ISO 29441:2010

Water quality — Determination of total nitrogen after UV digestion — Method using flow analysis (CFA and FIA) and spectrometric detection

ISO 29441:2010 specifies a method for the determination of total nitrogen after inline UV digestion, in various types of waters, such as ground, drinking, surface, and waste waters, in mass concentrations ranging from 2 mg/l to 20 mg/l for total nitrogen, all in the undiluted sample. Other mass concentration ranges are possible, provided the upper limit of the concentration range is exactly 10 times the lower limit (e.g. 0,2 mg/l to 2,0 mg/l). The range of application can be changed by varying the operating conditions.

Qualité de l'eau — Dosage de l'azote total après digestion UV — Méthode par analyse en flux (CFA et FIA) et détection spectrométrique

Kakovost vode - Določevanje celotnega dušika po UV razklopu - Metoda pretočne analize (CFA in FIA) in spektrometrijske detekcije

Ta mednarodni standard opredeljuje metodo določevanja celotnega dušika po razkroju UV v različnih vrstah vode, kot so podtalna, pitna in odpadna voda, pri masnih koncentracijah v razponu od 2 mg/l do 20 mg/l za celoten dušik in za vse v nerazredčenem vzorcu.
Drugi razponi masne koncentracije so mogoči, če je zgornja meja razpona koncentracije točno desetkratnik spodnje meje (npr. od 0,2 mg/l do 2,0 mg/l). Razpon uporabe se lahko spremeni z različnimi pogoji delovanja.
OPOMBA: Morska voda se lahko analizira s spremembami glede na občutljivost in prilagodljivost nosilne raztopine in raztopin za kalibracijo na slanost vzorcev.

General Information

• Status: Published
• Publication Date: 22-Mar-2010
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: ISO/TC 147/SC 2 - Physical, chemical and biochemical methods
• Drafting Committee: ISO/TC 147/SC 2 - Physical, chemical and biochemical methods
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 16-Dec-2020
• Ref Project: SIST ISO 29441:2011 - Water quality - Determination of total nitrogen after UV digestion - Method using flow analysis (CFA and FIA) and spectrometric detection

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 29441
First edition
2010-04-01

Water quality — Determination of total
nitrogen after UV digestion — Method
using flow analysis (CFA and FIA) and
spectrometric detection
Qualité de l'eau — Dosage de l'azote total après digestion UV —
Méthode par analyse en flux (CFA et FIA) et détection spectrométrique



Reference number
ISO 29441:2010(E)
©
ISO 2010

---------------------- Page: 1 ----------------------
ISO 29441:2010(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2010
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2010 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 29441:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Interferences .2
4 Principle.2
5 Reagents.2
6 Apparatus.6
7 Sampling and sample preparation.7
8 Procedure.8
9 Evaluation.10
10 Expression of results.10
11 Test report.11
Annex A (informative) Examples of flow systems (6.1 or 6.2) for the determination of total
nitrogen after inline UV digestion (2 mg/l to 20 mg/l) .12
Annex B (informative) Precision data .14
Bibliography.16

© ISO 2010 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 29441:2010(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 29441 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
iv © ISO 2010 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 29441:2010(E)
Introduction
Methods using flow analysis enable wet chemistry procedures to be automated and are particularly suitable
for the processing of many analytes in water in large series of samples at a high analysis frequency (up to 100
samples per hour).
A differentiation is made between flow injection analysis (FIA, References [1][2]) and continuous flow analysis
(CFA, Reference [3]). Both methods share the feature of an automatic dosage of the sample into a flow
system (manifold) where the analytes in the sample react with the reagent solutions on their way through the
manifold. The sample preparation can be integrated into the manifold. The reaction product is measured in a
flow detector (e.g. a flow photometer).

© ISO 2010 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 29441:2010(E)

Water quality — Determination of total nitrogen after UV
digestion — Method using flow analysis (CFA and FIA) and
spectrometric detection
WARNING — Persons using this International Standard should be familiar with normal laboratory
practice. This standard does not purport to address all of the safety problems, if any, associated with
its use. It is the responsibility of the user to establish appropriate safety and health practices and to
ensure compliance with any national regulatory conditions.
Waste containing cadmium in liquid or solid form shall be disposed of appropriately.
IMPORTANT — It is absolutely essential that tests conducted according to this International Standard
be carried out by suitably trained staff.
1 Scope
This International Standard specifies a method for the determination of total nitrogen after inline UV digestion,
in various types of waters, such as ground, drinking, surface, and waste waters, in mass concentrations
ranging from 2 mg/l to 20 mg/l for total nitrogen, all in the undiluted sample.
Other mass concentration ranges are possible, provided the upper limit of the concentration range is exactly
10 times the lower limit (e.g. 0,2 mg/l to 2,0 mg/l). The range of application can be changed by varying the
operating conditions.
NOTE Sea water can be analysed with changes in respect to sensitivity and adaptation of the carrier solution and
calibration solutions to the salinity of the samples.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 3696:1987, Water for analytical laboratory use — Specification and test methods
ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water
samples
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
ISO 8466-2, Water quality — Calibration and evaluation of analytical methods and estimation of performance
characteristics — Part 2: Calibration strategy for non-linear second-order calibration functions
ISO 13395, Water quality — Determination of nitrite nitrogen and nitrate nitrogen and the sum of both by flow
analysis (CFA and FIA) and spectrometric detection
© ISO 2010 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 29441:2010(E)
3 Interferences
Samples with extreme pH values and samples with a high buffering capacity are prone to interferences. It is
advisable to analyse several dilutions of the sample and to check the results for consistency.
High concentrations of organic substances can cause problems as the oxidation capacity may not be sufficient.
For samples containing more than 100 mg/l of total organic carbon (TOC), reduced yields in the determination
of nitrogen may arise. If the presence of more than 100 mg/l of TOC is suspected, the sample should be run
with several dilutions in order to check for consistency, or standard addition techniques should be applied.
If the sample comprises larger particles (diameter, d > 50 µm), a homogenisation device (6.3.3) is necessary.
In sea water samples, high concentrations of calcium and magnesium may occur. In an alkaline medium,
magnesium hydroxide or other hydroxides or calcium carbonate may be formed which interfere with the UV
digestion.
4 Principle
The sample is pretreated with a buffered peroxodisulfate solution and thermal UV radiation. Nitrate is formed
and determined either by flow injection analysis (FIA) or by continuous flow analysis (CFA). With FIA, the
sample is fed into a continuously flowing buffer solution (carrier stream) by means of an injection valve, or,
when applying CFA, it is continuously mixed with this buffer solution. Nitrate in the sample is reduced with
metallic cadmium to nitrite (Reference [4]). Subsequently a phosphoric acid reagent solution also flowing
continuously is admixed. Nitrite resulting from the reduction of nitrate diazotises sulfanilamide in acidic
solution to the diazonium salt which is then coupled with N-(1-naphthyl)ethylenediamine to form a red soluble

dye (see ISO 13395 and Reference [5]).
5 Reagents
During the analysis, unless otherwise stated, use only reagents of recognised analytical grade. Check the
blank value of the reagents regularly (see 8.4).
5.1 General reagents
5.1.1 Water, complying with ISO 3696:1987, grade 1.
5.1.2 Phosphoric acid, ρ(H PO ) = 1,71 g/ml.
3 4
5.1.3 Potassium peroxodisulfate, K S O .
2 2 8
5.1.4 Sodium hydroxide, NaOH.
5.1.5 Titanium tetrachloride, TiCl , liquid, commercially available.
4
5.1.6 Sulfanilamide, 4-aminobenzenesulfonamide, C H N O S.
6 8 2 2
5.1.7 N-(1-Naphthyl)ethylenediamine dihydrochloride,
[N-(1–naphthyl)-1,2-diaminoethane dihydrochloride, C H N ·2HCl].
12 14 2
5.1.8 Sodium nitrite, NaNO , dried to constant mass at 150 °C.
2
5.1.9 Potassium nitrate, KNO , dried to constant mass at 150 °C.
3
5.1.10 Imidazole, C H N .
3 4 2
2 © ISO 2010 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 29441:2010(E)
5.1.11 Hydrochloric acids.
5.1.11.1 Hydrochloric acid I, concentrated, w(HCI)= 37 %.
5.1.11.2 Hydrochloric acid II, c(HCl) = 4 mol/l.
5.1.11.3 Hydrochloric acid III, c(HCI) ≈ 0,1 mol/l.
5.1.12 Dichloromethane, CH Cl .
2 2
5.1.13 Copper(II) sulfate solution I, ρ(CuSO · 5H O) = 2,5 g/l.
4 2
5.1.14 Copper(II) sulfate solution II, ρ(CuSO · 5H O) = 20 g/l.
4 2
5.1.15 Boric acid, H BO .
3 3
5.1.16 Sulfuric acid I, ρ(H SO ) = 1,84 g/ml.
2 4
5.1.17 Sulfuric acid II, c(H SO ) = 1 mol/l.
2 4
5.1.18 Urea, CO(NH ) .
2 2
5.1.19 Cadmium (Cd) granulate, grain size e.g. 0,3 mm to 1,5 mm (for FIA preferably 0,3 mm to 0,8 mm). A
minimum reduction capacity of 90 % shall be reached (see 6.1.4 and 6.2.4).
5.1.20 Imidazole stock solution, c(C H N ) = 1 mol/l (Figure A.1, R1).
3 4 2
Dissolve 68,1 g of imidazole (5.1.10) in approximately 800 ml of water (5.1.1) in a 1 l beaker.
While stirring with a magnetic stirrer, add hydrochloric acid I (5.1.11.1) and adjust the pH to 7,5 using a pH
electrode (6.3.2).
Transfer to a 1 000 ml one-mark volumetric flask. Make up to the mark with water (5.1.1).
The solution is stable for 4 weeks if kept in a brown glass bottle at room temperature.
5.1.21 Urea stock solution, ρ(N) = 1 000 mg/l.
In a 500 ml one-mark volumetric flask, dissolve 1,071 7 g of urea (5.1.18) in water (5.1.1). Add 0,5 ml of
dichloromethane (5.1.12) for preservation. Make up to the mark with water.
The solution is stable for 1 year if kept at (4 ± 2) °C.
5.1.22 Urea working solution, ρ(N) = 20 mg/l.
Dilute 5 ml of urea stock solution (5.1.21) in a 250 ml one-mark volumetric flask with water (5.1.1). Acidify the
solution with sulfuric acid II (5.1.17) to pH u 2.
The solution is stable for 1 month if kept at (4 ± 2) °C.
5.1.23 Buffered copper(II) sulfate solution.
Mix 20 ml of the copper(II) sulfate solution II (5.1.14) and 20 ml of the imidazole stock solution (5.1.20) in a
50 ml beaker.
Prepare the solution freshly before use.
© ISO 2010 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 29441:2010(E)
5.1.24 Reagent solution, (Figure A.1, R2 and Figure A.2, R1; see also ISO 13395).
In a 500 ml one-mark volumetric flask, dissolve 5 g of sulfanilamide (5.1.6) and 0,5 g of
N-(1-naphthyl)ethylenediamine dihydrochloride (5.1.7) in water (5.1.1), add 75 ml of phosphoric acid (5.1.2).
Make up to the mark with water (5.1.1).
Stored in a brown glass bottle, the solution is stable for 1 month.
NOTE The solutions of sulfanilamide (5.1.6) and N-(1-naphthyl)ethylenediamine dihydrochloride (5.1.7) can also be
prepared separately and dosed into the manifold by different lines.
Prior to use, degas solution R2 for FIA, e.g. by membrane filtration (vacuum).
5.1.25 Nitrite(N) stock solution, ρ(N) = 100 mg/l.
In a 1 000 ml one-mark volumetric flask, dissolve 492,6 mg of sodium nitrite (5.1.8) in water (5.1.1). Make up
to the mark with water (5.1.1).
This solution is stable for at least 2 weeks if kept in a stoppered glass bottle at (4 ± 2) °C.
5.1.26 Nitrite(N) solution, ρ(N) = 20 mg/l.
Pipette 20 ml of the nitrite stock solution (5.1.25) into a 100 ml one-mark volumetric flask. Make up to the mark
with water (5.1.1).
Prepare the solution freshly before use.
5.1.27 Nitrate(N) solution, ρ(N) = 200 mg/l.
In a 100 ml one-mark volumetric flask, dissolve 144,4 mg of potassium nitrate (5.1.9) in water (5.1.1). Make up
to the mark with water (5.1.1). Acidify the standard solutions with sulfuric acid II (5.1.17) to pH < 2.
The solution is stable for at least 1 month.
5.1.28 Calibration solutions.
Prepare calibration solutions by diluting the nitrate(N) solution (5.1.27). At least five calibration solutions are
recommended.
For example, proceed according to Table 1 for the preparation of 10 calibration solutions.
Prepare all calibration solutions immediately before measurement.
5.1.29 Blank solution, for diluting the samples and measuring the blanks (Clauses 7 and 8).
Acidify water to pH ≈ 2 with sulfuric acid II (5.1.17).
5.2 Additional reagents for FIA (see 6.1)
5.2.1 FIA oxidising reagent I (Figure A.1, R3).
In a 250 ml one-mark volumetric flask, dilute 6,8 ml of sulfuric acid II (5.1.17) in about 200 ml of water (5.1.1).
Dissolve 7,2 g of boric acid (5.1.15) and 10,1 g of potassium peroxodisulfate (5.1.3) and make up to the mark
with water (5.1.1).
The solution is stable for 1 day if kept at 2 °C to 8 °C. Do not hermetically close the reagent container.
4 © ISO 2010 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 29441:2010(E)
Table 1 — Preparation of the calibration solutions for total nitrogen(N)
Nitrate(N) concentration Volume of nitrate(N) solution (5.1.27)
diluted with
water (5.1.1) to 100 ml
mg/l ml
2 1
4 2
6 3
8 4
10 5
12 6
14 7
16 8
18 9
20 10
5.2.2 FIA oxidising reagent II (Figure A.1, R4).
In a 250 ml one-mark volumetric flask, dissolve 6,0 g of sodium hydroxide (5.1.4) and 10,1 g of potassium
peroxodisulfate (5.1.3) in about 200 ml of water (5.1.1). Make up to the mark with water (5.1.1).
The solution is stable for 1 week if kept at 2 °C to 8 °C. Do not hermetically close the reagent container.
5.2.3 FIA carrier solution (Figure A.1, C).
Mix 1 000 ml of water (5.1.1) with 100 µl of copper(II) sulfate solution I (5.1.13). Prepare the solution freshly
before use.
Prior to use, degas the solution, e.g. by membrane filtration (vacuum).
5.3 Additional reagents for CFA (see 6.2)
5.3.1 Poly(ethylene glycol) dodecyl ether, [HO(CH CH O) C H ], surfactant, melting range 33 °C to
2 2 n 12 21
41 °C, aqueous solution with a mass fraction of 30 %.
5.3.2 CFA oxidising reagent (Figure A.2, R5).
Using a 1 000 ml volumetric flask, dissolve 45,0 g of potassium peroxodisulfate (5.1.3) in about 900 ml of
water (5.1.1). Dissolve 12,0 g of sodium hydroxide (5.1.4) in this solution. Make up to the mark with water
(5.1.1). Do not heat the solution, otherwise the peroxodisulfate spontaneously releases oxygen.
The solution is stable for 2 weeks if stored at room temperature.
A titanium catalyst can be used to improve digestion of nitrogen compounds. Prepare the catalyst by diluting
5 ml of titanium tetrachloride (5.1.5) with water (5.1.1) to 200 ml, and adding 0,25 ml of this solution to the
CFA oxidising reagent.
5.3.3 CFA buffer solution I (Figure A.2, R4).
Dissolve 24,0 g of boric acid (5.1.15) in a 1 000 ml one-mark volumetric flask in water (5.1.1). Make up to the
mark with water (5.1.1).
© ISO 2010 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO 29441:2010(E)
The solution is stable for 1 month if stored at room temperature.
5.3.4 CFA buffer solution II (Figure A.2, R3).
In a 1 000 ml one-mark volumetric flask, dissolve 5,0 g of Na EDTA (5.3.6) in 500 ml of the imidazole stock
2
solution (5.1.20). Make up to the mark with water (5.1.1), add 1 ml of poly(ethylene glycol) dodecyl ether
(5.3.1) and mix.
The solution is stable for 1 month if stored in a brown bottle at room temperature.
5.3.5 CFA buffer solution III (Figure A.2, R2).
Dilute 250 ml of the imidazole stock solution (5.1.20) to 1 000 ml with water (5.1.1). Add 1 ml of
poly(ethylene glycol) dodecyl ether (5.
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Qualité de l'eau - Dosage de l'azote total après digestion UV - Méthode par analyse en flux (CFA et FIA) et détection spectrométriqueWater quality - Determination of total nitrogen after UV digestion - Method using flow analysis (CFA and FIA) and spectrometric detection13.060.50VQRYLExamination of water for chemical substancesICS:Ta slovenski standard je istoveten z:ISO 29441:2010SIST ISO 29441:2011en01-junij-2011SIST ISO 29441:2011SLOVENSKI
STANDARD



SIST ISO 29441:2011



Reference numberISO 29441:2010(E)© ISO 2010
INTERNATIONAL STANDARD ISO29441First edition2010-04-01Water quality — Determination of total nitrogen after UV digestion — Method using flow analysis (CFA and FIA) and spectrometric detection Qualité de l'eau — Dosage de l'azote total après digestion UV — Méthode par analyse en flux (CFA et FIA) et détection spectrométrique
SIST ISO 29441:2011



ISO 29441:2010(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
COPYRIGHT PROTECTED DOCUMENT
©
ISO 2010 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.
+ 41 22 749 01 11 Fax
+ 41 22 749 09 47 E-mail
[e-mail] Web
www.iso.org Published in Switzerland
ii
© ISO 2010 – All rights reserved
SIST ISO 29441:2011



ISO 29441:2010(E) © ISO 2010 – All rights reserved
iii Contents Page Foreword.iv Introduction.v 1 Scope.1 2 Normative references.1 3 Interferences.2 4 Principle.2 5 Reagents.2 6 Apparatus.6 7 Sampling and sample preparation.7 8 Procedure.8 9 Evaluation.10 10 Expression of results.10 11 Test report.11 Annex A (informative)
Examples of flow systems (6.1 or 6.2) for the determination of total nitrogen after inline UV digestion (2 mg/l to 20 mg/l).12 Annex B (informative)
Precision data.14 Bibliography.16
SIST ISO 29441:2011



ISO 29441:2010(E) iv
© ISO 2010 – All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 29441 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemical methods. SIST ISO 29441:2011



ISO 29441:2010(E) © ISO 2010 – All rights reserved
v Introduction Methods using flow analysis enable wet chemistry procedures to be automated and are particularly suitable for the processing of many analytes in water in large series of samples at a high analysis frequency (up to 100 samples per hour). A differentiation is made between flow injection analysis (FIA, References [1][2]) and continuous flow analysis (CFA, Reference [3]). Both methods share the feature of an automatic dosage of the sample into a flow system (manifold) where the analytes in the sample react with the reagent solutions on their way through the manifold. The sample preparation can be integrated into the manifold. The reaction product is measured in a flow detector (e.g. a flow photometer).
SIST ISO 29441:2011



SIST ISO 29441:2011



INTERNATIONAL STANDARD ISO 29441:2010(E) © ISO 2010 – All rights reserved
1 Water quality — Determination of total nitrogen after UV digestion — Method using flow analysis (CFA and FIA) and spectrometric detection WARNING — Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions. Waste containing cadmium in liquid or solid form shall be disposed of appropriately. IMPORTANT — It is absolutely essential that tests conducted according to this International Standard be carried out by suitably trained staff. 1 Scope This International Standard specifies a method for the determination of total nitrogen after inline UV digestion, in various types of waters, such as ground, drinking, surface, and waste waters, in mass concentrations ranging from 2 mg/l to 20 mg/l for total nitrogen, all in the undiluted sample. Other mass concentration ranges are possible, provided the upper limit of the concentration range is exactly 10 times the lower limit (e.g. 0,2 mg/l to 2,0 mg/l). The range of application can be changed by varying the operating conditions. NOTE Sea water can be analysed with changes in respect to sensitivity and adaptation of the carrier solution and calibration solutions to the salinity of the samples. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696:1987, Water for analytical laboratory use — Specification and test methods ISO 5667-3, Water quality — Sampling — Part 3: Guidance on the preservation and handling of water samples 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 ISO 8466-2, Water quality — Calibration and evaluation of analytical methods and estimation of performance characteristics — Part 2: Calibration strategy for non-linear second-order calibration functions ISO 13395, Water quality — Determination of nitrite nitrogen and nitrate nitrogen and the sum of both by flow analysis (CFA and FIA) and spectrometric detection SIST ISO 29441:2011



ISO 29441:2010(E) 2
© ISO 2010 – All rights reserved 3 Interferences Samples with extreme pH values and samples with a high buffering capacity are prone to interferences. It is advisable to analyse several dilutions of the sample and to check the results for consistency. High concentrations of organic substances can cause problems as the oxidation capacity may not be sufficient. For samples containing more than 100 mg/l of total organic carbon (TOC), reduced yields in the determination of nitrogen may arise. If the presence of more than 100 mg/l of TOC is suspected, the sample should be run with several dilutions in order to check for consistency, or standard addition techniques should be applied. If the sample comprises larger particles (diameter, d > 50 µm), a homogenisation device (6.3.3) is necessary. In sea water samples, high concentrations of calcium and magnesium may occur. In an alkaline medium, magnesium hydroxide or other hydroxides or calcium carbonate may be formed which interfere with the UV digestion. 4 Principle The sample is pretreated with a buffered peroxodisulfate solution and thermal UV radiation. Nitrate is formed and determined either by flow injection analysis (FIA) or by continuous flow analysis (CFA). With FIA, the sample is fed into a continuously flowing buffer solution (carrier stream) by means of an injection valve, or, when applying CFA, it is continuously mixed with this buffer solution. Nitrate in the sample is reduced with metallic cadmium to nitrite (Reference [4]). Subsequently a phosphoric acid reagent solution also flowing continuously is admixed. Nitrite resulting from the reduction of nitrate diazotises sulfanilamide in acidic solution to the diazonium salt which is then coupled with N-(1-naphthyl)ethylenediamine to form a red soluble dye (see ISO 13395 and Reference [5]). 5 Reagents During the analysis, unless otherwise stated, use only reagents of recognised analytical grade. Check the blank value of the reagents regularly (see 8.4). 5.1 General reagents 5.1.1 Water, complying with ISO 3696:1987, grade 1. 5.1.2 Phosphoric acid, (H3PO4) = 1,71 g/ml. 5.1.3 Potassium peroxodisulfate, K2S2O8. 5.1.4 Sodium hydroxide, NaOH. 5.1.5 Titanium tetrachloride, TiCl4, liquid, commercially available. 5.1.6 Sulfanilamide, 4-aminobenzenesulfonamide, C6H8N2O2S. 5.1.7 N-(1-Naphthyl)ethylenediamine dihydrochloride, [N-(1–naphthyl)-1,2-diaminoethane dihydrochloride, C12H14N2·2HCl]. 5.1.8 Sodium nitrite, NaNO2, dried to constant mass at 150 °C. 5.1.9 Potassium nitrate, KNO3, dried to constant mass at 150 °C. 5.1.10 Imidazole, C3H4N2. SIST ISO 29441:2011



ISO 29441:2010(E) © ISO 2010 – All rights reserved
3 5.1.11 Hydrochloric acids. 5.1.11.1 Hydrochloric acid I, concentrated, w(HCI)= 37 %. 5.1.11.2 Hydrochloric acid II, c(HCl) = 4 mol/l. 5.1.11.3 Hydrochloric acid III, c(HCI) ≈ 0,1 mol/l. 5.1.12 Dichloromethane, CH2Cl2. 5.1.13 Copper(II) sulfate solution I, (CuSO4 · 5H2O) = 2,5 g/l. 5.1.14 Copper(II) sulfate solution II, (CuSO4 · 5H2O) = 20 g/l. 5.1.15 Boric acid, H3BO3. 5.1.16 Sulfuric acid I, (H2SO4) = 1,84 g/ml. 5.1.17 Sulfuric acid II, c(H2SO4) = 1 mol/l. 5.1.18 Urea, CO(NH2)2. 5.1.19 Cadmium (Cd) granulate, grain size e.g. 0,3 mm to 1,5 mm (for FIA preferably 0,3 mm to 0,8 mm). A minimum reduction capacity of 90 % shall be reached (see 6.1.4 and 6.2.4). 5.1.20 Imidazole stock solution, c(C3H4N2) = 1 mol/l (Figure A.1, R1). Dissolve 68,1 g of imidazole (5.1.10) in approximately 800 ml of water (5.1.1) in a 1 l beaker. While stirring with a magnetic stirrer, add hydrochloric acid I (5.1.11.1) and adjust the pH to 7,5 using a pH electrode (6.3.2). Transfer to a 1 000 ml one-mark volumetric flask. Make up to the mark with water (5.1.1). The solution is stable for 4 weeks if kept in a brown glass bottle at room temperature. 5.1.21 Urea stock solution, (N) = 1 000 mg/l. In a 500 ml one-mark volumetric flask, dissolve 1,071 7 g of urea (5.1.18) in water (5.1.1). Add 0,5 ml of dichloromethane (5.1.12) for preservation. Make up to the mark with water. The solution is stable for 1 year if kept at (4 ± 2) °C. 5.1.22 Urea working solution, (N) = 20 mg/l. Dilute 5 ml of urea stock solution (5.1.21) in a 250 ml one-mark volumetric flask with water (5.1.1). Acidify the solution with sulfuric acid II (5.1.17) to pH u 2. The solution is stable for 1 month if kept at (4 ± 2) °C. 5.1.23 Buffered copper(II) sulfate solution. Mix 20 ml of the copper(II) sulfate solution II (5.1.14) and 20 ml of the imidazole stock solution (5.1.20) in a 50 ml beaker. Prepare the solution freshly before use. SIST ISO 29441:2011



ISO 29441:2010(E) 4
© ISO 2010 – All rights reserved 5.1.24 Reagent solution, (Figure A.1, R2 and Figure A.2, R1; see also ISO 13395). In a 500 ml one-mark volumetric flask, dissolve 5 g of sulfanilamide (5.1.6) and 0,5 g of N-(1-naphthyl)ethylenediamine dihydrochloride (5.1.7) in water (5.1.1), add 75 ml of phosphoric acid (5.1.2). Make up to the mark with water (5.1.1). Stored in a brown glass bottle, the solution is stable for 1 month. NOTE The solutions of sulfanilamide (5.1.6) and N-(1-naphthyl)ethylenediamine dihydrochloride (5.1.7) can also be prepared separately and dosed into the manifold by different lines. Prior to use, degas solution R2 for FIA, e.g. by membrane filtration (vacuum). 5.1.25 Nitrite(N) stock solution, (N) = 100 mg/l. In a 1 000 ml one-mark volumetric flask, dissolve 492,6 mg of sodium nitrite (5.1.8) in water (5.1.1). Make up to the mark with water (5.1.1). This solution is stable for at least 2 weeks if kept in a stoppered glass bottle at (4 ± 2) °C. 5.1.26 Nitrite(N) solution, (N) = 20 mg/l. Pipette 20 ml of the nitrite stock solution (5.1.25) into a 100 ml one-mark volumetric flask. Make up to the mark with water (5.1.1). Prepare the solution freshly before use. 5.1.27 Nitrate(N) solution, (N) = 200 mg/l. In a 100 ml one-mark volumetric flask, dissolve 144,4 mg of potassium nitrate (5.1.9) in water (5.1.1). Make up to the mark with water (5.1.1). Acidify the standard solutions with sulfuric acid II (5.1.17) to pH < 2. The solution is stable for at least 1 month. 5.1.28 Calibration solutions. Prepare calibration solutions by diluting the nitrate(N) solution (5.1.27). At least five calibration solutions are recommended. For example, proceed according to Table 1 for the preparation of 10 calibration solutions. Prepare all calibration solutions immediately before measurement. 5.1.29 Blank solution, for diluting the samples and measuring the blanks (Clauses 7 and 8). Acidify water to pH ≈ 2 with sulfuric acid II (5.1.17). 5.2 Additional reagents for FIA (see 6.1) 5.2.1 FIA oxidising reagent I (Figure A.1, R3). In a 250 ml one-mark volumetric flask, dilute 6,8 ml of sulfuric acid II (5.1.17) in about 200 ml of water (5.1.1). Dissolve 7,2 g of boric acid (5.1.15) and 10,1 g of potassium peroxodisulfate (5.1.3) and make up to the mark with water (5.1.1). The solution is stable for 1 day if kept at 2 °C to 8 °C. Do not hermetically close the reagent container. SIST ISO 29441:2011



ISO 29441:2010(E) © ISO 2010 – All rights reserved
5 Table 1 — Preparation of the calibration solutions for total nitrogen(N) Nitrate(N) concentration Volume of nitrate(N) solution (5.1.27) diluted with water (5.1.1) to 100 ml mg/l ml 2 1 4 2 6 3 8 4 10 5 12 6 14 7 16 8 18 9 20 10 5.2.2 FIA oxidising reagent II (Figure A.1, R4). In a 250 ml one-mark volumetric flask, dissolve 6,0 g of sodium hydroxide (5.1.4) and 10,1 g of potassium peroxodisulfate (5.1.3) in about 200 ml of water (5.1.1). Make up to the mark with water (5.1.1). The solution is stable for 1 week if kept at 2 °C to 8 °C. Do not hermetically close the reagent container. 5.2.3 FIA carrier solution (Figure A.1, C). Mix 1 000 ml of water (5.1.1) with 100 µl of copper(II) sulfate solution I (5.1.13). Prepare the solution freshly before use. Prior to use, degas the solution, e.g. by membrane filtration (vacuum). 5.3 Additional reagents for CFA (see 6.2) 5.3.1 Poly(ethylene glycol) dodecyl ether, [HO(CH2CH2O)nC12H21], surfactant, melting range 33 °C to 41 °C, aqueous solution with a mass fraction of 30 %. 5.3.2 CFA oxidising reagent (Figure A.2, R5). Using a 1 000 ml volumetric flask, dissolve 45,0 g of potassium peroxodisulfate (5.1.3) in about 900 ml of water (5.1.1). Dissolve 12,0 g of sodium hydroxide (5.1.4) in this solution. Make up to the mark with water (5.1.1). Do not heat the solution, otherwise the peroxodisulfate spontaneously releases oxygen. The solution is stable for 2 weeks if stored at room temperature. A titanium catalyst can be used to improve digestion of nitrogen compounds. Prepare the catalyst by diluting 5 ml of titanium tetrachloride (5.1.5) with water (5.1.1) to 200 ml, and adding 0,25 ml of this solution to the CFA oxidising reagent. 5.3.3 CFA buffer solution I (Figure A.2, R4). Dissolve 24,0 g of boric acid (5.1.15) in a 1 000 ml one-mark volumetric flask in water (5.1.1). Make up to the mark with water (5.1.1). SIST ISO 29441:2011



ISO 29441:2010(E) 6
© ISO 2010 – All rights reserved The solution is stable for 1 month if stored at room temperature. 5.3.4 CFA buffer solution II (Figure A.2, R3). In a 1 000 ml one-mark volumetric flas
...