ISO 16918-1:2009

Steel and iron - Determination of nine elements by the inductively coupled plasma mass spectrometric method - Part 1: Determination of tin, antimony, cerium, lead and bismuth

ISO 16918-1:2009 specifies a method for analysing steel and iron for the trace element determinations of Sn, Sb, Ce, Pb and Bi using inductively coupled plasma mass spectrometry (ICP-MS). The method is applicable for trace elements in the mass fraction ranges (µg/g) as follows: Sn: 5 µg/g to 200 µg/g; Sb: 1 µg/g to 200 µg/g; Ce: 10 µg/g to 1 000 µg/g; Pb: 0,5 µg/g to 100 µg/g; Bi: from 0,3 µg/g to 30 µg/g. Interferences in the determination of trace elements using ICP-MS are listed in Annex B.

Acier et fer — Dosage de neuf éléments par spectrométrie de masse avec plasma induit par haute fréquence — Partie 1: Dosage de l'étain, de l'antimoine, du cérium, du plomb et du bismuth

General Information

• Status: Published
• Publication Date: 11-Jan-2009
• ICS: 77.080.01 - Ferrous metals in general
• Technical Committee: ISO/TC 17/SC 1 - Methods of determination of chemical composition
• Drafting Committee: ISO/TC 17/SC 1 - Methods of determination of chemical composition
• Current Stage: 9093 - International Standard confirmed
• Start Date: 09-Jan-2025
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 14453:2014 - Pulps - Determination of acetone-soluble matter
• Effective Date: 06-Jun-2022

Overview

ISO 16918-1:2009 specifies a standardized laboratory method for the determination of five trace elements in steel and iron - tin (Sn), antimony (Sb), cerium (Ce), lead (Pb) and bismuth (Bi) - using inductively coupled plasma mass spectrometry (ICP‑MS). The standard covers sample dissolution (wet digestion), instrument conditioning and measurement, calibration, internal standards and reporting. Applicable mass-fraction ranges are: Sn 5–200 µg/g, Sb 1–200 µg/g, Ce 10–1 000 µg/g, Pb 0.5–100 µg/g and Bi 0.3–30 µg/g. Annex B lists common ICP‑MS interferences relevant to these determinations.

Key topics and requirements

• Scope and principle: Wet digestion of test portion (HCl, HNO3, HF) by microwave or hot-plate, followed by ICP‑MS measurement with peristaltic sample introduction.
• Analytical ranges: Defined mass-fraction ranges for Sn, Sb, Ce, Pb and Bi to ensure method validity at trace levels.
• Reagents and purity: Use high‑purity acids and ultra‑pure water; specific reagent preparations (washing solution, aqua regia, matrix solutions) are specified.
• Sample preparation: Guidelines for sampling, dissolution, blanks and test-solution preparation to minimise contamination.
• Calibration and matrix matching: Calibration blank and solutions must be matrix‑matched to steel (iron matrix solution 10 000 mg Fe/L is defined).
• Internal standards: Use of internal standards (Y, Rh, Lu) to correct for instrument drift and matrix effects.
• Instrumentation: Procedure applicable to quadrupole, magnetic‑sector (high resolution) and TOF ICP‑MS; instrument warm‑up, conditioning and measurement protocols are addressed.
• Measurement specifications: Sections define minimum precision (RSD), limits of detection (LOD) and limits of quantification (LOQ).
• Quality control: Includes preparation of multi‑element standards, mass calibration solutions and guidance on checking reagent purity by mass-spectra scans.
• Interferences: Annex B gives interference information specific to Sn, Sb, Ce, Pb and Bi determinations by ICP‑MS.

Applications and users

ISO 16918-1:2009 is intended for:

• Metallurgical and steel testing laboratories performing trace element analysis for quality control and specification compliance.
• Manufacturers and foundries monitoring alloying and contaminant levels (tin, antimony, cerium, lead, bismuth).
• Regulatory and materials testing bodies requiring reproducible, comparable ICP‑MS results.
• Research institutions studying trace-element behavior in steels and iron. Practical uses include incoming raw-material screening, process control, failure analysis and certification of alloy composition.

Related standards

• ISO 16918-2 (Part 2): Determination of boron, silver, indium and thallium.
• Normative references used in the method: ISO 648, ISO 1042 (laboratory glassware) and ISO 14284 (sampling and preparation of steel and iron).

Keywords: ISO 16918-1:2009, ICP‑MS, steel and iron, trace element determination, tin antimony cerium lead bismuth, wet digestion, matrix-matched calibration, internal standards, LOD LOQ.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 16918-1
First edition
2009-01-15
Steel and iron — Determination of nine
elements by the inductively coupled
plasma mass spectrometric method —
Part 1:
Determination of tin, antimony, cerium,
lead and bismuth
Acier et fer — Dosage de neuf éléments par spectrométrie de masse
avec plasma induit par haute fréquence —
Partie 1: Dosage de l'étain, de l'antimoine, du cérium, du plomb et du
bismuth
Reference number
©
ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword .iv
1 Scope.1
2 Normative references.1
3 Principle.1
4 Reagents.2
5 Apparatus.4
6 Measurement specifications .5
6.1 Minimum precision (RSD).5
6.2 Limit of detection (LOD) and limit of quantification (LOQ) .5
7 Sampling.6
8 Washing.6
9 Procedure.6
9.1 Test portion.6
9.2 Blank test solution [blank sample solution].6
9.3 Preparation of the test solution .6
10 Standard solutions .8
10.1 Multi-element standard solutions of the elements Sn, Sb, Pb and Bi .8
10.2 Standard solutions of the element Ce.9
11 Preparation of internal standard solutions (“internal standards”) — Y, Rh and Lu.9
11.1 Preparation in polystyrene test tubes .9
11.2 Preparation in volumetric flasks.10
12 Calibration blank solution and calibration solutions .10
12.1 Preparation in volumetric flasks.10
12.2 Preparation in polystyrene test tubes .11
13 Conditioning of the ICP-MS instrument .14
14 ICP-MS measurements.14
15 Plotting of calibration graphs.14
16 Expression of results.15
16.1 Method of calculation.15
16.2 Precision.15
17 Test report.17
Annex A (informative) Additional information on the international co-operative tests.18
Annex B (informative) Interferences in the determination of elements Sn, Sb, Ce, Pb and Bi using
ICP- MS .28
Bibliography.29

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16918-1 was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 1, Methods of
determination of chemical composition.
ISO 16918 consists of the following parts, under the general title Steel and iron — Determination of nine
elements by the inductively coupled plasma mass spectrometric method:
⎯ Part 1: Determination of tin, antimony, cerium, lead and bismuth
⎯ Part 2: Determination of boron, silver, indium and thallium

iv © ISO 2009 – All rights reserved

INTERNATIONAL STANDARD ISO 16918-1:2009(E)

Steel and iron — Determination of nine elements by the
inductively coupled plasma mass spectrometric method —
Part 1:
Determination of tin, antimony, cerium, lead and bismuth
1 Scope
This part of ISO 16918 specifies a method for analysing steel and iron for the trace element determinations of
Sn, Sb, Ce, Pb and Bi using inductively coupled plasma mass spectrometry (ICP-MS). The method is
applicable for trace elements in the mass fraction ranges (µg/g) as follows:
Sn: 5 µg/g to 200 µg/g; Sb: 1 µg/g to 200 µg/g; Ce: 10 µg/g to 1 000 µg/g; Pb: 0,5 µg/g to 100 µg/g; Bi: from
0,3 µg/g to 30 µg/g.
Interferences in the determination of trace elements using ICP-MS are listed in Annex B.
2 Normative references
The following referenced documents are indispensable for the application 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 14284, Steel and iron — Sampling and preparation of samples for the determination of chemical
composition
3 Principle
A test portion is dissolved in an acid-mixture of hydrochloric acid, nitric acid and hydrofluoric acid using either
a microwave-assisted system or a traditional hot plate.
Diluted wet-digested samples are introduced into an inductively coupled plasma mass spectrometer (ICP-MS),
via a peristaltic pump. Simultaneous measurements of the intensities of elements with atomic mass units of
concern (mass spectra) are carried out using ICP-MS techniques.
Calibration blank and calibration solutions are matrix-matched with the major elements of steel, and mineral
acids are used for wet-digestion.
Internal standards are used throughout in order to compensate for any instrument drift.
4 Reagents
During the analysis, unless other stated, use only reagents of high purity quality containing less than
0,000 1 % mass fraction of each element or equivalent purity. The % given below refers to % mass fraction.
4.1 Hydrochloric acid, 30 % HCl, ρ 1,15 g/ml or 38 %, ρ 1,19 g/ml.
4.2 Nitric acid, 70 % HNO , ρ 1,42 g/ml.
4.3 Hydrofluoric acid, 49 % HF, ρ 1,16 g/ml.
4.4 Nitric acid, 65 % HNO , ρ 1,40 g/ml.
4.5 Ultra-pure water, produced by a water purification system giving a resistivity of 18 MΩ/cm or higher.
4.6 Washing solution for ICP-MS.
In a 500 ml plastic bottle (e.g. polyethylene) pour about 400 ml of ultra-pure water (4.5), then add 15 ml
hydrochloric acid (4.1), 5 ml nitric acid (4.2) and 2,5 ml hydrofluoric acid (4.3) and make it up to volume with
ultra-pure water (4.5).
The quality of the acids can be checked prior to use by a mass spectrum scan with the ICPMS instrument. It is
recommended to use a solution of 300 µl HCl (4.1) + 100 µl HNO (4.2) + 50 µl HF (4.3) with about 3 ml ultra-
pure water (4.5) and make it up to a volume of 10 ml. If peaks of elements of concern are present, a new flask
of acid shall be used and a new check of the same elements shall be carried out.
4.7 10 % nitric acid solution, HNO diluted 1+9.
In a 100 ml volumetric flask pour about 70 ml of ultra-pure water (4.5), then add 10 ml concentrated HNO
(4.2), and dilute to volume with ultra-pure water (4.5).
4.8 NaOH solution, 7,5 mol/l, ρ 1,33 g/ml.
4.9 NaOH solution, 0,2 mol/l.
Dispense 2,7 ml of 7,5 mol/l NaOH (4.8) into a 100 ml volumetric flask, and dilute to volume with ultra-pure
water (4.5).
The solution shall be stored in a polyethylene bottle or similar.
4.10 Aqua regia (HCl+HNO = 3+1).
Prepare aqua regia in a 30 ml beaker (or similar) by dispensing 9 ml HCl (4.1) and 3 ml HNO (4.2) into the
beaker.
4.11 Diluted aqua regia solution, diluted 4+10.
Dispense 100 ml ultra-pure water (4.5) into a 150 ml flask. Then add 40 ml aqua regia (4.10) and mix. Do not
make the solution up to volume.
4.12 50 % nitric acid solution, HNO diluted 1+1.
In a 100 ml volumetric flask, pour about 30 ml of ultra-pure water (4.5), then add 50 ml concentrated HNO
(4.2) and dilute to volume with ultra-pure water (4.5).
4.13 Perchloric acid, 70 % HClO , ρ 1,68 g/ml.
2 © ISO 2009 – All rights reserved

4.14 50 % hydrochloric acid solution, HCl diluted 1+1.
In a 100 ml volumetric flask, pour about 30 ml of ultra-pure water (4.5), then add 50 ml concentrated HCl (4.1)
and dilute to volume with ultra-pure water (4.5).
4.15 Iron, high purity quality containing less than 0,000 1 % mass fraction of each element.
4.16 Standard stock solutions, corresponding to 1 000 mg element per litre.
4.16.1 Tin standard stock solution
Dissolve 100,0 mg of high purity tin metal (99,9 % mass fraction, minimum) in 3 ml HCl (4.1) and 1 ml HNO
(4.2) in a 250 ml beaker. Heat gently to complete dissolution, cool, transfer into a 100 ml volumetric flask,
make the solution up to volume with ultra-pure water (4.5) and mix well.
Store the tin standard stock solution in a polyethylene bottle.
4.16.2 Antimony standard stock solution
Dissolve 100,0 mg of high purity antimony metal (99,9 % mass fraction, minimum) in 3 ml HCl (4.1) and 1 ml
HNO (4.2) in a 250 ml beaker. Heat gently to complete dissolution, cool, transfer into a 100 ml volumetric
flask, make the solution up to volume with ultra-pure water (4.5) and mix well.
Store the antimony standard stock solution in a polyethylene bottle.
4.16.3 Cerium standard stock solution
Dissolve 288,5 mg of pure cerium(IV) sulfate, Ce(SO ) 4H O, in 50 ml of a solution of diluted aqua regia
4 2 2
(4.11) in a 100 ml volumetric flask. After complete dissolution, make the solution up to volume with diluted
aqua regia (4.11) and mix well.
Store the cerium standard stock solution in a polyethylene bottle.
4.16.4 Lead standard stock solution
Dissolve 100,0 mg of high purity lead metal (99,9 % mass fraction, minimum) in 20 ml of 50 % HNO (4.12) in
a 250 ml beaker. Heat gently to complete dissolution, cool, transfer into a 100 ml volumetric flask, make the
solution up to volume with ultra-pure water (4.5) and mix well.
Store the lead standard stock solution in a polyethylene bottle.
4.16.5 Bismuth standard stock solution
Dissolve 100,0 mg of high purity bismuth metal (99,9 % mass fraction, minimum) in 3 ml HCl (4.1) and 1 ml
HNO (4.2) in a 250 ml beaker. Heat gently to complete dissolution, cool, transfer into a 100 ml volumetric
flask, make the solution up to volume with ultra-pure water (4.5) and mix well.
Store the bismuth standard stock solution in a polyethylene bottle.
4.16.6 Rhodium standard stock solution
Dissolve 203,6 mg of pure rhodium(III) chloride, RhCl , in 6 ml aqua regia (4.10), freshly prepared, in a 100 ml
volumetric flask. After complete dissolution, make the solution up to volume with ultra-pure water (4.5) and mix
well.
Store the rhodium standard stock solution in a polyethylene bottle.
4.16.7 Yttrium standard stock solution
Dissolve 127,0 mg of pure yttrium trioxide, Y O , in 6 ml aqua regia (4.10), freshly prepared, in a
2 3
100 volumetric flask. After complete dissolution, make the solution up to volume with ultra-pure water (4.5)
and mix well.
Store the yttrium standard stock solution in a polyethylene bottle.
4.16.8 Lutetium standard stock solution
Dissolve 113,7 mg of pure lutetium trioxide, Lu O , in 6 ml aqua regia (4.10), freshly prepared, in a 100 ml
2 3
volumetric flask. After complete dissolution, make the solution up to volume with ultra-pure water (4.5) and mix
well.
Store the lutetium standard stock solution in a polyethylene bottle.
4.16.9 Titanium standard stock solution
Dissolve 100,0 mg of pure titanium metal (99,9 % mass fraction, minimum) in 30 ml of 50 % HCl (4.14) and
0,2 ml of HF (4.3) in a 250 ml beaker. Heat gently to complete dissolution, cool, transfer into a 100 ml
volumetric flask, make the solution up to volume with ultra-pure water (4.5) and mix well.
Store the titanium standard stock solution in a polyethylene bottle.
4.17 Iron matrix solution, 10 000 mg of Fe per litre
Weigh 0,5 g of the high purity iron (4.15) to the nearest 0,01 mg and transfer it to a 250 ml beaker. Add 20 ml
ultra-pure water, and then 0,1 ml HCl (4.1) and finally 5 ml HNO (4.2). Heat gently to dissolve the iron chips.
After complete dissolution, cool, transfer into a 50 ml volumetric flask, make the solution up to volume with
ultra-pure water (4.5) and mix well.
Store the iron matrix solution in a polyethylene bottle.
4.18 Mass calibration solution, 100 µg/l of each of the elements Ti, Y, Rh, Sb, Ce, Pb and Bi
Dispense about 50 ml ultra-pure water (4.5) into a 1 000 ml volumetric flask, and then add 100 µl of each of
the standard stock solutions of Ti (4.16.9), Y (4.16.7), Rh (4.16.6), Sb (4.16.2), Ce (4.16.3), Pb (4.16.4) and Bi
(4.16.5). Make the solution up to volume with ultra-pure water (4.5) and mix well.
5 Apparatus
5.1 Laboratory glassware and plastic ware, including volumetric flasks, watch-glasses, beakers,
polyethylene bottles, polyethylene pipette tips, polystyrene tubes.
All volumetric glassware shall be Class A in accordance with ISO 648 and ISO 1042.
5.2 Micro-pipettes
The following micro-pipettes are used: 5 µl to 40 µl, 50 µl to 200 µl, 100 µl to 1 000 µl and 1 ml to 5 ml.
5.3 Microwave-assisted digestion system, consisting of a laboratory microwave oven and a carousel or
holder for polytetrafluoroethylene (PTFE) pressure vessels.
A time-step programme can be used, and during the wet-digestion procedure both pressure and temperature
are registered and can be followed on a monitor.
4 © ISO 2009 – All rights reserved

5.4 ICP-MS instruments
5.4.1 Magnetic sector ICP-MS (high resolution ICP-MS)
5.4.2 Quadropole ICP-MS (low resolution ICP-MS)
5.4.3 Time-of-flight ICP-MS (ICP-TOF-MS)
For optimum running of the ICP-MS instruments, the manual of each ICP-MS type shall be followed.
All three types of ICP-MS instrument are supplied with argon gas in order to supply an argon plasma. Prior to
analysis, the argon plasma is switched on and shall remain on for 30 min to 60 min to stabilize the instrument.
Meanwhile, ultra-pure water or washing solution should be pumped through the nebulizer and torch system.
The warm-up period depends on the type of ICP-MS instrument used.
Mass calibration should be performed every morning before starting analysis; seven elements should be
chosen in order to cover the periodic table of concern [Ti, Y, Rh, Sb, Ce, Pb and Bi (see 4.18)]. Other
elements can be used in a mass calibration solution, but they shall cover the atomic mass unit range which
will be used in the analysis.
Usually an auto-sampler device is connected to a peristaltic pump to automatically introduce samples into the
plasma. Manual introduction can also be used.
The instruments are conditioned by optimising the sensitivity. It is then very important to set the operational
parameters such as frequency, output power, plasma gas flow, auxiliary gas flow, nebulizer gas flow, sample
uptake rate, detection mode, integration time/peak, number of points/peak, number of replicates and washing
time. In practice, the sensitivity is optimised by introducing a calibration solution (e.g. a 100 µg/l rhodium
calibration solution or any other suitable calibration solution) into the plasma and then adjusting the
operational parameters.
6 Measurement specifications
6.1 Minimum precision (RSD)
Calculate the standard deviation of 10 measurements of a 10 µg/l element concentration of each element, in a
matrix-matched sample solution. The minimum precision (RSD) shall not exceed 5 %.
6.2 Limit of detection (LOD) and limit of quantification (LOQ)
Limit of detection (LOD) and limit of quantification (LOQ) are defined by the following equations respectively.
C
s
LOD=×3 σ×
XX−
sb
C
s
LOQ=×10 σ×
XX−
sb
where
σ is the standard deviation of intensity for the blank solution at 10 measurements;
X is the mean intensity for the standard solution at 10 measurements;
s
X is the mean intensity for the blank solution at 10 measurements;
b
C is the concentration of the standard solution, in µg/l.
s
7 Sampling
Sampling is carried out in accordance with ISO 14284 or appropriate national standards for steel.
8 Washing
All glassware and plastic materials are soaked in nitric acid (4.4) for at least 12 h and subsequently rinsed with
ultra-pure water (4.5). The labware shall then be stored in a dust-free place.
9 Procedure
9.1 Test portion
Weigh 100 mg, to the nearest 0,01 mg, of a test portion (sample) to be analysed.
NOTE This International Standard specifies the procedure for which the mass of test portion is 100 mg, but less than
100 mg of the test portion, e.g. 10 mg, can be chosen.
9.2 Blank test solution [blank sample solution]
In parallel with the determination of unknown samples, a blank test solution shall be analysed. The blank test
solution shall contain the same quantities of reagents as used for analysing unknown steel samples, plus the
same mass of high purity iron (4.15) as the test portion.
9.3 Preparation of the test solution
9.3.1 Test solution for the elements Sn, Sb, Pb and Bi
9.3.1.1 Microwave-assisted digestion method
The test portion is quantitatively transferred to a PTFE pressure vessel (about 120 ml) and 3 ml HCl (4.1),
1 ml HNO (4.2) and 0,5 ml HF (4.3) are added. The lid of the vessel is screwed tight. However, the acids can
be added to the vessel and they can remain overnight in the vessel with the lid loosely tightened. This usually
improves the wet-digestion procedure.
The wet digestion takes place in a microwave-assisted digestion system. The PTFE pressure vessels are
placed in a carousel or a special holder, which is put in a laboratory microwave oven, and the wet-digestion is
carried out by means of microwaves. The wet digestion is carried out according to a three-step procedure, i.e.
starting at a low temperature of about 50 °C for 10 min, then raising the temperature to about 100 °C for
10 min, and finally raising the temperature to 150 °C to 200 °C for 10 min.
The three-step procedure can be carried out simply by regulating the power of the microwave oven. Thus the
microwave-assisted digestion takes place for 30 min, and for a further 30 min the PTFE pressure vessels shall
cool before being taken out of the microwave oven. The temperature in the PTFE pressure vessels shall be
less than 50 °C before they are opened. Plastic gloves shall be worn when opening the PTFE pressure
vessels.
WARNING — Do not open the door of the microwave oven immediately after the end of the programme,
since there is always a risk that the security membrane of the PTFE pressure vessels can rupture and
blow out hot acids.
After cooling, the contents of the PTFE pressure vessels are transferred quantitatively to a 100 ml
polyethylene bottle or a 100 ml volumetric flask by carefully rinsing the PTFE pressure vessels with ultra-pure
water (4.5), making the bottles or flasks up to volume with ultra-pure water (4.5) and mixing well.
6 © ISO 2009 – All rights reserved

9.3.1.2 Digestion using open vessels on a hot plate
Place the test portion in a 50 ml PTFE beaker or quartz beaker with graphite bottom. Add 3 ml HCl (4.1),
cover the beaker with a watch-glass, and heat gently until solvent reaction ceases. Add 1 ml HNO (4.2) and
heat until fumes of nitrogen oxides have disappeared. Add 0,5 ml HF (4.3) and heat for 5 min. If necessary,
cool and add 5 ml of HClO (4.13) and heat strongly without a watch-glass until fuming commences.
Cover with a watch-glass and continue heating at a temperature at which a steady reflux of white perchloric
acid fumes is maintained on the walls of the beaker. Continue heating until there are no perchloric acid fumes
visible inside the beaker. Cool and transfer the solution quantitatively to a 100 ml volumetric flask by rinsing
the beaker with ultra-pure water (4.5). Make the solution up to volume with ultra-pure water (4.5) and mix well.
CAUTION — PTFE beakers with graphite bottoms can easily be destroyed by elevated temperatures,
and consequently the temperature must be increased very slowly.
9.3.2 Test solution for the element Ce
9.3.2.1 Microwave-assisted digestion method
The test portion is quantitatively transferred to a PTFE pressure vessel (about 120 ml), and 3 ml HCl (4.1) and
1 ml HNO (4.2) are added. The lid of the vessel is screwed tight. However, the acids can be added to the
vessel and they can remain overnight in the vessel with the lid loosely tightened. This usually improves the
wet-digestion procedure.
The wet digestion takes place in a microwave-assisted digestion system. The PTFE pressure vessels are
placed in a carousel or a special holder, which is put in a laboratory microwave oven, and the wet-digestion is
carried out by means of microwaves. The wet digestion is carried out according to a three-step procedure, i.e.
starting at a low temperature of about 50 °C for 10 min, then raising the temperature to about 100 °C for
10 min, and finally raising the temperature to 150 °C to 200 °C for 10 min.
The three-step procedure can be carried out simply by regulating the power of the microwave oven. Thus the
microwave-assisted digestion takes place over 30 min, and for a further 30 min the PTFE pressure vessels
shall cool before being taken out of the microwave oven. The temperature in the PTFE pressure vessels shall
be less than 50 °C before they are opened. Plastic gloves shall be worn when opening the PTFE pressure
vessels.
WARNING — Do not open the door of the microwave oven immediately after the end of the programme,
since there is always a risk that the security membrane of the PTFE pressure vessels can rupture and
blow out hot acids.
After cooling, the contents of the PTFE pressure vessels are transferred quantitatively to a 100 ml
polyethylene bottle or a 100 ml volumetric flask by carefully rinsing the PTFE pressure vessels with ultra-pure
water (4.5), making up to volume with ultra-pure water (4.5) and mixing well.
9.3.2.2 Digestion using open vessels on a hot plate
Place the test portion in a 100 ml glass beaker or quartz beaker. Add 3 ml HCl (4.1), cover with a watch-glass
and heat gently until solvent reaction ceases. Add 1 ml HNO (4.2) and heat until fumes of nitrogen oxides
have disappeared. If necessary, cool and add 5 ml of HClO (4.13) and heat strongly without a watch-glass
until fuming commences.
Cover with a watch-glass and continue heating at a temperature at which a steady reflux of white perchloric
acid fumes is maintained on the walls of the beaker. Continue heating until there are no perchloric acid fumes
visible inside the beaker. Cool and transfer the solution quantitatively to a 100 ml volumetric flask by rinsing
the beaker with ultra-pure water (4.5), making the solution up to volume with ultra-pure water (4.5) and mixing
well.
10 Standard solutions
Three standard solutions are prepared and used for further preparations of calibration solutions.
10.1 Multi-element standard solutions of the elements Sn, Sb, Pb and Bi
Multi-element standards of the four elements given above are prepared, starting with the standard stock
solution of each element (4.16.1, 4.16.2, 4.16.4, 4.16.5).
10.1.1 Preparation in polystyrene test tubes
Preparation of standard solutions directly in 10 ml polystyrene test tubes is convenient and time-saving.
The solutions are made up to volume with ultra-pure water (4.5). The preparation of the two standard solutions
is described in 10.1.1.1 and 10.1.1.2.
10.1.1.1 Preparation of multi-standard solution — Multi-standard : 10 mg/l
From each of the four standard stock solutions (4.16.1, 4.16.2, 4.16.4, 4.16.5) take 100 µl and add to a 10 ml
polystyrene test tube containing about 5 ml of ultra-pure water (4.5). Make up the multi-element solution to
1)
volume with ultra-pure water (4.5) by weighing . Seal the test tube with parafilm and mix the standard solution.
See Table 1.
Table 1 — Multi-standard solution
Volume of each Mass Test tube volume Concentration of each
standard stock element in test tube
solution – Standard after dilution
1 000
µl µg ml mg/l
100 100 10 10
10.1.1.2 Preparation of multi-standard solution — Multi-standard : 0,1 mg/l
0,1
Dispense 100 µl of multi-standard into a 10 ml polystyrene test tube and make the solution up to volume
with ultra-pure water (4.5) by weighing. Seal the test tube with parafilm and mix the standard solution. See
Table 2.
Table 2 — Multi-standard solution
0,1
Volume of Mass Test tube volume Concentration of each
multi-standard element in test tube
after dilution
µl µg ml mg/l
100 1,0 10 0,10
10.1.2 Preparation in volumetric flasks
Preparation of standard solutions can be done in a 100 ml volumetric flask. All sample solutions are made up
to volume with ultra-pure water (4.5). The multi-standard solutions are prepared according to 10.1.2.1 to
10.1.2.2.
1) Measuring net mass of solution in the test tube.
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10.1.2.1 Preparation of multi-standard solution — Multi-standard : 10 mg/l
From each of the four standard stock solutions (4.16.1, 4.16.2, 4.16.4, 4.16.5) 1,0 ml is taken and added to a
100 ml volumetric flask containing about 50 ml of ultra-pure water (4.5). The multi-element solution is made up
to volume with ultra-pure water (4.5). The standard solution is mixed and stored in the volumetric flask.
Table 3 — Multi-standard solution
Volume of each Mass Volume of volumetric flask Concentration of each
standard stock element in volumetric
solution – Standard flask after dilution
1 000
ml µg ml mg/l
1,0 1 000 100 10
10.1.2.2 Preparation of multi-standard solution — Multi-standard : 0,1 mg/l
0,1
Dispense 1,0 ml of multi-standard into a 100 ml volumetric flask, make the solution up to volume with ultra-
pure water (4.5) and mix well.
Table 4 — Multi-standard solution
0,1
Volume of Mass Volume of volumetric flask Concentration. of each
multi-standard element in the volumetric
flask after dilution
ml µg ml mg/l
1,0 10 100 0,10
10.2 Standard solutions of the element Ce
The element Ce must be determined separately, since there is a risk of precipitation of CeF if hydrofluoric
acid is used. The preparation of the standard solution Ce-Standard should be a straightforward procedure
following the dilution scheme starting with 10.1.1.1 and 10.1.2.1, respectively. Start with the cerium standard
stock solution (4.16.3).
11 Preparation of internal standard solutions (“internal standards”) — Y, Rh and Lu
11.1 Preparation in polystyrene test tubes
It is mandatory to use internal standards when analysing several samples, since there is always instrumental
drift due to the heavy matrix in wet-digested steel samples.
Internal standards of the elements Rh, Y and Lu are prepared in three separate polystyrene test tubes,
respectively. About 3 ml of ultra-pure wa
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