Monitoring is best achieved by mass spectrometry, an example of which is given here for GalP(His)6. [U-15N]GalP(His)6, pro- duced by growth of an overexpressing E. coli strain on 15NH3, was purified with affinity chromatography, and further purified from residual lipids and detergents with size exclusion chromatography (Venter, 2001).