thanks for chiming in everyone!

Gravimetric analysis is not an option for us unless the situation is dire, since it woudl disrupt the well-oiled work process here. But fair point and I have resorted to that in the past even w/o having issues with volumetric methods. Also, the techs here are very much used to volumetric work.

We filled to the line and THEN mixed. Also using some more ACN worked well for us.

I love the experience from the detergents industry! :)