Countercurrent Heat Exchanger; Flow Cell; Purge Valve; Pressure Relief Valve - Waters ACQUITY Refractive Index Detector Overview And Maintenance Manual

1 The ACQUITY Refractive Index Detector

Countercurrent heat exchanger

Achieving a stable baseline requires precise control of the temperature of the
flow cell and the fluid entering it. The low-dispersion, countercurrent heat
exchanger minimizes temperature fluctuations in the sample side of the flow
cell. The device's sample inlet and outlet lines are coaxial, which facilitates
heat exchange between incoming and outgoing fluids. The refractive index of
typical mobile phases used in liquid chromatography has a temperature
sensitivity of about 3% per °C.

Flow cell

The flow cell consists of two hollow prisms of fused quartz. Each prism has an
inlet and outlet. One of the prisms constitutes the cell's sample side through
which a constant flow of eluent passes during analysis. The columns used in
UPLC have smaller inner diameters (2.1 vs. 4.6 mm) and smaller particles
(1.7 vs. 3.5 μm). Peaks generated by UPLC will have volumes which are 4 to 5
times smaller than those observed with HPLC. Consequently, the flow cell
volume has been reduced to preserve this enhancement of peak resolution and
sensitivity.
The other prism constitutes the cell's reference side. It is filled with fresh
solvent when you purge the detector during equilibration. When you switch
from purging to normal operation, the purge valve opens, and the pressure
relief valve shuts, stopping the flow of solvent through the reference prism but
leaving the cell filled with fresh solvent.

Purge valve

During normal operation, the purge valve remains open. Fluid that passes
through the sample side of the flow cell flows through the purge valve and out
through the outlet tubing to the waste reservoir.
When you purge the detector, the purge valve closes causing fluid passing
through the sample side of the flow cell to exit through the reference side of
the flow cell, through the relief valve, and then to waste.

Pressure relief valve

During normal operation, the pressure relief valve remains closed. It opens
when the pressure inside the flow cell, whose maximum pressure rating is
1000 kPa (10 bar, 145 psi), becomes too high for the pressure relief valve to
30 October 13, 2014, 715003547 Rev. C