Let the change in density resulting from the presence of the solute at a concentration of 10-6 g/ml be (Dd). It follows, that to a first approximation,
| where (d1) | is the density of the solute, carbon tetrachloride, |
| (d2) | is the density of the mobile phase, n-heptane |
| and (Xs) | is the concentration of the solute to be detected. |
Thus for the example given,
The coefficient of cubical expansion of n-heptane is about 1.6 x 10-3 per oC. The temperature (Dq) that would produce a change equivalent to the presence of carbon tetrachloride at a concentration of 10-6 g/ml can, therefore, be calculated.
Thus,
