Method optimization
PlasmaQuant MS product family
84
Once an optimal flow rate is determined and set, you can further enhance
sensitivity by re-tuning the instruments ion optics parameters to achieve the
highest possible sensitivity for each reference isotope in iCRC mode. For more
information on auto-optimization of the ion optics in iCRC mode see section
"Automatic optimization" on page 79 . Note that the auto-optimization routine
requires a solution of 5 µg/L (5 ppb) As, 20 µg/L (20 ppb) Sc and 20 µg/L (20
ppb) Y in 1 % HNO
3
(no HCl).
7.
Change the iCRC tuning solution from Solution A to Solution B, without stopping
the time scan, and allow time for the signal/nebulization to stabilize.
Then monitor the net signal changes between the two tuning solutions for the
analytes of interest, such as
51
V
+
,
52
Cr
+
,
56
Fe
+
,
75
As
+
,
78
Se
+
and
80
Se
+
, etc. This can be
easily done by moving the mouse curser over the graph and reading off the X, Y
data displayed at the top. If the sensitivity for a selected analyte is too low, or the
background level is too high, then repeat the ion optics optimization.
8.
Once the optimal iCRC conditions have been found, save the parameters by clicking
the [S
AVE
] icon or selecting S
AVE
from the F
ILE
menu in the E
DIT
M
ETHOD
window,
then exit E
DIT
M
ETHOD
, and start/run the sample analysis worksheet.
8.5
Method optimization troubleshooting
If sensitivity is much lower than expected and no significant changes are observed
when changing the sheath/nebulizer gas flow and/or the ion mirror lens settings, then
check the following:
Inspect the sample introduction system and ensure that the tuning solution is
pumped into the spray chamber correctly and the solution waste from the spray
chamber is drained out properly.
Make sure that a correct tuning solution is used.
Check that the detector voltage is set up correctly (accessed from the I
NSTRUMENT
/
D
ETECTOR
S
ETUP
page).
If you cannot achieve a low oxide ratio or meet the required sensitivity for some
isotopes, complete the following:
Perform a torch alignment.
Prepare a fresh tuning solution.
Check the spray chamber temperature setting (accessed from the S
AMPLING
page).
When changing the temperature setting, wait for at least 10 min to allow
temperature stabilization.
Check the mass calibration and mass resolution (if mass calibration failed).
Try to perform an auto optimization.
Try cleaning the sampler and skimmer cones (or replacing with new ones).
If performance specifications are not met after running an ion optics auto
optimization, check the following:
Ensure that a correct tuning solution is used: 1 μg/L (1 ppb).
Start the time scan from the O
PTIMIZATION
page of the Method Editor. Slightly
change the voltage for the Entrance Lens (±5V) and Fringe Bias (±0.5V).