ISO/FDIS 10701

ISO/DIS FDIS 10701:2026(en)
ISO/TC 17/SC 1
Secretariat: JISC
Date: 2026-06-0907-31
Steel and iron— — Determination of sulfur content— — Methylene
blue spectrophotometric method
Aciers et fontes — Détermination des teneurs endu soufre — Méthode spectrophotométrique au bleu de
méthylène
FDIS stage
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ii
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 4
7 Sampling and sample preparation . 7
8 Procedure . 7
8.1 Test portion . 7
8.2 Blank test . 7
8.3 Determination . 7
8.4 Establishment of the calibration curves . 9
9 Expression of results . 10
9.1 Method of calculation . 10
9.2 Precision . 10
10 Notes on procedure . 11
11 Test report . 11
Annex A (informative) Additional information on the international precision test . 12
Annex B (informative) Graphical representation of precision data . 14
Bibliography . 16

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 1, Methods of
determination of chemical composition.
This second edition cancels and replaces the first edition (ISO 10701:1994), which has been technically
revised.
The main changes are as follows:
— Clause 2— Clause 2,, Normative references has been updated;
— — the mandatory Clause 3Clause 3,, terms and definitions has been added and subsequent clauses have
been renumbered;
— Clause 10— Clause 10,, Special case, has been moved into 8.3.18.3.1;;
— — the precision data has been re-evaluated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Steel and iron — Determination of sulfur content — Methylene blue
spectrophotometric method
1 Scope
This document specifies a methylene blue spectrophotometric method for the determination of sulfur in steel
and iron.
The method is applicable to sulfur contents between 0,000 3 % (mass fraction) to 0,010 % (mass fraction).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 14284, Steel and iron — Sampling and preparation of samples for the determination of chemical composition
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
4 Principle
Dissolution of a test portion in a mixture of hydrochloric and nitric acids.
Evaporation with perchloric acid until white fumes appear to remove hydrochloric and nitric acids.
Dissolution of the salts in hydrochloric acid. Evolution of hydrogen sulfide by reducing with a mixture of
hydroiodic and hypophosphorous acids in a nitrogen atmosphere, distillation, and absorption into a zinc
acetate solution.
Formation of methylene blue by reacting with N,N-dimethyl-p-phenylenediamine and iron(III) solution.
Spectrophotometric measurement at a wavelength of about 665 nm.
Niobium, silicon, tantalum and titanium interfere in the determination of sulfur.
Depending on the contents of the interfering elements, the application ranges and test portion masses given
in Table 1Table 1 apply.
Table 1 — Application ranges and test portions
Maximum allowable content of the interfering
elements
Test portion Application ranges 𝛥𝛥𝑤𝑤
𝑠𝑠
% (mass fraction)
g % (mass fraction)
Nb Si Ta Ti
0,5 1,0 0,3 1,0 1,0 0,000 3 to 0,001 0
1,0 2,0 0,6 2,0 0,50 0,001 0 to 0,010
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade with a very low
sulfur content, and only freshly prepared grade 2 water as specified in ISO 3696.
5.1 5.1 Hydrochloric acid, ρ about 1,19 g/ml.
5.2 5.2 Hydrochloric acid, ρ about 1,19 g/ml, diluted 1+ + 15.
5.3 5.3 Perchloric acid, ρ about 1,54 g/ml.
5.4 5.4 Hydrobromic acid, ρ approximately 1,48 g/ml.
5.5 5.5 Mixture of hydrochloric and nitric acids.
Mix one volume of hydrochloric acid (5.1(5.1)) and one volume of nitric acid, ρ about 1,40 g/ml.
Prepare immediately before use.
5.6 5.6 Reducing reagent solution.
Transfer 200 ml of hydriodic acid, ρ about 1,70 g/ml and 50 ml of hypophosphorous acid, ρ about 1,49 g/ml
into the purifying apparatus (see Figure 1Figure 1).). Purge with nitrogen (5.12(5.12)) at a flow rate of
100 ml/min for 10 min, to mix the acids and expel air from the system. Switch on the electric heating mantle.
Heat to boiling and boil gently for about 120 min at a temperature of about 115 °C in a current of nitrogen.
When purification is completed (see 10.310.3),), switch off the electric heating mantle. Then cool the solution
and keep it in a brown bottle.
5.7 5.7 Absorbing solution.
Dissolve 5 g of zinc acetate dihydrate [Zn(CH COO) .2H O] in 400 ml of water. Add 200 ml of sodium
3 2 2
hydroxide, 30 g/l, and 70 g of ammonium chloride, and then dilute to 1 000 ml with water.
5.8 5.8 Iron solution, 10 g/l.
Weigh, to the nearest 0,01 g, 1,00 g of pure iron, free from sulfur as sulfate. Transfer to a 300 ml beaker, cover
with a watch glass, dissolve by heating with an addition of 20 ml of hydrochloric acid (ρ about 1,19 g/ml,
diluted 1+ + 1) and boil gently for about 10 min. Then add 2 ml of nitric acid (ρ about 1,40 g/ml) drop by drop
to oxidize iron. Remove the oxides of nitrogen by boiling, and cool to room temperature. Transfer to a 100 ml
one-mark volumetric flask, dilute to the mark with water and mix.
5.9 5.9 Iron (lll) chloride solution.
Dissolve 1 g of iron (Ш) chloride hexahydrate (FeCl .6H O) in about 40 ml of water. Add 10 ml of hydrochloric
3 2
acid (5.1(5.1)) and dilute to 100 ml with water.
5.10 5.10 N,N-dimethyl-p-phenylenediamine in hydrochloric acid medium.
Dissolve 0,5 g of N,N-dimethyl-p-phenylenediamine dihydrochloride [NH C H N(CH ) .2HCl] in about 100 ml
2 6 4 3 2
of water. Add 230 ml of hydrochloric acid (5.1(5.1)) and dilute to 500 ml with water.
5.11 5.11 Sulfur standard solutions.
5.11.1 5.11.1 Sulfur standard solution, 1 g/l.
Weigh, to the nearest 0,000 1 g, 5,435 2 g of potassium sulfate [minimum purity: 99,5 % (mass fraction)],
previously dried at 110 °C for 2 h and cooled to room temperature in a desiccator. Dissolve in water, transfer
to a 1 000 ml one-mark volumetric flask quantitatively, dilute to the mark with water and mix.
1 ml of this standard solution contains 1 mg of sulfur.
5.11.2 5.11.2 Sulfur standard solution, 10 mg/l.
Transfer 10,0 ml of the standard solution (5.11.1(5.11.1)) to a 1 000 ml one-mark volumetric flask, dilute to
the mark with water and mix.
1 ml of this standard solution contains 10 µg of sulfur.
5.11.3 5.11.3 Sulfur standard solution, 1 mg/l.
Transfer 10,0 ml of the standard solution (5.11.2(5.11.2)) to a 100 ml one-mark volumetric flask, dilute to the
mark with water and mix.
Prepare the solution immediately before use.
1 ml of this standard solution contains 1 µg of sulfur.
5.12 5.12 Nitrogen[purity : >99,5 % (volume fraction)].
Key
1 double surface condenser or equivalent (34 cm long)
2 nitrogen inlet
3 hydrogen sulfide trap (18 cm ×2, 5 cm)
4 thermometer
5 three-neck flask (capacity:500 ml)
1 double surface condenser or equivalent (34 cm long)
2 nitrogen inlet
3 hydrogen sulfide trap (18 cm ×2, 5 cm)
4 thermometer
5 three-neck flask (capacity:500 ml)
Figure 1 — Example of an apparatus for purification of the reducing mixture
6 Apparatus
All volumetric glassware shall be class A, in accordance with ISO 648 or ISO 1042, as appropriate.
Ordinary laboratory apparatus, and the following.
6.1 6.1 Apparatus for reduction and distillation
Assemble the apparatus for reduction and distillation as shown in Figure 2Figure 2. Close-fitting ground-glass
joints shall be used.
When the apparatus is used for the first time, or after a long period of disuse, blank tests shall be carried out
repetitively until stable low blank values are obtained.
6.1.1 6.1.1 Decomposition flask, about 300 ml in volume.
6.1.2 6.1.2 Reflux condenser, about 150 mm in length.
6.1.3 6.1.3 Gas washing bottle, about 150 ml in volume.
6.1.4 6.1.4 Absorption flask, one-mark volumetric flask of capacity 20 ml or 100 ml.

Dimensions in millimetres
Dimensions in millimetres
Key
1 reflux condenser
2 nitrogen gas
3 decomposition flask (capacity: 300 ml)
4 gas inlet tube
5 absorption flask (capacity: 20 ml or 100 ml)
6 washing bottle
1 reflux condenser
2 nitrogen gas
3 decomposition flask (capacity: 300 ml)
4 gas inlet tube
5 absorption flask (capacity: 20 ml or 100 ml)
6 washing bottle
Figure 2 — Example of an apparatus for reduction and distillation
6.2 6.2 Spectrophotometer, equipped to measure absorbance at a wavelength of about 665 nm.
7 Sampling and sample preparation
Sampling and preparation of the test samples shall be carried out in accordance with ISO 14284 or appropriate
national standards for steel and iron.
8 Procedure
WARNING — Perchloric acid vapour can cause explosions in the presence of ammonia, nitrous fumes
or organic matter in general.
8.1 Test portion
Weigh, to the nearest 1 mg, the mass of test portion given below as a function of the expected sulfur content:
a) a) sulfur co
...