Mobile Phase Considerations When Using The Multimode Source - Agilent Technologies G1978B User Manual

3 Reference

Mobile phase considerations when using the multimode source

Mobile phase considerations when using the multimode source

Flow rate
In general, once the analyte response is optimized, the flow rate or mobile
phase composition may be changed without having to re-optimize the
vaporizer temperature or drying gas temperature. The IR emitters have a
feedback control that is provided by the vapor temperature sensor. Power to
the IR emitters is dynamically changed to maintain the vapor temperature at
the desired setpoint regardless of mobile phase changes.
ESI mode (or for compounds that have an ESI response in mixed mode)
Improved response will be obtained when lower amounts of electrolyte are
used in the mobile phase. The recommended electrolyte concentration is
lower, approximately one fifth that of prior recommendations. The need for
lower electrolyte concentrations is due to the physics of ESI ion formation and
charge separation in the multimode source. The following are example
recommended electrolyte concentrations:
• 1 mM ammonium acetate instead of 5 mM
• 0.02% formic acid instead of 0.1%
The electrolyte-response effect is not present in the dedicated ESI source; continue to use
N O T E
higher electrolyte concentrations with the dedicated ESI source.
Do not use pure solvents (i.e., no electrolyte) as mobile phases for ESI work as this practice
N O T E
results in unpredictable analyte response.
APCI mode (or for compounds that have an APCI response in mixed mode)
• In positive APCI mode, higher response is obtained using protic or neutral
• Acetronitrile is a strong enough gas-phase base to deprotonate some analyte
• Methanol, isopropyl alcohol, and acetone are preferred for positive mode
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solvents as the organic mobile phase component instead of acetonitrile.
ions, leading to reduced response (30-fold reduction has been seen).
APCI.
Multimode Source for 6410 Triple Quad LC/MS User Guide