Delloyd's Lab-Tech Chemistry
LABGUIDE
Determination of Iron by visible spectrophotometry
Equipment:
UV/ VIS spectrophotometer
Dri-block heater, Bottle-top dispensette.
Sample: Ferrous sulphate tablets (FeSO4)
Apparatus:
Boiling tubes, Filter paper #1, Funnels, Funnel racks, labels, Volumetric flasks 250ml and 100ml.
Chemicals:
Hydroxylamine hydrochloride: (H2NOH.HCl), FW = 69.49.
Sodium acetate: CH3COONa, FW = 82.03.
Glacial acetic acid, CH3COOH
Conc. nitric acid, HNO3
1:10-Phenanthroline: FW = 180.21
Ammonium iron(11) sulphate: (NH4)Fe(SO4)2.6H2O, FW = 392.14
Solutions preparation:
1. 10% hydroxylamine hydrochloride (hydroxyl ammonium chloride) Dissolve 25g of the salt in 250ml water.
2. Buffer pH 5.0. Dissolve 82.03g (1M) of sodium acetate in about 800mls of water, and add glacial acetic acid to give a pH of 5.0, and dilute to 1 liter.
3. 0.25% 1:10 o-phenanthroline. Dissolve 0.625g in 250 ml water.
4. 20ppm Fe soln. Make up a 1000ppm ammonium ferrous sulphate, (NH4)Fe(SO4)2.6H2O by dissolving 7.0g of salt in 1 liter. Then dilute 10mls of this soln. to 500mls to give a 20ppm soln.
Analytical notes:
Tablets as purchased, will vary as to Fe content and total FeSO4.
Typical values are:200 to 300mg total FeSO4, and 60 to 65mg Fe ++
1. Use five tablets and one blank. For this year (2004/05), a ground sample of tablet will be provided.
2. Weigh 0.1g and pre-digest overnight in boiling tubes with 5mls conc. HNO3.(use bottle-top dispensette in fume hood to add the acid)
3. Digest on Dri-block for 1 to 1 and a half hours at 130oC.
Operation of Instrument:
Follow Users Guide - obtain help and advice from Demonstrator or Technician
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