ISO 13548:2025

International
Standard
ISO 13548
First edition
Copper and zinc sulfide
2025-08
concentrates — Determination
of fluorine content by sodium
hydroxide fusion and fluoride ion
selective electrode detection
Concentrés sulfurés de cuivre et de zinc — Dosage du fluor
par fusion à l'hydroxyde de sodium et détection par électrode
sélective des ions fluorure
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 3
7 Instrument operating parameters . 4
8 Sampling and sample preparation . 4
8.1 Laboratory sample .4
8.2 Test sample .4
9 Procedure . 4
9.1 Number of determinations .4
9.2 Test portion .4
9.3 Blank test .5
9.4 Dissolution of the test portion by NaOH fusion .5
9.5 Leaching .5
9.6 Preparation of the leach solution .5
9.7 Preparation of solution for introduction to fluoride ion selective electrode.6
9.8 Preparation of the calibration solutions and stabilization solution .6
9.9 Preparation of fluorine calibration .6
9.9.1 General .6
9.9.2 Conditioning of the fluoride ion selective electrode .6
9.9.3 Potential stabilization .7
9.9.4 Temperature control .7
9.9.5 Electrode handling for concentration measurement .7
9.9.6 Procedure for reducing measurement variability.7
9.9.7 Calibration graph plotting method .7
9.10 Determination of fluorine content in the test solutions .7
10 Calculations . 7
11 Procedure for obtaining the final result . 9
12 Test report . 9
13 Precision . 9
13.1 Expression of precision .9
13.2 Procedure for obtaining the final result .10
13.3 Interlaboratory precision .10
13.4 Check of trueness .11
13.4.1 General .11
13.4.2 Type of certified reference material or reference material .11
Annex A (normative) Procedure for obtaining the final results .12
Annex B (informative) Procedure for the preparation and determination of the mass of a
predried test portion .13
Annex C (informative) Trueness test .15
Bibliography .18

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 183, Copper, lead, zinc and nickel ores and
concentrates.
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iv
International Standard ISO 13548:2025(en)
Copper and zinc sulfide concentrates — Determination of
fluorine content by sodium hydroxide fusion and fluoride ion
selective electrode detection
WARNING — This document can involve hazardous materials and equipment. It is the responsibility
of the user of this document to establish appropriate health and safety practices and determine the
applicability of regulatory limitations prior to use.
1 Scope
This document specifies a procedure for the determination of fluorine in copper and zinc sulfide concentrates
by sodium hydroxide fusion and fluoride ion selective electrode (FISE) detection. Fluoride ions are leached
from the sodium hydroxide fusion and presented to the FISE. Potential interfering ions are masked by the
use of a complexing agent and control of solution pH. If the aluminium content in the concentrate is up to a
mass fraction of 4,5 %, there is no effect of aluminium in this method. However, if the aluminium content in
the concentrate exceeds a mass fraction of 4,5 %, there is a possibility that it can affect the analytical results.
The method is applicable to fluorine in the following ranges:
— copper concentrates: mass fraction of 0,008 % to 0,3 %;
— zinc concentrates: mass fraction of 0,005 % to 0,1 %.
The results of the trueness test can be found in Annex C.
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 3696, Water for analytical laboratory use — Specification and test methods
ISO 9599, Copper, lead, zinc and nickel sulfide concentrates — Determination of hygroscopic moisture content of
the analysis sample — Gravimetric method
ISO 12743, Copper, lead, zinc and nickel concentrates — Sampling procedures for determination of metal and
moisture content
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
The test portion is decomposed by fusion with sodium hydroxide. Fluorine is then determined by ion
selective electrode after masking of potential interfering ions by use of a complexing agent and pH control.
5 Reagents
During the analysis, only reagents of analytical grade and grade 2 water of ISO 3696 shall be used. Particular
care should be taken to ensure all reagents are fluorine free, except for 5.2 and the solutions in 5.10, 5.11
and 5.12.
5.1 Sodium hydroxide (NaOH) pellets, AR grade.
5.2 Sodium fluoride (NaF > 99,90 %), AR grade.
5.3 Sodium nitrate (NaNO3), AR grade.
5.4 Tri-sodium citrate dihydrate (Na C H O ·2H O).
3 6 5 7 2
5.5 Nitric acid (ρ20 = 1,38 g/ml).
5.6 200 g/l tri-sodium citrate solution.
Dissolve 200 g of tri-sodium citrate dihydrate (5.4) in 1 000 ml of water.
5.7 Nitric acid (1+1).
5.8 Nitric acid (1+99).
5.9 5 g/l sodium hydroxide solution.
Dissolve 0,5 g of sodium hydroxide (5.1) in 100 ml of water.
5.10 Working fluorine standard (1 000 mg/l).
Dissolve 2,210 × 100/A g (A is the purity of a mass fraction of NaF % of sodium fluoride (5.2), dried from
between 500 °C to 550 °C for 1 h by using a platinum dish (6.24), in 400 ml of water. Transfer the solution
quantitatively into a 1 000 ml plastic volumetric flask (6.8). Dilute to volume with water. Store in a labelled
plastic bottle.
Alternatively, purchase a suitable high-quality prepared standard.
NOTE There are reference solutions with metrological traceability secured.
5.11 Working fluorine standard solution A (100 mg/l).
Pipette 10,0 ml of 1 000 mg/l fluorine standard solution (5.10) into a 100 ml plastic volumetric flask (6.8).
Dilute to volume with water. Store in a labelled plastic bottle.
Alternatively, purchase a suitable high-quality prepared standard.
NOTE There are reference solutions with metrological traceability secured.
5.12 Working fluorine standard solution B (10 mg/l).
Pipette 10,0 ml of 100 mg/l fluorine standard solution (5.11) into a 100 ml plastic volumetric flask (6.8).
Dilute to volume with water. Store in a labelled plastic bottle.

Alternatively, purchase a suitable high-quality prepared standard.
NOTE There are reference solutions with metrological traceability secured.
6 Apparatus
All laboratory glassware and equipment shall be shown to be free of fluorine contamination.
6.1 Balance, accurate and readable to ± 0,000 1 g.
6.2 Top loading balance, accurate and readable to ± 0,001 g.
6.3 Meker burner.
6.4 Muffle furnace, with temperature controller.
6.5 Laboratory hot plate, with temperature controller.
6.6 Laboratory timer.
6.7 Polypropylene or polytetrafluoroethylene beakers, 50 ml, 100 ml, 250 ml, 500 ml and 1 000 ml.
6.8 Polypropylene volumetric flasks, 100 ml and 1 000 ml.
6.9 Plastic funnels.
6.10 Watch glasses.
6.11 Plastic volumetric pipette.
6.12 Filter paper, with an ash content of a mass fraction of 0,06 % or less and a nominal particle retention
of about 8 µm.
6.13 Adjustable micro pipette.
6.14 Reagent dispensers.
6.15 Nickel or zirconium crucibles, 30 ml to 50 ml, with covers.
6.16 pH meter and electrode.
6.17 Combined ion selective fluoride electrode or single ion selective fluoride electrode and
reference electrode.
6.18 Temperature sensor.
6.19 mV meter or ion meter which allows direct readings in concentration.
6.20 Magnetic stirring bars, polytetrafluoroethylene coated, 25 mm in length.
6.21 Magnetic stirrer.
6.22 Desiccator, containing silica gel as the desiccant.
6.23 Burette stand and clamps or electrode selective clamp and stand.
6.24 Platinum dish, 30 ml to 50 ml.
7 Instrument operating parameters
Refer to the manufacturer’s instructions for optimizing electrode and meter operation.
8 Sampling and sample preparation
8.1 Laboratory sample
Laboratory samples shall be taken and prepared in accordance with the procedures described in ISO 12743.
8.2 Test sample
Prepare an air-equilibrated test sample and a hygroscopic moisture test sample in accordance with ISO 9599.
NOTE A test sample is not required if pre-dried test portions are used, see Annex B.
9 Procedure
9.1 Number of determinations
Carry out the determination at least in duplicate, as far as possible under repeatability conditions, on each
test sample.
NOTE Repeatability conditions exist where mutually independent test results are obtained with the same
method on identical test material in the same laboratory by the same operator using the same equipment within short
intervals of time.
9.2 Test portion
Place the crucible (6.15) onto a top loading balance (6.2). Zero the balance and add about 10 g of sodium
hydroxide pellets (5.1). Heat the crucible in a gentle flame and stir to dehydrate thoroughly for 1 min or
more. Place the crucible into the desiccator (6.22) and cool it to room temperature. Then immediately place
the crucible onto the top loading balance and tare the balance. Take the test portion by weighing from 50 µg
to less than 1 000 µg as fluorine amount into the crucible. The test portion shall be taken in accordance with
Table 1.
Table 1 — Mass of sample and fluorine concentration
Fluorine concentration Mass of sample
mass fraction, % g
0,005 to 0,1 1,00
0,1 to 0,2 0,50
At the same time as the test portions are taken for analysis, weigh test portions for the determination of
hygroscopic moisture in accordance with ISO 9599. Alternatively, the method specified in Annex B may be
used to prepare pre-dried test portions directly from the laboratory sample.
If the fluorine content is unknown, a preliminary survey of the approximate fluorine content should be
conducted in advance.
9.3 Blank test
Carry out a blank test in parallel with the analysis by using the same quantities of all reagents but omitting
the sample. The purpose of the blank test is to check for contamination of the apparatus used in the test
and the purity of the reagents. Evaluate as a blank by subtracting the amount of fluorine added from the
determination value of fluorine of the blank to which F is added.
Finally, the fluorine results in the blank test shall be deducted from the sample.
For the preparation of blank test solution, prepare the leaching solution for blank test in accordance with
9.4, 9.5 and 9.6. Check the performance of the plastic volumetric pipette (6.11) and adjustable micro pipette
(6.13) by using water. Using the plastic volumetric pipette, take a 50 ml aliquot of the leach solution in the
100 ml plastic beaker. Add 20,0 ml of 200 g/l tri-sodium citrate solution (5.6) using a reagent dispenser. And
add 100 µl of 1 000 mg/l fluorine standard solution and swirl the beaker gently to mix the contents. Adjust
the pH with nitric acid (5.7 and 5.8) or sodium hydroxide solution (5.9) to 6,5 to 7,0. Transfer the content of
the plastic beaker to a 100 ml plastic volumetric flask (V1) and make to the mark with water.
In the low concentration region of fluorine ions, the calibration curve is curved, and the blank cannot be
accurately evaluated. To properly evaluate the blank, add 100 µg of fluorine to the blank, subtract 100 µg
after measuring the solution and use that value as the blank.
9.4 Dissolution of the test portion by NaOH fusion
Heat the crucible into gentle flame and heat with stirring to dissolve the test portion thoroughly. When the
fusion is complete, remove the crucibles and place in order on a metal or ceramic plate and allow to cool.
In place of a Meker burner, a muffle furnace (6.4) can be used for dissolving the test portion by NaOH fusion.
This procedure does not include a roasting step because fluorine can volatilize during roasting. However, if
it is confirmed that fluorine does not volatilize, the sample can be roasted in a muffle furnace before adding
NaOH. The sample and NaOH are weighed and pre-fusion for 1 min or more with a Meker burner. Then put
the crucible in a muffle furnace heated to 500 °C, close the furnace door, and heat for about 10 min. Then
remove each crucible individually and swirl the fusion to mix before the fusion mix solidifies. When the
fusion is complete, remove the crucibles and place in order on a metal or ceramic plate. Allow to cool. Reset
the temperature of the furnace to room temperature ready for the next set of analyses.
Check for any unfused material, which will appear as grain-like lumps on the bottom of the crucible. Also
check for unfused sodium hydroxide pellets, which will appear as smooth rounded lumps. If lumps are
evident,
...