Standard Solution Help

[Tammy]

So I am preparing my standards of limonene in deionized water based on a paper. I will be doing headspace SPME on the standards. They found to make a calibration curve the concentration range 30-300 mg/l (% w/v) was the best.

My question is about converting the 300 mg/l (%w/v) to % v/v. I've found weighing liquids at such small amounts a hassle and not as accurate.

Is there a way to convert the milligrams to milliliters? Also can anyone offer reasons why so many papers do use w/v for liquid in liquid solution, I was very surprised.

[Schmitty]

If I need to prepare a solution of a volatile analyte in anything less-volatile, I will put a good amount of the solvent into a volumetric flask and tare that before adding the analyte of interest.

Regarding the "small" masses you need to weigh, perhaps you would be better served by creating a solution at 3000mg/l, then perform dilutions to get to the final concentrations you desire?

[Peter Apps]

To convert between mass and volume simply use the density. Weighing is far more precise and accurate than any volumetric operation.

Peter

[bhahn]

You are always better off making serial dilutions. The uncertainty drops significantly. Use the density to convert, if need be, but I think Mass/Volume is far better and also has less uncertainty than a small volume measurement. in your case, I would tare a 25 ml volumetric, add as close to 50 mg of pure Limonene as you can, record it. QS to volume. Divide the amount you recorded by 25. This is your stock solution. Use C1V1=C2V2 as your formula to make the rest of your standards using volumes only.
Good luck,
Bill
btw, I was a standard mfg for 20 years and advocate buying standards with a certificate of analysis to cover your butt.