Developing Methods
Varying Oven Temperature
71
Varying Oven Temperature
The oven temperature can have a profound effect on the concentration of
analyte that passes into the headspace gas. In general, as the oven temperature
increases, the amount of gas entering the headspace from the sample
increases, increasing the pressure in the vial and delivering more analyte to the
GC. This increases the sensitivity of the analysis.
When you pick an oven temperature, consider the following:
• Over-pressurization of the headspace vial could be dangerous.
• Unstable compounds could degrade at elevated temperatures.
There are two ways you can program the 7694 HS to increase oven temperature
in steps:
• Use Chain Methods (see “Chaining Methods” on page 65) and setting the
oven temperature higher in each method in the chain
• Use Param Increment (see “Advanced Function Descriptions” on
page 44).
Note Do not set the oven temperature within 10°C of the boiling point of any
solvents in the sample, except in special cases.
Note Loop and transfer line temperatures should be set higher than the highest
temperature the oven will reach in a programmed sequence.
Varying Event Times
Vial Equilibration Time
The time that the sample vial spends in the oven determines the amount of
analyte in the headspace gas and the presence or absence of equilibrium. The
7694 HS can be programmed to analyze a series of samples to determine if
equilibrium is reached.
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