Conversion of ppm to mg/kg
David F. Kong
Hi there.
Have forgotten the formula for conversion of ppm (parts per million) to
mg/kg or into molarity. I wish to convert 500 ppm into molar solution
(in water).
An e-mail reply to this address would be greatly appreciated! Thanks in
advance.
David F. Kong
Olaf Meeuwissen
usually don't tell you what kind `parts' per `(m/b)illion' of what they are
expressing. So, before even thinking of converting the units you have to figure
out what they are about. This is similar to the difference in mass and volume
percentages. Allow me to illustrate.
Take a 1 m% solution of oxygen in water. First question is whether the
percentage refers to the final solution or the initial amount of water. For a 1
% solution it doesn't matter much, but it sure does for a 50 % solution. In
most, but not all, cases the percentage refers to the result and we have 1 mass
unit of oxygen dissolved in 99 mass units of water. Hence, 1 mass unit of
oxygen per 100 mass units of solution (or 10,000 mass-ppm, if you like).
Now, how many volume procent is this? Before starting to answer, we have to ask
under what conditions we want to know the answer since volume is pressure and
temperature dependent! So, let's choose 293 K and 101.325 kPa (atmospheric
pressure). This means we will have to dissolve approximately 7.6 volume units
of oxygen in 1 volume unit of water. Slightly different, not?
BUT, does this mean the volume percentage is 88 v%? By no means! Volumes are
NOT additive! And this is not just because I choose a gas and a liquid. It is
well known that 50 mL of ethanol and 50 mL of water add up to about 95 mL of
solution.
The actual volume the oxygen takes up in the solution is nearly impossible to
quantify reliably through measurement or calculation, so no definitive answer
can be given.
To return to your question, if you has mass-ppm, the conversion to mg/kg is
exactly 1 (there are 1 million mg in 1 kg).
____
/ __ \ /\ ___ Olaf Meeuwissen (e-mail: ol...@usc.edu)
/ / / // /____ / __\ Dept. of Chemistry, Univ. of Southern California
/ / / // // __ \ _/ / -------------------------------------------------
/ /_/ // // /_/ / / _/ Be it the edge of time or space, there is nothing
\____//_/ \_____\ / / so awe-inspiring as a border.
/_/ -- Yukio Mishima
rm...@waikato.ac.nz
This reminds me of a funny thing that happened when I submitted a manuscript
to a Pulp and Paper journal, which dealt with quantitative C13 NMR analysis
of wood extractives.
The paper was accepted, but when the galley proofs came back for correction,
all the scales of the NMR spectra had been converted from ppm to mg/kg!
(sorry this doesn't answer your question, by the way!)
Rick Ede
Tom Ezell
DFK> Have forgotten the formula for conversion of ppm (parts per million)
DFK> to mg/kg or into molarity. I wish to convert 500 ppm into molar
DFK> solution (in water).
A part per million _is_ one mg per kg... so 500 ppm would then be 500 mg
of analyte per kg of water, which you would then convert the masses of
analyte to moles (500 mg / X mg/mol), then divide this by the number of
liters in a kg of water. Similarly, part per billion is micrograms per
kilogram...
Tom
... Old chemists never die, they merely fail to react.
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