1 (201)

Prévia do material em texto

Principles of Instrumental Analysis, 6th ed. Chapter 27
 
 11
(d) Increasing the flow rate may cause either increases or decreases in H depending on 
the flow rate as can be seen in Figure 26-8b. 
(e) Reducing particle size increases the surface area and thus decreases film thickness df 
in the CSu term in Equations 26-23 and 26-24. A decrease in particle size also makes the 
CMu term smaller. Both effects lead to a smaller plate height (Table 26-3). 
(f) Decreasing temperature will decrease the diffusion rates DM and DS. In Table 26-3, it 
can be seen that the B/u term becomes smaller and the CSu and CMu terms become larger 
with decreasing diffusion coefficients. This can lead to an increase in H if the CSu and 
CMu terms dominate or a decrease in H if the B/u term dominates. In most cases, H 
increases as the temperature decreases. 
27-28. Gas-solid chromatography is used primarily for separating low molecular mass gaseous 
species such as carbon dioxide, carbon monoxide and oxides of nitrogen. 
27-29. Gas-solid chromatography has limited application because active or polar compounds are 
retained more or less permanently on the stationary phase. In addition, severe tailing is 
often observed due to the nonlinear characteristics of the physical adsorption process.