Question

1. You are performing a separation experiment with gas chromatography and notice that your peaks have overlapping elution times. Provide three possible approaches you could take to improve the resolution of the peaks. Explain how these changes would provide a higher resolution using the resolution equation. Which of your listed approaches would be the most cost effective?

Answer 1

Possible approaches to improve resolution:

a) Temperature decrease

b) Carrier gas flow rate

c) Column length and width.

Explanation:

a) Decrease in temperature will allow the components of analytes to vaporize according to their boiling points and not all of them together. This leads to sequential volatilization of components and hence better resolution. Optimum temperature is about 10°C above the boiling point of least volatile component.

b) Mostly N₂ is used as carrier gas but He and H₂ provide better resolution. Important factor is flow rate of carrier gas, if it is low then resolution is better because it provides enough time for separation to occur.

c) Increased column length and decreased width provide better resolution. It is again due to fact that larger column will provide efficient partitioning and hence better resolution.

Smaller width will allow better partitioning between mobile and stationary phases thus improving resolution.

Most cost effective is altering the column temperature. It does not require actual alteration in the components and also, does not increases analysis time much.