Page 207 - Illustrated Pocket Dictionary of Chromatography

210 VISCOMETRY DETECTOR

This diagram is to show that the viscosity is not a simple linear function of the
composition of two solvents. In the case of alcohols, here methanol, this increase
in viscosity is nearly double that pf pure water. This has major implications for the
operating backpressure if a water/methanol gradient is used over this composition
range. In essence, the backpressure will nearly double before decreasing toward
the viscosity of pure methanol.

viscometry detector Measures the intrinsic viscosity of a solu-
tion through the use of one or more capillaries across which the pres-
sure drop is measured (through a differential pressure transducer).
For a signal capillary the pressure drop, Dp, is defined by Poiseiulle’s
law:

Dp= 8 F p r 4
h
where h is the viscosity, F is the flow rate and r is the radius of
the capillary. The single-capillary design is very sensitive to flow rate
fluctuations. The multiple-capillary systems are used to compensate
for this issue.