Matching made easier ?

But only if your GC is functioning properly! (most are not set up correctly) Those that use Kovat Indices are more likely to give better results!

My experience has not been good with University GLC equipment most seem to have been damaged by students and not set up correctly. Government R&D facilities while a little better are just not good enough for commercial flavour analysis. Flavour companies do have some of the best setups for GLC or GC/MS analysis but it all comes down to the operator and how fanatical he/she is in perfecting the system. So don't trust any analysis until it has been verified.

Assuming you have a good system, why waste your valuable time making matches by trial and error when you can jump to almost the end of the process (or at least half way) with a GC/MS analysis. SPME is great for aroma analysis of finished products!

While this will not give you the complete picture it helps and reduces the time spent on this process.

SPME flavour analysis

Flavour analysis

Aroma chemicals and their retention Index

Analysis of alcoholic beverages

Solid phase micro extraction

Flavour Analysis and perception

http://www.labhut.com/education/headspace/introduction01.php

Partition Coefficient

The partition coefficient is the equilibrium distribution of an analyte between the sample phase and the gas phase.

Samples must be prepared to maximise the concentration of the volatile components in the headspace and minimise unwanted contamination from other compounds in the sample matrix. To help determine the concentration of an analyte in the headspace, you will need to calculate the partition coefficient (K).

Calculating the Partition Coefficient

Partition Coefficient (K) = Cs/Cg

where Cs is the concentration of analyte in sample phase;
Cg is the concentration of analyte in gas phase

K values of common solvents in
air-water systems at 40°C

Partition Coefficients of Common Compounds

Compounds that have low K values will tend to partition more readily into the gas phase and have relatively high responses and low limits of detection. An example of this would be hexane in water: at 40°C, hexane would have a K value of 0.14 in an air-water system.

Compounds that have high K values will tend to partition less readily into the gas phase and have relatively low responses and high limits of detection. An example of this would be ethanol in water: at 40°C, ethanol has a K value of 1355 in an air-water system.

Partition coefficient values for other common compounds are shown in the table on the right.

Sensitivity vs Partition Coefficient Graph

Sensitivity is increased when K is minimised

Sensitivity is increased as the partition coefficient is decreased and volatiles can more readily enter the gas phase. This is illustrated by the graph on the left.

K can be lowered by changing the temperature at which the vial is equilibrated or by changing the composition of the sample matrix. In the case of ethanol, K can be lowered from 1355 to 328 by raising the temperature of the vial from 40°C to 80°C.

The partition coefficient may also be changed by adding salts or by changing the Phase Ratio.