Influence of materials on water intended for human consumption - GC-MS identification of water leachable organic substances

This European Standard describes a method for identifying organic chemicals that are amenable to GC-MS analysis using the procedures described and which may migrate from a product into water intended for human consumption. A method of semi-quantitatively estimating the concentrations of the organic substances identified is also provided.
NOTE   The method to be used for the preparation of migration waters is specified by separate EN standards, as noted below.

Identifizierung mittels GC-MS von durch Wasser auslaugbaren organischen Substanzen aus Materialien für den Kontakt mit Trinkwasser

Diese Europäische Norm beschreibt eine Methode zur Identifizierung organischer Substanzen, die der GC MS-Analyse mit den beschriebenen Verfahren zugänglich sind und von Produkten in Trinkwasser migrieren können. Ein Verfahren zur semi-quantitativen Bestimmung der Konzentrationen der ermittelten organischen Stoffen wird ebenfalls angegeben.
ANMERKUNG   Das Verfahren zur Herstellung von Migrationswässern ist in einzelnen Europäischen Normen festgelegt, die nachfolgend genannt sind.

Influence sur l'eau des matériaux en contact avec l'eau destinée à la consommation humaine - Identification par CG-SM de substances organiques lixiviables à l’eau

La présente Norme européenne définit une méthode de détection et d’identification des substances chimiques organiques compatibles avec l’analyse par CG-SM par les modes opératoires décrits et capables de migrer d’un produit vers l’eau destinée à la consommation humaine. Elle ne fournit pas tous les outils nécessaires pour permettre l'identification complète de toutes les substances détectées. La présente norme fournit également une méthode d'estimation semi-quantitative des concentrations des substances organiques détectées. Il convient toutefois de considérer les concentrations comme étant seulement indicatives.
NOTE   La méthode de préparation des eaux de migration à utiliser est spécifiée dans d’autres Normes européennes, mentionnées ci-dessous.

Vpliv materialov na pitno vodo - Identifikacija GC-MS vodno lužljivih organskih snovi

Ta evropski standard opisuje metodo za identifikacijo organskih snovi, ki so primerne za analizo GC-MS z opisanimi postopki in ki lahko iz produkta migrirajo v pitno vodo. Navedena je tudi metoda semikvantitativne ocene koncentracij identificiranih organskih snovi
OPOMBA   Metoda, ki jo je treba uporabiti za pripravo migracijske vode, je opredeljena v ločenih standardih EN, kot so navedeni spodaj.

General Information

Status
Published
Publication Date
17-Mar-2015
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
19-Feb-2015
Due Date
26-Apr-2015
Completion Date
18-Mar-2015

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Vpliv materialov na pitno vodo - Identifikacija GC-MS vodno lužljivih organskih snoviIdentifizierung mittels GC-MS von durch Wasser auslaugbaren organischen Substanzen aus Materialien für den Kontakt mit TrinkwasserInfluence sur l'eau des matériaux en contact avec l'eau destinée à la consommation humaine - Identification par CG-SM de substances organiques lixiviables à l’eauInfluence of materials on water intended for human consumption - GC-MS identification of water leachable organic substances71.040.50Fizikalnokemijske analitske metodePhysicochemical methods of analysis67.250Materiali in predmeti v stiku z živiliMaterials and articles in contact with foodstuffs13.060.20Pitna vodaDrinking waterICS:Ta slovenski standard je istoveten z:EN 15768:2015SIST EN 15768:2015en,de01-april-2015SIST EN 15768:2015SLOVENSKI

STANDARD
SIST EN 15768:2015
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 15768
January 2015 ICS 13.060.20; 67.250; 71.040.50 English Version

Influence of materials on water intended for human consumption - GC-MS identification of water leachable organic substances

Influence sur l'eau des matériaux en contact avec l'eau destinée à la consommation humaine - Identification par CG-SM de substances organiques lixiviables à l'eau

Identifizierung mittels GC-MS von durch Wasser auslaugbaren organischen Substanzen aus Materialien für den Kontakt mit Trinkwasser This European Standard was approved by CEN on 29 November 2014.

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 © 2015 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 15768:2015 ESIST EN 15768:2015

EN 15768:2015 (E) 2 Contents Page Foreword ..............................................................................................................................................................4 Introduction .........................................................................................................................................................5 1 Scope ......................................................................................................................................................6 2 Normative references ............................................................................................................................6 3 Terms and definitions ...........................................................................................................................6 4 Principle ..................................................................................................................................................9 5 Reagents .................................................................................................................................................9 5.1 General ....................................................................................................................................................9 5.2 Required reagents .................................................................................................................................9 6 Apparatus ............................................................................................................................................ 13 7 Storage of migration waters, procedural blanks and laboratory blanks ...................................... 14 8 Method of analysis.............................................................................................................................. 14 8.1 Extraction procedure .......................................................................................................................... 14 8.2 GC-MS analysis ................................................................................................................................... 15 8.2.1 Safety precautions .............................................................................................................................. 15 8.2.2 Mass spectrometer operating parameters ....................................................................................... 15 8.2.3 Setting up the mass spectrometer and data system ...................................................................... 15 8.2.4 Initial tuning and mass calibration of the mass spectrometer ...................................................... 15 8.3 Setting up the GC-MS system ........................................................................................................... 15 8.4 GC-MS operating conditions for analysis of solvent extracts ....................................................... 16 8.5 Production of required outputs from the GC-MS data system ...................................................... 17 9 Quality assurance (QA) and quality control (QC) procedures ....................................................... 17 9.1 The mass calibration of the mass spectrometer ............................................................................. 17 9.2 The performance of the GC-MS system ........................................................................................... 17 9.3 The performance of the method ........................................................................................................ 17 9.4 Performance of the analyst ................................................................................................................ 18 9.5 Uncertainty of the method ................................................................................................................. 18 10 Expression of results ......................................................................................................................... 18 10.1 Semi-quantitative estimation of concentrations of substances detected .................................... 18 10.2 Identification of substances detected .............................................................................................. 19 10.3 Reporting of results ............................................................................................................................ 19 11 Test report ........................................................................................................................................... 20 11.1 General ................................................................................................................................................. 20 11.2 Test results .......................................................................................................................................... 21 Annex A (normative)

Additional procedural details ..................................................................................... 23 A.1 Checking suitability of apparatus used for concentrating solvent extracts ................................ 23 A.2 Procedure for calculation of recoveries of internal standards ...................................................... 23 A.3 Standard solutions for checking GC column performance ........................................................... 24 Annex B (informative)

Outline of general approach for identification of substances detected............... 25 B.1 General approach - Introduction ....................................................................................................... 25 B.2 GC-MS Test Solution .......................................................................................................................... 25 SIST EN 15768:2015

EN 15768:2015 (E) 3 B.3 Typical Leachate .................................................................................................................................. 26 B.4 Identifying substances ........................................................................................................................ 26 B.5 Overloading .......................................................................................................................................... 27 Annex C (informative)

Guidance on the interpretation of results ................................................................ 28 C.1 Introduction .......................................................................................................................................... 28 C.2 Initial assessment of test report ........................................................................................................ 28 C.3 Assessment of results of analysis .................................................................................................... 28 Annex D (informative)

Guidance on the identification of substances ......................................................... 30 D.1 A suggested strategy to assist in identifying substances in extracted leachates ....................... 30 D.2 Resolution of co-eluting peaks .......................................................................................................... 30 D.3 Proceeding when background subtraction does not help .............................................................. 31 D.4 Tentatively identifying a substance using boiling points and retention indices .......................... 31 D.5 Library search results and identifying “unknown” substances ..................................................... 32 D.6 Interpretation of the mass spectrum ................................................................................................. 32 D.7 Reporting confidence in a substance identification ........................................................................ 33 D.8 How to report alternative identifications and when this is appropriate ........................................ 33 D.9 What to do if library search fails to assign a reasonable identification ........................................ 34

SIST EN 15768:2015

EN 15768:2015 (E) 4 Foreword This document (EN 15768:2015) has been prepared by Technical Committee CEN/TC 164 “Water supply”, the secretariat of which is held by AFNOR. 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 July 2015 and conflicting national standards shall be withdrawn at the latest by July 2015. 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. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association. This document has been prepared on the basis of co-normative research project EVK1-CT 2000-00052 and work funded by DG Enterprise and Industry (Grant Agreement S12.403892). This document describes methods of identification only, and should not be used or quoted as a specification. References to this document should indicate that the methods of identification used are in accordance with EN 15678:2015. 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. SIST EN 15768:2015

EN 15768:2015 (E) 5 Introduction Organic substances that migrate from products containing such substances have, when used in contact with water intended for human consumption, the potential to cause health concerns for consumers. The potential health effects of these chemicals are assessed in three stages as follows: a) preparation of migration waters by exposing a portion of the material to water under controlled conditions; b) analysis of the migration waters; c) assessment of the identities and concentrations of the substance detected. The analysis of organic substances present in migration waters can involve two different types of analytical methods as follows: d) a screening method, which allows a variety of substances to be detected and a semi-quantitative assessment to be made of their concentrations; e) accurate quantitative methods for the determination of specific target substances known to be present in the chemical formulations of the materials. This standard describes the analytical procedures based upon gas chromatography and mass spectrometry (GC-MS) used to screen migration waters for organic substances derived from finished products such as pipes, protective coatings, membranes, etc. This method is suitable for migration waters from all products that can potentially release organic chemicals into water when they are used in contact with water intended for human consumption, and which are the subject of an application for approval by the national regulatory body. It may be one of several methods that form part of the overall approval process. The method may also be used as part of an approval audit process. The method does not provide accurate quantitative results and other analytical methods are recommended for accurate quantitative determination of specific target substances. SIST EN 15768:2015

EN 15768:2015 (E) 6 1 Scope This European Standard describes a method for detecting and identifying organic chemicals that are amenable to GC-MS analysis using the procedures described and which can migrate from a product into water intended for human consumption. This European Standard does not provide all the necessary tools to completely identify all the substances that are detected. A method of semi-quantitatively estimating the concentrations of the organic substances detected is also provided, however, concentrations should only be seen as indicative. NOTE The method to be used for the preparation of migration waters is specified by separate ENs, as noted below. 2 Normative references EN 12873-1, Influence of materials on water intended for human consumption - Influence due to migration - Part 1: Test method for factory-made products made from or incorporating organic or glassy (porcelain/vitreous enamel) materials EN 12873-2, Influence of materials on water intended for human consumption - Influence due to migration - Part 2: Test method for non-metallic and non-cementitious site-applied materials EN 12873-3, Influence of materials on water intended for human consumption - Influence due to migration - Part 3: Test method for ion exchange and adsorbent resins EN 12873-4, Influence of materials on water intended for human consumption - Influence due to migration - Part 4: Test method for water treatment membranes EN ISO 3696, Water for analytical laboratory use - Specification and test methods (ISO 3696)

3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 u atomic mass unit, defined as 1/12 of the mass of a single atom of carbon-12 in the gas phase (i.e. unbound), at rest and in its ground state 3.2 asymmetry factor

As measure of the absorption of a compound during gas chromatographic analysis Note 1 to entry: The asymmetry factor (As) can be derived from Formula (1). +=(ab)Abs2 (1) where a is the distance from the leading edge of the peak at the point on the baseline where the perpendicular dropped from the peak maximum crosses it; b is the corresponding distance from the trailing edge of the peak. Locate the apex of the peaks that require their asymmetry values calculated. For each peak, drop a perpendicular line down at a right-angle to the baseline. SIST EN 15768:2015

EN 15768:2015 (E) 7

Note 2 to entry: Some manufacturer's GC-MS software packages allow the calculation of peak asymmetries to be produced automatically. Check the criteria used for the measurement, as some packages perform the calculation at 5 % of the peak height. 3.3 electron impact ionization ionization by a beam of electrons 3.4 GC-MS analytical instrument comprising a gas chromatograph (GC) linked to a mass spectrometer (MS) 3.5 GC-MS general survey analysis acquisition of a series of mass spectra (up to several thousand) during the course of a gas chromatographic run, by operating the mass spectrometer in a continuous cyclic scanning mode over a wide m/z range 3.6 injection standard organic substance added to the final solvent extract prior to analysis Note 1 to entry: An injection standard is added to allow the recoveries of the internal standards to be calculated, by providing a means of normalizing the GC-MS responses for solvent extracts and GC-MS standards. 3.7 internal standard organic substance added to the migration water at a known concentration prior to the commencement of the analysis Note 1 to entry: Internal standards are added for the following reasons (a) to demonstrate that the analysis has been undertaken successfully, and (b) to provide a reference to allow other substances detected to be quantified. Ideally, the internal standards should not be present in the migration waters being analysed; for this reason, isotopically labelled standards are used. 3.8 test water water used to prepare the migration water, as specified in EN 12873-1, EN 12873-2, EN 12873-3 or EN 12873-4 depending on the material being tested 3.9 laboratory blank water, as specified in EN ISO 3696, known to contain negligible levels of contamination, to which internal standards (3.7) have been added and which is then analysed in the same way as the migration water Note 1 to entry: Laboratory blanks are used to check for potential contamination of either migration waters or solvent extracts which may occur within the laboratory during the course of the analysis. 3.10 migration water aqueous solution that results from leaving test water in contact with the test material under the specified test conditions 3.11 procedural blank aqueous solution that results from leaving test water in contact with tanks or containers identical to those used to prepare the migration water in the absence of the test material SIST EN 15768:2015

EN 15768:2015 (E) 8 Note 1 to entry: Procedural blanks are used to check for potential contamination of migration waters that can arise during the migration procedure. For example, substances can migrate from the tanks or containers used into the test water, or aerial contamination can occur if volatile substances are present in the laboratory atmosphere. Further details are provided in the European Standards regarding the preparation of migration waters. 3.12 mass spectrometric resolution measure of the capability of a mass spectrometer to correctly distinguish two mass spectral peaks, having sequential mass to charge (m/z) values, as separate peaks Note 1 to entry: If z =1, this is generally denoted by m2 / (m2 - m1), where m2 has the higher m/z value and m1 has the lower m/z value. Note 2 to entry: Mass spectrometer set up so that the resolution is 650 will satisfactorily resolve and assign the correct masses to mass spectral peaks at m/z 649 and m/z 650. Although the mass spectrometric resolution of a mass spectrometer using a magnetic field for mass resolution remains constant throughout the mass range scanned, a quadrupole mass spectrometer is usually operated so that unit mass resolution is achieved over the mass range scanned (i.e. at m/z 200 the resolution is 200, whereas at m/z 500 the resolution is 500). 3.13 m/z mass (m)-to-charge (z) ratio of an ion Note 1 to entry: As most ions produced by electron impact ionization are singly charged, this ratio usually corresponds to the mass of an ion. However, exceptionally, ions can possess multiple charges. 3.14 solvent extract solution containing substances partitioned from the migration waters into the extraction solvent (in this case dichloromethane) 3.15 total ion current

TIC sum of all the separate ion currents carried by the individual ions contributing to a single mass spectrum 3.16 TIC chromatogram graphical representation of the TIC versus time 3.17 Linear Retention Index Linear Retention Index −−×+×=+)()(100100)(n1nnxRTRTRTRTn (2) where n is the number of carbon atoms in n-alkane prior to substance of interest; RTn

is the retention time (min) of n-alkane; RTn + 1 is the retention time (min) of next n-alkane; RTx is the retention time (min) of substance of interest SIST EN 15768:2015

EN 15768:2015 (E) 9 3.18 threshold value concentration below which detection and/or identification is uncertain 4 Principle A mixture of isotopically-labelled internal standards is added to each of the migration waters to be analysed immediately before the extraction solvent dichloromethane is added. After solvent extraction, the extract is concentrated, an injection standard added, and the resultant concentrated extract is then analysed by GC-MS to determine the identity of any organic chemicals that may be present above a pre-set threshold value. The mass spectrometer is used in a repetitive full-scan mode operating with positive electron impact ionization and the mass spectra produced are recorded by, and stored on, the GC-MS data system. Wherever possible, each substance detected above the threshold value is identified, and semi-quantified by reference of its TIC to the TIC responses obtained for the internal standards. NOTE The procedure to be used to identify organic substances from their mass spectra is given in Annex B. 5 Reagents 5.1 General Only reagents of analytical grade shall be used, except where specified otherwise. All reagents shall be of sufficient purity to ensure that they do not give rise to interferences during the GC-MS analysis. NOTE Contamination can arise from various sources, e.g. the laboratory atmosphere, glassware, plastics and rubber materials. The use of procedural blanks and laboratory blanks assists in detecting and identifying the source of any contamination and are used to correct results for the effects of contamination. 5.2 Required reagents 5.2.1 Reagent water, having a conductivity of < 2 mS/m, a total organic carbon content of < 0,2 mg/l carbon, and free from organic contaminants which can interfere with the GC-MS analysis of the extracts. Suitable water can be prepared by reverse osmosis, de-ionization or distillation. 5.2.2 Hydrochloric acid, concentrated (density 1,18 g/ml). 5.2.3 Hydrochloric acid solution (6 mol/l), prepared as follows: — slowly add (0,5 ± 0,01) l of concentrated hydrochloric acid (5.2.2) to (0,5 ± 0,01) l of reagent water (5.2.1); — this solution should be replaced on a six monthly basis. NOTE Care is needed in preparing this solution which can generate heat. 5.2.4 Sulfuric acid, concentrated (density 1,84 g/ml). 5.2.5 Sulfuric acid solution (0,5 mol/l), prepared as follows: — slowly add (14,0 ± 0,5) ml of sulfuric acid (5.2.4) to (300 ± 5) ml of reagent water (5.2.1) and make up to (500 ± 5) ml with reagent water; — this solution should be replaced on a yearly basis. NOTE Care is needed in preparing this solution which can generate heat. SIST EN 15768:2015

EN 15768:2015 (E) 10 5.2.6 Sodium hydroxide solution (0,5 mol/l), prepared as follows: — dissolve (20,0 ± 0,1) g of sodium hydroxide pellets in reagent water (5.2.1) and make up to 1 l; — replace this solution on a two weekly basis. NOTE Care is needed in preparing this solution which can generate heat. 5.2.7 Dichloromethane, glass distilled grade, batches should not be used until they have been verified as free from significant contamination, see Note 2. NOTE 1 Other grades can be suitable but it is necessary to demonstrate that any impurities present do not interfere with the detection of substances of interest or the internal standards, or introduce unacceptable contamination, see Note 2. NOTE 2 Generally any peak in the solvent after contaminants have been concentrated by evaporation (200 ml of solvent reduced to 500

5.2.8 Acetone, glass distilled grade, batches should not be used until they have been verified as free from significant contamination, see Note 2. NOTE 1 Other grades can be suitable but it is necessary to demonstrate that any impurities present do not interfere with the detection of substances of interest or the internal standards, or introduce unacceptable contamination, see Note 2. NOTE 2 Generally any peak in the solvent after the acetone has been diluted 5 times with dichloromethane with an estimated concentration greater than 1

5.2.9 Ascorbic acid solution, prepared as follows: — dissolve (4,0 ± 0,1) g of ascorbic acid in reagent water (5.2.1) and make up to 1 l. Before use, extract the ascorbic acid solution with two 100 ml aliquots of dichloromethane, discarding the solvent afterwards. Transfer the ascorbic acid solution to a suitable screw-capped bottle. The solution is stable for use for one month after preparation. 5.2.10 Sodium sulphate (anhydrous), prepared as follows: — remove any organic contaminants by heating at (500 ± 50) °C for ≥ 4 h, and store so that rehydration is minimized and re-contamination cannot occur. 5.2.11 Internal standards Use the following isotopically-labelled (≥98 atom % a) substances: — d6-benzene; — d21-2,6-di-t-butyl-4-methylphenol (d21-BHT); — d5-chlorobenzene; — d34-hexadecane; — d8-naphthalene; — d10-phenanthrene; — d5-phenol; SIST EN 15768:2015

EN 15768:2015 (E) 11 — d62-squalane; — d10-p-xylene. 5.2.12 Internal standards stock solutions Make up individual standards stock solutions in acetone (5.2.8) as follows: — d6-benzene (2,0 ± 0,05) mg/ml; — d21-BHT (8,0 ± 0,20) mg/ml; — d5-chlorobenzene (2,0 ± 0,05) mg/ml; — d34-hexadecane (1,0 ± 0,02) mg/ml; — d8-naphthalene (1,0 ± 0,02) mg/ml; — d10-phenanthrene (2,0 ± 0,05) mg/ml; — d5-phenol (8,0 ± 0,20) mg/ml; — d10-p-xylene (1,0 ± 0,02) mg/ml. Due to its volatility, it is difficult to make standard solutions of d6-benzene by weighing; it is recommended that suitable volumes of d6-benzene are measured using calibrated micro-syringes or positive displacement pipettes, based on its density (0,950 g/ml), and injected below the surface of the acetone. Make up the following stock solution in dichloromethane (5.2.7) — d62-squalane (8,0 ± 0,20) mg/ml. The stock solutions are stable for at least 12 months, provided they are stored in the dark at (−18 ± 5) °C. 5.2.13 Internal standards intermediate solution The internal standards intermediate solutions are ten-fold dilutions of each of the individual standard stock solutions, see 5.2.12. Prepare the intermediate solutions as follows: — place (2,5 ± 0,025) ml of the d62-squalane stock solution (5.2.12) in a 25 ml volumetric flask; — gently evaporate the dichloromethane, using nitrogen blow down, until it is completely removed. This can be verified by evaporating to constant mass; — place (2,5 ± 0,025) ml of each of the other eight individual standard stock solutions (5.2.12) into the volumetric flask, ensuring that the d6-benzene stock solution is added last, and make up to the graduation mark with acetone (5.2.8). The d6-benzene stock solution is added last in order to minimize any potential evaporative losses of this standard. qhis solution is stable for at least six months provided it is stored in the dark at (−18 ± 5) °C. SIST EN 15768:2015

EN 15768:2015 (E) 12 5.2.14 Internal standards spiking solution The internal standards spiking solutions are hundred-fold dilutions of each of the individual standard stock solutions, see 5.2.12. Prepare the spiking solutions as follows: — add (1,00 ± 0,01) ml of the internal standards intermediate solution (5.2.13) to (8 ± 0,5) ml acetone in a 10 ml volumetric flask; — make up to the graduation mark with acetone. Store this solution in the dark at (−18 ± 5) °C. This solution should be renewed every three months, or sooner if during its use any indication is obtained that the concentrations of any of the internal standards have changed. 5.2.15 Injection standard Use d10-1-methylnaphthalene (≥ 98 atom % D). 5.2.16 Injection standard stock solution Prepare the injection standard stock solution as follows: — weigh (25 ± 0,02) mg d10-1-methylnaphthalene (5.2.15) and add to approximately 20 ml dichloromethane contained in a 25 ml volumetric flask; — shake to dissolve and then make up to the graduation mark with dichloromethane. This solution contains 1 mg/ml and is stable for 12 months provided it is stored in the dark at (−18 ± 5) °C. 5.2.17 Injection standard spiking solution Prepare the injection standard spiking solution as follows: — take 1 ml of the injection stan

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