. Evaporative light scattering detector
The principal variables affecting the ELSD response were the nebulization
and evaporation temperatures and, as it was the case with the
C-CAD, attenuation of the signal, nitrogen pressure and filter. The nebulization
and evaporation temperatures depend on the composition of
mobile phase. In the instrument's manual, a nebulizer temperature setting
between 30 °C and 35 °C is generally given as optimal; and when
organic solvents such as acetonitrile (boiling point b80 °C) are used
the optimal temperature has to be raised up to 40 °C. Both temperatures
were studied simultaneously in the range 35–55 °C for nebulization
and 45–65 °C for evaporation, maintaining the mandatory difference
of 10 °C between both values. At higher temperature, the baseline was
instable and the area peak values lower. The best results were obtained
with a nebulization temperature of 45 °C and an evaporation temperature
of 55 °C which were fixed for further experiments. In this detector,
the attenuation of the signal can be modulated between 1 and 9, the
highest response corresponding to 9; this value was set to obtain the
higher sensitivity although it negatively affects to the background
noise, increasing the baseline instability. The nitrogen pressure provided
by the nitrogen generator was of 36 psi. For this evaporative detector a
high filter was selected as optimum value among the three options
available (high, medium and low).