Detector calibration
PlasmaQuant MS product family
88
Before any replicate measurements are made for a solution, one very short pre-read
scan (100 µs) is performed using maximum attenuation; the detector is least sensitive
in this mode. This pre-reading gives an indication of what the counts per second
obtained will be for that solution; if a reading is obtained that indicates that the
detector will over-range – produce counts above 4x10
6
c/s – then that particular mass
will not be scanned for that replicate. The software will then flag that replicate in the
associated solution as over-range. This prevents detector damage, and avoids making
any measurements in the non-linear region of detector operation.
Prior to using the auto attenuation, you must calibrate/set up the detector attenuation
factors for all isotopes or analytes of interest. The D
ETECTOR
A
TTENUATION
page is
designed for the calibration of attenuation factors, and this page can be accessed from
the I
NSTRUMENT
window by selecting the D
ETECTOR
A
TTENUATION
tab.
Check the detector calibration each time the operating voltage of the detector is
changed after a detector scan.
Within the D
ETECTOR
A
TTENUATION
page, you can:
Calibrate and/or set up the detector attenuation factors
Display the detector calibration results, including attenuation factors and RSD of
the factors
Show the attenuation factors graphically
Save the new attenuation factors to your worksheet
View the attenuation factors from existing worksheets
It is not necessary to perform a detector calibration if the auto attenuation function is
not used/selected in your method/worksheet (if you are only ever measuring very low
concentrations).
9.2
Instrument initialization and solution preparations
To calibrate the detector attenuation system, you need two attenuation calibration
solutions, A and B. Typically these would be multi-element calibration standards, such
as those you were going to use for your analysis. The absolute concentration of these
solutions is not as important as the ability to generate appropriate signals for the
detector. Typically, 1 µg/L (1 ppb) and 50 µg/L (50 ppb) calibration standards work
very well, but if you find you get too many over-range error messages when doing the
attenuation, then you may need a more dilute Solution B. Ideally, these solutions
would contain all the elements you wish to analyze as well as any Internal Standards
you may want to use. In reality, it is not always possible to get every desired element
into the same solution due to chemical compatibility or stability issues. In cases like
this, more than one attenuation calibration can be combined into your final analytical
worksheet, or the attenuation factor table can be edited manually.
Before performing a detector calibration, it is very important to check the following:
Ensure that the PlasmaQuant MS instrument is warmed up and set up properly.
Check the torch alignment, mass resolution, mass calibration, and detector
settings. Refer to the Aspect MS software help for details on how to set up the
instrument either manually or automatically.