Operational Parameters - Agilent Technologies InfinityLab 1290 Infinity II User Manual

1 Introduction to the Detector
System Overview

Operational Parameters

The ELS Detector responds to all compounds that are less volatile than the
mobile phase and is independent of a compound's optical properties. It therefore
provides advantages over other spectroscopic detectors for detecting
compounds that are deficient in a UV chromophore or fluorophore.
The removal of aqueous mobile phase within an ELSD is typically achieved by
setting the evaporator temperature to the eluent's boiling point (for example
100 °C) to remove the solvent. For nonvolatile compounds, operating at these
high temperatures maximizes the signal response.
However, at these temperatures volatile and semivolatile compounds are
destroyed and are therefore not detected. This is problematic for small
molecules, such as pharmaceuticals and drug candidates.
The ELS detector is designed to evaporate difficult solvents at ambient and
subtemperatures to maximize detection of semivolatile compounds.
The ELSD has patented technology that reduces the evaporation time of highly
aqueous solvents at low temperature, and also prevents the evaporation tube
becoming saturated, which would otherwise prevent further evaporation
occurring.
Using this patented evaporation gas technology, a 20 µm droplet of water at
30 °C can be dried ca. 3x faster than just temperature alone. Using the Agilent
1290 Infinity II ELSD (G7102A), water can be evaporated as low as 20 °C,
providing maximum sensitivity to thermally sensitive compounds. For maximum
sensitivity of nonvolatile compounds, the evaporation gas can be turned off at
higher evaporation temperatures.
Therefore, unlike other ELS detectors, where the evaporator temperature is set
according to the type of mobile phase, the ELS detector evaporator temperature
is independent of the mobile phase. So, the ELS detector can be set at 30 °C for
all types of mobile phase provided the evaporator gas flow is adjusted
accordingly. This method of operation ensures that the ELSD sensitivity is
maximized even for low molecular weight compounds.
To prevent against unnecessary gas usage, a controlled gas shutoff valve is
integrated into the detector gas manifold. This shutoff valve will only allow gas to
pass into the instrument when in RUN mode. Should the instrument default to
STANDBY mode, the gas will reduce to a default value of 1.2 SLM for 15 min
before closing.
Agilent InfinityLab ELSD User Manual 12