3.A gas chromatographic peak from a 25 m long column has an adjusted retention time of 11.2 minutes, and a width at half height of 20 seconds. How many theoretical plates are present in the column? What is the value of H?

4. A sample of pesticide is analyzed by gas chromatography. A 0.1 m l injection of a standard containing 0.234 m g/l gives a peak of area 34873. The same size injection of an unknown sample solution gives an area of 39945. What is the concentration of the pesticide in the sample solution?

5. In gas chromatography predict the effect on the efficiency of a separation when the following changes are made:
a. Particle size of the packing is increased
b. Gas flow is increased
c. Thickness of liquid phase in a capillary column is increased

1. decreases efficiency
2. depends on whether flow is above or below the minimum in the van Deemter curve. Moving closer to the minimum increases the efficiency.
3. Increasing phase thickness increases the capacity, but reduces efficiency.