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Anal. Chem. 1981, 53, 1706-1708
All A,' type ions (Ani - CO and /or A,' - NH3) required for sequence analysis are present except A6+. Accordingly, the order of the two amino acids at the C terminus is ambiguous. This situation can be resolved by searching the spectrum for either the Zlf ion or the fragment ion having the formula NH2CHRCONHCHRCO+,derived from the Z3+species. In Figure 1D this latter ion occurs at m / z 235 and defines residues 5 and 6 as His-Pro rather than the alternative, His-Phe. The above results suggest a new strategy for sequencing proteins and oligopeptides. We envision that this will entail degradation of the protein to peptides, the optimal length of which will be determined by the mass range of the available mass spectrometer (1000-3000 amu) rather than by the volatility of the mixture components. The mixture of peptides will then be fractionated by high-pressure liquid chromatography and each fraction will be analyzed directly, without further purification, by the combination of secondary ion/ collision activated dissociation mass spectrometry on a multianalyzer instrument. Generation and analysis of the peptides could be completed in a matter of hours. ACKNOWLEDGMENT The authors thank P. J. Gale and C. Magee for several helpful discussions. LITERATURE CITED (1) Biemann, K. "Biochemical Applications of Mass Spectrometry"; Waller, 6. R., Dermer, 0. C., Eds.; Wiiey: New York, 1980 First Suppiementary Volume, pp 469-525.
(2) Hunt, D. F.; Buko, A. M.; Ballard, J. M.; Shabanowitz, J.; Giordani, A.
B. Biomed. Mass Spectrosc., In press. (3) Morris, H. R.; Dickenson, R. J.; Williams, D. H. Biochem. Blophys. Res. Commun. 1973, 51, 247-255. (4) Day, R. J.; Unger, S. E.; Cooks, R. G. Anal. Chem. 1980, 52, 557A572A. (5) Devienne, F. M.; Roustan, J . 4 . C. R . Hebd. Seances Acad. Scl., Ser. B 1978, 283, 397-399. (6) Surman, D. J.; Vickerman, J. C. J . Chem. SOC., Chem. Commun. l a e l . 324-325. (7) Barber, M.; Bordoli, R. S.; Sedgwlck, R. D.; Tyler, A. N. J. Chem. SOC.,Chem. Commun. 1981, 325-327. (8) Hunt, D. F. "Abstracts of Papers", 181st Natlonal Meeting of the American Chemical Society, Atlanta, GA, March 29, 1981; Amerlcan Chemical Society: Washlngton, DC, 1981; Paper No. 59, (9) Hunt, D. F.; Shabanowitz, J.; Giordani, A. B. Anal. Chem. 1980, 52, 386-390. (IO) Hunt, D. F.; Bone, W. M.; Shabanowltz, J. 28th Annual Conference on Mass Spectrometry and Allied Topics, New York, May 25, 1980, Abstract No. RPMP 18.
Donald F. Hunt* W.M. Bone J. Shabanowitz J. Rhodes J. M. Ballard Department of Chemistry University of Virginia Charlottesville, Virginia 22901
RECEIVED for review April 21, 1981. Accepted June 8,1981. This work was supported by research grants from the NIH (AM26533) and the U S . Army Research Office (DAAG2980-C-0101).
Identification of Spilled Crude Oils by Vapor-Phase Ultraviolet Absorption Spectrometry Sir: Several analytical techniques are employed for the identification of crude oil spills in seawater. A major problem in oil spills is the weathering effect; it can be overcome by procedures involving the use of combined and computerized analytical techniques as reported in exhaustive reviews dealing with the subject ( 1 , Z ) . Vapor-phase ultraviolet absorption spectrometry has been recently employed to detect organics in water (3); it gives useful information particularly when applied to known-source pollutants. The purpose of this work is to evaluate vapor-phase ultraviolet absorption spectrometry for the rapid identification of crude oil spills in seawater and to investigate the influence of weathering on this instrumental approach. EXPERIMENTAL SECTION Apparatus. An atomic absorption spectrophotometer Perkin-Elmer Model 5OOO equipped with deuterium lamp and HGA 76-18 electrothermal atomizer is employed for vapor-phase UV absorption spectrometry measurements. The absorption signals are displayed on a strip chart recorder. Samples are introduced in the graphite furnace by means of an Eppendorf micropipet (Hamburg, West Germany). Reagents. Crude oils from America, Africa, Asia, and Europe are investigated. They are listed in Table I together with their origin countries. Cyclohexane, n-hexane, isooctane, and benzene from E. Merck (Darmstadt, West Germany) are pure reagent grade. Crude oils are weathered after the method proposed by Brown and Lynch (4). Procedure. Both unweathered and weathered oils are diluted 1 5 (w/w) with benzene. Twenty microliters of oil solution is introduced into the graphite furnace and the following heating cycle is performed: the temperature is raised to 140 "C (4.4 OC/s heating rate) and maintained €or 45 s. After this drying stage,
Table I. Crude Oils List no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
specific gravity
crude
country
(15/4 "C)
Boscan Umm Shaif Murban Zueitina Santa Maria Safaniya Ras Tanura Arabian Light Basrah Iranian Light Qua Iboe Belayim Shengli Brass River Forties
Venezuela Abu Dhabi Abu Dhabi Libya Italy Saudi Arabia Saudi Arabia Saudi Arabia Iraq Iran Nigeria Egypt China Nigeria U. K.
0.963 0.842 0.828 0.830 0.920 0.887 0.861 0.862 0.871 0.860 0.848 0.896 0.910 0.822 0.842
the temperature is increased to 900OC (22 OC/s heating rate) and the UV absorption of the evolving vapors is recorded at 190 nm (0.7 nm bandwidth). The furnace is then purged at 2700 "C for 10 s. An argon flow (2.5 mL/s) is maintained during the whole heating cycle. RESULTS AND DISCUSSION Various solvents have been employed to dilute the crudes, some of which are not completely dissolved by aliphatic solvents. Benzene shows the best performance especially with heavy crudes (Le., Boscan, Belayim, etc.) but, because of its strong absorptivity in the UV region, requires a drying stage
0003-2700/81/0353-1406$01.25/0Q 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 11, SEPTEMBER 1981 e 1787
012
05
06
os
04
01
080
I
082
I
084
I
086
I
088
I
090
I
092
~ p e c i f i cgravity, 1 5 o C / 4 o C
Flgure 2. Absorbance ratios A,IA, (absorbance at the sharp band maximum over the absorbance at the broad band maximum) vs. specific graviities of unweathered oils.
*
Figure 1. Thermal ultraviolet profiles of crude olils listed In Table I. Weathered oils are indicated by W.
long enough to allow its complete removal. The heating rate of 22 ‘C/s has proven to be the fastest without loss of “thermal resolution”. Slower rates do not improve the “specificity” of the thermal ultraviolet (TUV) profiles. Argon flow rate does not affect the resolution; however, low flow rates (
