Water quality — Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb), dissolved bound nitrogen (DNb), total bound phosphorus (TPb) and dissolved bound phosphorus (DPb) after wet chemical catalysed ozone hydroxyl radical oxidation (COHR)

This document specifies a multi‑parameter method for the determination of total organic carbon (TOC), total nitrogen (TNb) and total phosphorus (TP) in drinking water, raw water, ground water, surface water, sea water, saline water, process water, domestic and industrial wastewater, after a chemical oxidation process. It is applicable to both dissolved and bound suspended materials. The method allows for determination of TOC, TN and TP. The lower and upper working ranges for these parameters are dependent upon instrument conditions (for example sample volume, reaction chemistry amounts) and can be adjusted for a wider range. Typical measurement ranges are shown in Figures C.1 to C.3. The analysis procedure is carried out instrumentally by a single oxidation process. Dissolved nitrogen gas is not included in the TNb measurement in this method. When present in the sample, elemental carbon, cyanate and thiocyanate will be included in the TOC result.

Qualité de l'eau — Détermination du carbone organique total (COT), du carbone organique dissous (COD), de l'azote total lié (TNb), de l'azote dissous lié (DNb), du phosphore total lié et du phosphore dissous lié (DPb) après oxydation par l'ozone avec des radicaux hydroxyles et catalyseur en milieux aqueux (COHR)

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Published
Publication Date
01-Sep-2020
Current Stage
6060 - International Standard published
Start Date
06-May-2020
Completion Date
02-Sep-2020
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ISO 21793:2020 - Water quality -- Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb), dissolved bound nitrogen (DNb), total bound phosphorus (TPb) and dissolved bound phosphorus (DPb) after wet chemical catalysed ozone hydroxyl radical oxidation (COHR)
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ISO 21793:2020 - Water quality -- Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb), dissolved bound nitrogen (DNb), total bound phosphorus (TPb) and dissolved bound phosphorus (DPb) after wet chemical catalysed ozone hydroxyl radical oxidation (COHR)
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INTERNATIONAL ISO
STANDARD 21793
First edition
2020-08
Water quality — Determination
of total organic carbon (TOC),
dissolved organic carbon (DOC), total
bound nitrogen (TN ), dissolved
bound nitrogen (DN ), total bound
phosphorus (TP ) and dissolved
bound phosphorus (DP ) after wet
chemical catalysed ozone hydroxyl
radical oxidation (COHR)
Qualité de l'eau — Détermination du carbone organique total
(COT), du carbone organique dissous (COD), de l'azote total lié
(TN ), de l'azote dissous lié (DN ), du phosphore total lié et du
b b
phosphore dissous lié (DP ) après oxydation par l'ozone avec des
radicaux hydroxyles et catalyseur en milieux aqueux (COHR)
Reference number
ISO 21793:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 21793:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 21793:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Interferences ............................................................................................................................................................................................................ 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 TOC .................................................................................................................................................................................................................... 3

5.3 TN ....................................................................................................................................................................................................................... 3

5.4 TP ........................................................................................................................................................................................................................ 4

6 Reagents ........................................................................................................................................................................................................................ 4

7 Solution preparations ..................................................................................................................................................................................... 5

7.1 Blank solution .......................................................................................................................................................................................... 5

7.2 Sample oxidation solutions .......................................................................................................................................................... 5

7.2.1 Sulfuric acid TIC and catalyst solution .......................................................................................................... 5

7.2.2 Base oxidation solution .............................................................................................................................................. 5

7.2.3 TP solution ............................................................................................................................................................................ 5

7.2.4 TP hydrolysis solution ................................................................................................................................................. 5

7.3 Calibration stock solutions ........................................................................................................................................................... 6

7.4 Individual calibration standard solutions ....................................................................................................................... 6

7.4.1 TOC .............................................................................................................................................................................................. 6

7.4.2 TN ........................................................................................................................................... ....................................................... 6

7.4.3 TP .................................................................................................................................................................................................. 7

7.4.4 Combined calibration standard solutions .................................................................................................. 7

7.5 System check stock solutions ..................................................................................................................................................... 7

7.5.1 TOC and TN stock solution ...................................................................................................................................... 7

7.5.2 TP stock solution ............................................................................................................................................................. 7

7.6 Particle processing control solution ..................................................................................................................................... 7

7.7 Gases ................................................................................................................................................................................................................ 8

8 Apparatus ..................................................................................................................................................................................................................... 8

9 Quality requirements for the analytical system .................................................................................................................. 8

9.1 System check ............................................................................................................................................................................................. 8

9.2 Recovery and variation of replicate determinations for particle processing control

for TOC, TN , and TP ....................................................................................................................................................................... 9

b b

10 Sampling and sample preparation .................................................................................................................................................... 9

10.1 Sampling and sample injection ................................................................................................................................................. 9

11 Procedure..................................................................................................................................................................................................................... 9

11.1 General ........................................................................................................................................................................................................... 9

11.2 Calibration ...............................................................................................................................................................................................10

11.3 Validity check of the calibration function .....................................................................................................................10

11.4 Measurement .........................................................................................................................................................................................10

11.4.1 General...................................................................................................................................................................................10

11.4.2 Determination .................................................................................................................................................................10

12 Evaluation .................................................................................................................................................................................................................11

13 Expression of results .....................................................................................................................................................................................11

14 Test report ................................................................................................................................................................................................................11

© ISO 2020 – All rights reserved iii
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ISO 21793:2020(E)

Annex A (normative) Determination of total organic carbon that includes purgeable

organic carbon by difference ................................................................................................................................................................13

Annex B (informative) Performance data TOC/TN .............................................................................................................................15

Annex C (informative) Informative validation data, system check recovery and particle

check recovery for TOC/TN/TP ..........................................................................................................................................................17

Bibliography .............................................................................................................................................................................................................................31

iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 21793:2020(E)
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).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

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 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

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.
© ISO 2020 – All rights reserved v
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ISO 21793:2020(E)
Introduction

Total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TN ), dissolved

bound nitrogen (DN ), total bound phosphorus (TP ) and dissolved bound phosphorus (DP ) are an

b b b

analytical convention, the respective result of which is a parameter used for water quality control

purposes. These parameters represent the sum of organically bound carbon, the sum of inorganic and

organic nitrogen, and the sum of inorganic and organic phosphorus. These parameters can be dissolved

in water or bonded to dissolved or suspended matter under specified conditions. If the sample is not

filtered the parameter is associated with suspended matter. This document does not give information

on the nature of the substances.
vi © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 21793:2020(E)
Water quality — Determination of total organic carbon
(TOC), dissolved organic carbon (DOC), total bound
nitrogen (TN ), dissolved bound nitrogen (DN ), total
b b
bound phosphorus (TP ) and dissolved bound phosphorus
(DP ) after wet chemical catalysed ozone hydroxyl radical
oxidation (COHR)

WARNING — Persons using this document should be familiar with normal laboratory practices.

This document does not purport to address all safety problems, if any, associated with its use. It

is the responsibility of the user to establish appropriate safety and health practices.

IMPORTANT — It is essential that tests conducted in accordance with this document be carried

out by suitably qualified staff.
1 Scope

This document specifies a multi-parameter method for the determination of total organic carbon (TOC),

total nitrogen (TN ) and total phosphorus (TP) in drinking water, raw water, ground water, surface

water, sea water, saline water, process water, domestic and industrial wastewater, after a chemical

oxidation process. It is applicable to both dissolved and bound suspended materials.

The method allows for determination of TOC, TN and TP. The lower and upper working ranges for

these parameters are dependent upon instrument conditions (for example sample volume, reaction

chemistry amounts) and can be adjusted for a wider range. Typical measurement ranges are shown in

Figures C.1 to C.3.

The analysis procedure is carried out instrumentally by a single oxidation process.

Dissolved nitrogen gas is not included in the TN measurement in this method. When present in the

sample, elemental carbon, cyanate and thiocyanate will be included in the TOC result.

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 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method

for the determination of repeatability and reproducibility of a standard measurement method

ISO 8245, Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved

organic carbon (DOC)

ISO 8466-1, Water quality — Calibration and evaluation of analytical methods and estimation of

performance characteristics — Part 1: Statistical evaluation of the linear calibration function

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
© ISO 2020 – All rights reserved 1
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ISO 21793:2020(E)

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org ./ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
total carbon
sum of organically and inorganically bound carbon present in water
3.2
total inorganic carbon
TIC

sum of inorganic carbon present in water measured under the conditions of this method

Note 1 to entry: TIC is measured as CO originating only from carbonates, hydrogen carbonates and dissolved

carbon dioxide.
3.3
total organic carbon
TOC

sum of organically bound carbon present in water, bonded to dissolved or suspended matter, including

cyanate, thiocyanate, and elemental carbon measured
3.4
purgeable organic carbon
POC

organic carbon present in water which can be purged under the conditions of this method

3.5
non purgeable organic carbon
NPOC
organic carbon present in water which is not purged
3.6
total nitrogen

sum of organically and inorganically bound nitrogen present in water or suspended matter

3.7
total phosphorus

sum of organically and inorganically bound phosphorus present in water and suspended matter

measured under the conditions of this method
4 Principle

Wet chemical oxidation of the sample by hydroxyl radicals, and catalysed ozone for the measurement of

TOC, TN , and TP .
b b

Organic carbon (TOC) is oxidized to carbon dioxide (CO ). For the determination of total organic carbon

that includes purgeable organic carbon by difference, the procedure shall be as specified in Annex A.

Detection is by nondispersive infrared (NDIR) spectrometry.

Detection is by photometric analysis in the ultraviolet wavelength range 200 nm to 220 nm. Detection

is by colorimetric analysis using a photometer under the visible spectra between 380 nm and 470 nm

wavelengths.
2 © ISO 2020 – All rights reserved
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ISO 21793:2020(E)

This document can be applied for the determination of TOC, TN and TP separately, or for simultaneous

b b

analysis, which consists of a non-dispersive infrared carbon dioxide analyser and a visible and UV

photometer.

Quality control is necessary to verify the validity of the calibration function. Replicate determinations

can be necessary, depending on the matrix. The method of standard addition can be used if matrix

interferences are expected.

Inorganic carbon is removed by acidification and purging with a carrier gas (see 11.4).

Performance results from the interlaboratory trial is provided in Annex B. Supplemental single

laboratory performance data is provided in Annex C.
5 Interferences
5.1 General

Depending on concentration and analysis range, interferences with the determination of TOC, TN

and TP can arise from possible sample carry over effects. In some cases, replicate injections can be

necessary. When carryover is suspected, insert a reagent blank in the analytical run, immediately after

the suspect sample.

Interferences can arise from memory effects. Replicate injections maybe necessary (11.4.1).

Samples with high pH values, highly buffered samples and samples with high chloride content can cause

interference.

Large suspended particles can lead to a loss of quality of the analytical result. If a homogenized sample

containing suspended particles produces results (obtained from replicate measurements) which

deviate by more than 10 %, an accurate TOC TN and TP result cannot be obtained on the sample.

b b

Seek advice from the manufacturer to resolve these interferences. Particles in general can cause

interference with sample injection. To mitigate particle interference, samples can be homogenized or

filtered using filters and screen meshes. When the sample is filtered through a 0,45 µm membrane

filter, the TOC result represents dissolved organic carbon (DOC) and dissolved TN and TP as specified

d d

in ISO 8245, results from samples analysed without filtration are reported as TOC, TN and TP .

b b

If a homogenized sample containing large suspended material produces results (obtained from replicate

measurements) which deviate by more than 10 % from each other, an accurate and precise TOC, TN , or

TP result cannot be quantified.
5.2 TOC

Inorganic carbon (for example CO or ions of carbonic acid) present in the sample can interfere with

the determination of TOC or DOC. Inorganic carbon is removed by acidification and sparging prior to

sample oxidation.

NOTE Purgeable organic carbon (POC) compounds, such as benzene, toluene, cyclohexane and chloroform,

can partly escape during the acidification and sparging of the TIC. In the presence of these substances, the TOC

concentration can be determined by applying the TC-TIC method (see Annex A).

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re-analyse.
5.3 TN

Depending on sample matrix conditions, interferences may occur with the measurement of TN .

If interferences are suspected, perform a suitable sample dilution, or by applying standard addition

techniques.
© ISO 2020 – All rights reserved 3
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ISO 21793:2020(E)

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re-analyse.
5.4 TP

Depending on sample matrix conditions, interferences can occur with the measurement of TP . If

interferences are suspected, perform a suitable sample dilution, or by applying standard addition

techniques.

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re-analyse.
6 Reagents
Use only reagents of analytical grade.

Dry all solid reagents for at least 1 h at (105 ± 5) °C. Store the dried solid in a desiccator before weighing.

NOTE There is no need to dry cellulose before usage.

Prepare concentrations and volumes of solutions as described in the manufacturers’ instrument

manuals. Alternatively, use commercially available stock solutions at the required concentration.

6.1 Water.

The contents of bound nitrogen, phosphorus, and carbon in water being used for the preparation of

samples and solutions shall be sufficiently low to be negligible in comparison with the lowest TOC, TN

and TP concentrations to be determined.
6.2 Sulfuric acid, H SO , ρ = 1,84 g/ml.
2 4
6.3 Manganese sulfate monohydrate, MnSO ·H O, ≥99 %.
4 2
6.4 Sodium hydroxide, NaOH, ≥97 %.
6.5 Hydrochloric acid, w(HCl) = 37 %.
6.6 Ammonium heptamolybdate tetrahydrate, [(NH ) Mo O ·4H O], ≥99 %.
4 6 7 24 2
6.7 Ammonium metavanadate, NH VO , ≥99 %.
4 3
6.8 Potassium hydrogen phthalate, (C H KO ), ≥99,7 %.
8 5 4
6.9 Sodium nitrate, NaNO , ≥99 %.
6.10 Potassium dihydrogen phosphate, KH PO , ≥99 %.
2 4
6.11 Nicotinic acid, C H NO , >99,5 %.
6 5 2
6.12 Triethyl phosphate, (C₂H₅)₃PO₄.

6.13 Cellulose, (C H O ) , microcrystalline, of particle size ranging from 0,02 mm to 0,1 mm.

6 10 5 n
4 © ISO 2020 – All rights reserved
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ISO 21793:2020(E)
7 Solution preparations
7.1 Blank solution
Use water (6.1) as the blank solution.
7.2 Sample oxidation solutions
7.2.1 Sulfuric acid TIC and catalyst solution

Prepare the sulfuric acid TIC and catalyst by slowly adding 49,9 ml of sulfuric acid (6.2) to 800 ml

of water (6.1) in a 1 000 ml volumetric flask. Dilute to volume with water (6.1) and cool to room

temperature. Add 0,04 g of manganese sulfate (6.3) to the sulfuric acid/water mixture. Determine the

acid normality and adjust to (1,80 N ± 0,01N) H SO .
2 4

NOTE For higher sulfuric acid TIC and catalyst oxidation concentration, maintain an acid to base

concentration (7.2.2) ratio of 3:2, keeping the amount of manganese sulfate at 0,04 g.

The range of sulfuric acid normality should be 1,8 N to 2,5 N.
7.2.2 Base oxidation solution

Prepare the sodium hydroxide solution by slowly adding 48 g of NaOH (6.4) to a 1 000 ml volumetric

flask containing approximately 500 ml of water (6.1). Mix the solution until the NaOH has dissolved,

then stopper the flask and allow the solution to come to room temperature. Bring solution to volume

with water (6.1).

For higher sodium hydroxide concentrations, maintain an acid (7.2.1) to base concentration ratio of 3:2.

The range of sodium hydroxide molarity should be 1,2 M to 1,7 M.
7.2.3 TP solution

7.2.3.1 Prepare the hydrochloric acid reagent (solution A) by slowly adding 494 ml of concentrated

HCl (6.5) to 500 ml of water (6.1) in a 1 000 ml volumetric flask. Mix gently and allow the solution to

come to room temperature. Bring the solution to volume with water (6.1), then stopper the flask.

7.2.3.2 Prepare the ammonium heptamolybdate tetrahydrate reagent (solution B) by adding 25 g

of ammonium heptamolybdate tetrahydrate (6.6) to 300 ml of water (6.1) in a 500 ml beaker. Stir to

dissolve.

7.2.3.3 Prepare the ammonium metavanadate reagent (solution C) by adding 2,5 g of ammonium

metavanadate (6.7) to 300 ml of water (6.1) in a 500 ml beaker. Dissolve by bringing the solution to a

boil. Cool to room temperature.

7.2.3.4 While stirring, slowly add solution C (7.2.3.3) to 330 ml of solution A (7.2.3.1) in a 1 000 ml

volumetric flask. Cool to room temperature.

7.2.3.5 Finally while stirring, slowly pour the content of solution B (7.2.3.2) into the volumetric flask

that contains the mixture of solution A and solution C (7.2.3.4) and bring to volume with water (6.1).

7.2.4 TP hydrolysis solution

Prepare the hydrochloric acid solution by adding 249 ml of concentrated HCl (6.5) to an empty 1 000 ml

volumetric flask. Slowly add 600 ml water (6.1) to the flask. Mix gently and allow the solution to come

to room temperature. Bring the solution to volume with water (6.1), then stopper the flask.

© ISO 2020 – All rights reserved 5
---------------------- Page: 11 ----------------------
ISO 21793:2020(E)
7.3 Calibration stock solutions
7.3.1 Potassium hydrogen phthalate stock solution, ρ(C) = 1 000 mg/l.

Place 2,125 g of potassium hydrogen phthalate (6.8) in a 1 000 ml volumetric flask. Dissolve and dilute

to volume with water (6.1). The solution is stable for six months if stored in a tightly stoppered glass

bottle at (3 ± 2) °C.
7.3.2 Sodium nitrate stock solution, ρ(N) = 1 000 mg/l.

Place 6,07 g of NaNO (6.9) in a 1 000 ml volumetric flask. Dissolve and dilute to volume with water (6.1).

The solution is stable for one month if stored at (3 ± 2) °C.
7.3.3 Potassium dihydrogen phosphate stock solution, ρ(P) = 1 000 mg/l.

Prepare a 1 000 mg/l TP stock solution using potassium dihydrogen phosphate (K H PO ). Place 4,43 g

2 4

of K H PO (6.10) in a 1 000 ml volumetric flask. Dissolve and dilute to volume with water (6.1).

2 4
The solution is stable for one month if stored at (3 ± 2) °C.
7.4 Individual calibration standard solutions
7.4.1 TOC

Depending on the TOC or DOC concentration expected in the sample, use the potassium hydrogen

phthalate stock solution (7.3.1) to prepare 5 to 10 calibration solutions distributed over the expected

working range as evenly as possible (see Annex C).
For example, proceed as follows for the range 1,0 mg/l C to 10 mg/l C.

Pipette the following volumes into a series of 1 000 ml volumetric flasks: 1,0 ml, 2,0 ml, 3,0 ml,

4,0 ml, 5,0 ml, 6,0 ml, 7,0 ml, 8,0 ml, 9,0 ml and 10,0 ml of the potassium hydrogen phthalate stock

solution (7.3.1) and dilute to volume with water (6.1).

The concentrations of carbon in these calibration solutions are: 1 mg/l, 2 mg/l, 3 mg/l, 4 mg/l, 5 mg/l,

6 mg/l, 7 mg/l, 8 mg/l, 9 mg/l and 10 mg/l, respectively.
Prepare the calibration solutions on the day of use.
7.4.2 TN
Depending on the nitrogen con
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 21793
ISO/TC 147/SC 2
Water quality — Determination
Secretariat: DIN
of total organic carbon (TOC),
Voting begins on:
2020­03­10 dissolved organic carbon (DOC), total
bound nitrogen (TN ), dissolved
Voting terminates on:
2020­05­05
bound nitrogen (DN ), total bound
phosphorus (TP ) and dissolved
bound phosphorus (DP ) after wet
chemical catalysed ozone hydroxyl
radical oxidation (COHR)
Qualité de l'eau — Détermination du carbon organique total (COT),
du carbone organique dissous (COD), de l'azote total lié (TNb), de
l'azote dissous lié (DNb), du phosphore total lié et du phosphore
dissous lié (DPb) après oxydation par l'ozone avec des radicaus
hydroxyles et catalyseur en milieus aqueux
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 21793:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 21793:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 21793:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Interferences ............................................................................................................................................................................................................ 3

5.1 General ........................................................................................................................................................................................................... 3

5.2 TOC .................................................................................................................................................................................................................... 3

5.3 TN ....................................................................................................................................................................................................................... 3

5.4 TP ........................................................................................................................................................................................................................ 4

6 Reagents ........................................................................................................................................................................................................................ 4

7 Solution preparations ..................................................................................................................................................................................... 5

7.1 Blank solution .......................................................................................................................................................................................... 5

7.2 Sample oxidation solutions .......................................................................................................................................................... 5

7.2.1 Sulfuric acid TIC and catalyst solution .......................................................................................................... 5

7.2.2 Base oxidation solution .............................................................................................................................................. 5

7.2.3 TP solution ............................................................................................................................................................................ 5

7.2.4 TP hydrolysis solution ................................................................................................................................................. 5

7.3 Calibration stock solutions ........................................................................................................................................................... 6

7.4 Individual calibration standard solutions ....................................................................................................................... 6

7.4.1 TOC .............................................................................................................................................................................................. 6

7.4.2 TN ........................................................................................................................................... ....................................................... 6

7.4.3 TP .................................................................................................................................................................................................. 7

7.4.4 Combined calibration standard solutions .................................................................................................. 7

7.5 System check stock solutions ..................................................................................................................................................... 7

7.5.1 TOC and TN stock solution ...................................................................................................................................... 7

7.5.2 TP stock solution ............................................................................................................................................................. 7

7.6 Particle processing control solution ..................................................................................................................................... 7

7.7 Gases ................................................................................................................................................................................................................ 8

8 Apparatus ..................................................................................................................................................................................................................... 8

9 Quality requirements for the analytical system .................................................................................................................. 8

9.1 System check ............................................................................................................................................................................................. 8

9.2 Recovery and variation of replicate determinations for particle processing control

for TOC, TN , and TP ....................................................................................................................................................................... 9

b b

10 Sampling and sample preparation .................................................................................................................................................... 9

10.1 Sampling and sample injection ................................................................................................................................................. 9

11 Procedure..................................................................................................................................................................................................................... 9

11.1 General ........................................................................................................................................................................................................... 9

11.2 Calibration ...............................................................................................................................................................................................10

11.3 Validity check of the calibration function .....................................................................................................................10

11.4 Measurement .........................................................................................................................................................................................10

11.4.1 General...................................................................................................................................................................................10

11.4.2 Determination .................................................................................................................................................................10

12 Evaluation .................................................................................................................................................................................................................11

13 Expression of results .....................................................................................................................................................................................11

14 Test report ................................................................................................................................................................................................................11

© ISO 2020 – All rights reserved iii
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ISO/FDIS 21793:2020(E)

Annex A (normative) Determination of total organic carbon that includes purgeable

organic carbon by difference ................................................................................................................................................................13

Annex B (informative) Performance data TOC/TN .............................................................................................................................15

Annex C (informative) Informative validation data, system check recovery and particle

check recovery for TOC/TN/TP ..........................................................................................................................................................17

Bibliography .............................................................................................................................................................................................................................31

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ISO/FDIS 21793:2020(E)
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 non­governmental, 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).

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. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on 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 the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,

Physical, chemical and biochemical methods.

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.
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ISO/FDIS 21793:2020(E)
Introduction

Total organic carbon (TOC), dissolved organic carbon (DOC) total bound nitrogen (TN ), dissolved

bound nitrogen (DN ), total bound phosphorus (TP ) and dissolved bound phosphorus (DPb) are an

b b

analytical convention, the respective result of which is a parameter used for water quality control

purposes. These parameters represent the sum of organically bound carbon, the sum of inorganic and

organic nitrogen, and the sum of inorganic and organic phosphorus. These parameters can be dissolved

in water or bonded to dissolved or suspended matter under specified conditions. If the sample is not

filtered the parameter is associated with suspended matter. This document does not give information

on the nature of the substances.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 21793:2020(E)
Water quality — Determination of total organic carbon
(TOC), dissolved organic carbon (DOC), total bound
nitrogen (TN ), dissolved bound nitrogen (DN ), total
b b
bound phosphorus (TP ) and dissolved bound phosphorus
(DP ) after wet chemical catalysed ozone hydroxyl radical
oxidation (COHR)

WARNING — Persons using this document should be familiar with normal laboratory practices.

This document does not purport to address all safety problems, if any, associated with its use. It

is the responsibility of the user to establish appropriate safety and health practices.

IMPORTANT — It is essential that tests conducted in accordance with this document be carried

out by suitably qualified staff.
1 Scope

This document specifies a multi‑parameter method for the determination of total organic carbon (TOC),

total nitrogen (TN ) and total phosphorus (TP) in drinking water, raw water, ground water, surface

water, sea water, saline water, process water, domestic and industrial wastewater, after a chemical

oxidation process. It is applicable to both dissolved and bound suspended materials.

The method allows for determination of TOC, TN and TP . The lower and upper working ranges for these

parameters are dependent upon instrument conditions (for example sample volume, reaction chemistry

amounts) and can be adjusted for a wider range. Typical ranges are shown in Figures C.6 to C.8.

The analysis procedure is carried out instrumentally by a single oxidation process.

Dissolved nitrogen gas is not included in the TN measurement in this method. When present in the

sample, elemental carbon, cyanide and cyanate will be included in the TOC result.

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 5725­2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method

for the determination of repeatability and reproducibility of a standard measurement method

ISO 8245, Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved

organic carbon (DOC)

ISO 8466­1, Water quality — Calibration and evaluation of analytical methods and estimation of

performance characteristics — Part 1: Statistical evaluation of the linear calibration function

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org ./ obp
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ISO/FDIS 21793:2020(E)
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
total carbon
sum of organically and inorganically bound carbon present in water
3.2
total inorganic carbon
TIC

sum of inorganic carbon present in water measured under the conditions of this method

Note 1 to entry: TIC is measured as CO originating only from carbonates, hydrogen carbonates and dissolved

carbon dioxide.
3.3
total organic carbon
TOC

sum of organically bound carbon present in water, bonded to dissolved or suspended matter, including

cyanate, thiocyanate, and elemental carbon measured
3.4
purgeable organic carbon
POC

organic carbon present in water which can be purged under the conditions of this method

3.5
non purgeable organic carbon
NPOC
organic carbon present in water which is not purged
3.6
total nitrogen

sum of organically and inorganically bound nitrogen present in water or suspended

3.7
total phosphorus

sum of organically and inorganically bound phosphorus present in water and suspended matter

measured under the conditions of this method
4 Principle

Wet chemical oxidation of the sample by hydroxyl radicals, and catalysed ozone for the measurement of

TOC, TN , and TP .
b b

Organic carbon (TOC) is oxidized to carbon dioxide (CO ). For the determination of total organic carbon

that includes purgeable organic carbon by difference, the procedure shall be as specified in Annex A.

Detection is by nondispersive infrared (NDIR) spectrometry.

Detection is by photometric analysis in the ultraviolet wavelength range 200 nm to 220 nm. Detection

is by colorimetric analysis using a photometer under the visible spectra between 380 nm and 470 nm

wavelengths.

This document can be applied for the determination of TOC, TN and TP separately, or for simultaneous

b b

analysis, which consists of a non‑dispersive infrared carbon dioxide analyser and a visable and UV

photometer.
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ISO/FDIS 21793:2020(E)

Quality control is necessary to verify the validity of the calibration function. Replicate determinations

can be necessary, depending on the matrix. The method of standard addition can be used if matrix

interferences are expected.

Inorganic carbon is removed by acidification and purging with a carrier gas (see 11.4).

Performance results from the interlaboratory trial is provided in Annex B. Supplemental single

laboratory performance data is provided in Annex C.
5 Interferences
5.1 General

Depending on concentration and analysis range, interferences with the determination of TOC, TN

and TP can arise from possible sample carry over effects. In some cases, replicate injections can be

necessary. When carryover is suspected, insert a reagent blank in the analytical run, immediately after

the suspect sample.

Interferences can arise from memory effects. Replicate injections maybe necessary (11.4.1).

Samples with high pH values, highly buffered samples and samples with high chloride content can cause

interference.

Large Suspended particles can lead to a loss of quality of the analytical result. If a homogenized sample

containing suspended parcticles produces results (obtained from replicate measurements) which

deviate by more than 10 %, an accurate TOC TN and TP result cannot be obtained on the sample.

b b

Seek advice from the manufacturer to resolve these interferences. Particles in general can cause

interference with sample injection. To mitigate particle interference, samples can be homogenized or

filtered using filters and screen meshes. When the sample is filtered through a 0,45 µm membrane

filter, the TOC result represents dissolved organic carbon (DOC) and dissolved TN & TP as specified in

ISO 8245, results from samples analysed without filtration are reported as TOC, TN and TP .

b b

If a homogenized sample containing large suspended material produces results (obtained from replicate

measurements) which deviate by more than 10 % from eachother, an accurate and precise TOC, TN , or

TP result can not be quantified.
5.2 TOC

Inorganic carbon (for example CO or ions of carbonic acid) present in the sample can interfere with

the determination of TOC or DOC. Inorganic carbon is removed by acidification and spargingprior to

sample oxidation.

NOTE 1 Purgeable organic carbon (POC) compounds, such as benzene, toluene, cyclohexane and chloroform,

can partly escape during the acidification and sparging of the TIC. In the presence of these substances, the TOC

concentration can be determined by applying the TC‑TIC method (see Annex A).

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re‑analyse.
5.3 TN

Depending on sample matrix conditions, interferences may occur with the measurement of TN .

If interferences are suspected, perform a suitable sample dilution, or by applying standard addition

techniques.

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re‑analyse.
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ISO/FDIS 21793:2020(E)
5.4 TP

Depending on sample matrix conditions, interferences can occur with the measurement of TP . If

interferences are suspected, perform a suitable sample dilution, or by applying standard addition

techniques.

Interference from chloride can occur at chloride concentrations greater than 3 %. If chloride

interference is suspected, dilute the sample and re‑analyse.
6 Reagents
Use only reagents of analytical grade.

Dry all solid reagents for at least 1 h at (105 ± 5) °C. Store the dried solid in a desiccator before weighing.

NOTE There is no need to dry cellulose before usage.

Prepare concentrations and volumes of solutions as described in the manufacturers’ instrument

manuals. Alternatively, use commercially available stock solutions at the required concentration.

6.1 Water.

The contents of bound nitrogen, phosphorus, and carbon in water being used for the preparation of

samples and solutions shall be sufficiently low to be negligible in comparison with the lowest TOC, TN

and TP concentration to be determined.
6.2 Sulfuric acid, ρ = 1,84 g/ml.
6.3 Manganese sulfate monohydrate, MnSO ·H O, ≥99 %.
4 2
6.4 Sodium hydroxide, NaOH, ≥97 %.
6.5 Hydrochloric acid, ω(HCl) = 37 %.
6.6 Ammonium heptamolybdate tetrahydrate, [(NH ) Mo O ·4H O], ≥99 %.
4 6 7 24 2
6.7 Ammonium metavanadate, NH VO , ≥99 %.
4 3
6.8 Potassium hydrogen phthalate, (C H KO ), ≥99,7 %.
8 5 4
6.9 Sodium nitrate, NaNO , ≥99 %.
6.10 Potassium dihydrogen phosphate, KH PO , ≥99 %.
2 4
6.11 Nicotinic acid, C H NO , >99,5 %.
6 5 2
6.12 Trietyl phosphate.

6.13 Cellulose, (C H O ) , microcrystalline, of particle size ranging from 0,02 mm to 0,1 mm.

6 10 5 n
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ISO/FDIS 21793:2020(E)
7 Solution preparations
7.1 Blank solution
Use water (6.1) as the blank solution.
7.2 Sample oxidation solutions
7.2.1 Sulfuric acid TIC and catalyst solution

Prepare the sulfuric acid TIC and catalyst by slowly adding 49,9 ml of sulfuric acid (6.2) to 800 ml

of water (6.1) in a 1 000 ml volumetric flask. Dilute to volume with water (6.1) and cool to room

temperature. Add 0,04 g of manganese sulfate (6.3) to the sulfuric acid/water mixture. Determine the

acid normality and adjust to (1,80 N ± 0,01N) H SO .
2 4

NOTE For higher sulfuric acid TIC and catalyst oxidation concentration, maintain an acid to base

concentration (7.2.2) ratio of 3:2, keeping the amount of manganese sulfate at 0,04 g.

The range of sulfuric acid normality should be 1,8 N to 2,5 N.
7.2.2 Base oxidation solution

Prepare the sodium hydroxide solution by slowly adding 48 g of NaOH (6.4) to a 1 000 ml volumetric

flask containing approximately 500 ml of water (6.1). Mix the solution until the NaOH has dissolved,

then stopper the flask and allow the solution to come to room temperature. Bring solution to volume

with water (6.1).

For higher sodium hydroxide concentrations, maintain an acid (7.2.1) to base concentration ratio of 3:2.

The range of sodium hydroxide molarity should be 1,2 M to 1,7 M.
7.2.3 TP solution

7.2.3.1 Prepare the hydrochloric acid (A) solution by adding 249 ml of concentrated HCl (6.5) to an empty

1 000 ml volumetric flask. Slowly add 600 ml water (6.1) to the flask. Mix gently and allow the solution to

come to room temperature. Bring the solution to volume with water (6.1), then stopper the flask.

7.2.3.2 Prepare the ammonium heptamolybdate tetrahydrate (B) solution by adding 25 g of ammonium

heptamolybdate tetrahydrate (6.6) to 300 ml of water (6.1) in a 500 ml beaker. Stir to dissolve.

7.2.3.3 Prepare the ammonium metavanadate solution (C) by adding 2,5 g of ammonium

metavanadate (6.7) to 300 ml of water (6.1) in a 500 ml beaker. Dissolve by bringing the solution to a

boil. Cool to room temperature.

7.2.3.4 While stirring, slowly add the contents of solution A (7.2.3.1) to solution B (7.2.3.2) in a

1 000 ml volumetric flask. Cool to room temperature.

7.2.3.5 Finally while stirring, slowly pour the content of solution C (7.2.3.3) into the volumetric flask

that contains the mixture of solution A and B (7.2.3.4) and bring to volume with water (6.1).

7.2.4 TP hydrolysis solution

Prepare the hydrochloric acid solution by adding 249 ml of concentrated HCl (6.5) to an empty 1 000 ml

volumetric flask. Slowly add 600 ml water (6.1) to the flask. Mix gently and allow the solution to come

to room temperature. Bring the solution to volume with water (6.1), then stopper the flask.

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ISO/FDIS 21793:2020(E)
7.3 Calibration stock solutions
7.3.1 Potassium hydrogen phthalate stock solution, ρ(C) = 1 000 mg/l.

Place 2,125 g of potassium hydrogen phthalate (6.8) in a 1 000 ml volumetric flask. Dissolve and dilute

to volume with water (6.1). The solution is stable for six months if stored in a tightly stoppered glass

bottle at (3 ± 2) °C.
7.3.2 Sodium nitrate stock solution, ρ(N) = 1 000 mg/l.

Place 6,07 g of NaNO (6.9) in a 1 000 ml volumetric flask. Dissolve and dilute to volume with water (6.1).

The solution is stable for one month if stored at (3 ± 2) °C.
7.3.3 Potassium dihydrogen phosphate stock solution, ρ(P) = 1 000 mg/l.

Prepare a 1 000 mg/l TP stock solution using potassium dihydrogen phosphate (K H PO ). Place 4,43 g

2 4

of K H PO (6.10) in a 1 000 ml volumetric flask. Dissolve and dilute to volume with water (6.1).

2 4
The solution is stable for one month if stored at (3 ± 2) °C.
7.4 Individual calibration standard solutions
7.4.1 TOC

Depending on the TOC or DOC concentration expected in the sample, use the potassium hydrogen

phthalate stock solution (7.3.1) to prepare 5 to 10 calibration solutions distributed over the expected

working range as evenly as possi
...

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