Question

N mtu QUESTIONS 1. What are dependent variables of a van-Deemter plot 2. What is a dynamic range problem and how does it affect the efficiency of a chromatographic analysis? Why does a TCD respond to all analytes except the carrier gas? What are the relative advantages and disadvantages of packed and open tubular columns in GC 5. Predict the elution order of the following analytes from a Carbowax 20 M column: hexane. acetaldehyde, octane, benzene, toluene, ethylbenzene, o-xylene and butanol?

Answer 1

Solution 1: Dependent variable is dependent on the independent variable. Van Deemter equation is a theoretical treatment of the peak broadening with in a chromatographic column. It is a plate height equation that corelate between plate height and mobile phase velocity.

H = A+ B/u + C*u where H= HETP (plate height), A = Eddy diffusion term, B = longitudinal diffusion term, C= resistance to the mass transfer co-efficient , u = linear velocity. This H - u plot that's efficiency of carrier gas interms of plate height and linear velocity is very useful for optimum mobile phase velocity. It depends on the following factors..

• Column length
• Partical size
• Packing quality
• Linear velocity
• Instrumental quality
• Retention factor