Micromass Quattro Ultima, User Manual

Page: 142 / 227

The source can be tuned to fragment ions within the ion tunnel 1 vacuum housing.
This can provide valuable structural information for low molecular weight analytes.
The most common methods of delivering sample to the electrospray source are:
•
Syringe pump and injection valve.
A flow of mobile phase solvent passes through an injection valve to the
electrospray source. This is continuous until the pump syringes empty and need
to be refilled. Sample is introduced through the valve injection loop (usually 10
or 20µl capacity) switching the sample plug into the mobile phase flow. Tuning
and acquisition are carried out as the sample plug enters the source. (At a flow
rate of 10 µl/min a 20µl injection lasts 2 minutes.)
•
Reciprocating pump and injection valve.
A flow of mobile phase solvent passes through an injection valve to the
electrospray source. Sample injection and analysis procedure is the same as for
the syringe pump. The pump reservoirs are simply topped up for continuous
operation. The most suitable reciprocating pumps for this purpose are those
which are specified to deliver a flow between 1 µl/min and 1 ml/min. A constant
flow at such rates is more important than the actual flow rate. The injection
valve on reciprocating pumps may be replaced by an autosampler for
unattended, overnight operation.
•
Infusion pump.
The pump syringe is filled with sample in solution. The infusion pump then
delivers the contents of the syringe to the source at a constant flow rate. This
arrangement allows optimisation and analysis while the sample flows to the
source at typically 5-30 µl/min. Further samples require the syringe to be
removed, washed, refilled with the next sample, and replumbed.
A 50:50 mixture of acetonitrile and water is a suitable mobile phase for the syringe
pump system and the reciprocating pump systems. This is appropriate for positive and
negative ion operation.
Positive ion operation may be enhanced by 0.1 to 1% formic acid in the sample
solution.
Negative ion operation may be enhanced by 0.1 to 1% ammonia in the sample
solution. Acid should not be added in this mode.
These additives should not be used for flow injection analysis (FIA) studies, to
allow easy change over between positive and negative ion analysis.
Degassed solvents are recommended for the syringe and reciprocating pumps.
Degassing can be achieved by sonification or helium sparging. The solvents should be
filtered, and stored under cover at all times.
Electrospray
Page 142
Quattro Ultima
User's Guide