1 (196)

Prévia do material em texto

Principles of Instrumental Analysis, 6th ed. Chapter 27
 
 6
stationary phase while it is in the column with a chemical reagent that creates cross links 
between the molecules making up the stationary phase. 
27-18. (a) Band broadening arises from very high or very low flow rates, large particles making 
up the packing, thick layers of stationary phase, low temperature and slow injection rates. 
(b) Band separation is enhanced by maintaining conditions so that k lies in the range of 1 
to 10, using small particles for packing, limiting the amount of stationary phase so that 
particle coatings are thin, and injecting the sample rapidly. 
27-19. The retention index for an analyte is a measure of the rate at which it is carried through a 
column compared with the rate of movement of two normal alkanes, one that moves 
faster than the analyte and the other thatmoves more slowly. To obtain the retention 
index of an analyte on a given column, the log of the adjusted retention times for the two 
alkanes and the analyte are determined. The retention index for butane is always 400 and 
for pentane 500. The retention index for the analyte is then derived by interpolation 
between the two logarithmic retention indexes of the alkane (see solution to Problem 27-
21). 
27-20. The distribution coefficient for a polar compound will be larger on the carbowax 20M 
column than on the nonpolar SE-30 column. 
27-21. 
Sample Adjusted Retention Time Rt′ = tR – tM Retention Index, I 
n-Pentane 1.59 500 
n-Hexane 3.66 600 
1-Hexene 2.58 
 
For 1-hexene,