Water quality — Determination of available weak and dissociable (WAD) cyanide — Part 1: Method using ligand exchange, flow injection analysis (FIA), gas-diffusion and amperometric detection

This document specifies operationally defined methods for the determination of available WAD cyanide in various types of water such as drinking, ground, and surface, waters, and metallurgical processing tailings reclaim, heap leach barren, mill slurry tailings and leaching solutions, with cyanide concentrations from 5 µg/l to 2 000 mg/l expressed as cyanide ions in the undiluted sample. The range of application can be changed by varying the operation conditions, e.g. by using a different injection volume, thicker membrane, detector response, etc. NOTE ISO 2080:2008, 3.105, defines free cyanide. The concentration of available WAD cyanide includes free cyanide and some of the metals complexed in solution as determined by a specified analytical method but not all of the metal complexes present in total cyanide (3,191). In this method, six suitable mass concentration ranges from 5 µg/l to 50 µg/l, from 50 µg/l to 500 µg/l, from 0,5 mg/l to 5 mg/l, from 5 mg/l to 50 mg/l, from 50 mg/l to 500 mg/l and from 500 mg/l to 2 000 mg/l are described.

Qualité de l'eau — Détermination du cyanure à acide faible dissociable (WAD) disponible — Partie 1: Méthode par échange de ligand, analyse par injection en flux (FIA), diffusion gazeuse et détection ampérométrique

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INTERNATIONAL ISO
STANDARD 20950-1
First edition
2018-05
Water quality — Determination of
available weak and dissociable (WAD)
cyanide —
Part 1:
Method using ligand exchange, flow
injection analysis (FIA), gas-diffusion
and amperometric detection
Qualité de l'eau — Détermination du cyanure à acide faible
dissociable (WAD) disponible —
Partie 1: Méthode par échange de ligand, analyse par injection en flux
(FIA), diffusion gazeuse et détection ampérométrique
Reference number
ISO 20950-1:2018(E)
©
ISO 2018

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ISO 20950-1:2018(E)

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© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 20950-1:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Interferences . 2
4.1 Interferences by oxidizing agents . 2
4.2 Interferences by sulfide . 2
5 Principle . 2
6 Reagents . 3
7 Apparatus . 7
8 Sampling and sample preparation . 7
8.1 General . 7
8.2 Oxidizing agents . 7
8.3 Sulfide removal . 8
8.4 Preservation . 8
9 Procedure. 8
9.1 Flow system set up . 8
9.2 Reagent blank measurement . 9
9.3 Checking the suitability of the flow injection system . 9
9.3.1 Cyanide electrode stabilization . 9
9.3.2 Performance verification of the system . 9
9.4 Calibration . 9
9.5 Sample measurement .10
9.5.1 General.10
9.5.2 Manual ligand addition options .10
9.5.3 Automated ligand addition .11
9.5.4 Cyanide measurement.11
10 Calculations.11
11 Expression of results .11
12 Test report .11
Annex A (informative) Examples of flow injection systems .13
Annex B (normative) Determination of the real cyanide concentration in the potassium
cyanide solution (6.5.1) or potassium tetracyanozincate solution (6.6.1) .15
Annex C (informative) Performance data .16
Bibliography .17
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ISO 20950-1:2018(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 on the voluntary nature of standards, the meaning of ISO specific terms and
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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.
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ISO 20950-1:2018(E)

Introduction
Methods using flow analysis automate wet chemical procedures are particularly suitable for the
determination of many analytes in water in large sample series at a high analysis frequency.
Analyses can be performed by flow injection analysis (FIA) using 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 by a flow detector (e.g. amperometer).
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INTERNATIONAL STANDARD ISO 20950-1:2018(E)
Water quality — Determination of available weak and
dissociable (WAD) cyanide —
Part 1:
Method using ligand exchange, flow injection analysis
(FIA), gas-diffusion and amperometric detection
WARNING — Persons using this document should be familiar with normal laboratory practice.
This document 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.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this document
be carried out by suitably qualified staff.
1 Scope
This document specifies operationally defined methods for the determination of available WAD
cyanide in various types of water such as drinking, ground, and surface, waters, and metallurgical
processing tailings reclaim, heap leach barren, mill slurry tailings and leaching solutions, with cyanide
concentrations from 5 µg/l to 2 000 mg/l expressed as cyanide ions in the undiluted sample. The range
of application can be changed by varying the operation conditions, e.g. by using a different injection
volume, thicker membrane, detector response, etc.
NOTE ISO 2080:2008, 3.105, defines free cyanide. The concentration of available WAD cyanide includes free
cyanide and some of the metals complexed in solution as determined by a specified analytical method but not all
of the metal complexes present in total cyanide (3,191).
In this method, six suitable mass concentration ranges from 5 µg/l to 50 µg/l, from 50 µg/l to 500 µg/l,
from 0,5 mg/l to 5 mg/l, from 5 mg/l to 50 mg/l, from 50 mg/l to 500 mg/l and from 500 mg/l to
2 000 mg/l are described.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-3, Water quality — Sampling — Part 3: 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
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO 20950-1:2018(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
available WAD cyanide
sum of HCN, cyanide ions and cyanide bound in the metal-cyano complexes that are dissociated, using
ligand reagents, if necessary, and sulfuric acid into HCN/CN¯ in accordance with this document
4 Interferences
4.1 Interferences by oxidizing agents
Test for the presence of oxidizing agents, which can continue to oxidize the cyanide, leading to low
results.
4.2 Interferences by sulfide
Sulfide will diffuse through the gas diffusion membrane and can be detected in the amperometric flow
cell, causing high results. Oxidized products of sulfide can also rapidly convert CN¯ to SCN¯ at a high pH.
A two-stage process is specified for sulfide removal. The initial stage should be carried out as soon as
possible. Lead acetate test strips might not be sensitive enough to detect low levels of sulfide; therefore,
treatment should be performed on samples where sulfide is suspected. Interference can be confirmed
by analysing the sample with or without treatment.
If the measured cyanide in the untreated sample is significantly higher than in the treated sample,
sulfide is likely present and treatment shall be performed to remove sulfide. In addition, the use of the
sulfide removal and acidification reagent (6.8.4) is specified in this method. Its use will ensure removal
of sulfide interference up to 50 mg/l of sulfide. This shall be applied within 24 h of taking the sample
(see Clause 8).
[7]
NOTE USEPA method OIA-1677 uses of 0,1 mol/l HCl as acidification reagent, in the absence of sulfide in
the samples.
5 Principle
The analytical procedure employed for determination of available WAD cyanide is divided into two
parts: sample pre-treatment and cyanide detection. In the pre-treatment step, proprietary or non-
proprietary ligand exchange reagents are added at room temperature to the sample, if needed to
release the cyanide ions from mercury and nickel cyanide complexes. The ligand-exchange reagents
form thermodynamically stable complexes with the transition metal ions, including: zinc, copper,
cadmium, mercury, nickel and silver resulting in the release of bound cyanide ion from some metal-
cyano complexes. Cyanide is not released from the more stable iron, gold and cobalt cyanide complexes.
The sample is treated with ligand exchange reagents, if necessary, and introduced into a carrier
solution of the flow injection analysis (FIA) system via an injection valve and confluence downstream
with a sulfuric acid solution containing sulfide removal reagent to measure available WAD cyanide.
Ligand exchange reagents are needed to release cyanide from mercury cyanide and nickel cyanide
complexes when the concentrations of mercury or nickel cyanides, relative to the weak and dissociable
cyanide, will increase the result by more than 5 % relative. The released hydrogen cyanide (HCN) gas
diffuses through a hydrophobic gas diffusion membrane into an alkaline acceptor stream where the
CN‾ is captured and sent to an amperometric flow cell detector with a silver-working electrode. In the
presence of cyanide, silver electrode surface is oxidized at the applied potential (Eapp = 0,0 V vs. the
reference electrode). The anodic current measured is proportional to the concentration of cyanide in
the standard or sample injected.
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ISO 20950-1:2018(E)

Calibrations and sample data are processed with the instrument's data acquisition software.
The user should be aware that the described method is operationally defined; the analytical protocol of
this document has to be followed strictly to assure comparable results as the actual method conditions
used can affect the result obtained.
6 Reagents
WARNING — Cyanide solutions and wastes are toxic. Waste containing these substances shall be
removed appropriately.
Use only reagents of recognized analytical grade.
6.1 Water, grade 1, as defined in ISO 3696.
6.2 Sodium hydroxide solution I, acceptor solution, c(NaOH) = 0,1 mol/l.
6.3 Sodium hydroxide solution II, c(NaOH) = 1,0 mol/l.
6.4 Sodium hydroxide solution III, c(NaOH) = 0,01 mol/l.
6.5 Potassium cyanide, KCN.
6.5.1 Potassium cyanide solution, KCN, ρ(CN) = 1 000 mg/l, (see Annex B).
Dissolve (2 500 ± 1) mg of potassium cyanide, KCN (6.5), in sodium hydroxide solution III (6.4) in a
1 000 ml graduated flask and make up to volume with sodium hydroxide solution III (6.4).
NOTE Some laboratories substituted sodium cyanide for potassium cyanide for stock solution preparation
during the interlaboratory test.
This solution is stable for six months at (5 ± 3) °C, if stored in the dark or brown bottles.
Alternatively, a potassium tetracyanozincate solution (6.6.1) may be used.
6.5.2 Cyanide solution I, ρ(CN) = 10 mg/l.
Pipette 1,00 ml of the potassium cyanide solution (6.5.1) in a 100 ml graduated flask and bring to
volume with sodium hydroxide solution III (6.4).
This solution is stable for one week at (5 ± 3) °C, if stored in the dark or brown bottles.
6.6 Potassium tetracyanozincate, K Zn(CN) .
2 4
6.6.1 Potassium tetracyanozincate solution, K Zn(CN) , ρ(CN) = (1 000 ± 2) mg/l, commercially
2 4
available.
This solution is stable for six months at (5 ± 3) °C, if stored in the dark.
6.6.2 Potassium tetracyanozincate solution I, ρ(CN) = 10 mg/l.
Pipette 1,00 ml of the potassium tetracyanozincate solution (6.6.1) in a 100 ml graduated flask and
bring to volume with sodium hydroxide solution III (6.4).
This solution is stable for one week at (5 ± 3) °C, if stored in the dark or brown bottles.
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ISO 20950-1:2018(E)

6.7 Calibration solutions.
Prepare five to ten calibration solutions with cyanide concentrations, equidistantly distributed
over the working range, either by appropriate dilution of the cyanide solution I (6.5.2) or potassium
tetracyanozincate solution I (6.6.2).
If, for example, six calibration solutions should be prepared to cover the range of 5 µg/l to 50 µg/l,
proceed as follows:
Pipette 25 ml of the cyanide solution I (6.5.2) or potassium tetracyanozincate solution I (6.6.2), in
a 500 ml graduated flask and make up to volume with sodium hydroxide solution III (6.4). This
solution contains 0,5 mg/l cyanide.
Pipette, in 100 ml graduated flasks, 1 ml, 3 ml, 5 ml, 7 ml, 9 ml, or 10 ml, respectively, of the above
mentioned 0,5 mg/l cyanide solution and make up to volume with sodium hydroxide solution III (6.4).
These solutions contain nominally 5 µg/l, 15 µg/l, 25 µg/l, 35 µg/l, 45 µg/l, and 50 µg/l of cyanide,
respectively. Correct calibration solution concentrations based on the concentration found on
titration of the potassium cyanide solution (6.5.1) or potassium tetracyanozincate solution (6.6.1)
used, following the procedure in Annex B by multiplying the nominal value by ρ(CN)/1 000 and
round to the nearest µg/l.
Or, for example, if six calibration solutions should be prepared to cover the range of 50 µg/l to 500 µg/l,
proceed as follows:
Pipette 25 ml of the cyanide solution I (6.5.2) or potassium tetracyanozincate solution I (6.6.2),
in a 50 ml graduated flask and make up to volume with sodium hydroxide solution III (6.4). This
solution contains 5 mg/l cyanide.
Pipette, in 100 ml graduated flasks, 1 ml, 3 ml, 5 ml, 7 ml, 9 ml, or 10 ml, respectively, of the above
mentioned 5 mg/l cyanide solution and make up to volume with sodium hydroxide solution III (6.4).
These solutions contain nominally 50 µg/l, 150 µg/l, 250 µg/l, 350 µg/l, 450 µg/l, and 500 µg/l
of cyanide, respectively. Correct calibration solution concentrations based on the concentration
found on titration of the potassium cyanide solution (6.5.1), following the procedure in Annex B by
multiplying the nominal value by ρ(CN)/1 000 and round to the nearest µg/l.
NOTE Use of calibration solutions less than or equal to 500 µg/l for samples with cyanide concentrations
< 500 µg/l improved accuracy and precision during interlaboratory testing.
6.8 Reagents for the determination of available WAD cyanide.
6.8.1 Ag/AgCl reference electrode filling solution.
Fill the reference electrode as recommended by the instrument manufacturer.
6.8.2 Bismuth nitrate pentahydrate, Bi(NO ) ·5H O.
3 3 2
6.8.3 Sulfuric acid (I), ρ = 1,84 g/ml; 95 % to 97 % (mass fraction).
6.8.4 Sulfide removal and acidification reagent.
Weigh 1 g bismuth nitrate pentahydrate, Bi(NO ) ·5H O and add it to a 500 ml beaker. Add 55 ml of
3 3 2
water (6.1), then carefully add 55 ml of concentrated sulfuric acid (6.8.3) to the beaker. Gently, stir
the beaker until the bismuth nitrate pentahydrate has dissolved in the acid solution. Carefully, add
approximately 250 ml of water (6.1) to the beaker with stirring and allow to cool. Then quantitatively
transfer the beaker contents to a 1 l volumetric flask and fill to volume with water (6.1).
CAUTION — This is an exothermic reaction and the solution will become hot when preparing
this solution.
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ISO 20950-1:2018(E)

6.8.5 Cyanide electrode stabilization solution, approximately 5 mg/l as CN‾.
Pipette 500 µl of potassium cyanide solution (6.5.1) or potassium tetracyanozincate solution (6.6.1),
into a 100 ml volumetric flask containing 1,0 ml of sodium hydroxide solution I (6.2). Dilute to volume
with water (6.1).
This solution is stable for one week if stored at (5 ± 3) °C.
NOTE Lower cyanide concentrations can be used, provided the detector signal is near saturation and sharp,
repeatable peaks are produced.
6.9 Ligand-exchange reagents.
1)
6.9.1 Ligand-exchange reagent A , optional proprietary organic amine reagent for nickel, follow
manufacturers’ instruction for preparation.
2)
6.9.2 Ligand-exchange reagent B , optional proprietary specially purified organic sulfide reagent for
mercury, follow manufacturers’ instruction for preparation.
6.9.3 Mixed ligand exchange reagent, for automated ligand addition as shown in Figure A.2.
Transfer 0,125 ml of WAD reagent A (6.9.1) and 0,250 ml of WAD reagent B (6.9.2) into a 100 ml
volumetric flask containing 50 ml water (6.1). Dilute to volume with water (6.1) and mix. The solution
should be stored at room temperature.
6.9.4 Tetraethylenepentamine, (NH CH CH NHCH CH ) NH.
2 2 2 2 2 2
6.9.5 Ligand exchange reagent 1 (tetraethylenepentamine (TEP) solution).
Weigh 0,10 g tetraethylenepentamine (TEP) (6.9.4) into a 100 ml volumetric flask. Dilute to volume with
water (6.1). The solution should be stored at room temperature. Commercially prepared or alternative
ligand exchange reagents can be used if equivalent results can be demonstrated. Commercial reagents
should be used in accordance with manufacturer's instructions.
6.9.6 Dithizone, C H NHNHCSN = NC H .
6 5 6 5
6.9.7 Ligand exchange reagent 2 (dithizone solution)
Weigh 0,010 g of dithizone (6.9.6) into a 100 ml volumetric flask containing 1 ml of 1 mol/l NaOH (6.3).
Dilute to volume with water (6.1). Sonicate if necessary until all of the dithizone has dissolved. The
solution should be stored at room temperature. Commercially prepared or alternative ligand exchange
reagents can be used if equivalent results can be demonstrated. Commercial reagents should be used in
accordance with manufacturer's instructions.
6.10 Reagents for ligand addition quality control.
6.10.1 Mercury(II) cyanide, Hg(CN) .
2
6.10.2 Mercury(II) cyanide stock solution.
Weigh 0,485 4 g Hg(CN) (6.10.1) into a 100 ml volumetric flask. Place 1 ml of 1 mol/l NaOH (6.3) in
2
the flask and dilute to volume with water (6.1). Hg(CN) as ρ(CN) = 1 000 mg/l. Store the solution in an
2
amber glass bottle under refrigeration at (5 ± 3) °C.
1) OI Analytical WAD Reagent A, PN A001416 has been found to be suitable for this analysis.
2) OI Analytical WAD Reagent B, PN A001417 has been found to be suitable for this analysis.
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ISO 20950-1:2018(E)

6.10.3 Mercury(II) cyanide intermediate solution.
Pipette 10 ml of the mercury(II) cyanide stock solution (6.10.2) into a 100 ml volumetric flask containing
1 ml of 1 mol/l NaOH (6.3). Dilute to volume with water (6.1). Hg(CN) as CN¯ = 100 mg/l. Store the
2
solution in an amber glass bottle under refrigeration at (5 ± 3) °C.
6.10.4 Mercury(II) cyanide recovery solution.
Pipette 100 µl of mercury(II) cyanide intermediate solution (6.10.3) into a 100 ml volumetric flask
containing 1 ml of 1 mol/l NaOH (6.3). Dilute to volume with water (6.1). Hg(CN) as ρ(CN) = 100 µg/l.
2
Prepare fresh daily.
6.10.5 Potassium nickel(II) cyanide, K Ni(CN) ·H O.
2 4 2
6.10.6 Potassium nickel cyanide stock solution.
Weigh 0,248 8 g of K Ni(CN) · H O (6.10.5) into a 100 ml volumetric flask. Place 1 ml of 1 mol/l
2 4 2
NaOH (6.3) in the flask and dilute to volume with water (6.1). K Ni(CN) as ρ(CN) = 1 000 mg/l. Store
2 4
the solution in an amber glass bottle under refrigeration at (5 ± 3) °C.
6.10.7 Potassium nickel cyanide intermediate solution.
Pipette 10 ml of the potassium nickel cyanide stock solution (6.10.6) into a 100 ml volumetric flask
containing 1 ml of 1 mol/l NaOH. Dilute to volume with water (6.1). K Ni(CN) as ρ(CN) = 100 mg/l.
2 4
Store the solution in an amber glass bottle under refrigeration at (5 ± 3) °C.
6.10.8 Potassium nickel cyanide recovery solution.
Pipette 100 µl of potassium nickel cyanide intermediate solution (6.10.7) into a 100 ml volumetric flask
containing 1 ml of 1 mol/l NaOH (6.3). Dilute to volume with water (6.1). K Ni(CN) as ρ(CN) = 100 µg/l.
2 4
Prepare fresh daily.
6.11 Reagents for sample pre-treatment and preservation.
6.11.1 Sodium acetate trihydrate, NaC H O ·3H O.
2 3 2 2
6.11.2 Acetic acid, CH COOH.
3
6.11.3 Acetate buffer solution.
Dissolve 410 g of sodium acetate trihydrate (NaC H O ·3H O) (6.11.1) in 500 ml of water (6.1). Add
2 3 2 2
acetic acid (approximately 500 ml) (6.11.2) to yield a pH of 4,5.
6.11.4 Lead carbonate, PbCO , powder, dissolving 50 g/l concentration in solution is recommended
3
prior to use.
DANGER — Harmful if swallowed or if inhaled, may cause cancer, may damage fertility or the
unborn child, may cause damage to organs through prolonged or repeated exposure, very toxic
to aquatic life with long lasting effects. Handle carefully using personal protective equipment
and dispose properly.
6.11.5 Lead acetate test paper, commercially available.
6.11.6 Sodium arsenite, NaAsO , powder.
2
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ISO 20950-1:2018(E)

DANGER — Fatal if swallowed or in contact with skin; toxic if inhaled; may cause cancer;
very toxic to aquatic life with long lasting effects. Handle carefully using personal protective
equipment and dispose properly.
6.11.7 Potassium iodide starch test paper, commercially available.
7 Apparatus
7.1 Flow injection analysis system
A suitable example of the system is shown in Figure A.1. Alternative systems are also applicable if the
requirements in Clause 9 are achieved (see Annex A for examples of flow injection systems and Annex C
for the results of an interlaboratory trial for flow systems).
7.1.1 Autosampler or another device, allowing a reproducible introduction of the sample.
7.1.2 Reagent reservoirs.
7.1.3 Low pulsation pump, with specific chemically inert pump tub
...

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