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You will not see any signals from the IRM compounds unless there is a spray present and the
mobile phase contains electrolytes. The IRM signals will be unstable during the startup and
stabilization of the spray, which may take ten minutes or longer at a drying gas temperature of
350 °C and flow of 4 L/min.
The accurate mass values are:
Compound
Methyl stearate
HP-1221
Figure 4. Example spectrum of the IRM compounds, 1 scan/second (9,816 transients/scan).
Instrument: 6510 QTOF; IRM preparation: 200 µL of 100 µg/mL methyl stearate and 2% HP-1221 in
ACN, allow ACN to evaporate, followed by 200 µL FC-70; drying gas temperature: 325 °C; gas flow: 5
L/min; mobile phase: 300 nL/min of 0.1% formic acid in 97/3 water/ACN.
To enable reference mass correction:
• Enter the m/z value into the Reference Mass tab of the Acquisition software and check
the box in front of the entry. Repeat for the other IRM compound if it is used.
• Check the box "Enable Reference Mass".
• The acquisition mass range in MS mode must be set wide enough to include the
reference masses selected.
• Save the method.
Shortly after loading the IRM solutions, the ion signals should stabilize at around 20,000 to
150,000 counts abundance when the instrument is operated at ca. 5,000—10,000 transients per
spectrum. Actual values depend on the amount that was loaded, cleanliness of the interface
assembly, operating parameters used for the MS, mobile phase composition, number of
transients per scan, and other factors. It is desirable to keep the abundances above 5,000
counts for all scan speeds to obtain adequate ion statistics. With current electronics (March
m/z value for proton adduct (positive mode)
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18 July 2011
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