What is the different in using ( ppm ) or ( %)

[Newchromatographer]

Well , why we sometimes we use ( % ) in gas chromatography when we use headspace analysis as example and we don't use ( ppm ) ?

what is different between the or other concentration ?

Any help please ?

[chromatographer1]

The amount of an impurity is usually based on weight percent. For example if methanol is found in phenol it might be 1% by weight, 1mg of methanol in 100mg of sample of phenol (which means there is 99mg of phenol and 1mg of methanol). This determination may be done by headspace or conventional gas chromatography. If the amount of methanol is very small then it may be expressed as ppm weight units. For example 100 ng of methanol found in 100 mg of phenol is 1 ppm. If the 1% of methanol mentioned earlier is expressed as ppm then the amount would be 10,000 ppm. If the amount of impurity is large then the description is usually given as wt percent but if trace then it is expressed as ppm.

Both are assumed to be expressed on a weight basis.

Rodney George
consultant

[Consumer Products Guy]

Think of percent as parts per hundred and ppm as parts per million, a difference of 10000.

ppm allows use of whole numbers and less decimals, like 12 ppm instead of a 0.0012%

[Newchromatographer]

The amount of an impurity is usually based on weight percent. For example if methanol is found in phenol it might be 1% by weight, 1mg of methanol in 100mg of sample of phenol (which means there is 99mg of phenol and 1mg of methanol). This determination may be done by headspace or conventional gas chromatography. If the amount of methanol is very small then it may be expressed as ppm weight units. For example 100 ng of methanol found in 100 mg of phenol is 1 ppm. If the 1% of methanol mentioned earlier is expressed as ppm then the amount would be 10,000 ppm. If the amount of impurity is large then the description is usually given as wt percent but if trace then it is expressed as ppm.

Both are assumed to be expressed on a weight basis.

Rodney George
consultant

That's a magic answer

thanks for your help Rodney

[Newchromatographer]

Think of percent as parts per hundred and ppm as parts per million, a difference of 10000.

ppm allows use of whole numbers and less decimals, like 12 ppm instead of a 0.0012%

So my dear , do you mean when i ever see ( %) i multiply by 10 000 to get ( ppm ) .This is also a great thinking thanks for you

i thing i will read more because sometimes is really confusing when some analyst prefer to use as an example ( mmol ) intsted of other concentration

thanks aLL