We report here an examination of the mass spectrometric fragmentation behavior of molecular ions generated (and excited) by electron ionization (EI) from several asphaltene model compounds simulating both the island and archipelago structural models. This behavior is compared to that of protonated molecules generated from the same compounds by atmospheric pressure chemical ionization (APCI) and excited by collision-activated dissociation (CAD). The fragmentation behavior of the protonated molecules and molecular ions is surprisingly similar. Both types of ions yielded distinct fragmentation patterns for both types of model compounds. Ions derived from the island-type model compounds fragment predominantly by losing their alkyl chains (with either all carbons or all but one), one after another, which allows for the identification of the chain lengths and counting the number of chains. Increasing the length of the alkyl chains reduces the extent of spontaneous fragmentation occurring upon EI, likely because of more efficient cooling of the fragmenting ions via emission of infrared (IR) light made possible by the reduced fragmentation rates of the longer chains. Ions derived from the archipelago model compounds with ethylene bridges connecting two or three aromatic cores (without alkyl side chains) readily undergo cleavages in these bridges. Increasing the length of the alkyl chain between the aromatic cores reduces the extent of fragmentation caused by EI. Similarly, the addition of long external alkyl chains to archipelago model compounds with an ethylene bridging two aromatic cores greatly hinders fragmentation upon EI. When these molecules are protonated and subjected to high-energy CAD, they appear to fragment almost randomly but, nevertheless, indicating some preference for cleavages of the bonds in the chain connecting the aromatic cores. A comparison of these findings to the fragmentation patterns observed for protonated asphaltenes indicates that the asphaltene molecules studied are likely composed of many isomeric and isobaric molecules. Each may contain several aromatic rings and a distribution of mostly aliphatic alkyl chains (and possibly naphthenic rings) ranging in size from 1 to at least 14 carbons, several containing methyl branching at the α carbons. The results do not allow for the unambiguous differentiation between island- and archipelago-type structures, although they are in a better agreement with the island model.

Laser-induced acoustic desorption (LIAD)/electron ionization (EI) was used to study asphaltene model compounds and asphaltenes derived from North American crude oil in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer (MS). Successful desorption by LIAD of all model compounds (including a polyphenylated vanadoyl porphyrin) as intact neutral molecules into the mass spectrometer indicates that this method allows the evaporation of most if not all components of asphaltenes into mass spectrometers for further characterization. Electron ionization is a universal ionization method that ionizes all organic compounds. Hence, it is not surprising that all the model compounds studied were successfully ionized by using this method. Furthermore, this method yielded stable molecular ions for all model compounds studied. Because LIAD/EIMS provides MW information for these model compounds, this is almost certainly also true for all components of asphaltenes. Examination of asphaltene samples derived from North American crude oil by using this technique yielded a MW distribution of about 350-1050 Da and provided structural information for asphaltene components.

The gas-phase reactions of ClMn(H2O)+ with a variety of volatile and nonvolatile, saturated and unsaturated hydrocarbons have been examined by using Fourier transform ion cyclotron resonance mass spectrometry (FT/ICR). The ClMn(H2O)+ ion reacts rapidly by exclusive H2O ligand displacement with all the hydrocarbons studied, including highly branched alkanes that usually fragment upon ionization. These observations are rationalized on the basis of the electronic structure of ClMn+. Collision-activated dissociation of the product ions provides structural information which promises to allow the distinction and structural characterization of isomeric hydrocarbons. These findings suggest that the ClMn(H2O)+ ion is a highly promising chemical ionization reagent for mass spectrometric characterization of hydrocarbons, including those that commonly exist in petroleum

Laser-induced acoustic desorption (LIAD), combined with chemical ionization with the ClMn(H(2)O)(+) ion, is demonstrated to facilitate the analysis of base oils by Fourier transform ion cyclotron resonance mass spectrometry. The LIAD/ClMn(H(2)O)(+) method produces only one product ion, [ClMn + M](+), for each component (M) in base oils, thus providing molecular weight (MW) information for the analytes. With the exception of one sample, no fragmentation was observed. The mass spectra indicate the presence of homologous series of ions differing in mass by multiples of 14 Da (i.e., CH(2)). All peaks in the spectra correspond to ions with even m/z values and hence are formed from hydrocarbons with no nitrogen atoms, in agreement with the compositional nature of base oils. The MW distributions measured for two groups of base oil samples cover the range 350-600 Da, which is in excellent agreement with the values determined by gas chromatography. Moreover, the hydrocarbon types (i.e., paraffin and cycloparaffins with different numbers of rings) present in each base oil sample can be determined based on the m/z values of the product ions. Finally, the results obtained by using LIAD/ClMn(H(2)O)(+) indicate that the efficiency of the technique (combined desorption and ionization efficiency) is similar for different hydrocarbon types and fairly uniform over a wide molecular weight range, thus allowing quantitative analysis of the base oils. Hence, the product ions' relative abundances were used to determine the percentage of each type of hydrocarbon in the base oil. In summary, three important parameters (MW distributions, hydrocarbon types, and their relative concentrations) can be obtained in a single experiment. This mass spectrometric technique therefore provides detailed molecular-level information for base oils, which cannot be obtained by other analytical methods.