1. Quantitative Gas Chromatography
Chem 2223 Lab Prep

2. Goals and Objectives Goals Specific Objectives
To become familiar with basic methods of quantitative analysis by gas chromatography
Specific Objectives
Use the standard additions technique to determine the identities and concentrations of the components in a mixture of volatile organic compounds

3. Setup

4. Solutes and Internal Standard
Compound
Structure or Formula
Boiling Point, oC
Relative Polarity
Methanol
(solvent)
CH3OH
64.6
Polar
Toluene
110.6
Nonpolar
Ethylbenzene
135.2
p-Xylene
138.4
Bromobenzene
(internal standard)
156.0

5. Internal Standard Method
Description
In this approach, an internal standard is added to the sample, and the response from the analyte peak is compared to the internal standard. This approach corrects for minor variations in the injection volume.
Response Factor (RF)
The response factor accounts for differences in the detector response between the analyte and standard.

6. Sample Chromatogram and Integration ReportIS X
AX = 27.01
AIS = 17.80

7. Calibration Curve with Internal Standard
Standards
Each contains fixed mass of internal standard, various masses of std analyte
Calibration curve shows linear response. Slope = response factor*
Unknown
Add known amount of internal standard
Inject and measure Ax/Ais
Determine cx/cis for your unknown from calibration curve. Since cis is known, cx for your unknown is simply
cx = (cx/cis)cis
*This expression for the response factor is not used directly in your calculations. The following expression which accounts for the intercept is more rigorous (in practice the intercept is very near zero). Calculations based on the calibration data do take the intercept into account.