Analytical Problems Hints And Tips; Poor Precision - Thermo Scientific iCAP 7000 Series Manual

iCAP Customer Familiarisation Manual iCAP Customer Familiarisation Manual

9 Analytical Problems Hints and Tips

Analytical Problems Hints and Tips
9.1

Poor Precision

Poor Precision
A quick test should be run to determine if the poor analytical results are matrix quick test should be run to determine if the poor analytical results are matrix quick test should be run to determine if the poor analytical results are matrix
related.
A 10 ppm solution of a few common elements such as Cu, Mn, Ba, Cd, Zn and A 10 ppm solution of a few common elements such as Cu, Mn, Ba, Cd, Zn and A 10 ppm solution of a few common elements such as Cu, Mn, Ba, Cd, Zn and
Fe should be put together and a metho Fe should be put together and a method made using the primary lines and
default conditions. default conditions.
After standardisation, the standard should read back, on the iCAP for example, After standardisation, the standard should read back, on the iCAP for example, After standardisation, the standard should read back, on the iCAP for example,
with a precision of typically 0.2 to 0.5 percent (with a 10 second integration with a precision of typically 0.2 to 0.5 percent (with a 10 second integration with a precision of typically 0.2 to 0.5 percent (with a 10 second integration
time). If the precision obtained is substantially greater than this try Torch time). If the precision obtained is substantially greater than this try Torch time). If the precision obtained is substantially greater than this try Torch
alignment then go o alignment then go on to trouble-shoot further if the problem remains.
If the instrument meets these specifications then the sample matrix itself is If the instrument meets these specifications then the sample matrix itself is If the instrument meets these specifications then the sample matrix itself is
suspect.
Possibly modifying plasma parameters such as power will help the situation. Possibly modifying plasma parameters such as power will help the situation. Possibly modifying plasma parameters such as power will help the situation.
Poor precision generally relates to Poor precision generally relates to
problems in the sample introduction lems in the sample introduction
system.
First check to ensure that the First check to ensure that the
nebuliser pressure or flow is set nebuliser pressure or flow is set
correctly by aspirating a 1000 ppm correctly by aspirating a 1000 ppm
Yttrium solution (Sodium will also Yttrium solution (Sodium will also
work if no Yttrium is available). work if no Yttrium is available).
Check to ensure that the centre Check to ensure that the centre
orange "bullet" is even with or slightly orange "bullet" is even with or slightly
above the top of the Radial torch. If above the top of the Radial torch. If
not, adjust the nebuliser pressure up not, adjust the nebuliser pressure up
or down until the "bullet" looks correct. or down until the "bullet" looks correct.
At this point the nebuliser
should be approximately 0.15 mPa should be approximately 0.15 mPa
(150kPa/25psi) for aqueous solutions.
If the pressure is substantially higher, If the pressure is substantially higher,
the nebuliser orifice is generally to the nebuliser orifice is generally to
blame and should be cleaned. blame and should be cleaned.
Pooling and dripping in the spray Pooling and dripping in the spray
chamber can also cause many chamber can also cause many
precision problems. You may be able ecision problems. You may be able
to see this visually using the Y test to see this visually using the Y test
described above.
If the Yttrium "bullet" is If the Yttrium "bullet" is bouncing up
and down inside the plasma, it is and down inside the plasma, it is
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shoot further if the problem remains.
nebuliser pressure
for aqueous solutions.
This document is part numbered 849940090071 This document is part numbered 849940090071
d made using the primary lines and
Version 1.02