Troubleshooting ICP-MS Instrument Drift

Answer

This Information Applies To: Agilent ICP-MS systems (7700/7800/7850/7900/8800/8900)

Issue

Drift up is most often a sign of poor cone conditioning.

Drift downwards is often associated with build up on the sample introduction components during an analysis. This build-up is more typical when running higher matrix samples with high percent total dissolved solids (%TDS) which causes salt build-up on the nebulizer, torch injector, cones, and lenses. 

Sometimes drift can occur both up and down during the span of an analysis. It is important to evaluate if it is drift, or simply the result of matrix effects from a sample or a problem with poor internal standard mixing. If the drift appears to be non-matrix related, it may be due to either static charge, or an issue in the sample introduction. 

Steps to Follow

1. Check the sample introduction system for signs of wear or damage and perform maintenance or replace components as necessary.
   1. Check and clean or replace the nebulizer, spray chamber, and peristaltic pump tubing (see the video Troubleshooting and maintenance of ICP-MS System for optimal performance Part 2: Sample Introduction)
   2. Check and clean or replace the torch, bonnet, shield, and torch stand components. (Troubleshooting and maintenance of ICP-MS Systems to get optimal performance: Part 3: Torch Box)
   3. Inspect the dilution gas, makeup, nebulizer/carrier gas connections (Figure 1), and the gas connections that come out the elbows on the left panel of the ICP-MS (Figure 1; Item 4). A loose gas connection can cause unstable signal.
      

      
      
      Figure 1. Gas connections
      1. Dilution gas connection, 2. Makeup gas connection, 3. Nebulizer/carrier gas connections, 4. Gas connections on left panel
      
      

   4. Inspect and if neceddasy, replace the connector block. Verify that there is a good connection between the ground clip on the peri-pump (Figure 2; Item 2) and the conductive connector on the connector block (Figure 2; Item 1). Proper grounding is essential to minimize the buildup of static charges that affects stability. Confirm that the tubing going to the connector block is in good condition and the tubing is not kinked. With the peristaltic pump turned on, introduce solution to the sample and internal standard line to verify there are no leaks present.
      

      
      
      Figure 2. Connector block
      1. Conductive connector, 2. Ground clip on the peri-pump
      
      

   5. Clean or replace the sampling cone, skimmer cone, and lens stack. Look for signs of damage or clogging (See the video Troubleshooting and maintenance of ICP-MS Systems for optimal performance: Part 4: Interface Region).
      Remember to condition cones after cleaning or replacing (See the article ICP-MS Cone Conditioning)
      

      Tips: The Easy-fit x-lens assembly is a single-piece assembly that cannot be disassembled or cleaned. It can only be replaced.

2. Perform a stability test using the default conditions in no-gas mode.
   1. Directly connect the peri-pump to the autosampler and bypass any accessories (i.e. Humidifier, Advanced Valve System, etc.). 
   2. Disconnect the internal standard line from the connection block and install the plug (Figure 3).
      

      
      
      Figure 3. Plugged connection block
      1. Internal standard line plugged
      
      

   3. Condition any new or cleaned cones if it has not been performed already during troubleshooting. (See the article ICP-MS Cone Conditioning)
   4. Perform the Startup and generate a Performance Report ensuring the signal is good and there are no obvious performance issues.
   5. Keep only the no-gas tune mode. Remove all other tune modes.
   6. Create a sample list with calibration standards followed by a quality control (QC) check solution, such as a mid-level standard, bracketing every five samples. Run rinse solution as the samples and add around 50 samples in total (Figure 4).
      

      
      
      Figure 4. Sample list
      
      

   7. In the batch calibration page, clear the use of any internal standard corrections (Figure 5). 
      

      
      
      Figure 5. Batch calibration page
      1. ISTD column set to <None>
      
      

   8. Add meters such as internal temperature, inlet temperature, analyzer pressure, IFBK pressure, and nebulizer/carrier gas BP (backpressure), see the article How to Select Meters in ICP-MS MassHunter Software.
   9. Perform the run and monitor the meters over the course of the run.
   10. Check the recovery of the QC check solution.
   11. If drift is present, determine if it was temperature, vacuum, or nebulizer backpressure related.
   12. If no drift is present, proceed to step 3.
3. Perform a stability test in all tune modes. 
   1. Using the same conditions as step 2, perform the same analysis with all your tune modes.
   2. If drift occurs in any cell gas mode, purge the cell gas lines and confirm that the stabilization time between tune modes is appropriate (See the article How To Purge the ICP-MS Helium Cell Gas Line to Ensure a Good Tune in Helium Mode).
   3. If no drift occurs, proceed to step 4.
4. Perform a stability test with internal standards.
   1. Using the same conditions in step 3 with all tune modes, reinstall your internal standard line.
   2. If needed, add the internal standards to your analyte list.
   3. Perform the analysis.
   4. If the internal standard stability is poor, or high internal standard RSDs are present, troubleshoot the poor internal standard mixing (see the article Internal Standard (ISTD) Mixing Issues on ICP-MS).
   5. If there is no drift, proceed to step 5.
5. Using your original method conditions, perform a stability test using a sample that is typical of your matrix (instead of the rinse solutions previously used) and a check the sample. 
   1. If the results are satisfying, resume normal operations of your instrument. 
   2. If there is drift, re-evaluate your method conditions and determine if they are appropriate for your matrix type. You may need to perform bench dilutions or use HMI modes to achieve better stability.

Learn how to effectively troubleshoot your Agilent ICP-MS System: Agilent 7800/7850/7900 ICP-MS with MassHunter Agilent 8900 Triple Quadrupole ICP-MS with MassHunter e-learning course available from Agilent education