Intensity issues for standard blank during the first calibration

Hi everyone : We use an ICPMS 7800 and, before and after the first standard calibration, the signal intensity vary a lot.

The intensity for most of the elements tracked decrease strangely, even if we take care of cleaning the autosampler probe with washes before and after the calibration.

  • Matrix of Standards : 2.7% v/v HNO3
  • Matrix of wash ("Rince pre-std", "Diluent Blank") : 2% HNO3, 0.5% HCl

As you can see on the screenshot below, the intensity for the same solution can vary from single to double. On the same note, the intensity of the wash before calibration decrease slowly for most elements tracked, even with 10 washes. As a result, all the blanks following are negative until the next recalibration.

 (knowing that we leave the ICPMS warm up 20 minutes at its start, before doing the performance report, a tune of the instrument, adding the internal standard line and 10 minutes of wash again, so the ICPMS is turned on for approximately an hour before the "Rince Pre-Std".  We wash it as well at the end of each analysis with a dedicated wash solution, according to Agilent advises.)

do you have any idea what could happen here? Thanks!

  • It appears you have Zn contamination in your "Rince Pre-std" solution. 

  • What happen when u try with a conc about 3 ug/l ?

  • Does anyone in your lab use a dandruff shampoo? The most common shampoos have zinc pyrithione as the active ingredient. Do a swab sample of your lab where standards and blanks are prepared to see if you have Zn contamination.

  • Thanks for the advice : actually an Agilent employee told us the same thing during the previous PM, so we acid-cleaned all the apparatus (autosampler wash reservoir included) : the "Rince Pre-Std" has been very carefully prepared, and I honestly don't know where the contamination could come from.
    If I can ask : how can we spot the Zn contamination here? Is it due to the intensity level for this solution (above 2500cps), or due to the intensity variation for the same solution?

  • Actually I couldn't try lower than 13ug/l for Zn ; I will prepare a 3ug/l solution for the next analysis : what would happen?

  • Good to know! I asked around but nobody used dandruff shampoo for a while in the labs where the solutions were prepared
    The swab test is an excellent idea, thank you very much.

  • You're quite welcome. 

    Another possibility - we had an unidentifiable Zn contamination that we traced to the cardboard cap liner in some of our sample (digestate) bottles. If you use this type of bottle, the cap has a cardboard liner that has a shiny surface. That shiny surface is mineral-derived, and when we digested a bunch of bottle caps, we found  a strong Zn signature (plus a few other ions such as Mg, Al, Ca, etc.). So take a look at your containers, raw sample, digestate, and standards, and see if any of them have this cap liner. 

  • What is your instrument LDL? I'm guessing it's higher than 3 µg/L. And what is your required method detection limit? You may be chasing ghosts if those figures are near your lowest standard concentration of 13µg/L.

  • Hi,

    We see this issue with decreasing Zn counts over the run and it seems to originate from inadequate rinsing of the sample introduction (primarily the peri-pump tubing) in the sample/calibration matrix prior to calibration.  If we run, the same sequence immediately after the first run, oftentimes that will resolve the Zn issue.  Obviously a more efficient way to handle this would be to find a better rinse protocol prior to the run.

    From the data you provided, it looks to me like Zn is rinsing out of your sample/standard path.

  • Well, there is probably a misunderstanding due to my poor knowledge in spectrometry :  Actually the DL for Zn given by Masshunter software is 0.01ug/l, when the DL I calculated myself with dedicaced blank solutions is closer to 0.06ug/l (is it only possible?)
    We have required method detection limits for other elements, but not for Zn

Was this helpful?