The temperature-controlled evaporation tube dries the aerosol droplets that come from the spray chamber. The evaporation tube evaporates the more volatile components in the mobile phase to produce dried particles composed of non-volatile analyte and background residue.

The efficiency of the drying procedure depends on the set temperature. Additional factors, such as the mobile phase composition, the pump flow rate and the sample composition, also play an important role.

Note the following when selecting an evaporation temperature:

  • As a standard, the Evaporator Temperature Nominal is set to 35 °C.

  • When selecting a different evaporation temperature, observe the evaporation temperature specification for the detector. See Performance Specifications.

  • Changes in the evaporation temperature affect the response of the detector.

  • When the temperature was changed, the evaporation tube requires time to equilibrate. The Wait For Temp Ready parameter makes sure that the detector is only ready for analysis when the evaporation tube is equilibrated.

    If the parameter is disabled, it is recommended to wait approximately 30 minutes before you start sample analysis.

How to optimize the evaporation temperature

  • Perform three or more injections of a reference standard for the analytical method for which you want to optimize the evaporation temperature.

  • Use a different evaporation temperature setting for each reference injection, ranging from low to high temperature. Select the most appropriate setting as starting point. See the Guidelines for selecting the evaporation temperature below.

TIP

Using performance metrics such as the precision and sensitivity of the detector can help to receive the optimal evaporation temperature.

Guidelines for selecting the evaporation temperature

The following guidelines are recommended for selecting an optimal evaporation temperature:

  • In general, use the lowest evaporation temperature within the specified temperature range that provides acceptable limits of sensitivity.

  • As a starting point, use an evaporation temperature of 35 °C.

  • Higher evaporation temperature settings can be used when analytes of interest have low volatility, relative to the background. Since the volatility of background residue is typically unknown, experimentation is required for optimizing this parameter for a given method.

  • Perform screening runs at two evaporation temperature settings.

    • VH-D20 detector: Use a minimum of two evaporation temperatures. Typically, 35 °C and 40 °C are appropriate if the temperature range is unknown. If required, perform additional tests in a maximum of 5 °C increments.

    • VF-D20 detector: Use two evaporation temperatures, depending on whether the temperature range is known. If the temperature range is unknown, 35 °C and 50 °C are an appropriate starting point for screening runs.

  • Consider that higher evaporation temperature settings may inadvertently reduce response for low-analyte levels, even if they are considered as non-volatile analytes.

  • Remember to check the limits of sensitivity by actual analysis of low-level standards. Also, check the analyte signal reproducibility at each evaporation temperature setting.

  • For detection of semi-volatile analytes, you can use lower evaporation temperature settings. However, this may lead to higher background levels and noise.

NOTICE

Do not use non-volatile modifiers, such as sodium phosphate. Observe the mobile phase guidelines in this manual. See Mobile Phase Guidelines for the Detector.