In The APHA method to measure total iron , how to prepare calibration standards for measuring total iron if I am using the ferrous ammonium sulphate salt .Also how is the ferric Iron meaured ?

Answer 1

Prepare aqueous solutions of the standard. Usually, the standard can be prepared from solid electrolytic iron wire, or it can be made using ferrous ammonium sulfate. Either way, make the standard solution to be 200 ug Fe per ml of solution. Then dilute this STOCK solution to whatever values you wish, for example to 20 ug/ml, 10 ug/ml, 5 ug/ml, etc. and these will be your standards to be read in the spectrophotometer. This will give you total iron because the hydroxylamine will reduce the iron to the ferrous state.

To find ferric, you omit the hydroxylamine and determine ferrous only. Then subtract ferrous from total to get ferric.