Reliable identification in GC-MS analysis with two independent analytical information sources

Introduction

Main flavour and fragrance components prior to gas chromatographic (GC) separation are usually identified with mass spectrometry (MS) using spectral comparison and literature data. In the GC - MS peak identification of complex samples, the main difficulty is  related to  the almost identical mass spectra of terpenes. Hence, MS identification should be accompanied by additional information, namely retention index (RI), that can support the MS similarity search. There are several ways to calculate the RI of an unknown compound according to the specific chromatographic conditions [1-4].   The widely accepted way for programmed temperature retention index, denominated also as  linear retention index (LRI), calculation is expressed as follows [4, 5]:

where t_R is the retention time, z is carbon atom number, i is the peak of interest, n is the difference in carbon atom number of the two standards (n -alkanes : n =1, even or odd fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs) : n=2). The Flavour and Fragrance Natural and Synthetic Compounds Library (FFNSC) is  a  comprehensive database containing mass spectrum of about 3500 individual flavour and fragrance molecules, acquired mainly from pure standards.  Moreover, for each compound embedded experimental LRI values on  three different stationary phases (SLB- 5ms, Equity -1 and Supelcowax -10) are also reported. Boosting the MS similarity search with simultaneous LRI filter of GCMSsolution a fast and reliable peak assignment can be achieved. Using two different types of stationary phases and the MS spectra and exploiting the multi-LRI feature of the FFNSC Library the identification will not be tentative, but confirmed by three individual analytical information.

The FFNSC Library can be  an  excellent support and applied in  essential oil characterization, food aroma profile analysis, determination of fragrances in non- food matrix (e-liquids, cosmetics). In  this application note some examples are reported.