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Change in the Ferric Ion section of the Ferrous Sulfate Heptahydrate monograph for reagent chemicals.

Question asked by Sam McDonald on Dec 5, 2017

Q:
explanation as to the change in the Ferric Ion section of the Ferrous Sulfate
Heptahydrate monograph for reagent chemicals.

 

The
new text:  11th edition

 

Place 0.20 g of the sample and 0.5 g of sodium bicarbonate in a dry 125 mL glass-stoppered conical flask. For the control,
place 0.10 g of the sample and 0.5 g of sodium bicarbonate in a similar flask.To each flask, add 94 mL of a freshly boiled and cooled solution of dilutesulfuric acid (1:25), and loosely stopper the flasks until effervescence stops.To the control, add 0.01 mg of ferric ion (Fe
3+). Add 6 mL of ammonium thiocyanate reagent solution to each flask. Any redcolor in the solution of the sample should not exceed that in the control.

 

To the control, add 0.01 mg of ferric ion (Fe3+)

 

The old text: 10th edition

 

Place 0.20 g of the sample and 0.5 g of sodiumbicarbonate in a dry 125 mL glass-stoppered conical flask. For the control,
place 0.10 g of the sample and 0.5 g of sodium bicarbonate in a similar flask.To each flask, add 94 mL of a freshly boiled and cooled solution of dilutesulfuric acid (1:25), and loosely stopper the flasks until effervescence stops.To the control, add 0.1 mg of ferric ion (Fe
3+). Add 6 mL of ammonium thiocyanate reagent solution toeach flask. Any red color in the solution of the sample should not exceed that in the control.

 

To the control, add 0.1 mg of ferric ion (Fe3+)

 

The difference is a tenfold reduction in concentration of
the control’s concentration.  The current test is failing by edition 11
method, but passing the 10 edition test.

 

 

Specification is NMT 0.1% Ferric Ion

 

Sam

 

samuel.mcdonald@dsm.com

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