Hi, We're looking at the clearance of chaotrophs - does anyone know of a simple /chemical/ assay for guanidine hydrochloride? (we can't look at conductivity). R -- Richard P. Grant MA DPhil | rgrant at cmtech.co.uk work: www.cmtech.co.uk | home: www.avnet.co.uk/adastra -- In Ventum Faciens Aquam --