2. Total iron content in food can be
quantified spectrophotometrically in food
industries.
However, this method largely applies the
calorimetric determination of mineral
content in food as the precursor to the
ICP-AES method.
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3. Calorimetric method
This method makes use of Chromogens
Chromogens are available that react with a wide
variety of minerals.
These chromogens react with its corresponding
minerals to produce a soluble coloured product
that can be quantified by absorption of light at a
specified wavelength.
Concentration of the mineral is then determined
from a standard curve developed during analysis.
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4. CRUCIBLE AND
WEIGHING OF
SAMPLE
• Approximately 5g of the sample is put
in a crucible and weighed
DRYING OF THE
SAMPLE
• The sample is then heated in a hot plate
and heated until sample stops smoking.
ASHING
• The sample is then ashed in a furnace
set at 550°C until ash is white
CALORIMETRIC PROCEDURE
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5. DISSOLUTION
OF SAMPLE
• Ash is dissolved in small amounts of 1N HCL and diluted to 50ml
volumes with 0.1N HCL.
• 0.500ml of dilute sample and standard is transferred into 10ml test
tubes
ADDITION OF
CHROMOGENS
• 1.250ml of ascorbic acid (0.02% in 0.2 N HCL, made fresh daily) is
added, vortexed and set for 10 minutes
• 2.00ml of 30% ammonium acetate is added and vortexed.(pH needs
to be > 3 for colour development)
SAMPLE TO
ICP-AES
• Sample is introduced into the ICP-AES(Inductively coupled plasma
Atomic Emission Spectrometer
• Absorbance is measured at 562nm. Concentration is determined from
the standard curve.
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6. Points to note from the flow chart
Generally, the sample must be ashed or treated in another
manner to isolate and/or release the minerals from organic
complexes that would otherwise inhibit the reaction with the
chromogen.
The mineral of interest must then be solubilized from a dry ash
and subsequently handled in a manner that prevents its
precipitation. The mineral ash must be treated (E.g. reduced or
oxidised) to ensure that all mineral is in a form that reacts with
the chromogen.
The ferrozine reagent only reacts with ferrous iron, and not with
Ferric iron. (Ascorbic acid added is to convert all ionic iron to the
detectable ferrous iron)
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8. How ICP-AES works
Measures the intensity of light emitted by atoms or ions of the
elements of interest at specific wavelengths.
It uses emission spectroscopy to detect and quantify elements
in a sample.
Uses argon plasma[Hot partially ionized gas](6000°C to
10,000°C) for atomization and excitation of the sample atoms.
The excited element in the sample is compared against the
standard sample and quantified based on the wavelengths of
emission.
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