Photometric accuracy in UV/Vis

Hey guys,

I'm calibrating a UV/Vis, instrument model 8453, and I seem to consistently give varying results for the photometric accuracy test (with potassium dichromate).  The protocol requires it be done under 4 minutes.  My question is, why?  Is it unstable?  I'm concerned that the varying pass/fail results could be due to the readings not being done fast enough (?), even if it's under 4 minutes.

Thanks for any info!

B

  • Hi B

    We regularly do the photometric accuracy verification as part of teaching lab exercises. I am assuming that you are preparing the dichromate and blank solutions yourself. 

    A few ideas ( apologies if you already done these)

    • Make sure the lamps have been on at least 45 minutes as mentioned in the software
    • The two solutions should be prepared daily and matched such that the blank H2SO4 prepared is the same as that used to prepare the dichromate solution.
    • The dichromate needs to be known purity and the mass of dichromate entered in the software adjusted for the purity
    • Use the same cuvette for both measurements and use it in the same orientation
    • Most importantly, acclimatize the cuvette with at least 3 or 4 portions of your solution before measuring it.

     

    You might also want to check that the deuterium lamp is still within specifications using the software

     

     

    Hopefully this helps

    kevin

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