PHAR 4634 - Chapter 2 Page 2

Logarithms

If N = bx then x = logb N

e.g. 100 = 102 thus log (100) = 2 base 10 assumed

100 is the antilog of 2.

These are called common logs. Natural logs use the base e (=2.7183)

To convert from common to natural:-

2.303 x log N = ln N

e.g. ln (100) = 2.303 x log (100) = 2.303 x 2 = 4.606

Figure II-2

Common logs are used with equilibrium equations and buffer or pH calculations. Logarithms to base e are used in pharmacokinetics.

See also Parrott, E.L. and Saski, W. 1977. Experimental Pharmaceutics, Burgess, p298.

This page was last modified: 12 February 2001