Chromatography Forum

Dear All,
I would like to prepare standard calibration curve for pesticide analysis.
Range are 0.01 , 0.1, 2 and 5 ppm.
I have 10 ppm OP mix standard about 5 ml.
I wanna prepare just 1 ml each of these concentration.
What is differences between make up volume and mix volumes??( I have not very small volumetric flask, just 10 ml I have, I don't want to and no need to prepare 10 ml, for me 1 ml is enough)
So how should I prepare??
Can I prepare by mixing, I meant mix the standard solution + solvent??

eg. I want to prepare 1 ppm standard 1 ml from 10 ppm stock.

C1V1=C2V2
1ppm x 1ml = 10 ppm x V2
V2 = 1ppm x 1ml /10 ppm
V2 = 0.1 ml = 100 uL

So can I take 100 uL of 10 ppm standard into the vial and add 900 uL of solvent??
Is this same with make up volume??
I am confusing , please help me.

Thanks,
K.M.P

Range are 0.01 , 0.1, 2 and 5 ppm.

Stock is 10 ppm

Take X microliters of stock and add X microliters of solvent and you have 2X volume of 5 ppm std.

Take X microliters of stock and add 4X microliters of solvent and you have 5X volume of 2 ppm std.

Take X microliters of stock and add 99X microliters of solvent and you have 100X volume of 0.1 ppm std.

Take X microlters of stock and add 999X microliters of solvent and you have 1000X volume of 0.01 ppm std.

If the solvents for the stock and the dilution are the same, then the final volume will be the sum of the added volumes.

If you are doing large dilution ratios (e.g. 1:100) then even if the solvents are different the bias in the final volume will be smaller than the bias and random error usually associated with handling such small volumes of volatile solvents.

Alternatively, do everything by mass and do not measure volumes at all.

Peter

In my opinion it is ok to do what Rod and Peter suggest if the method is desribed in detail if published for some reason, certainly the results should not be claimed to be molarity. The weighing method may fit the definition of molality if done correctly.

Many Thanks to all.