Crude ash is what the feed and food industries call ash, burn the sample directly at about 550 °C and the inorganic matter left behind is crude ash. It is essentially the same as the pharmacopeial total ash.
In proximate analysis, crude ash sits alongside crude protein, crude fat and crude fiber to estimate the sample's total mineral matter.
Key procedure
Sample, char to prevent spattering, ashing in a muffle furnace at 550 °C (plus or minus 20 °C) until carbon-free, constant weight, calculate. Constant weight again uses an inter-cycle difference below 0.3 mg (0.1 mg balance).
Relation to total ash
Crude ash is approximately total ash; both are directly ashed inorganic residues, differing only in industry or standpoint (AOAC/feed vs pharmacopeia). The values are usually close, and the IRT-A covers both with one instrument.
