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.

A mass spectrometric method has been developed for the identification of the carboxylic acid functional group in analytes evaporated and ionized by electrospray ionization (ESI). This method is based on gas-phase ion-molecule reactions of ammoniated ([M + NH4]+) and sodiated ([M + Na]+) analyte molecules with trimethyl borate (TMB) in a modified linear quadrupole ion trap mass spectrometer. The diagnostic reaction involves addition of the deprotonated analyte to TMB followed by the elimination of methanol. A variety of analytes with different func-tionalities were examined, and this reaction was only observed for molecules containing the carboxylic acid functionality. The selectivity of the reaction is attributed to the acidic hydrogen present in the carboxylic acid group, which provides the proton necessary for the elimination of methanol. The diagnostic products are easily identified based on the m/z value of the product ion, which is 72 Th (thomson) greater than the m/z value of the charged analyte, and also by the character-istic isotope pattern of boron. The applicability of this method for pharmaceutical analysis was demonstrated for three nonsteroidal anti-inflammatory drugs: ibuprofen, naproxen, and ketoprofen.

We report here the construction and characterization of a high-power laser-induced acoustic desorption (LIAD) probe designed for Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometers to facilitate analysis of non-volatile, thermally labile compounds. This "next generation" LIAD probe offers significant improvements in sensitivity and desorption efficiency for analytes with larger molecular weights via the use of higher laser irradiances. Unlike the previous probes which utilized a power limiting optical fiber to transmit the laser pulses through the probe, this probe employs a set of mirrors and a focusing lens. At the end of the probe, the energy from the laser pulses propagates through a thin metal foil as an acoustic wave, resulting in desorption of neutral molecules from the opposite side of the foil. Following desorption, the molecules can be ionized by electron impact or chemical ionization. Almost an order of magnitude greater power density (up to 5.0 × 10 9 W/cm 2 ) is achievable on the backside of the foil with the high-power LIAD probe compared to the earlier LIAD probes (maximum power density ~9.0 × 10 8 W/cm 2 ). The use of higher laser irradiances is demonstrated not to cause fragmentation of the analyte. The use of higher laser irradiances increases sensitivity since it results in the evaporation of a greater number of molecules per laser pulse. Measurement of the average velocities of LIAD evaporated molecules demonstrates that higher laser irradiances do not correlate with higher velocities of the gaseous analyte molecules.

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.