WHEAT FLOUR FORTIFICATION WITH IRON - Idpas.org

Appendix 3.10
Wet digestion using sulfuric and nitric acids
Used by the Institute of Nutrition and Food Technology, University of Chile
I. Materials
Volumetric flask, 1 L
Volumetric flasks, 250 mL
Volumetric flasks, 100 mL
Volumetric flasks, 25 mL
Beakers, 250 mL
Volumetric pipettes, 100 mL, 500 mL, 200-1000 mL
Graduated tubes
Test tubes, 10 mL
II. Equipment
Analytical balance
Hot-block digestion unit
Wet ashing fume hood
Kjeldahl flasks
III. Reagents
A. Iron Standard Solutions
1. Stock standard solution. Fe 1000 mg/L. Dissolve 1.0 g Fe wire metal in 10 mL (65%) HNO3
ultrapure. Dilute to 1000 mL with deonized water.
2. Intermediate standard solution. Fe 10 mg/L. Dilute 10 mL stock standard solution to 1000 mL
with deonized water.
3. Working standard solution. Fe 1 µg/mL. Dilute 10 mL intermediate standard solution to 100 mL
with deonized water.
IV. Procedure
Rinse all glassware with concentrated HCl diluted 1:1 with deonized water.
1. Weigh 1 g homogenized sample (dry weight) into a 100 mL Kjeldahl flask.
2. Add 6 mL of concentrated (97%) H2SO4 ultrapure and then 4 mL of (65%) HNO3 ultrapure to
the sample, and predigest at room temperature for 12 hours.
3. Place the flasks in a hot-block digestion apparatus and heat at 150°C for 4 hours.
4. Remove the flask from the hot-block, and allow to cool at room temperature.
5. After adequate cooling add 10 mL of 1 N HCl ultrapure, return the flasks to digestion rack and
heat at 90°C until the samples are clear.
6. Subsequently, remove the Kjeldahl flasks and transfer the sample digest to 50 mL volumetric
flask (rinse the Kjeldahl flask five times with 5 mL of deonized water), and make up to volume with
deonized water.
V. Interpretation
Iron is measured by atomic absorption spectrophotometric method using the following conditions:
wavelength 248 nm, slit 0.2 nm, and flame air-C 2
H 2
(lean-blue).
VI. Notes
None
VII. Reference
Manuel Olivares, MD, Fernando Pizarro MT, Angelica Letelier MT, Eva Hertrampf, MD, and
Tomas Walter, MD. Instituto de Nutricion y Tecnologia de los Alimentos, Universidad de Chile.
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