by
lmh » Tue Jan 22, 2019 11:43 am
I'm very confused by this thread. The original solution was 1.05g in 100mL, which sounds like approximately 1% (sanity check: the answer must be in the vicinity of 1).
Let's work it out both ways:
The original solution was about 1.05g dissolved in 100mL (of methanol?)
This is 10.5g in 1000mL
Methanol has a density of 792g per 1000mL
Therefore our solution is 10.5g/792g
10.5/792 = 0.01326
The solution is 1.326% by weight (assuming it's in methanol, which is lighter than water)
The ten-fold dilution, in methanol, is 0.1326%
I assume you made the solution approximately, but have assayed it to check its true concentration, so we will now work the other way.
The assay of the ten-fold dilution came out at 89.315 mg/L
This is 0.089315g/L
or 0.089315g per 792g (assuming methanol, where 1L weighs 792g)
0.089315/792 = 0.0001128
= 0.01128%
This is 10-fold away from what we expect, which is worrying. What standard was used for calibration of the LC method? Does the LC method already include any dilution factors in its data-processing?
(sanity check: 89mg/L is about 100mg/L, or about 0.1g/L, or about 0.01g/100mL, which is about 0.01%)
[I have assumed methanol because in your follow-up mail you named methanol as the solvent. There are people who take w/w to mean w/v based on solvents weighing 100g/100mL, but I think if you're going to use w/w, it should mean what it says. 1% w/w should mean that if I take 100g of the solution, I will have 1g of the solute. Therefore, to me, the solvent matters.]