In gas-liquid column chromatography the detector observes compounds based on their specific properties. Both a qualitative and quantitative analysis can be determined for a sample.

1. Qualitative analysis: the retentions times of a sample are compared to the retention times of a known standard in order to identify the peaks.

2. Quantitative analysis: the mole % of the components present in a mixture can be determined. If one assumes that the detector responds equally to each of the components in the mixture then the area under the peaks is proportional to the amount of the compound eluted. However, the detector's response to varying compounds differ.

a. Response factor - detector response differs among compounds. In the case of a TCD, not all compounds have the same thermal conductivity. Likewise, in the case of a FID not all compounds ionize the same.Thus it is necessary to apply a correction factor to the measured areas in a gas chromatogram.

b. There are two types of correction factors commonly used:

1) molar response correction factor: Multiplying the peak area for each component by the mole response factor will yield the corrected mole value.

2) weight response correction factor: multiplying the peak area for each component by the weight response factor will yield the corrected weight value.

EXAMPLE 1.

Determine the mole % of the following peak areas obtained from a gas chromatogram.

Given:

 

Compound Benzene Heptane Ethanol

Uncorrected Area 14,300 8,200 12,500

Mole Response Factor 1.00 0.70 1.39

Solution:

First Multiply the area by the mole response factor

Next, determine the mole %

Determine the weight % for the above example.

Given:

 

Compound Benzene Heptane Ethanol

Weight Response Factor 1.00 0.90 0.82

Solution:

First Multiply the area by the weight response factor

Next, determine the weight %