Common Refractive Index Detection Problems; Environmental Factors; Inhomogeneities In Solution - Waters ACQUITY Refractive Index Detector Overview And Maintenance Manual

By detecting how far the image shifts (Δx), the refractometer measures the
difference in RI (Δn) between the solvent-sample solution and the solvent
alone.
The shift in the ratio of the amount of the light beam striking each element of
the dual-element photodiode results in a change in the output voltage from
the refractive index detector. The data system registers the changes in output
voltage as peaks in the chromatogram.

Common refractive index detection problems

Changes in solution density caused by factors other than sample
concentration are the most common source of problems in refractive index
detection. Changes in solution density can be due to these causes:
• Environmental factors such as changes in temperature or pressure
• Inhomogeneities in the solution

Environmental factors

Even small changes in ambient temperature can cause baseline drift.
Backpressure pulses from a dripping waste tube can cause short-term
baseline cycling. Refer to the ACQUITY online Help for more information.

Inhomogeneities in solution

The differential refractometer measures the difference in refraction between
the reference solvent and the sample solution. Most common inhomogeneity
problems are the result of improper solvent preparation.
• The mobile phase must be of constant composition.
• Gradient separations are not recommended because the Δn from the
mobile phase change can be larger than that from the analyte peak and
can exceed the detection range (5 × 10
contents.
• For maximum sensitivity, use the same solvent to prime all solvent lines
on the binary solvent manager or quaternary solvent manager.
Because the refractive index detector is sensitive to contaminants, replacing
tubing can often require long wash times. See

Common refractive index detection problems

RIU) from the reference cell
–4
Chapter 2 for more information.
October 13, 2014, 715003547 Rev. C 23