calculation of residual solvent in drug substance

[martinamarie]

Hi, is the potency of the standard, eg ethanol, taken into account when calculating the amount of residual solvent in drug substance
Thanks
Tina

[Terry]

You do have to take the potency (purity) of reference standard (RS) into accunt.

The purity of RS can be obtained obtain from the COA provied by the RS supplier.

Terry

[chromatographer1]

Remember that ethanol is hydroscopic and can change in purity if the standard was originally anhydrous. At most a 5% change but it might be enough to make a difference.

Rodney George
consultant

[GaryR]

You may also need to take into account the density if you are reporting your results in ppm (mg/kg) or %(w/w). This can make a huge difference to your results.
Not a problem if you prepare your standards by weight, but if you prepare volumetrically you need to factor it in.