SIST EN ISO 17943:2017

SLOVENSKI STANDARD
SIST EN ISO 17943:2017
01-junij-2017
.DNRYRVWYRGH'RORþHYDQMHKODSQLKRUJDQVNLKVSRMLQYYRGL0HWRGDKHDGVSDFH
PLNURHNVWUDNFLMHQDWUGQLID]L+6630(YNRPELQDFLMLVSOLQVNR
NURPDWRJUDILMRPDVQRVSHNWURPHWULMR*&06,62
Water quality - Determination of volatile organic compounds in water - Method using
headspace solid-phase micro-extraction (HS-SPME) followed by gas chromatography-
mass spectrometry (GC-MS) (ISO 17943:2016)
Wasserbeschaffenheit - Bestimmung flüchtiger organischer Verbindungen in Wasser -
Verfahren mittels Headspace-Festphasenmikroextraktion (HS-SPME) gefolgt von der
Gaschromatographie und Massenspektrometrie (GC-MS) (ISO 17943:2016)
Qualité de l'eau - Détermination de composés organiques volatils dans l'eau - Méthode
utilisant une micro-extraction en phase solide (MEPS) de l'espace de tête suivie d'une
chromatographie en phase gazeuse-spectrométrie de masse (CG-SM) (ISO
17943:2016))
Ta slovenski standard je istoveten z: EN ISO 17943:2016
ICS:
13.060.50 3UHLVNDYDYRGHQDNHPLþQH Examination of water for
VQRYL chemical substances
71.040.50 Fizikalnokemijske analitske Physicochemical methods of
metode analysis
SIST EN ISO 17943:2017 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST EN ISO 17943:2017

---------------------- Page: 2 ----------------------

SIST EN ISO 17943:2017


EN ISO 17943
EUROPEAN STANDARD

NORME EUROPÉENNE

April 2016
EUROPÄISCHE NORM
ICS 13.060.50
English Version

Water quality - Determination of volatile organic
compounds in water - Method using headspace solid-
phase micro-extraction (HS-SPME) followed by gas
chromatography-mass spectrometry (GC-MS) (ISO
17943:2016)
Qualité de l'eau - Détermination de composés Wasserbeschaffenheit - Bestimmung flüchtiger
organiques volatils dans l'eau - Méthode utilisant une organischer Verbindungen in Wasser - Verfahren
micro-extraction en phase solide (MEPS) de l'espace de mittels Headspace-Festphasenmikroextraktion (HS-
tête suivie d'une chromatographie en phase gazeuse- SPME) gefolgt von der Gaschromatographie und
spectrométrie de masse (CG-SM) (ISO 17943:2016) Massenspektrometrie (GC-MS) (ISO 17943:2016)
This European Standard was approved by CEN on 13 February 2016.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17943:2016 E
worldwide for CEN national Members.

---------------------- Page: 3 ----------------------

SIST EN ISO 17943:2017
EN ISO 17943:2016 (E)
Contents Page
European foreword . 3
2

---------------------- Page: 4 ----------------------

SIST EN ISO 17943:2017
EN ISO 17943:2016 (E)
European foreword
This document (EN ISO 17943:2016) has been prepared by Technical Committee ISO/TC 147 “Water
quality” in collaboration with Technical Committee CEN/TC 230 “Water analysis” the secretariat of
which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2016, and conflicting national standards shall
be withdrawn at the latest by October 2016.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 17943:2016 has been approved by CEN as EN ISO 17943:2016 without any modification.

3

---------------------- Page: 5 ----------------------

SIST EN ISO 17943:2017

---------------------- Page: 6 ----------------------

SIST EN ISO 17943:2017
INTERNATIONAL ISO
STANDARD 17943
First edition
2016-04-01
Water quality — Determination of
volatile organic compounds in water
— Method using headspace solid-
phase micro-extraction (HS-SPME)
followed by gas chromatography-mass
spectrometry (GC-MS)
Qualité de l’eau — Détermination de composés organiques volatils
dans l’eau — Méthode utilisant une micro-extraction en phase solide
(MEPS) de l’espace de tête suivie d’une chromatographie en phase
gazeuse-spectrométrie de masse (CG-SM)
Reference number
ISO 17943:2016(E)
©
ISO 2016

---------------------- Page: 7 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

---------------------- Page: 8 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 3
3 Principle . 3
4 Interferences . 4
4.1 Sampling . 4
4.2 Extraction . 4
4.3 Gas chromatography and mass spectrometry . 5
5 Reagents . 5
6 Apparatus . 7
7 Sampling and sample pretreatment . 8
8 Procedure. 8
8.1 Sample preparation and extraction . 8
8.2 Gas chromatography . 9
8.3 Identification of individual compounds by means of mass spectrometry (GC-MS) . 9
8.4 Blank value measurements .11
9 Calibration .11
9.1 General .11
9.2 Calibration of the total procedure using the internal standard .12
10 Calculation of the results .13
11 Expression of results .13
12 Test report .14
Annex A (informative) Examples of suitable SPME fibres .15
Annex B (informative) Examples of GC columns .16
Annex C (informative) Examples of internal standards .17
Annex D (informative) Suitable gas chromatographic conditions and example
chromatograms for compounds of Table 1 .19
Annex E (informative) General information on SPME .33
Annex F (informative) Performance data .34
Bibliography .43
© ISO 2016 – All rights reserved iii

---------------------- Page: 9 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 2, Physical,
chemical and biochemical methods.
iv © ISO 2016 – All rights reserved

---------------------- Page: 10 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

Introduction
Volatile organic compounds (VOCs) are often found in the manufacturing processes of paints,
adhesives, petroleum products, pharmaceuticals, and refrigerants. Some are used as gasoline additives,
solvents, hydraulic fluids, and dry-cleaning agents. This group of compounds belongs to the group of
anthropogenic chemicals. VOC contamination of water resources is a human-health concern because
many are toxic and are known or suspected human carcinogens.
For the determination of VOCs, several published procedures are available (see References
[4],[5],[6],[7],[9],[12],[13], and [14]).
© ISO 2016 – All rights reserved v

---------------------- Page: 11 ----------------------

SIST EN ISO 17943:2017

---------------------- Page: 12 ----------------------

SIST EN ISO 17943:2017
INTERNATIONAL STANDARD ISO 17943:2016(E)
Water quality — Determination of volatile organic
compounds in water — Method using headspace solid-
phase micro-extraction (HS-SPME) followed by gas
chromatography-mass spectrometry (GC-MS)
WARNING — Persons using this International Standard should be familiar with normal
laboratory practice. This International 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.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this
International Standard be carried out by suitably qualified staff.
1 Scope
This International Standard specifies a method for the determination of volatile organic compounds
(see Table 1). This comprises, for example, halogenated hydrocarbons, trihalogenated methanes,
gasoline components (such as BTEX, MTBE, and ETBE), naphthalene, 2-ethyl-4-methyl-1,3-dioxolane,
and highly odorous substances like geosmin and 2-methylisoborneol in drinking water, ground water,
surface water, and treated waste water, by means of headspace solid-phase micro-extraction (HS-SPME)
followed by gas chromatography-mass spectrometry (GC-MS). The limit of determination depends on
the matrix, on the specific compound to be analysed, and on the sensitivity of the mass spectrometer.
For most compounds to which this International Standard applies, it is at least 0,01 µg/l. Validation
data related to a concentration range between 0,02 µg/l and 2,6 µg/l have been demonstrated in an
interlaboratory trial. Additional validation data derived from standardization work show applicability
of the method within a concentration range from 0,01 µg/l to 100 µg/l of individual substances. All
determinations are performed on small sample amounts (e.g. sample volumes of 10 ml).
This method may be applicable to other compounds not explicitly covered by this International Standard
or to other types of water. However, it is necessary to demonstrate the applicability for each case.
Table 1 — Volatile organic compounds determinable by this method
d
Name Molecular formula CAS registry no. Molar mass Density
g/mol kg/l
tert-amyl methyl ether (TAME) C H O 994–05–8 102,17 0,76
6 14
benzene C H 71–43–2 78,12 0,88
6 6
bromobenzene C H Br 108–86–1 157,01 1,50
6 5
bromochloromethane CH BrCl 74–97–5 129,38 1,99
2
bromodichloromethane CHBrCl 75–27–4 163,83 1,98
2
n-butylbenzene C H 104–51–8 134,22 0,86
10 14
sec-butylbenzene C H 135–98–8 134,22 0,86
10 14
tert-butylbenzene C H 98–06–6 134,22 0,87
10 14
chlorobenzene C H Cl 108–90–7 112,56 1,11
6 5
a
Signals of substances may overlap in chromatograms as they might co-elute.
b
Density of liquid at boiling point (−13,4 °C)
c
Refer to Tables F.1 and F.2 for validation data and additional information.
d
CAS: Chemical Abstracts Service.
© ISO 2016 – All rights reserved 1

---------------------- Page: 13 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

Table 1 (continued)
d
Name Molecular formula CAS registry no. Molar mass Density
g/mol kg/l
2-chlorotoluene C H Cl 95–49–8 126,59 1,08
7 7
4-chlorotoluene C H Cl 106–43–4 126,59 1,07
7 7
dibromochloromethane CHBr Cl 124–48–1 208,34 2,45
2
1,2-dibromo-3-chloropropane (DBCP) C H Br Cl 96–12–8 236,33 2,03
3 5 2
1,2-dibromoethane C H Br 106–93–4 187,86 2,18
2 4 2
dibromomethane CH Br 74–95–3 173,83 2,48
2 2
1,2-dichlorobenzene C H Cl 95–50–1 147,00 1,30
6 4 2
1,3-dichlorobenzene C H Cl 541–73–1 147,00 1,29
6 4 2
1,4-dichlorobenzene C H Cl 106–46–7 147,00 1,25
6 4 2
1,1-dichloroethane C H Cl 75–34–3 98,96 1,20
2 4 2
1,2-dichloroethane C H Cl 107–06–2 98,96 1,25
2 4 2
1,1-dichloroethene C H Cl 75–35–4 96,95 1,21
2 2 2
cis-1,2-dichloroethene C H Cl 156–59–2 96,94 1,28
2 2 2
trans-1,2-dichloroethene C H Cl 156–60–5 96,94 1,26
2 2 2
dichloromethane CH Cl 75–09–2 84,93 1,33
2 2
1,2-dichloropropane C H Cl 78–87–5 112,99 1,16
3 6 2
1,3-dichloropropane C H Cl 142–28–9 112,99 1,19
3 6 2
c
2,2-dichloropropane C H Cl 594–20–7 112,99 1,08
3 6 2
1,1-dichloropropene C H Cl 563–58–6 110,97 1,19
3 4 2
c
cis -1,3-dichloropropene C H Cl 10061–01–5 110,97 1,23
3 4 2
c
trans-1,3-dichloropropene C H Cl 10061–02–6 110,97 1,21
3 4 2
ethylbenzene C H 100–41–4 106,17 0,86
8 10
ethyl tert-butyl ether (ETBE) C H O 637–92–3 102,17 0,73
6 14
2-ethyl-4-methyl-1,3-dioxolane C H O 4359–46–0 116,16 0,90
6 12 2
2-ethyl-5,5-dimethyl-1,3-dioxane C H O 768–58–1 144,21 0,88
8 16 2
geosmin C H O 16423–19–1 182,30 0,99
12 22
hexachlorobutadiene C Cl 87–68–3 260,76 1,67
4 6
isopropylbenzene (cumene) C H 98–82–8 120,19 0,86
9 12
4-isopropyltoluene (p-cymene) C H 99–87–6 134,21 0,86
10 14
2-methylisoborneol C H O 2371–42–8 168,28 0,97
11 20
methyl tert-butyl ether (MTBE) C H O 1634–04–4 88,15 0,74
5 12
naphthalene C H 91–20–3 128,17 1,14
10 8
n-propylbenzene C H 103–65–1 120,19 0,86
9 12
styrene C H 100–42–5 104,15 0,91
8 8
1,1,1,2-tetrachloroethane C H Cl 630–20–6 167,85 1,55
2 2 4
1,1,2,2-tetrachloroethane C H Cl 79–34–5 167,85 1,59
2 2 4
tetrachloroethene C Cl 127–18–4 165,83 1,62
2 4
tetrachloromethane CCl 56–23–5 153,82 1,59
4
toluene C H 108–88–3 92,14 0,87
7 8
a
Signals of substances may overlap in chromatograms as they might co-elute.
b
Density of liquid at boiling point (−13,4 °C)
c
Refer to Tables F.1 and F.2 for validation data and additional information.
d
CAS: Chemical Abstracts Service.
2 © ISO 2016 – All rights reserved

---------------------- Page: 14 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

Table 1 (continued)
d
Name Molecular formula CAS registry no. Molar mass Density
g/mol kg/l
tribromomethane (bromoform) CHBr 75–25–2 252,75 2,89
3
1,2,3-trichlorobenzene C H Cl 87–61–6 181,45 1,68
6 3 3
1,2,4-trichlorobenzene C H Cl 120–82–1 181,45 1,45
6 3 3
1,3,5-trichlorobenzene C H Cl 108–70–3 181,45 1,87
6 3 3
1,1,1-trichloroethane C H Cl 71–55–6 133,40 1,34
2 3 3
1,1,2-trichloroethane C H Cl 79–00–5 133,40 1,44
2 3 3
trichloroethene C HCl 79–01–6 131,39 1,46
2 3
trichloromethane (chloroform) CHCl 67–66–3 119,38 1,47
3
1,2,3-trichloropropane C H Cl 96–18–4 147,43 1,38
3 5 3
1,2,4-trimethylbenzene C H 95–63–6 120,19 0,88
9 12
(pseudocumene)
1,3,5-trimethylbenzene (mesitylene) C H 108–67–8 120,19 0,86
9 12
b
vinyl chloride C H Cl 75–01–4 62,5 1,88
2 3
a
m-xylene C H 108–38–3 106,17 0,86
8 10
o-xylene C H 95–47–6 106,17 0,88
8 10
a
p-xylene C H 106–42–3 106,17 0,86
8 10
a
Signals of substances may overlap in chromatograms as they might co-elute.
b
Density of liquid at boiling point (−13,4 °C)
c
Refer to Tables F.1 and F.2 for validation data and additional information.
d
CAS: Chemical Abstracts Service.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 5667-5, Water quality — Sampling — Part 5: Guidance on sampling of drinking water from treatment
works and piped distribution systems
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 Principle
The analytes to be determined are extracted from the headspace above the water sample by means of
solid-phase micro-extraction (SPME) according to their equilibrium of distribution. Extraction fibres
are used whose surface is coated with suitable adsorbents. After the extraction, the SPME fibre is
removed from the sample vial (headspace vial) and introduced into the injector of a gas chromatograph.
The analytes are transferred to the capillary column by thermal desorption. The substances are
separated and detected using GC-MS.
© ISO 2016 – All rights reserved 3

---------------------- Page: 15 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

4 Interferences
4.1 Sampling
To avoid interferences, collect samples as specified in Clause 7 observing the instructions specified in
ISO 5667-1, ISO 5667-3, and ISO 5667-5.
4.2 Extraction
Commercially available SPME fibres often differ in quality. There may also be variations in the
selectivity of the materials of the individual batches, thus, possibly causing significant deviations in
extraction yield (see Annex E). However, apart from a higher detection limit of individual substances,
which may be the result, this does not generally impair the suitability of such fibres.
Inadequately conditioned fibres often result in lower extraction yields (see Annex E) and poorly
reproducible results, therefore, precondition new fibres by baking them out according to Clause 8.
Used fibres shall also be conditioned before they are used again. For this purpose, use two sample vials
containing only water (5.2) at the beginning of each sample sequence before starting with the first
sample (see 8.1).
The performance of the fibres used may decrease slightly throughout a long sample sequence. Therefore,
measure reference solutions (see 5.8.4) at regular intervals within the sample sequence. The fibre can
be used as long as the method shows the sensitivity required for the substances under investigation.
Depending on the matrix to be analysed, the durability of the fibre can be expected to be sufficient for
the analysis of more than 500 samples.
Adding sodium chloride to the sample results in an improvement of the extraction yield for the majority
of the substances listed in Table 1. It is recommended to add salt until the sample is nearly saturated
(see 8.1). It is necessary to add exactly the same amount of salt to all samples of a calibration sequence
and/or a sample sequence.
Salt deposits may accumulate in the metal syringe needle of the fibre holder after extended use. Heavier
salt encrustations will always have to be expected if the metal syringe needle of the fibre holder is
accidentally immersed in the water sample. This may damage the fibre and the injector liner. Therefore,
precisely adjust the immersion depth of the metal syringe needle into the vial. If there are visible salt
deposits, rinse the needle with water (5.2) to dissolve any salt deposits.
For automatic operation, sample, vials should be used with caps having thin septa (e.g. 0,9 mm to
1,3 mm) to avoid any mechanical problems when piercing the septum with the metal syringe needle
(see 6.4).
Thin septa should always be used when using autosamplers that agitate the sample vials with a circular
motion during the extraction process. Otherwise, the metal syringe needle (and the exposed fibre) may
be damaged during extraction.
To ensure the precision and accuracy of the measurement results, maintain the extraction times
constant during sample measurements or while measuring reference solutions (e.g. 10 min). For this
purpose, preferably use automatic samplers which are suitable for SPME.
The extraction of some of the substances listed in Table 1 applying the procedure described in Clause 8
depends on the temperature. It is therefore necessary to maintain the extraction temperature constant
for all samples of a sample sequence (e.g. at 40 °C). Somewhat higher extraction yields are often obtained
at higher temperatures. However, the extraction temperature should not be significantly higher than
40 °C (see 8.1) so as to minimize desorption of the analytes resulting from higher temperatures and to
avoid condensation on the fibre.
4 © ISO 2016 – All rights reserved

---------------------- Page: 16 ----------------------

SIST EN ISO 17943:2017
ISO 17943:2016(E)

4.3 Gas chromatography and mass spectrometry
Seek the help of experienced operators and refer to the information given in the user manual to
eliminate interferences caused, for example, by the injection system or by insufficient separation.
Check the performance and stability of the analytical system at regular intervals (e.g. by performing
measurements with reference solutions of known composition).
Use an injector liner with an internal diameter which is as small as possible (e.g. 1 mm) to enable
focusing of those substances on the column which elute particularly early (e.g. vinyl chloride).
The required immersion depth (position) of the fibre in the GC injector shall be determined for thermal
desorption. It corresponds to the hottest point of the injector and shall be maintained constant over a
sequence of measurements.
When using injectors with a septum, preferably, use SPME syringe needles with a diameter which is as
small as possible (e.g. 24-gauge needles) so as to avoid damaging the septum. Before piercing a septum,
the fibre should be drawn into the needle over a length of at least 1 mm to prevent the fibre from
fracturing. Use pre-pierced septa where possible. When using septumless injectors, it is preferable to
use SPME syringe needles with a larger diameter (e.g. 23-gauge needles) as they are more stable and
easier to seal (see 6.14).
5 Reagents
5.1 General
The content of impurities present in the reagents and contributing to the blank value shall be negligibly
small as compared to the analyte concentration which is to be determined. Check the blank value (8.4)
at regul
...