1
Introduction
Should I Use Sheath, Auxiliary, and/or Sweep Gases?
Thermo Electron Corporation
LTQ XL Getting Started
7
Should I Use Sheath,
Auxiliary, and/or
Sweep Gases?
Nitrogen gas can be applied to the system using any combination of the
three gas sources: Auxiliary gas, Sweep gas, and/or Sheath gas. When Sheath
gas is used, nitrogen is applied as an inner coaxial gas (when used in tandem
with Auxiliary gas), helping to nebulize the sample solution into a fine mist
as the sample solution exits the ESI or APCI nozzle. (Sheath gas is not used
with the NSI source.) When Auxiliary gas is being used, nitrogen flows
through the ion source nozzle, the vapor plume is affected; the spray is
focused and desolvation is improved. When Sweep gas is used, the nitrogen
flows out from behind the sweep cone and can result in solvent declustering
and adduct reduction.
When you are analyzing complex matrices such as plasma or nonvolatile salt
buffers, Sweep gas is required for ruggedness. In full-scan MS or data
dependent scan experiments, the signal-to-noise ratio can be improved by
application of Sweep gas. In some cases, signal intensity can be increased by
using Auxiliary gas, particularly for higher LC flow rates.
All analyses are analyte dependent and require separate optimization with
Sheath gas, Sweep gas, and Auxiliary gas to determine which combination
will yield optimum performance. It is especially important to optimize with
each gas independently before you perform experiments using MS
n
techniques and before you perform any
quantitative analysis experiments
because optimum results could be achieved with any combination of
Sheath, Sweep, and/or Auxiliary gas. See
and
Table 3
for additional
information on using supplemental gas flows.
