Internal standard issues in He mode ICP-MS 7800

Hello! Hoping someone has some ideas on a new problem we've been having. We are an environmental lab that runs EPA 200.8 with no He for drinking waters. This method is working. However when we use He mode for our other methods we cannot get it to calibrate. One or more internal standards just splits off way out of range during calibration. We have replaced pumped tubing and tubing going to and from the connector block. Cleaned the torch, nebulizer, cones, and ion lenses.  Purged the cell for 30 minutes. Anyone have ideas or tips??

  • it's hard to see but it looks like the 6Li go way of in the calibration line. what's the 7Li doing? Give the 7Li also a upwards count rate in de calibration? Is the 6Li reacting the same in NoGas and He mode?

  • Hi,

    i guess when you speak from connector block, you mean the T-Piece which is connected to the peripump.

    And if so, you are doing an online ISTD addition.

    6Li is not a very good internal std for He-Mode due to its low mass related drop of sensitivity. Anyway, the 6Li in NoGas looks quite high. Is it possible, that your  Multielement Standard contains 6Li?

    Are you using a "white white" tube for the sample and a "orange blue" tube for the ISTD? If so, you could try to use "black black" tubes for both. This means that you have a 1:1 dilution of your sample with internal std. So you will loose cps, but gain the mixing of sample and istd. If you try this option, you should reduce the ISTD concentration to 1:10 of the original value.

    Looking to the attached picture, you have shown us the calibration for 51V. This looks bad, because of a possible interfered signal comming from ArCl (if you are using HCl). To be honest, ArCl is quite a small molecule, which is not sufficiently eliminated by collision in helium mode.

    Best Regards


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