Solvent Selection - Thermo Scientific Surveyor RI Plus Hardware Manual

3
Operation

Solvent Selection

Solvent Selection
32 Surveyor RI Plus Detector Hardware Manual
Detector response can be enhanced or degraded by the choice and preparation of the mobile
phase. In addition to providing proper separation, the solvent must also be compatible with
the detector and provide a sufficient refractive index difference so that the sample can be
measured.
Any refractive index detector is sensitive to small changes in solvent composition, and the
majority of problems associated with refractive index detectors can be traced to this cause.
Changes in composition can occur from incompletely mixed binary or ternary solvents,
column bleed, leaching of prior samples or solvents, decomposition of the solvent, or by
changing the amount of dissolved gas in the solvent.
Binary and ternary solvents must be thoroughly mixed and remain mixed to prevent baseline
offsets. This detector is typically sensitive to changes in composition in the low parts per
million range. Pre-mixed solvents in a stirred reservoir provide the most stable operation.
Stream mixing of solvents from separate reservoirs can result in baseline upsets. Solvent
delivery systems used in HPLC ordinarily have compositional mixing precision of about 1%
and not parts per million. Solvents mixed and delivered by the pump will show compositional
changes detectable by the refractive index detector even after passage through the
chromatographic system. This effect can be minimized but not eliminated by adding
additional mixing before the injector.
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