In 1815, the British physician William Prout had advanced the theory that the molecular masses of elements were multiples of the mass of hydrogen. This "whole number rule" (and especially deviations from it) played an important role in the discussion whether elements could be mixtures of isotopes. F. Soddy's discovery (1910) that lead obtained by decay of uranium and of thorium differed in mass was considered a peculiarity of radioactive materials. The question of the existence of isotopes came up when the instruments developed by J.J. Thomson and by W. Wien to study cathode and canal rays by deflection in electric and magnetic fields were steadily improved. In 1913, Thomson mentioned a weak line at mass 22 accompanying the expected one at mass 20 when he analyzed the mass spectrum of neon. Subsequently Aston obtained the mass spectrum of chlorine with masses at 35 and 37. Still in 1921, Thomson objected heavily to the idea of isotopes. The isotope problem was finally settled, but more accurate mass measurements showed that even isotopic weights differed to some extent from the whole numbers. Based on earlier ideas of P. Langevin and J.-L. Costa, F.W. Aston and A.J. Dempster developed the idea of packing fractions and mass defects due to the transformation of a portion of the matter comprising the atomic nucleus into energy. While the determination of the exact isotopic masses had improved over the years, the accurate determination of isotopic abundances remained a problem as long as photographic recording was used. Here especially A.O. Nier pioneered using dual collectors and compensation measurements. This was the prerequisite for the discovery that isotopic ratios varied somewhat in nature. M. Dole discovered the fractionation of oxygen isotopes by photosynthesis and respiration. Today 13C/12C-ratios are employed to detect adulterations of food and in doping analysis, and 14C/13C-ratios obtained by accelerator mass spectrometry are used for dating historical objects, just to give some examples.

The fluid catalytic cracking (FCC) behavior of compound types present in the >650 °F resid from Brass River (Nigerian) crude was investigated. Liquid chromatography and distillation were employed for separation of selected compound type fractions from the resid; the resulting fractions were then cracked using a bench scale FCC unit. The FCC behavior for each compound type was defined in terms of the resulting product distribution (yields of gas, gasoline, etc.) sulfur and nitrogen partitioning, and in selected cases, gasoline composition. Results obtained from Brass River fractions were compared to those obtained from an earlier FCC study of compound types from Wilmington, CA, >650 °F resid. Correlations were derived for gasoline and coke yields from feedstocks derived from either crude. Brass River is a sweet, paraffinic crude which gives rise to a >650 °F resid with very favorable FCC characteristics. Although the bulk of the FCC gasoline was produced from cracking hydrocarbon types present, significant gasoline production also occurred from heteroatomic compounds (acids/bases) in Brass River. Conversely, negligible gasoline production was observed previously from cracking Wilmington acid/base types. However, feedstocks from both crudes exhibited greater conversion of sulfide sulfur to H2S compared to thiophenic forms of sulfur, and greater carryover of acidic forms of nitrogen (e.g., carbazole) compared to basic forms (e.g., quinoline). Overall gasoline composition depended on hydrocarbon type composition of feedstocks but was also influenced by presence of acids and/or bases in the feed. On the other hand, the detailed distribution of isomers within a given gasoline homolog, e.g., C3-benzenes or C9 isoparaffins, was nearly independent of feed composition. Results obtained for Brass River will serve as benchmarks for future FCC data obtained from low-quality feedstocks.

A vanadium-enriched fraction from the >700 °C resid of Cerro Negro heavy petroleum was analyzed by high-resolution, low-energy, electron-ionization mass spectrometry (low-eV HR/MS). This fraction, isolated in a prior investigation by liquid chromatographic methods, was known to contain 19 500 ppm vanadium, or 4.6 wt % of the total vanadium in the whole resid. On the basis of UV-visible absorption spectra, the concentration of porphyrinic vanadium in the fraction was previously estimated to be 11 000 ppm or 56.4 wt % of the total vanadium. Because the porphyrinic vanadium accounted for only about one-half of the total, an independent method was needed to characterize the nonporphyrinic vanadium in the fraction. Low-eV HR/MS with sample introduction by probe microdistillation was selected because of its capability for characterizing aromatic and polar compounds in low-volatility, high molecular weight mixtures. Etioporphyrins (C n H 2n-28 N 4 VO) with molecular weights ranging from 487 to 879 were found to be the most abundant vanadium-containing compounds in the fraction. Deoxophylloerythroetioporphyrins (C n H 2n-30 N 4 VO) with molecular weights ranging from 499 to 863 were the second most abundant. In addition, other compound types having the formula C n H 2n+z N 4 VO, where z ranges from -32 to -50, excluding -46, were found. Additional saturated and aromatic rings present in compounds with more negative z numbers would appreciably alter their UV-visible absorption spectra relative to those of etioporphyrins. That is, the response of the other porphyrin types would be lower than that of etioporphyrins at 570 nm, the wavelength used for the determination of vanadyl porphyrins. Thus, the broad distribution of vanadyl porphyrin types identified in the fraction by low-eV HR/MS strongly suggests that at least a part of the apparent "nonporphyrinic vanadium" thought to be present in the fraction is, in fact, porphyrinic and is explained by the use of molar absorptivities based solely on those of etioporphyrins to calculate total porphyrin content.

Results for a monoaromatics fraction from the 535-675 °C distillate of a Wilmington, CA, crude oil demonstrate the efficacy of probe mlcrodlstlllation/mass spectrometry for the qualitative and quantitative analysis of mixtures containing relatively nonvolatile substances. The probe temperature was controlled by a programmer either linearly or to maintain a constant ion current by feedback of the voltage from the Ion current monitor to the programmer. Ions were produced by 70-eV and 10-eV electrons and by field Ionization. Qualitatively, all three methods of Ionization produced the same spectral patterns. Detectable compounds are distributed in

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