fuel oil, respectively, by the Coast Guard were not subjected to ASTM D3326-74T distillation, since neat asphalts characteristically have a starting boiling point at about 275 "C. Neat No. 6 fuel oils characteristically boil initially at about 260 "C. End points of both products are above 600 "C. The unknowns from the river and knowns from the source were treated alike and dried at 100 "C at 0.02-mm pressure for 30 min under nitrogen atmosphere. Since more than 95% of the material in neat No. 6 fuel oils and 100%of neat asphalt boil above 280 "C, the neat asphalts and No. 6 fuel oils were not distilled in accordance to ASTM D332674T.
LITERATURE CITED (1) F. K. Kawahara, J. F. Santner, and E. C. Julian, Anal. Chem., 46, 266
(1974). (2) F. K. Kawahara and Y. Y. Yang, Anal. Chem., 48, 651 (1976).
(3) ASTM D.3326-74T, Annual Book of ASTM Standards, Part 31 (1974).
F. K. Kawahara*
P&C Branch, EMSL Office of Research & Development EPA Cincinnati, Ohio 45268
J. F. Santner N.T.C., MOTD Office of Water Program Operations Office of Water and Hazardous Material EPA Cincinnati, Ohio 45268 RECEIVEDfor review May 24, 1976. Accepted August 13, 1976.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 13, NOVEMBER 1976
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