4
Flavor Compounds in Distilled Liquor Products
Distilled liquor products contain awide range of volatile and non-volatile compounds in
an ethanol/water matrix. Themost abundant fusel alcohols and esters can be determined
by simple split injection, which alsominimizes the amount of matrix ethanol andwater
transferred to the column. However, many trace-level fatty acids and their esters, which
oftenareused to indicateproduct quality inalcoholicbeverages suchaswhiskeyand rum,
cannot be determined by this approach. Capillary gas chromatography is a powerful tool
for the analysis of these compounds, but the large ranges in volatilities and acidities can
make it difficult toquantify all of the components in a single chromatographic separation.
In addition, because the concentrations can vary widely, a splitless injection technique
with some type of preconcentration step often is necessary. One example of this is large
volume injection (LVI) with a venting step, which can be optimized to remove most of
thematrix ethanol andwater. Since some water will enter the chromatographic column,
a stabilized phase, such as the Stabilwax
®
-DA phase, should be used.
Byusingabondedpolyethyleneglycol (PEG) capillarycolumn, flavor compounds indis-
tilled liquor products can be quantified in a single splitless injection. A Stabilwax
®
-DA
column was selected for this application, to improve peak shape and reproducibility for
acidic components. An acidic functionality added to the PEG stationary phase reduces
adsorption of acidic components and significantly reduces peak tailing. An optimized
configuration of 30m, 0.18mm ID, and 0.18µm film thicknessminimizes analysis times.
Tooptimize the chromatographic conditions for this analysis,weused a testmixture con-
tainingacids, esters, and flavor compounds typically found inalcoholicbeverages (Figure
3).A computer modeling program, ezGC
™
, was used to optimize the column configura-
tion, temperature program, and inlet flow for this system.
To test the applicability of this column in these dimensions, the critical pair of caproic
acid and ethyl lauratewas studied. These components can be very difficult to resolve on
standard Carbowax
®
-type columns, especially if peak tailing or broadening occurs, or if
one component is present at a significantlyhigher concentration.TheStabilwax
®
-DA col-
umn achieves baseline resolution of these two compounds in a reasonable analysis time
(Figure 4).
PeakList
Conc. (ppm)
1. ethyl octanoate
100
2. acetic acid
100
3. propionic acid
100
4. isobutyric acid
100
5. decanol 3
50
6. ethyl decanoate
50
7. ethyl laurate
50
8.
cis
-lactone
100
9. 2-phenylethanol
50
10.
trans
-lactone
100
11. methyl myristate
50
12. ethyl myristate
50
13. octanoic acid
100
14. ethyl palmitate
50
15. decanoic acid
100
16. dodecanoic acid
100
17. vanillin
100
Stabilwax
®
-DA 30m, 0.18mm ID, 0.18µm (cat.# 550752)
Inj.:
1µL splitless (hold 0.5min.) at conc. shown
in peak list, in ethyl acetate, 4mm ID splitless
liner w/wool (cat.# 20814-202.1)
Inj. temp.:
240°C
Carrier gas:
hydrogen
Make-up gas: nitrogen
Linear velocity: 28psi@ 240°C
Oven temp.:
70°C to 240°C at 12°C/min. (hold 3min.)
Det.:
FID
GC_FF00500
Acids, esters, and flavor compounds typically found in alcoholic beverages arewell resolved on a Stabilwax
®
-DA column.
Figure 3
Performance information on
six polyethylene glycol (PEG)
columns—free on request.
Lit. Cat. #59890
Additional Restek
Literature
