Residue on ignition means the sample is ignited at higher
temperature in the muffle furnace for the period of time.
If it is not converted as a complete ash(grey colour)add
dilute sulphuric acid to the residue and evaporate the
acidic solution again keep into the furnace to convert ash
is called sulphated ash.
When a sample is ignited to ash as such this is called residue on ignition as the meaning itself tells us., while the sulphated ash is certain samples need to be charred with sulphuric acid before ignition and the residue contains sulphates which is called sulphated ash. Eventhough USP and BP says the samething this is product specific.
Residual on ignition mesure only present metal in inert
atm.not convert in oxide.
Residual on ignition mesure present of metal oxide in
Sulphated ash mesure only present of metal oxide. using