Liquid Chromatography Detectors - LC Detectors Based on Refractive Index Measurement > Page 19

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,