Page 411 - Biosystems Engineering

388 Cha pte r T h i r tee n

Measuring
vessel
Conductivity
measuring cell

Monouring
solution
Reaction vessel
Sample
Heating block

FIGURE 13.5 Rancimat apparatus.

Rapid Method for Determining the Oxidation of Fatty Acids Samples were
dissolved in isooctane for gravimetric transfer into 5-mL high-pressure
headspace vials. The isooctane was evaporated under a stream of
nitrogen followed by equilibration of the vials in air for 10 min. The
vials were then sealed with Teflon tape before heating.

Capillary Gas Chromatography Sample vials were heated at 85°C for
0, 5, 35, 65, and 95 min. With a gas-tight syringe, 1 mL of headspace
volatile was injected directly into a Hewlett Packard gas chromato-
graph (GC) with a flame ionization detector, integrator, and IBM
computer for data handling and storage. Helium was the carrier gas
in the fused silica capillary, 30 m × 0.32 mm, the injector was set at
250°C and the detector at 270°C; the temperature was programmed at
50 to 110°C (at 4°C/min) and from 110 to 220°C (at 20°C/min) with a
1-min hold. Volatiles were identified by comparing retention times to
reference standards. 30

GC/MS Analysis Confirmation of volatile identities was accom-
plished on a HP GC/MS (mass spectrometer) containing a similar
capillary column; ionization energy was 70 eV, and scan range was 38
to 260 m/z. After the respective fatty acids (i.e., Lo/DHA), were
heated (80°C/100 min), 100 μL of the headspace volatile was injected
into a DB5 silica capillary column 30 m × 1.0 mm. Conditions remained
as described earlier. After the ionization pattern was recorded from
GC/MS system, and the relative retention times were generated
using the GC technique, most of the volatile compounds could be
identified.