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 G7102A ELSD, 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.
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