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Topic: Parts per billion  (Read 4230 times)

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Offline AccordionGirl

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Parts per billion
« on: April 14, 2009, 07:35:29 PM »
If I was given, say, "25 ppb of lead ion in a polluted pond," do they mean moles of lead per mols solution, or grams lead/total mass?
Thanks!
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Offline ARGOS++

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Re: Parts per billion
« Reply #1 on: April 14, 2009, 07:51:08 PM »

Dear AccordionGirl;

The later is correct (mass per mass, or volume per volume):
         http://en.wikipedia.org/wiki/Parts_per_notation#Parts-per_expressions  

Good Luck!
                    ARGOS++
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Offline Borek

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Re: Parts per billion
« Reply #2 on: April 15, 2009, 02:50:59 AM »
To be unambiguous parts per notation, just like percentage, should contain additional information about whether it is mass/mass or volume/volume or even atom/atom.

Quite often 1ppm is meant to be 1 mg/1L of solution, which is only an approximation (1L=1kg for a pure water and for diluted water solutions) and is not a dimensionles quantity.
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Offline AccordionGirl

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Re: Parts per billion
« Reply #3 on: April 15, 2009, 07:22:46 PM »
So, ppb could technically refer to either? Moles or mass? Or volume?
But I get the impression that mass is the most commonly used, and if no units are given, they probably mean a mass ratio. Correct?

Thank you guys!
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Offline ARGOS++

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Re: Parts per billion
« Reply #4 on: April 15, 2009, 07:32:15 PM »

Dear AccordionGirl;

Per mole is quite uncommon if not explicitly marked.
ppm is often "misused" as mg/Liter for diluted aqueous solutions, because density of water is 1.0 g/ml.
Otherwise you are correct.

Good Luck!
                    ARGOS++
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Offline AccordionGirl

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Re: Parts per billion
« Reply #5 on: April 15, 2009, 07:37:11 PM »
Thank you!
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Offline ARGOS++

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Re: Parts per billion
« Reply #6 on: April 15, 2009, 07:39:07 PM »

Dear AccordionGirl;

You 're welcome!   ─   Soon again.

Good Luck!
                    ARGOS++

 P.S.: Thank you too!
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