The graph shows van Deemter curves for n-nonane at 70 degree C in the 3.0-m-long

Question

The graph shows van Deemter curves for n-nonane at 70 degree C in the 3.0-m-long microfabricated column in Box 24-2 with a 1- to 2-mu m-thick stationary phase. Why would air be chosen as the carrier gas? What is the danger of using air as carrier gas? Measure the optimum velocity and plate height for air and for H_2 carrier gases. How many plates are there in the 3-m-long column for each carrier gas at optimum flow rate? How long does unretained gas take to travel through the column at optimum velocity for each carrier gas? If stationary phase is sufficiently thin with respect to column diameter, which of the two mass transfer terms (23-40 or 23-41) becomes negligible? Why? Why is the loss of column efficiency at high flow rates less severe for H_2 than for air carrier gas?

Explanation / Answer

(a) Air is choosen as a gas carrier because it posses better chromatography then H2 this is because it has more no. of n as compare to that of H2 and as N increases the quality or the chromatography is good as the N is dependent on height of plate as H=L / N that means there should be low H for good chromatography. For the same value of v air las lesser value of N then that of H2.

The drawback of using air as carrier is low tolerance to speeding

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