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Varian ELSD Service Manual
OPTIMISING DETECTOR PERFORMANCE
General Considerations
The Varian ELSD instrument should be thought of as a detector like any other designed for liquid chromatography.
The main distinguishing feature is the ability to evaporate the solvent from the column eluent. Therefore, normal
system set-up precautions should be remembered when starting to use the instrument. Any solvent intended for use
with the ELSD should be fully miscible with any previously used in the liquid chromatograph; if there is any
uncertainty, a mutually miscible solvent should be run through the system as an intermediate liquid. The sample loop
should also be flushed with miscible solvent where necessary. The intended eluent should be thoroughly degassed,
contain no non-volatile salts or material and should be fully compatible with the column(s). All connections should be
made with zero dead volume fittings and tubing with an I.D. <0.010”.
The Varian ELSD requires nitrogen (purity >98%), capable of generating 60-100psi inlet pressure. If in-house
nitrogen is not available then we recommend the use of a nitrogen generator, giving a constant uninterrupted supply
of high purity gas. Air can be used with non-flammable solvent systems. The eluent of choice should be fully volatile
under the chosen detector parameters – any non-volatilised eluent will increase baseline noise and reduce
sensitivity.
Optimisation Parameters
Gas Flow
An increase in gas flow rate causes a decrease in signal response. Lower gas flow rates are more favourable since
less gas is consumed and a better sensitivity is achieved. However, there comes a point at which this benefit is
counterbalanced by the increase in baseline noise due to inefficient evaporation of the eluent. In general, gas flow
rates of 1.0-2.0SLM tend to be a reasonable compromise between baseline stability and high reproducible response
for eluent flow rates >0.5ml/min. Reducing the eluent flow allows a reduction in the gas flow rate to maintain the
optimum particle stream concentration, resulting in greater sensitivity.
When operating the Varian 385-LC at sub-ambient temperatures in aqueous solvents, gas flow values of >2.0SLMs
maybe necessary to control the baseline noise.
Evaporator Temperature
The effects of altering the evaporator temperature tend to be less dramatic than changing the gas flow, although the
temperature must be high enough to evaporate the solvent and to sufficiently dry the particle plume without having a
detrimental effect on the sample being studied.
The Varian ELSD can be operated at sub-ambient temperatures to improve the detection of semi-volatile
compounds. In aqueous solvents, baseline noise may become too excessive at temperatures <15°C. However, for
organic solvents, the baseline can be controlled down to 10°C, provided the gas flow is increased to compensate
.
Nebuliser Temperature
The nebuliser temperature is the parameter requiring least adjustment. In the majority of cases the nebuliser
temperature is set to the temperature of the chromatography system. However, increasing this temperature can
improve instrument performance by increasing the efficiency of nebulisation by reducing the viscosity and surface
tension of incoming solvent. Setting the nebuliser temperature too high may result in a deterioration of detector
performance due to solvent boiling in the nebuliser, giving rise to increased noise on the baseline due to spiking
Optimisation Procedure
Set the system at the minimum evaporator and nebuliser temperatures and a gas flow rate of 1.6 SLM. Make an
initial injection of the test component and monitor the signal response. With each subsequent injection increase the
