SIST EN ISO 15192:2026

SLOVENSKI STANDARD
01-marec-2026
Nadomešča:
SIST EN ISO 15192:2021
Tla in odpadki - Določanje kroma Cr(VI) v trdnem mediju z alkalnim razklopom in
ionsko kromatografijo s spektrofotometrijsko detekcijo (ISO 15192:2025)
Soil and waste - Determination of chromium(VI) in solid material by alkaline digestion
and ion chromatography with spectrophotometric detection (ISO 15192:2025)
Boden und Abfall - Bestimmung von sechswertigem Chrom in Feststoffen durch
alkalischen Aufschluss und Ionenchromatographie mit photometrischer Detektion (ISO
15192:2025)
Déchets et sols - Dosage du chrome(VI) dans les matériaux solides par digestion
alcaline et chromatographie ionique avec détection spectrophotométrique (ISO
15192:2025)
Ta slovenski standard je istoveten z: EN ISO 15192:2025
ICS:
13.080.10 Kemijske značilnosti tal Chemical characteristics of
soils
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 15192
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2025
EUROPÄISCHE NORM
ICS 13.080.10 Supersedes EN ISO 15192:2021
English Version
Soil and waste - Determination of chromium(VI) in solid
material by alkaline digestion and ion chromatography
with spectrophotometric detection (ISO 15192:2025)
Déchets et sols - Dosage du chrome(VI) dans les Boden und Abfall - Bestimmung von sechswertigem
matériaux solides par digestion alcaline et Chrom in Feststoffen durch alkalischen Aufschluss und
chromatographie ionique avec détection Ionenchromatographie mit photometrischer Detektion
spectrométrique (ISO 15192:2025) (ISO 15192:2025)
This European Standard was approved by CEN on 13 September 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15192:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 15192:2025) has been prepared by Technical Committee ISO/TC 190 "Soil
quality" in collaboration with Technical Committee CEN/TC 444 “Environmental characterization of
solid matrices” the secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2026, and conflicting national standards shall
be withdrawn at the latest by March 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 15192:2021.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 15192:2025 has been approved by CEN as EN ISO 15192:2025 without any modification.

International
Standard
ISO 15192
Third edition
Soil and waste — Determination
2025-09
of chromium(VI) in solid
material by alkaline digestion
and ion chromatography with
spectrophotometric detection
Déchets et sols — Dosage du chrome(VI) dans les matériaux
solides par digestion alcaline et chromatographie ionique avec
détection spectrophotométrique
Reference number
ISO 15192:2025(en) © ISO 2025
ISO 15192:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 15192:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Safety remarks . 1
5 Principle . 2
5.1 Digestion .2
5.2 Determination .2
5.3 Interferences and sources of error .2
6 Apparatus . 3
7 Reagents . 3
8 Sample pretreatment . 6
9 Alkaline digestion procedure . 6
9.1 General .6
9.2 Preparation of test solutions using a hotplate or heating block .6
10 Analytical procedure . 7
10.1 General information.7
10.2 Instrumental set-up .7
10.3 Calibration .7
10.4 Test solution measurement .7
10.5 Quality control .8
10.5.1 General .8
10.5.2 Blank test solution .8
10.5.3 Verification of method .8
10.5.4 Duplicate samples.8
10.5.5 Soluble Cr(VI) spiked samples .8
10.5.6 Cr(III) spiked samples .9
10.5.7 Interpretation of quality control data .9
11 Calculation . 9
12 Expression of results .10
13 Test report . 10
Annex A (informative) Ion chromatographic system .11
Annex B (informative) Requirements for test portion preparation .13
Annex C (informative) Validation . 14
Annex D (informative) Background on methods for the determination of Cr(VI) in solid samples . 19
Bibliography .23

iii
ISO 15192:2025(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
and physical characterization, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 444, Environmental characterization of solid matrices, in accordance with the
Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 15192:2021), which has been technically
revised.
The main changes are as follows:
— integration of the determination of the total chromium in the alkaline digestion solution;
— addition of barium chromate as an alternative to lead chromate for the verification of the method in 10.5.3;
— the text has been editorially revised, including updating of references.
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
ISO 15192:2025(en)
Introduction
Under environmental conditions chromium in compounds exists in the trivalent, Cr(III), or the hexavalent,
Cr(VI) state. Chromium is an essential trace element for mammals, including man, whereas it is presumed
that Cr(VI) compounds are genotoxic and carcinogenic in humans. Interconversion of trivalent and
hexavalent chromium species can occur during sample preparation and analysis, but these processes are
minimised, to the extent possible, by the sample preparation methods prescribed by this document.

v
International Standard ISO 15192:2025(en)
Soil and waste — Determination of chromium(VI) in solid
material by alkaline digestion and ion chromatography with
spectrophotometric detection
1 Scope
This document specifies the determination of Cr(VI) in solid waste material and soil by alkaline digestion
and ion chromatography with spectrophotometric detection. This method is applicable to determine Cr(VI)
mass fractions in solids more than 0,1 mg/kg.
NOTE In case of reducing or oxidising waste matrix no valid Cr(VI) content can be reported.
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 8466-1, Water quality — Calibration and evaluation of analytical methods — Part 1: Linear calibration
function
ISO 11464, Soil quality — Pretreatment of samples for physico-chemical analysis
ISO 11465, Sludge and solid environmental matrices — Determination of dry residue or water content and
calculation of the dry matter fraction on a mass basis
EN 15002, Characterization of waste — Preparation of test portions from the laboratory sample
EN 15934, Sludge, treated biowaste, soil and waste — Calculation of dry matter fraction after determination of
dry residue or water content
EN 16179, Sludge, treated bio waste and soil — Guidance for sample pretreatment
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 Safety remarks
Anyone dealing with waste and soil analysis shall be aware of the typical risks of the material irrespective of
the parameters determined. Waste and soil samples can contain hazardous (e.g. toxic, reactive, flammable,
infectious) substances, which can be liable to biological and/or chemical reaction. Consequently, these
samples should be handled with special care. The gases which can be produced by microbiological or
chemical activity are potentially flammable and can pressurise sealed bottles. Bursting bottles are likely to
result in hazardous shrapnel, dust and/or aerosol. It is presupposed that national regulations are followed
with respect to all hazards associated with this method.

ISO 15192:2025(en)
Avoid any contact with the skin, ingestion or inhalation of Cr(VI) compounds. Cr(VI) compounds are
genotoxic and carcinogenic to humans.
5 Principle
5.1 Digestion
This document describes an alkaline digestion procedure for extracting Cr(VI) from soluble, adsorbed and
precipitated forms of chromium compounds in solid waste materials and soil. To quantify the content of
Cr(VI) in a solid matrix, three criteria shall be satisfied:
a) digestion solution shall solubilize all species of Cr(VI);
b) conditions of the digestion shall not induce reduction of native Cr(VI) to Cr(III);
c) method shall not cause oxidation of native Cr(III) contained in the sample to Cr(VI).
The alkaline digestion described in this document meets these criteria for a wide spectrum of soils and
wastes. Under the alkaline conditions of the digestion, negligible reduction of Cr(VI) or oxidation of native
2+
Cr(III) is expected. The addition of Mg in a phosphate buffer to the alkaline solution minimises air oxidation
[52][28][32]
of trivalent chromium.
NOTE Background on methods for the determination of Cr(VI) in solid samples is given in Annex D.
5.2 Determination
Quantification of Cr(VI) in the alkaline digestion solution should be performed using a suitable technique
with appropriate accuracy. For this purpose, e.g. ion chromatography is used to separate Cr(VI) from
interferences. Following this ion chromatographic separation, Cr(VI) is measured spectrophotometrically
either at 365 nm (direct UV detection) or after post-column derivatisation with 1,5-diphenylcarbazide in
acid solution at 540 nm. Post-column derivatisation involves reaction of 1,5-diphenylcarbazide with Cr(VI)
to produce trivalent chromium and diphenylcarbazone. These then combine to form a trivalent chromium-
diphenylcarbazone complex containing the characteristic magenta chromagen (λ = 540 nm).
max
NOTE The choice of detection method is based upon the required sensitivity. Direct UV detection is less sensitive
than detection after post-column derivatisation with 1,5-diphenylcarbazide (see Annex C).
Hyphenated methods with suitable chromatographic separation and detection techniques, such as
inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma atomic emission
spectroscopy (ICP-OES), may be used once validation of the chosen analytical method has been performed.
A preliminary determination of the total chromium in the alkaline digestion solution by such techniques as
ICP-MS, ICP-OES, or graphite furnace atomic absorption spectrometry can reduce the number of samples
where the determination of Cr(VI) is required. If the content of alkaline-extractable total chromium is lower
than the legislative limit for Cr(VI) then the determination of Cr(VI) may be omitted.
Due to the high element concentrations, e.g. sodium, in the alkaline digestion solutions, the calibration
strategy shall be adapted appropriately. In many cases, matrix matching of the calibration solutions and
dilution of the sample together with addition of internal standards or using the standard addition method are
necessary. The analytical method needs to be validated on alkaline digestion solutions prior to routine use.
5.3 Interferences and sources of error
— Ion chromatography shall be used for the separation of Cr(VI) from possible interferences in the alkaline
[29]
digestion solution from solid material.
— For waste materials or soils, where the Cr(III)/Cr(VI) ratio is expected to be high, Cr(VI) results can be
biased due to method induced oxidation. This can be particularly expected in soils high in Mn content
[48]
and amended with soluble Cr(III) salts or freshly precipitated Cr(OH) .
ISO 15192:2025(en)
— Cr(VI) can be reduced to Cr(III) during digestion from the sample due to reaction with reducing agents
such as divalent iron. This problem is minimised in the described procedure using alkaline digestion
[28]
solution.
— Cr(III) can be oxidised to Cr(VI) in hot alkaline solutions. This problem is minimised in the described
[13][28][32][48]
procedure by adding magnesium to the alkaline digestion solution.
— Overloading the analytical column capacity with high concentrations of anionic species (e.g. chloride)
[44]
can cause underestimation of Cr(VI).
6 Apparatus
6.1 Digestion equipment.
6.1.1 Hotplate with a magnetic stirrer, thermostatically controlled with a digestion vessel of 250 ml
covered with a watch glass, or
6.1.2 Heating block with a magnetic stirrer, thermostatically controlled with a digestion vessel of
250 ml covered with a watch glass.
NOTE Other thermostatically controlled digestion equipment with a magnetic stirrer can be used once validation
has been performed.
6.2 Filtration equipment, suitable for using 0,45 µm membrane filters.
6.3 Membrane filters, 0,45 µm pore size, chemically inert.
6.4 Ion chromatographic system.
All components which come into contact with the sample or eluent stream shall be comprised of inert
materials, e.g. polyetherether ketone (PEEK), as shall all connecting tubing (see Annex B).
6.5 Ion chromatographic column, suitable for chromate separation with a sufficient ion exchange
capacity.
6.6 Detection system.
6.6.1 UV-VIS spectrophotometer, at 365 nm, or
6.6.2 VIS spectrophotometer, at 540 nm after post column derivatisation.
7 Reagents
During the analysis, only use reagents of recognised analytical grade, and water as specified in 7.1.
7.1 Water.
‒1
Water with an electrical conductivity less than 0,1 mS m (equivalent to resistivity greater than 0,01 MΩ m
at 25 °C). The water used should be obtained from a purification system that delivers ultrapure water having
a resistivity greater than 0,18 MΩ m (usually expressed by manufacturers of water purification systems as
18 MΩ cm).
ISO 15192:2025(en)
® 1)
7.2 Sulfuric acid (H SO ), CAS Registry Number (CAS RN) 7664-93-9, concentrated, ρ(H SO )
2 4 2 4
approximately 1,84 g/ml, w(H SO ) approximately 98 %.
2 4
7.3 Sodium carbonate (Na CO ), CAS RN 497-19-8, anhydrous, w(Na CO ) > 99,9 %.
2 3 2 3
7.4 1,5-Diphenylcarbazide (C H N O), CAS RN 140-22-7, w(C H N O) > 98 %;.
13 14 4 13 14 4
7.5 Propanone(acetone)(C H O), CAS RN 67-64-1.
3 6
7.6 Methanol (CH O), CAS RN 67-56-1.
7.7 Potassium dichromate (K Cr O ), CAS RN 7778-50-9, w(K Cr O ) > 99,9 %.
2 2 7 2 2 7
Dry to constant weight at 110 °C, cool and store in a desiccator.
7.8 Sodium hydroxide (NaOH), CAS RN 1310-73-2, w(NaOH) > 99 %.
7.9 Magnesium chloride hexahydrate(MgCl ·6H O), CAS RN 7791-18-6, w(MgCl ·6H O) > 99 %.
2 2 2 2
7.10 Dipotassium hydrogen phosphate(K HPO ), CAS RN 7758-11-4, w(K HPO ) > 99 %.
2 4 2 4
7.11 Potassium dihydrogen phosphate(KH PO ), CAS RN 7778-77-0, w(KH PO ) > 99 %.
2 4 2 4
7.12 Lead chromate(PbCrO ), CAS RN 7758-97-6, w(PbCrO ) > 99 %.
4 4
7.13 Diphenylcarbazide reagent solution.
Dissolve 0,125 g of 1,5-diphenylcarbazide (7.4) in 25 ml of propanone (7.5) or methanol (7.6) in a 250 ml
volumetric flask. Fill 125 ml of water into a separate container, slowly add 7 ml of concentrated sulfuric acid
(7.2), swirl to mix and allow to cool. Degas with for example helium or argon for 5 min to 10 min prior to
adding to the 1,5-diphenylcarbazide solution. After combining the solutions, fill up to the mark with water
and degas additionally for 5 min to 10 min. The solution is stable for up to 1 week if stored in a brown glass
bottle at 2 °C to 6 °C in the dark.
7.14 Eluent solution.
Use an eluent solution (see Annex A) appropriate to separate chromate over the ion chromatographic
column (6.5).
NOTE Eluents can be prepared manually or automatically by in-line dilution or electrochemically in situ.
7.15 Alkaline digestion solution.
0,5 mol/l sodium hydroxide (NaOH) / 0,28 mol/l sodium carbonate (Na CO ).
2 3
Dissolve 20,0 g of sodium hydroxide (7.8) in approximately 500 ml of water (7.1). Add 30,0 g of sodium
carbonate (7.3) and swirl to mix. Quantitatively transfer the solution into a 1 l volumetric flask. Dilute to the
mark with water. The pH of the digestion solution shall be checked before use. The pH shall be 11,5 to 12.
Store in a polyethylene bottle at room temperature. This reagent is stable for one month. ®
1) Chemical Abstracts Service (CAS) Registry Number is a trademark of the American Chemical Society (ACS). This
information is given for the convenience of the users of this document and does not constitute an endorsement by ISO of
the product names. Equivalent products may be used if they can be shown to lead to the same results.

ISO 15192:2025(en)
7.16 Calibration solutions of Cr(VI).
7.16.1 Cr(VI) standard stock solution, 1 000 mg/l Cr(VI).
Dissolve 0,282 9 g of potassium dichromate (7.7) in 75 ml of water (7.1) in a 100 ml volumetric flask. Dilute
to the mark with water, close and mix thoroughly. Store the solution in a polypropylene bottle. This reagent
is stable for one year.
7.16.2 Cr(VI) working standard solution, 10 mg/l Cr(VI).
Pipette 10,0 ml of the Cr(VI) standard stock solution (7.16.1) into a 1 l volumetric flask, dilute to the mark
with water (7.1), close and mix thoroughly. This reagent is stable for one month.
7.16.3 Cr(VI) calibration solutions.
Prepare a set of at least 5 calibration solutions by diluting the Cr(VI) working standard solution with a
1 + 1 diluted alkaline digestion solution (7.15). Add 25 ml of the alkaline digestion solution (7.15) into a
50 ml volumetric flask, pipette the appropriate volume of Cr(VI) working standard solution (7.16.2) into the
volumetric flask and dilute to the mark with water (7.1), close and mix thoroughly. Prepare fresh solutions
on the day of use.
7.16.4 Cr(VI) spiking solutions.
The Cr(VI) working standard solution (7.16.2) can be used to spike samples.
7.17 Phosphate buffer solution.
0,5 mol/l dipotassium hydrogen phosphate (K HPO ) / 0,5 mol/l potassium dihydrogen phosphate
2 4
(KH PO ), pH 7.
2 4
Dissolve 87,09 g K HPO (7.10) and 68,04 g of KH PO (7.11) in approximately 700 ml of water and swirl to
2 4 2 4
mix. Transfer the solution into a 1 l volumetric flask. Dilute to the mark with water.
7.18 Magnesium chloride solution.
Dissolve 85,4 g MgCl ·6H O (7.9) in a 100 ml volumetric flask, dilute to the mark with water (7.1), close and
2 2
mix thoroughly.
7.19 Chromium chloride hexahydrate (CrCl .6H O), CAS 10060-12-5, w(CrCl ·6H O) > 96 %.
3 2 3 2
7.20 Cr(III) spiking solution.
Use a commercial standard solution with a certified Cr(III) concentration, for example 1 000 mg/l Cr(III).
Observe the manufacturer’s expiration date or recommended shelf life.
Alternatively, dissolve an appropriate known amount of chromium chloride hexahydrate (7.19) in water (7.1)
in a 100 ml volumetric flask, dilute to the mark with water (7.1), close and mix thoroughly. Store the solution
in a polypropylene bottle. This reagent is stable for one year. Before using, determine the Cr concentration of
the spiking solution.
7.21 Barium chromate (BaCrO ), CAS 10294-40-3, w(BaCrO ) > 99 %.
4 4
7.22 Sand, CAS 14808-60-7, purified by acid and calcinated for analysis, or equivalent.

ISO 15192:2025(en)
7.23 Insoluble Cr(VI) control mixture.
A control mixture is prepared by weighing 1 g of barium chromate (7.21), adding 10 g of sand (7.22) and
subsequent homogenization and grinding. From this mixture, a portion of 1 g is mixed again with 10 g of
sand, with subsequent homogenization and grinding. A 2,5 g of this final mixture contains 20,66 mg BaCrO .
WARNING — Avoid any contact with the skin, ingestion or inhalation of Cr(VI) compounds. Cr(VI)
compounds are genotoxic and carcinogenic to humans.
8 Sample pretreatment
Samples shall be collected using appropriate devices and placed in plastic or glass containers.
NOTE Requirements for test portion preparation are summarised in Annex B.
Samples shall be stored field moist at (4 ± 2) °C until analysis. Pre-treat the sample according to EN 16179,
ISO 11464 or EN 15002 if not otherwise specified.
Particle size reduction below 250 µm is necessary for solid waste and soil especially when Cr(VI) is
suspected to be included in the matrix, whereby heating and contact with stainless steel shall be avoided.
After digestion the sample shall be analysed as soon as possible.
Cr(VI) has been shown to be quantitatively stable in field moist soil samples for 30 days from the time of
sample collection. In addition, Cr(VI) has also been shown to be stable in the alkaline digestion solution for
[13]
up to 7 days after digestion from soil.
9 Alkaline digestion procedure
9.1 General
Use either the hotplate (6.1.1) or heating block (6.1.2) to prepare test solutions for determination of Cr(VI)
in solid waste materials and soil.
9.2 Preparation of test solutions using a hotplate or heating block
9.2.1 Adjust the temperature setting by preparing and monitoring a temperature blank (a 250 ml vessel
filled with 50 ml digestion solution). Maintain a digestion solution temperature of (92,5 ± 2,5) °C. Do not
allow the solution to boil or evaporate to dryness.
9.2.2 Transfer (2,5 ± 0,1) g of the test portion weighed to the nearest 0,1 mg into a clean 250 ml
digestion vessel.
NOTE For very high expected concentrations of Cr(VI) a smaller representative test portion can be used.
9.2.3 Add (50 ± 1) ml of the alkaline digestion solution (7.15) to each sample, and also add 1 ml of
magnesium chloride solution (7.18) containing approximately 400 mg of MgCl and 0,5 ml of phosphate
buffer solution (7.17). Cover all digestion vessels. If using a heating block, reflux condensers can be used.
9.2.4 Heat the samples to (92,5 ± 2,5) °C with continuous stirring, then maintain the samples at
(92,5 ± 2,5) °C for at least (60 ± 5) min with stirring continuously.
9.2.5 Cool each solution to room temperature. Transfer the contents quantitatively to the filtration
equipment (6.2), rinsing the digestion vessel three times with small portions of water (7.1). Filter through
a 0,45 µm membrane filter (6.3). Rinse the filtration equipment with water, transfer the filtrate to a 100 ml
volumetric flask and fill up to the mark with water.

ISO 15192:2025(en)
NOTE Alternatively the sample can be centrifuged or allowed to settle before filling up to the mark with water.
10 Analytical procedure
10.1 General information
The standard method for the determination of Cr(VI) in the alkaline digestion solution is the ion
chromatographic method with spectrophotometric detection described in this clause.
NOTE In certain cases, direct determination of Cr(VI) in the alkaline digestion solution is possible (see Annex A).
10.2 Instrumental set-up
10.2.1 Set up the ion chromatograph in accordance with manufacturer’s instructions.
10.2.2 For post-column derivatisation, optimise the ratio of eluent solution and reagent flow rates or adjust
the sulfuric acid concentration of the diphenylcarbazide reagent solution (7.13) to obtain the best signal to
background ratio. The ratio between the eluent solution and reagent flow rates is kept constant. The total
flow rate shall not exceed the maximum flow rate and the diphenylcarbazide reagent shall not be present in
excess. A typical value for the ratio between the eluent solution and reagent flow rates is 3:1. After the flow
rates are adjusted, allow the system to equilibrate for 15 min.
10.2.3 For direct detection, adjust the UV-VIS detector (6.6.1) to measure within a range of 355 nm to
375 nm, preferably at 365 nm. For measuring after post-column derivatisation with 1,5-diphenylcarbazide
(7.5), adjust the VIS detector (6.6.2) to measure within a range of 530 nm to 550 nm, preferably at 540 nm.
10.3 Calibration
10.3.1 Inject a suitable volume (typically 20 µl to 250 µl), of each calibration solution (7.16.3) into the ion
chromatographic system (6.4).
10.3.2 Determine the absorbance for each of the calibration solutions using either peak height or peak
area mode.
10.3.3 Prepare a calibration graph using a linear plot of the peak height or peak area as a function of
calibration solution concentration by least squares regression analysis using suitable software, according to
ISO 8466-1.
10.4 Test solution measurement
10.4.1 Inject a suitable volume, for example 50 µl, of filtered sample solutions (9.2) into the ion
chromatographic system (6.4).
10.4.2 Determine the concentrations of Cr(VI) in the test solutions (9.2) by comparison with the calibration
graph (10.3.3).
10.4.3 If the Cr(VI) concentration of the sample exceeds the calibration range, dilute the sample with a
1 + 1 diluted alkaline digestion solution (7.15) and re-analyse. Take note of the dilution when calculating the
mass concentration of Cr(VI) in the material under investigation.
NOTE For samples expected to have very high concentrations of Cr(VI), it can be necessary to dilute the test
solutions before they are first analysed. Otherwise, swamping of the diphenylcarbazide reagent can occur and no
colour will develop.
ISO 15192:2025(en)
If the chromium (VI) concentration of the sample falls lower than the calibration range, establish a separate
calibration function for the lower working range, if necessary.
10.5 Quality control
10.5.1 General
Process quality control (QC) samples with each batch of test samples, as detailed below.
10.5.2 Blank test solution
To assess glassware contamination and/or reagents, process in parallel at least one blank solution following
the same digestion procedure as applied to the test samples but omitting the test portion. If contamination
is detected control the procedure until the level of Cr(VI) is less than 0,5 times the lowest concentration to
be reported and repeat the digestions.
Analyse the blank solutions according to a frequency of 1 blank per 20 test portions or at least once in each
series of measurement.
10.5.3 Verification of method
Prepare a soluble Cr(VI) standard solution from a stock standard solution from a different source than that
used for preparing the calibration solutions. In parallel with processing the test samples, prepare a blank
solution spiked with this soluble Cr(VI) standard solution following the same digestion procedure as applied
to the test samples but omitting the test portion. Recovery of Cr(VI) shall be within range of 80 % to 120 %.
Process this QC sample within each batch.
Alternatively, to evaluate the dissolution of all Cr(VI) species during the digestion process, an insoluble spike,
e.g. 20 mg PbCrO (7.12) or BaCrO (7.23), may be used. In parallel with processing the test samples, prepare
4 4
a blank solution spiked with, for example 20 mg of PbCrO or 2,5 g of the BaCrO mixture (7.23), following
4 4
the same digestion procedure as applied to the test samples but omitting the test portion. Recovery of Cr(VI)
shall be within range of 75 % to 125 %.
NOTE A smaller amount of the insoluble Cr(VI) or a next dilution step of the control mixture quality control
sample can be used, as long as the homogeneity of the control sample on that mass level has been tested.
Prepare a Cr(III) standard solution from the Cr(III) spiking solution (7.20). In parallel with processing the
test samples prepare a blank solution spiked with this Cr(III) standard solution following the same digestion
procedure as applied to the test samples but omitting the test portion. Conversion of Cr(III) to Cr(VI) shall
be less than 5 %. Process this QC sample within each batch.
10.5.4 Duplicate samples
Process method duplicated samples to estimate the method accuracy according to a frequency of at least 1
duplicate sample per 20 test portions or minimum of 1 per batch.
NOTE Duplicate samples can have a relative percent difference (RPD) of less than 20 %. RPD calculations are
typically applicable when the concentration of the two samples are ≥ 5× reporting limit. If the concentration is near
the laboratory reporting limit, an absolute criterion value can be used.
10.5.5 Soluble Cr(VI) spiked samples
Process soluble spikes, e.g. Cr(VI) spiking solutions (7.16.4), on a routine basis to estimate the method
accuracy in relation to possible reduction processes. Spiked samples consist of solid material to which
known amounts of Cr(VI) have been added.
Soluble pre-digestion matrix spikes should be analysed at a frequency of at least 1 spike sample per 20 test
portions or 1 per batch. The matrix spike is then carried through the digestion process. More frequent
matrix spikes should be analysed if the sample characteristics within the analytical batch appear to have

ISO 15192:2025(en)
significant variability based on visual observation. An acceptance range for matrix spike recoveries is 75 %
to 125 %.
10.5.6 Cr(III) spiked samples
Process the Cr(III) spiking solution (7.20) on a routine basis to estimate the method accuracy in relation to
the possible oxidation processes, expressed as a percent Cr(VI) recovery relative to the spiked amount of
Cr(III). Spiked samples consist of solid material to which known amounts of Cr(III) have been added.
The conversion of the Cr(III) spike can be used to assess the risk of method induced oxidation of native
Cr(III) contained in the sample to Cr(VI) and shall be less than 5 %.
10.5.7 Interpretation of quality control data
If the verification procedure performed in 10.5.3 and the recoveries from the spiked samples performed in
10.5.5 and 10.5.6 meet laboratory criteria, the analytical result can be judged to be valid.
NOTE 1 An acceptable range for Cr(VI) spike recoveries is 75 % to 125 % in soil, sludge, sediments and similar
[41]
waste materials according to EPA-method 3060 A.
If the verification procedure performed in 10.5.3 meets the laboratory criteria, but the recovery from
a spiked sample performed in 10.5.5 does not meet the laboratory criteria, this indicates that the sample
reduced Cr(VI) (e.g. anoxic sediments) and the concentration of native Cr(VI) in the unspiked sample cannot
be quantified. Such a result indicates that the combined and interacting influences of redox potential, pH
2+
and reducing agents (e.g. organic acids, Fe and sulfides) caused reduction of the Cr(VI) spike. In this case
report the value of the unspiked sample and indicate that the sample exhibits a highly reducing condition.
NOTE 2 The assessment of the reducing/oxidising tendency of the sample matrix can be accomplished by
characterisation of each sample for additional analytical parameters, such as pH, ferrous iron (FeII), sulfides, organic
carbon content and the oxidation potential. Analysis of these additional parameters establishes the tendency of Cr(VI)
to exist or not exist in the unspiked samples and assists i
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