Instrumental Signal Drift

Issue

Signal drift

Environment

• iCAP Q
• iCAP RQ
• iCAP TQ
• ECCN: EAR99

Resolution

To troubleshoot an instrumental drift follow these steps:

1. Make sure that the total dissolved solids level of the solution being aspirated is below the recommended levels and appropriate to the sample introduction system used (including skimmer cone insert).
2. Make sure that the cones have been appropriately conditioned, especially if the cones are new.
3. Make sure that the sample flow rate is consistent and continuous and is being drained appropriately from the spray chamber.
4. Check that the laboratory temperature is stable.
5. Check that the temperature of the cooling water supplied to the instrument is stable.
6. Make sure that the cooling water lines at the Peltier cooling are securely connected.
7. Make sure that the vacuum system is stable.
8. Check peristaltic pump:
   1. Make sure that the tubings of the peristaltic pump are not damaged or blocked.
   2. Make sure that the peristaltic pump is stable and solution transfer into the spray chamber is smooth.
   3. Check that the tension on the peristaltic pump tubing is correct and that the pump tubing is in good condition.
9. Check nebulizer:
   1. Make sure that the nebulizer is not damaged or blocked.
   2. Make sure that the nebulizer tubing is not damaged or clogged.
10. Make sure that the waste line is properly connected to the spray chamber and is not damaged or blocked.
11. Make sure that the plasma torch is in good condition with no cracked or melted areas.
12. Make sure that the torch body is aligned correctly inside the torch holder.
13. Make sure that the waste tubing is inserted in the waste container and the container is empty.

Analysis

This effect is typically related to the level of matrix in the samples analyzed with higher matrices causing a more significant signal drift. Typically, if cones are conditioned, typically with a matrix sample containing less than 0.2 total dissolved solids, then drift should not be an issue.

If signal drifts with time for samples that have an appropriate level of matrix, then it is strongly recommended to condition the cones before performing analysis.

In an extreme case, where the matrix content is significantly too high, material can build up on the sampler and skimmer and the cone orifices become smaller. When this happens, the total ion beam is reduced and the sensitivity of the instrument will decrease significantly. Removal and cleaning of the cones will usually resolve this problem.

Cause

The usual cause of signal drift is gradual deposition of undissociated sample matrix on the ICP-MS interface (sample and skimmer cones).