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UDC 661.63 : 543.42
IS0
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
IS0 RECOMMENDATION
R 849
PHOSPHORIC ACID FOR INDUSTRIAL USE
DETERMINATION OF 1RON CONTENT
2,2’-BIPYRIDYL SPECTROPHOTOMETRIC METHOD
1st EDITION
October 1968
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Copies to be obtained through the national standards organizations.
Also issued in French and Russian.
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BRIEF HISTORY
The IS0 Recommendation R 849, Phosphoric acid for industrial use - Determination of iron content --
2,2’-bipyridyl spectrophotometric method, was drawn up by Technical Committee ISO/TC 47, Chemistry, the
Secretariat of which is held by the Ente Nazionale Italian0 di Unificazione (UNI).
Work on this question by the Technical Committee began in 1960 and led, in 1966, to the adoption of a Draft
IS0 Recommendation.
In December 1.966, this Draft IS0 Recommendation (No. 1110) was circulated to all the IS0 Member Bodies
for enquiry. It was approved, subject to a few modifications of an editorial nature, by the following Member Bodies :
Austria India
Spain
Belgium Israel Switzerland
Brazil
Italy Thailand
Bulgaria Japan
Turkey
Chile Korea, Rep. of U.A.R.
’ Czechoslovakia New Zealand United Kingdom
France Poland U.S.S.R.
Germany Romania Yugoslavia
Hungary South Africa, Rep. of
One Member Body opposed the approval of the Draft :
Netherlands
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which decided, in
October 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 849-1968 (E)
October 1968
IS0 Recommendation R 849
PHOSPHORIC ACID FOR INDUSTRIAL USE
DETERMINATION OF IRON CONTENT
2,2’-BIPYRIDYL SPECTROPHOTOMETRIC METHOD
1. SCOPE
This IS0 Recommendation describes a method for the spectrophotometric determination of the iron content of
phosphoric acid for industrial use.
2. FIELD OF APPLICATION
The method is applicable to the determination of iron content, expressed as Fe, greater than 0.001 %.
2.1 Special case
Phosphoric acid for industrial use containing polyphosphoric acids (see section 8).
NOTE. - In case there is no certainty of absence of polyphosphoric acids, carry out the determination according to
the procedure of the special case directly.
3. PRINCIPLE
Preliminary reduction of trivalent iron by means of hydroxylammonium chloride.
Formation of a bivalent iron - 2,2 ‘-bipyridyl complex in presence of ammonium acetate at pH 3.1, at a
temperature of 75 “C (under the test conditions, phosphate ions do not interfere).
Spectrophotometric measurement of the coloured complex at a wavelength of about 522 nm.
4. REAGENTS
Distilled water or water of equivalent purity should be used in the test.
4.1 Hydrochloric acid, approximately d = 1.19, 37 o/o (m/m) or 12 N solution.
4.2 2,2 ‘-bipyridyl, 5 g/l hydrochloric acid solution.
Dissolve 0.50 g of 2,2 ‘-bipyridyl in 10 ml of approximately d = 1.19 hydrochloric acid solution and
dilute to 100 ml.
4.3 Ammonium acetate, 300 g/l solution.
Dissolve 300 g of ammonium acetate in water and dilule to 1000 ml.
4.4 Hydroxylammonium chloride, 100 g/l solution.
Dissolve 10 g of hydroxylammonium chloride (NH2 OH.HCl) in water and dilute to 100 ml.
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ISO/R 849-1968 (E)
4.5 Iron standard solution, containing 2.00 g/l of Fe.
Weigh, to the nearest 1 mg, 7.022 g of ammonium ferrous sulphate hexahydrate and place in a beaker of
suitable capacity. Add 50 ml of 100 g/l sulphuric acid solution, transfer quantitatively to a 500 ml
one-mark volumetric flask and dilute to the mark.
1 ml of this standard solution contains 2.0 mg of Fe.
4.6 Iron standard solution, containing 0.020 g/l of Fe.
Transfer 10.0 ml of the standard solution (4.5) to a 1000 ml one-mark volumetric flask and dilute to the
mark.
1 ml of this standard solution contains 20 pg of Fe.
The solution should be prepared just before use.
5. APPARATUS
Ordinary laboratory apparatus and
5.1 pH-meter, fitted with glass electrode, sensitivity at least 0.1 pH unit.
5.2 Spectrophotometer, or
5.3 Photoelectric absorptiometer.
6. PROCEDURE
6.1 Test portion
Weigh by difference, to the nearest 1 mg, approximately 5 g of the test sample.
If this quantity contains more than 500 pg of Fe, reduce the quantity of test portion, so as to have a
lower iron content preferably between 200 and 300 pg.
6.2 Blank test
At the same time as the analysis, carry out a blank test using the procedure described in clause 6.4
and the same quantities of all reagents. However, for the preparation of the coloured solution, use the
same volume of ammonium acetate solution (4.3) as that used in the determination.*
6.3 Preparation of calibration curve
6.3.1 Preparation of standard matching solutions for spectrophotometric measurement in a 1 cm cell.
6.3.1.1 PRELIMINARY CHECK OF THE PH. Place 5 ml of hydrochloric acid solution (4.1) in a beaker of
suitable capacity (100 ml, for example), dilute to approximately 50 ml, add 1 ml of the hydro-
xylammonium chloride solution (4.4) and 5 ml of the 2,2’-bipyridyl solution (4.2). Allow to
stand for about 10 minutes and, using the pH-meter (5.1) adjust the pH of the solution to
pH 3.1 by addition of the ammonium acetate solution (4.3). Note the
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