电喷雾萃取电离质谱法用于掺假白酒的快速分析

Rapid Analysis of Adulterated Chinese Liquor by Extractive Electrospray Ionization Mass Spectrometry

采用自行研制的电喷雾萃取电离源(EESI)与LTQ-XL质谱仪耦合,并结合主成分分析(PCA)和聚类分析(CA),建立了一种能在无需样品预处理的条件下直接、快速、准确鉴别茅台等八种掺假白酒(混掺水和工业酒精,且通过酒精计调控掺假酒的酒精度与真酒保持一致)的新方法.同时,利用串联质谱能够对目标组分进行准确鉴定.研究结果表明,EESI-LTQ-MS检测单个样品的时间小于1 min,且重现性好,PCA区分正确率高达96.5%.通过设置未知样分析进一步验证了该方法的可行性.此外,还结合单光子电离飞行时间质谱法(SPI-TOF-MS)对检测谱图进行对比分析.阐述了EESI和SPI两种电离技术在挥发性有机物分析上具有各自的优势,且两种检测手段具有互补的特点.为市场上酒类饮品真假的快速鉴别及品质鉴定建立了一个综合的分析方法,对于快速筛选伪劣酒类产品具有非常重要的应用价值.

A novel analytical platform based on a home-made extractive electrospray ionization （EESI） source coupled with LTQ-XL mass spectrometer has been developed for fast and accurate identification of eight different kinds of adulterated Chinese liquors such as Maotai. Alcohol concentration in each liquor sample was measured by an alcohol meter and was adjusted to the same value by adding water and industrial alcohol. Measurements were done in positive ion detection mode under optimized experimental conditions. The ESI voltage was set to ＋4 kV, the pressure of the sheath gas （N2） was 1.2 MPa, the temperature of the heated capillary was set to 150 ℃, and the primary ions were created by elecospraying metha- nol/water/acetic acid mixture （4 ： 4 ： 2, V ： V ： F） at 5 μL·min^-1. Normalized mass spectra of authentic and counterfeit liq- uors were differentiated by principal component analysis （PCA）. Reproducibility of the method was characterized by cluster analysis （CA）. Several constituents of liquor vapor were identified by tandem mass spectrometry （MS/MS）. To perform MS/MS experiments, ions of interest were isolated with a mass-to-charge window width of 1.4 u. and then subjected to colli- sion-induced dissociation （CID） with 16%--24% collision energy for 30 ms. The analysis time for a single sample was less than 1 min. The accuracy of identification predicted by PCA was 96.5%. The feasibility of this method was verified by test- ing several unknown samples. In addition to EESI-LTQ-MS, volatile compounds in Maotai vapor were also studied by single photon ionization time-of-flight mass spectrometry （SPI-TOF-MS）, and molecular fingerprints obtained by these two meth- ods were compared. These two detection means showed their respectively outstanding advantages and synergy for the analysis of volatile organic compounds （VOCs）. The introduced method provides an important tool for the quality control of alcoholic beverages with high speed and simplicity of analysis on the market.