BENFIELD LIQUOR - DETERMINATION OF IRON

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Plant Analytical Techniques
BENFIELD LIQUOR: DETERMINATION OF IRON

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Benfield Liquor: Determination of Iron

1

SCOPE AND FIELD OF APPLICATION
This method is suitable for the determination of the total iron in Benfield
liquor samples up to a concentration of approximately 100 ppm m/v.

2

PRINCIPLE
A solution containing a compound of the metallic element under
investigation is aspirated into the flame of an atomic absorption
spectrophotometer, causing evaporation of the solvent and leaving a solid
residue. This process is rapidly followed by vaporization of the solid
residue with concomitant molecular dissociation into its constituent atoms
which are capable of absorbing radiant energy. The absorption of the
radiation from the light source by the atomic vapor is measured and
displayed by the spectrophotometer, in graphical format.

3

REAGENTS
During the analysis, use only reagents of analytical reagent grade, unless
otherwise specified, and water which has been deionized and then
distilled from an all glass apparatus, or water of equivalent purity.
3.1

Hydrochloric acid (SG 1.18)

THIS REAGENT CAUSES BURNS AND PRODUCES A HARMFUL VAPOR.
3.2

Ferric nitrate, standard spectroscopic solution in approximately 0.5
mol/L nitric acid. 1 mL = 1.00 mg iron

3.3

Stock standard iron solution: dilute 10 mL of the ferric nitrate
solution (3.2) to 100 mL with water in a one-mark volumetric flask. 1
mL = 100 µg Iron


3.4

4

Working standard iron solutions: dilute 2.5 and 5.0 mL of the stock
standard iron solution (3.3) to 100 mL with water in four one-mark
volumetric flasks. These working standard solutions will be
equivalent to 2.5 and 5.0 µg/m.l (ie ppm m/v) iron respectively.

APPARATUS
4.1

Standard volumetric glassware, class A.

4.2

Atomic absorption spectrophotometer. A Philips PU 9400 model,

or similar, is suitable.


5

PROCEDURE
5.1

Test portion, and preparation of the test solution.
Pipette 5.0 ml of test sample into a glass beaker then add 15 ml of
hydrochloric acid (3.1). Heat to dissolve any precipitate, if evident,
then allow to cool and transfer to a 100 ml one-mark volumetric
flask Dilute to the mark with water.

5.2

Blank solution
Prepare a blank solution, using the same reagent quantities as for
the test solution (5.1), but omitting the test portion.

5.3

Determination


5.3.1 The operating conditions for the atomic absorption
spectrophotometer (4.2) are as follows:
Lamp - iron hollow cathode;
Wavelength - 248.3 nm;
Band pass - 0.2-0.5 nm;
Flame - air/acetylene, fuel lean, blue.
5. 3.2 Aspirate, the lowest concentration working standard solution
(3.4), the blank solution (5.2), the rest of the working standard
solutions, and the test solution (5.1). consecutively into the atomic
absorption spectrophotometer (4.2). in accordance with the
manufacturer's instructions.

ASPIRATE THE WORKING STANDARD SOLUTIONS CONSECUTIVELY
FROM THE LOWEST TO THE HIGHEST CONCENTRATION.
TEST SAMPLES OF IRON CONCENTRATION > 50 PPM M/V MUST BE
FURTHER DILUTED TEN-FOLD PRIOR TO ASPIRATION.
5. 3.3 The atomic absorption spectrophotometer will establish the
absorbance-concentration relationship to give the concentration equivalent
of the measured test solution absorbance.
6

EXPRESSION OF RESULTS
6.1 The iron in the test solution (5.l), expressed as ppm m/v, is given by
automated interpolation from the standard curve displayed on the atomic
absorption spectrophotometer.
6.2 As dilution of the test portion is necessary, the iron in the test
sample, expressed as ppm m/v, is given by the expression
C1 x V2
V1


Where
C1 is the concentration of iron in the test solution (in ppm m/v) derived
automatically from the standard curve;
V2 is the volume of the test solution n (in mL, ie 100 mL);
V1 is the volume of the test portion taken for dilution (in mL; ie 5.0 mL.);
6.3 For test samples of iron concentration > 50 ppm m/v, a further tenfold dilution of the test solution will be necessary. The iron, expressed as
ppm m/v, is given by the expression
C1 x V2 x 10
V1


BENFIELD LIQUOR - DETERMINATION OF IRON

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