Calibration
Spectral Cross-Sensitivity
Due to the proximity of the spectral lines used to detect some ions
there are issues with spectral cross-sensitivity when samples contain
mixtures of ions.
There are also a significant number of potential chemical interferences
which must be counteracted in addition to taking the precautions
outlined.
Determining Ca when Na is present
Since the Na signal is very strong in comparison with Ca the effects of
cross-sensitivity on Na is very small and can generally be ignored.
However, the influence of Na on Ca can be substantial.
To enable the determination of Ca in the presence of Na, the
instrument applies a correction factor to take account of the
overlapping spectra.
During Ca measurement a value is deducted from the Ca signal
dependent on the Na signal. The scale of this adjustment is
determined and stored as an internal parameter during a correction
procedure.
Determining Ba when K is present
For the determination of Ba in the presence of K a correction is also
carried out by the firmware to take account of the overlapping
spectra. In this case both signals are strong, but the influence of K on
Ba is far greater than Ba on K.
When Ba is calibrated the readings on the K channel are stored.
During Ba measurement the value of K is determined and a
proportional amount is deducted from the Ba signal.
Perform single or multi-point calibrations for Ba and K separately. Do
not mix the ions during calibration.
Testing Na & K
It should be noted that Na readings are not truly linear even at
low concentrations.
When testing Na and K it is better to look at the correlation
number for K rather than Na. For Serum testing the R
2
number
for K should be very close to 1 (>=0.98) –if it is not, then the
calibration should be repeated.
Better accuracy will be achieved by using small calibration ranges
close to the point of interest.
If a large range needs to be available at all times then additional
calibration points should be used and a full calibration may be
required at frequent intervals.
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Calibration fluids and kits
We stock a wide range of calibration
fluids and specially developed kits ready
for same day dispatch* to aid with your
analytical requirements. Check out the
fluid brochure for the complete range of
dilutable and ready to use standards.
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