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preface to fifteenth edition

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PRACTICAL LABORATORY INFORMATION 11.31<br />

11.4.2.7 Time of Analysis. The retention time required <strong>to</strong> perform a separation is given by<br />

t 16Rs 2<br />

R <br />

2<br />

(1 k) 3<br />

<br />

H<br />

2<br />

1 (k) u<br />

Now t R is a minimum when k 2, that is, when tR<br />

3t M.<br />

There is little increase in analysis time<br />

when k lies between 1 and 10. A twofold increase in the mobile-phase velocity roughly halves the<br />

analysis time (actually it is the ratio H/u which influences the analysis time). The ratio H/u can be<br />

obtained from the experimental plate height/velocity graph.<br />

11.4.2.8 High-Performance Liquid Chroma<strong>to</strong>graphy. Typical performances for various experimental<br />

conditions are given in Table 11.15. The data assume these reduced parameters: h 3,<br />

v 4.5. The reduced plate height is<br />

The reduced velocity of the eluent is<br />

H L<br />

h <br />

d Nd<br />

ud<br />

v <br />

D<br />

p<br />

p<br />

p<br />

Ldp<br />

<br />

t D<br />

M M M<br />

In these expressions, d p is the particle diameter of the stationary phase that constitutes one plate<br />

height. D M is the diffusion coefficient of the solute in the mobile phase.<br />

TABLE 11.15<br />

Typical Performances in HPLC for Various Conditions<br />

Performances<br />

N t M ,s<br />

Column parameters<br />

L, cm d p , m P, atm (psi)<br />

2 500 30 2.3 3 18.4 (270)<br />

2 500 30 3.7 5 18.4 (270)<br />

2 500 30 7.5 10 18.4 (270)<br />

5 000 30 4.5 3 74 (1088)<br />

5 000 30 7.5 5 74 (1088)<br />

5 000 30 15.0 10 74 (1088)<br />

10 000 30 9.0 3 300 (4410)<br />

10 000 30 15.0 5 300 (4410)<br />

10 000 30 30.0 10 300 (4410)<br />

10 000 30 9.0 3 300 (4410)<br />

10 000 60 9.0 3 150 (2200)<br />

10 000 90 9.0 3 100 (1470)<br />

15 000 90 2.3 3 223 (3275)<br />

15 000 120 2.3 3 167 (2459)<br />

11 100 30 10.0 3 369 (5420)<br />

11 100 37 10.0 3 300 (4410)<br />

11 100 101 10.0 3 100 (1470)<br />

27 800 231 25.0 3 300 (4410)<br />

Assumed reduced parameters: , These are optimum values from a graph of reduced plate height versus reduced<br />

h 3 v 4.5.<br />

linear velocity of the mobile phase.

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