The counts for the analyte and internal standard from the same solution kept going up (ICP-MS 7800)


I am running ICP-MS to determine Co Assay and also elemental impurities. 

1. in the elemental impurities test, standard internal recovery kept going up from 100-113%. The internal standard was introduced into the system with online tubing. 

2. The first run of  Cobalt Assay, Co, and standard internal counts kept going up from 100%-107% (against the beginning point).  The internal standards were added to the Co solution, so Co and internal standards were introduced into the system in the same way through the peristaltic pump.  The increase rate for Co and internal standards are almost the same.  

3. In The second run of Cobalt, internal standards and Co were introduced into the system as the same as the first run. The trends for Co and internal standards were still there,  but recovery against the beginning point were from 100%-102%. 

My questions are: 

1  Is this trend normal? should it be random in a certain range? 

2. is this trend relative to the introducing system, like a pump, and nebulizer? 

3. if the system has something wrong, what can we do to fix it? 

  • Hi  

    I'm sorry that a response hasn't been provided. Have you been able to resolve your problem? If you have been able to resolve the problem, please let us know what you did..

    In case you haven't, I'd recommend:

    The recovery values around 100% is perfect, if you obtain values > 100% ( it could mean that sample isn't coming in the system properly eg tubing, sample probe, nebulizer...), on the contrary if the recovery is < 100%, it could mean that ISTD isn't coming in the system  ok.  eg tubing, ISTD solution has been spent or the ISTD isn't coming in constantly

    It's important check if all ISTD behave the same way or only happen with one of them. Also there is a problem with the ISTD solution.

    To check  if the system is ok, you can run the Start Up, overall Performance Report, where you can check the sensitivity for 7Li , 59Co and 205Tl. If in this scenario, the counts for all masses are ok, it mean that  Sample Instroduction should be ok

     Thanks in advance 


  • Some drift is normal throughout an analysis, but if you are seeing upward drift that means your sensitivity is improving over time. This is very common with cone conditioning. As your cones become more "conditioned" your drift will decrease. New cones or cleaned cones all need to be conditioned. Since your drift is lessening overtime I suspect that was the case. You can expedite the conditioning by aspirating a 50ppm Ca solution for ~30 minutes followed by your rinse solution for ~15 minutes prior to your analysis. 

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