Duan Penggao, Qian Kuangnan, Habicht Steven C, Pinkston David S, Fu Mingkun, Kenttämaa Hilkka I
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Anal Chem. 2008 Mar 15;80(6):1847-53. doi: 10.1021/ac702476p. Epub 2008 Feb 22.
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.
激光诱导声解吸（LIAD）与ClMn(H₂O)⁺离子的化学电离相结合，被证明有助于通过傅里叶变换离子回旋共振质谱法对基础油进行分析。LIAD/ClMn(H₂O)⁺方法对基础油中的每种成分（M）仅产生一种产物离子[ClMn + M]⁺，从而为分析物提供分子量（MW）信息。除了一个样品外，未观察到碎片化现象。质谱表明存在质量相差14 Da倍数（即CH₂）的同系离子系列。光谱中的所有峰均对应于m/z值为偶数的离子，因此由不含氮原子的烃形成，这与基础油的组成性质一致。对两组基础油样品测量的分子量分布范围为350 - 600 Da，与气相色谱法测定的值非常吻合。此外，每种基础油样品中存在的烃类类型（即具有不同环数的石蜡和环烷烃）可根据产物离子的m/z值确定。最后，使用LIAD/ClMn(H₂O)⁺获得的结果表明，该技术的效率（解吸和电离效率之和）对于不同烃类类型相似，并且在很宽的分子量范围内相当均匀，从而允许对基础油进行定量分析。因此，产物离子的相对丰度被用于确定基础油中每种烃类的百分比。总之，在一次实验中可以获得三个重要参数（分子量分布、烃类类型及其相对浓度）。因此，这种质谱技术为基础油提供了详细的分子水平信息，这是其他分析方法无法获得的。
