The majority of the Class 1 and Class 2 ICH residual solvents listed in the USP <467> Monograph can be determined by GC- Headspace analysis. However, there has always been 8 Class 2 solvents that were excluded because they were not sufficiently volatile. While <467> allows analysis of Class 3 solvents based on modification of the analytical preparations, headspace analysis is still the prescribed option. This leaves another 4 Class 3 solvents, which are not amenable to this technique.

Some years ago Butterworth developed a USP compliant in-house screening procedure for all headspace amenable Class 1, 2 and 3 solvents (64 individual targets) but still excluded the 12 less volatile/higher boiling point solvents. We have now produced an in-house procedure, using direct injection GC, which meets the requirements of the USP for the analysis of 10 of the outstanding 12 solvents.

For the remaining 2 ICH Class 3 solvents, Formic and Acetic acid, Butterworth use either IC or HPLC procedures, where the technique chosen is dependent upon the material being analysed and is verified for use by standard addition etc.

The application of the new direct injection method means that we can now screen for all 76, ICH residual solvents using only 3 USP compliant procedures.