ISO 13933:2014

INTERNATIONAL ISO
STANDARD 13933
First edition
2014-07-15
Steel and iron — Determination of
calcium and magnesium — Inductively
coupled plasma atomic emission
spectrometric method
Aciers et fontes - Détermination du calcium et du magnésium -
Méthode par spectrométrie d’émission atomique avec plasma induit
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 1
5 Apparatus . 3
5.1 Inductively coupled plasma atomic emission spectrometer . 3
5.2 Polytetrafluoroethylene (PTFE) beakers with PTFE cover . 4
6 Sampling . 5
7 Procedure. 5
7.1 Test portion . 5
7.2 Blank test . 5
7.3 Determination . 5
7.4 Adjustment of the apparatus . 7
7.5 Measurement of the calibration solutions . 7
7.6 Plotting a calibration curve . 8
7.7 Measurements of the test solution . 8
8 Expression of results . 8
8.1 Method of calculation . 8
8.2 Precision . 8
9 Test report . 9
Annex A (normative) Procedure for the determination of instrumental criteria .10
Annex B (informative) Additional information on international cooperative test .12
Annex C (informative) Graphical representation of precision data .14
Bibliography .16
Foreword
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The committee responsible for this document is ISO/TC 17, Steel, Subcommittee SC 1, Methods of
determination of chemical composition.
iv © ISO 2014 – All rights reserved

INTERNATIONAL STANDARD ISO 13933:2014(E)
Steel and iron — Determination of calcium and
magnesium — Inductively coupled plasma atomic emission
spectrometric method
1 Scope
This International Standard specifies a method for determination of calcium and magnesium contents in
iron, cast iron, steel, and alloyed steel by inductively coupled plasma (ICP) atomic emission spectrometry.
The method is applicable to the determination of calcium and magnesium contents (mass fraction) in
the range of 0,000 5 % to 0,006 % and 0,000 5 % to 0,20 %, respectively.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
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 Principle
A test portion is dissolved in a hydrochloric, nitric and hydrofluoric acid mixture and fumed with
perchloric acid. Hydrochloric acid, nitric acid, and an internal standard element (if used) are added and
the solution is diluted to a known volume. The solution is filtered if necessary, nebulized into an ICP
spectrometer and the intensity of the emitted light from each element measured simultaneously with
the intensity of the light emitted by the internal standard element.
4 Reagents
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade with very
low calcium and magnesium contents and only grade 2 water as specified in ISO 3696.
4.1 Pure iron, containing less than 0,5 μg/g of calcium and magnesium.
4.2 Hydrochloric acid, ρ about 1,19 g/ml.
4.3 Hydrochloric acid, ρ about 1,19 g/ml, diluted 1 + 1.
4.4 Hydrochloric acid, ρ about 1,19 g/ml, diluted 1 + 4.
4.5 Hydrochloric acid, ρ about 1,19 g/ml, diluted 1 + 100.
4.6 Nitric acid, ρ about 1,42 g/ml.
4.7 Hydrofluoric acid, ρ about 1,14 g/ml.
4.8 Perchloric acid, ρ about 1,67 g/ml.
4.9 Acid mixture.
Mix two volumes of hydrochloric acid (4.2), one volume of nitric acid (4.6), and three volumes of water.
4.10 Calcium standard solutions.
4.10.1 Calcium stock solution, corresponding to 1 000 mg of calcium per litre.
Dry several grams of calcium carbonate [purity ≥99,9 % (mass fraction)] in an oven at 100 °C ± 5 °C
for at least 1 h and cool to room temperature in a desiccator. Weigh, to the nearest 0,000 1 g, 2,497 g of
the dried product into a 400 ml beaker, add 20 ml of hydrochloric acid (4.3), cover with a watch-glass
and heat gently until the product is completely dissolved. Cool to room temperature and transfer the
solution into a 1 000 ml one-mark volumetric flask. Dilute to the mark with water and mix.
1 ml of this stock solution contains 1,000 mg of calcium.
4.10.2 Calcium standard solution A, corresponding to 100 mg of calcium per litre.
Transfer 10,00 ml of calcium stock solution (4.10.1) into a 100 ml one-mark volumetric flask. Add 10 ml
of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,100 mg of calcium.
4.10.3 Calcium standard solution B, corresponding to 10 mg of calcium per litre.
Transfer 10,00 ml of calcium standard solution A (4.10.2) into a 100 ml one-mark volumetric flask. Add
10 ml of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,010 mg of calcium.
4.10.4 Calcium standard solution C, corresponding to 1,0 mg of calcium per litre.
Transfer 10,00 ml of calcium standard solution B (4.10.3) into a 100 ml one-mark volumetric flask. Add
10 ml of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,001 mg of calcium.
4.11 Magnesium standard solutions
4.11.1 Magnesium stock solution, corresponding to 1 000 mg of magnesium per litre.
Weigh, to the nearest 0,000 1 g, 1,000 g of pure magnesium [purity ≥99,9 % (mass fraction)] and transfer
into a 250 ml beaker. Add 20 ml of water, then add hydrochloric acid (4.3) drop by drop while swirling
until the acid action ceases and continue adding hydrochloric acid (4.3) to a total volume of 20 ml. Cover
with a watch-glass and heat to boil for 10 min. After cooling, transfer the solution quantitatively into a
1 000 ml one-mark volumetric flask. Dilute to the mark with water and mix.
1 ml of this stock solution contains 1,000 mg of magnesium.
2 © ISO 2014 – All rights reserved

4.11.2 Magnesium standard solution A, corresponding to 100 mg of magnesium per litre.
Transfer 10,00 ml of magnesium stock solution (4.11.1) into a 100 ml one-mark volumetric flask. Add
10 ml of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,100 mg of magnesium.
4.11.3 Magnesium standard solution B, corresponding to 10 mg of magnesium per litre.
Transfer 10,00 ml of magnesium standard solution A (4.11.2) into a 100 ml one-mark volumetric flask.
Add 10 ml of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,010 mg of magnesium.
4.11.4 Magnesium standard solution C, corresponding to 1,0 mg of magnesium per litre.
Transfer 10,00 ml of magnesium standard solution B (4.11.3) into a 100 ml one-mark volumetric flask.
Add 10 ml of hydrochloric acid (4.4). Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,001 mg of magnesium.
4.12 Yttrium internal standard solution, corresponding to 100 mg of yttrium per litre.
Calcine several grams of yttrium oxide [purity ≥99,9 % (mass fraction)] in a muffle furnace at
850 °C ± 10 °C for at least 40 min and then cool to room temperature in a desiccator. Weigh 0,127 0 g of
the calcined product into a 400 ml beaker, add 10 ml of hydrochloric acid (4.3), cover with a watch-glass,
and heat gently until the product is completely dissolved. Cool to room temperature and transfer the
solution to a 1 000 ml one-mark volumetric flask. Dilute to the mark with water and mix.
1 ml of this standard solution contains 0,100 mg of yttrium.
5 Apparatus
All volumetric glassware shall be class A and calibrated in accordance with ISO 385, ISO 648, or ISO 1042,
as appropriate.
Ordinary laboratory apparatus and the following shall be used.
5.1 Inductively coupled plasma atomic emission spectrometer
The inductively coupled plasma atomic emission spectrometer used will be satisfactory if, after
optimizing according to 7.4, it meets the performance criteria given in 5.1.2 to 5.1.4.
The spectrometer can be either a simultaneous or a sequential one. If a sequential spectrometer can be
equipped with an extra arrangement for simultaneous measurement of the internal standard line, it can
be used with the internal standard technique. If the sequential spectrometer is not equipped with this
arrangement, the internal standard cannot be used and an alternative technique without an internal
standard shall be applied.
5.1.1 Analytical wavelengths
This method does not specify any particular emission line. It is mandatory that each laboratory carefully
investigates the wavelengths available on its own equipment to find the most suitable one regarding
sensitivity and absence of interferences.
In Table 1, however, several suggestions are given together with possible interferences. These
wavelengths have been carefully investigated
The wavelength of the internal standard element chosen shall not interfere with the analytical
wavelengths, nor should the internal element wavelength be interfered by elements present in the test
solution. It is, however, recommended to use Y 371,03 nm or Y 360,07 nm. This wavelength is free of
interferences from the elements.
Table 1 — Analytical wavelengths together with interfering elements
Wavelength
Element Possible interferences
nm
Ca 393,66 none
Mg 279,55 none
371,03 none
Y
360,07 none
Other elements can be used as internal standards, but they shall not be present in the sample, and
shall not interfere with the elements to be determined at the appropriate wavelengths. Likewise, the
elements present in the test solution shall not interfere with the internal standard at the wavelength
chosen. The excitation requirements of the internal standard should be similar to those of the elements
to be determined.
5.1.2 Minimum practical resolution of the spectrometer
Calculate the bandwidth, according to A.1, for the wavelength used. The bandwidth shall be less than
0,030 nm.
5.1.3 Minimum short-term precision
Calculate the short-term precision according to A.2. The relative standard deviation (RSD) shall not
exceed 1 % of the mean absolute or ratioed intensities for concentrations 100 to 1 000 times the limit
of detection (LOD) (5.1.4). For concentrations that are 10 to 100 times the LOD (5.1.4), the RSD shall not
exceed 5 %.
5.1.4 Limit of Detection (LOD) and Limit of Quantification (LOQ)
Calculate the LOD and LOQ, according to A.3, for the analytical wavelengths used. The calculated values
shall be below the values given in Table 2.
Table 2 — Limit of Detection (LOD) and Limit of Quantification (LOQ)
Wavelength LOD LOQ
Element
nm mg/l mg/l
Ca 393,66 0,003 4 0,010
Mg 279,55 0,004 6 0,014
5.1.5 Linearity of the calibration curve
The linearity of the calibration curve is checked by calculating the correlation coefficient. This coefficient
shall be higher than 0,999.
5.2 Polytetrafluoroethylene (PTFE) beakers with PTFE cover
NOTE For the determination of magnesium, glass beakers and watch-glass covers can be used.
5.3 Volumetric flask, of capacity 100 ml, made of polypropylene or polyethylene terephthalate (PET).
4 © ISO 2014 – All rights reserved

5.4 Filter, 0,22 μm pore size, 47 mm diameter PTFE, or polycarbonate filter membrane.
5.5 Suction filtration system, including a flask, a filter funnel, and a vacuum filtration device.
6 Sampling
Sampling shall be carried out in accordance with ISO 14284 or with an appropriate national standard
for steels and cast irons.
7 Procedure
WARNING — Perchloric acid vapour can cause explosions in the presence of ammonia, nitrous
fumes, or organic matter in general.
All glassware and plasticware shall first be washed with hydrochloric acid (4.3), then with water. The
quantities of calcium and magnesium in the glassware and plasticware can be checked by measuring
the intensity of the emitted light of water poured into glassware and plasticware after washing with
acid and rinsing with water. If contamination from calcium and magnesium is present, the glassware
and plasticware are unsuitable and should be replaced or cleaned again.
For each set of determinations, all reagents, including water, calibration and test solutions, shall be from
the same batch.
7.1 Test portion
Place the sample or the pure iron in a PTFE beaker. Add 10 ml of hydrochloric acid (4.5) and swirl the
beaker gently. Discard the hydrochloric acid s
...