Developing Methods
Changing the Sample Loop
73
but water-miscible systems, dilute the sample with water. This decreases the
solubility of most organic molecules in the sample and increases their
concentration in the headspace.
Matrix effects are important when developing external standards. The
composition of the matrix in the standard should closely resemble that of the
sample, or accuracy suffers. The effect of the matrix on a standard can be
compensated for by using the standard addition method or by quantifying
results using MHE.
Changing the Sample Loop
Although the 1 ml sample loop is usually adequate, a larger sample injection for
trace analysis might be desired. A 3 ml loop is available. See “Changing the
Sample Loop” on page 92.
Note A larger sample injection may broaden some peaks, especially on a capillary
column.
Sample Size
A larger sample size may give greater sensitivity. Peak areas are often strongly
influenced by the relative amount of the gas and condensed phases in the
sample vial. Increasing the sample size may give corresponding increases in
peak areas. If sensitivity is not an issue, small samples may be preferred
because the required equilibration time is shorter.
Vial Pressurization and Time
Vial Pressurization
With many liquid (e.g. aqueous) samples, the pressure developed in the vial
may be sufficient to ensure filling the valve loop without additional pressure.
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