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convert pmol/kg to ppm

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  • convert pmol/kg to ppm

    Hi

    I need to convert a rare earth element in seawater from pmol/kg to ppm. I've tried the following conversion method but am unsure whether it's correct. Please can someone look over?

    Lutetium= 174.9668 (MW)

    Lu = 0.4025 pmol/kg
    = 0.4025 x 1E-9 = 4.025E-10 mmol x 174.9668 g = 7.0424E-11 g/kg
    = 7.0424E-11 * 1000 = 7.04241E-08 mg/kg = 7.04241E-08 ppm

    It doesn't seem right. I'd appreciate any assistance!

    Thanks
    Dianna

  • #2
    I am having a little trouble following your method as pico is 10-12, but I get the same answer. My approach:

    0.4025 pmol/kg x 174.9668 g/mol = 70.424 pg/kg = 70.424 x 10-15

    Multiplying by 106 for ppm, 70.424 x 10-9 ppm.
    Might be better expressed as 0.070424 ppt (parts per trillion)

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    • #3
      Thanks John! Good to get a second opinion, it's so bizarre though as the reported average seawater concentration for Lu is 0.227 ppm. Anyway thanks for replying! Cheers

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      • #4
        Originally posted by Dianna View Post
        Thanks John! Good to get a second opinion, it's so bizarre though as the reported average seawater concentration for Lu is 0.227 ppm. Anyway thanks for replying! Cheers
        Are you sure the units are right, picomoles per kilogram.
        0.227 ppm is about 1.3 µmol/kg

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        • #5
          Hi there, sorry i'm a bit late to this discussion. I can't find any articles that suggest the seawater conc. of Lu is anywhere near 0.2ppm. The articles below suggest more like 0.15ppt (parts per trillion, or ng/L). Lu is not a common element.

          http://www.seafriends.org.nz/oceano/seawater.htm


          https://www.researchgate.net/publica...ber_lite_XAD-4

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