Analysis of Base Oil Fractions by ClMn(H₂O)⁺ Chemical Ionization Combined with Laser-Induced Acoustic Desorption/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Abstract

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.

HPLC/APCI Mass Spectrometry of Saturated and Unsaturated Hydrocarbons by Using Hydrocarbon Solvents as the APCI Reagent and HPLC Mobile Phase

“…This sample had been analyzed previously by our group using a different method [17]. The molecular weight distribution determined here agrees with that determined by using the earlier method, ClMn(H 2 O) + chemical ionization combined with laserinduced acoustic desorption/Fourier-transform ion cyclotron resonance mass spectrometry [17], in spite of the observation that the method introduced here also caused some fragmentation.…”

“…Further, the molecular weight distribution determined for a base oil sample is in good agreement with that determined by another method, laser-induced acoustic desorption/chemical ionization/Fourier-transform ion cyclotron resonance mass spectrometry [17].…”

“…Atmospheric pressure photoionization (APPI) can ionize nonpolar polycyclic aromatic hydrocarbons but it cannot be used to ionize saturated hydrocarbons [22]. Laserinduced acoustic desorption (LIAD)/Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR) using ClMn(H 2 O) + as the chemical ionization reagent ion has been reported to allow the evaporation and ionization of nonpolar hydrocarbons without fragmentation under ultrahigh vacuum, but this approach requires special instrumentation [16,17].…”

Petroleomics: Chemistry of the underworld

“…APPI FT-ICR MS (9) can accumulate one mass spectral dataset in a few seconds and is thus better suited for signal averaging of a few hundred scans for increased dynamic range. APPI of petroleum requires the ultrahigh resolution of FT-ICR MS for two reasons: (i) APPI ionizes a broader range of compound classes, and thus the mass spectrum contains approximately five times as many peaks as an ESI mass spectrum of the same crude oil sample; and (ii) the same analyte molecule may produce both M ϩ• and (MϩH) ϩ ions, making it necessary to resolve M ϩ• containing one 13 C from (MϩH) ϩ containing all 12 C, a mass difference of only 4.5 mDa (see below). Laser desorption/ionization mass spectrometry, although highly useful for biomolecule analysis, does not provide a reliable representation of petroleum components because of significant aggregation and fragmentation at the laser power required to generate a useful number of gas-phase ions (10).…”

Generation of multiply charged peptides and proteins by radio frequency acoustic desorption and ionization for mass spectrometric detection

“…One L aliquots of melittin, BNP-32, and ubiquitin ( ϳ1 g of analyte) were deposited onto a quartz crystal microbalance (QCM) electrode before radio frequency actuation for desorption. Continuous electrospray parallel to/above the sampling surface enabled the ionization of Laser-induced acoustic desorption (LIAD) [1][2][3][4] demonstrates the soft desorption of analyte using a shock wave generated by a laser pulse and the potential to couple post-desorption ionization techniques such as chemical ionization at atmospheric pressure. Array of micro-machined ultrasonic electrosprays [5][6][7] (AMUSE), applies an rf signal to a ceramic piezoelectric transducer with a solution cavity between a micromachined silicone nozzle array for droplet-on-demand generation.…”