Metals in Hemp and Cannabis

Greetings All,

I just finished watching the  webinar regarding the AOAC method for cannabis and hemp.  From what I gather, it is recommended to use 0.5g of material, 10 mLs of concentrated acid (9mLs nitric and 1 mL hydrochloric) then the final digest is taken up to a volume of 50mLs with DI water.  That makes for a sample having 1% TDS and a 20% acid concentration. Is there another dilution of the sample somewhere in the method before introduction to the instrument?  I don't see anything in any of the documentation or the presentation materials.  I'm trying to wrap my head around the final sample matrix and the concentrations that the instrument is actually measuring.

Thanks,

Tom

Parents
  • Hello Tom,

    There was no other dilution applied to the prepared cannabis samples prior to analysis.
    The calibration standards were prepared using a mix of 1% nitric and 0.5% hydrochloric acid.

    The acid concentrations in the final sample digests are higher than those used for the calibration standards. However, it was noted that these acid concentrations gave reliable digestion of all the sample matrices and good chemical stability for all the analytes.

    There is more detail available in the Agilent application note titled "Determination of Heavy Metals in Cannabis and Hemp Products Following AOAC Method for ICP-MS - Routine monitoring of As, Cd, Hg, Pb, and other elements using an Agilent 7850 ICP-MS" available for review/download from the Agilent website at this URL:
    https://www.agilent.com/cs/library/applications/application-cannabis-aoac-7850-icp-ms-5994-4080en-agilent.pdf

    Hope that addresses your question,
    Cheers Eric

Reply
  • Hello Tom,

    There was no other dilution applied to the prepared cannabis samples prior to analysis.
    The calibration standards were prepared using a mix of 1% nitric and 0.5% hydrochloric acid.

    The acid concentrations in the final sample digests are higher than those used for the calibration standards. However, it was noted that these acid concentrations gave reliable digestion of all the sample matrices and good chemical stability for all the analytes.

    There is more detail available in the Agilent application note titled "Determination of Heavy Metals in Cannabis and Hemp Products Following AOAC Method for ICP-MS - Routine monitoring of As, Cd, Hg, Pb, and other elements using an Agilent 7850 ICP-MS" available for review/download from the Agilent website at this URL:
    https://www.agilent.com/cs/library/applications/application-cannabis-aoac-7850-icp-ms-5994-4080en-agilent.pdf

    Hope that addresses your question,
    Cheers Eric

Children
  • Thanks Eric,

    So can you please verify my understanding.  The application note is suggesting introduction of a sample containing 20% acid into the ICP-MS instrument? Am I making an error in my calcuations? (9mLs HNO3 and 1mL HCl in a final volume of 50 mL).  Would that not take a toll on the Ni cones?

    Thanks,

    Tom

  • First let me say you have the correct understanding. In theory, the acid concentration after dilution to 50mL will be around 20% - perhaps a little lower after digestion.

    You are correct that this matrix will degrade the cones faster than a lower concentration of acid - but the nickel cones are surprisingly resistant and you will still get good lifetime from those cones.

    Apart from being the most economical, nickel tipped cones are also relatively robust. Pure nickel is ductile and tough with good resistance to corrosion in the normal atmosphere.
    The base material for the cone - which is copper - is more susceptible to corrosion. For challenging applications, we do offer nickel plated cones that provide improved resistance with challenging applications where higher acid concentrations are used. The nickel plating reduces the corrosion of the base material, extending cone lifetime and enabling a simpler cleaning routine for the cone (when this is required).

    There is also the option of using the platinum tipped cones for this application. The platinum tipped cones are more robust and will provide longer life - but they are more expensive and are usually reserved for the most challenging applications where even more concentrated acids are used - or where organic solvents are being used.

    I hope that clarifies this concern,

    Cheers Eric

  • Many Thanks Eric,

    You have confirmed my thoughts on this. I was not aware that there was an option for a nickle plated base vs copper - good to know.

    Best Regards,

    Tom

Was this helpful?