Chromatography Forum

Just to make sure

1- how can i prepare (1 ppm from liquid chemical) becauae i know how to prepare 1ppm from solid chemical ( weigh 1 mg in i L ) but in term of liquid do i need to know the liqiud density ?

2- how can i express the following triplicate analysis :

case 1 :one sample analysed six times by HPLC ( is n here = 6 )
case 2 :the sample repeated three times and analysed on duplicate ( is n here = 6 )

i want the reader to know the two cases without much talk

Thank you very much

To answer the first part, 1 mg/L = 1 ppm only to the extent that the density of water is 1.0 g/mL . So, yes, for other liquids you do need to know the density. My advice is to *never* use vague terms like "ppm", but instead say exactly what you mean.

With respect to part 2, *I'm* not sure what you mean. Does "one sample analyzed six times" mean that six separate weighings/preps/separations were done from original sample? Or that one weighing/prep was done and then injected six times? And does "repeated three times and analyzed in duplicate" mean three weighing/preps, with each one then injected twice?

i want the reader to know the two cases without much talk

While I appreciate the desire to be concise, I think that it's misguided in this situation. You need to provide enough information for the reader to understand unambiguously. In all cases n=6 for statistical calculations, but you are looking at different parts of the process.

Case 1 sounds like one sample prep INJECTED 6 times, so yes n=6 which gives you RSD of INJECTIONS.

Case 2 sounds like 3 sample preps, each injected twice (what I do here), in which case n=2. Check RSD and Mean for each prep and then use THOSE to calculate final RSD and mean (n=3)

Case 1 sounds like one sample prep INJECTED 6 times, so yes n=6 which gives you RSD of INJECTIONS.

Case 2 sounds like 3 sample preps, each injected twice (what I do here), in which case n=2. Check RSD and Mean for each prep and then use THOSE to calculate final RSD and mean (n=3)

I kind of dissagee on Case 2

I believe it's duplicate sample preps that are each injeced 3 times (n=3 for each sample then n=2 for the average of the replicates)