Detection and determination of specified additives in mineral insulating oils (IEC 60666:2010)

The methods described in this International Standard concern the detection and determination of specified additives in unused and used mineral insulating oils. The detection methods may be applied to assess whether or not a mineral insulating oil contains an additive as specified by the supplier. The determination methods are used for the quantitative determination of additives known to be present or previously detected by the appropriate detection method.

Nachweis und Bestimmung spezifizierter Additive in Isolierflüssigkeiten auf Mineralölbasis (IEC 60666:2010)

Détection et dosage d'additifs spécifiques présents dans les huiles minérales isolantes (CEI 60666:2010)

La CEI 60666:2010 fournit des méthodes concernant la détection et le dosage d'additifs spécifiques dans les huiles minérales isolantes neuves et usagées. Les méthodes de détection peuvent être appliquées pour vérifier si une huile isolante minérale contient ou non un additif comme le déclare le fournisseur. Les méthodes de dosage sont utilisées pour le dosage quantitatif des additifs préalablement décelés par la méthode de détection appropriée. Les modifications principales par rapport à l'édition précédente sont les suivantes: - un changement dans le titre de ' Détection et dosage d'additifs antioxydants spécifiques présents dans les huiles isolantes '; - les nouvelles Annexes B et C, qui donnent des méthodes pour la détermination de deux additifs différents de l'anti-oxydant.

Odkrivanje in ugotavljanje specifičnih aditivov v mineralnih izolacijskih oljih (IEC 60666:2010)

Metode, opisane v tem mednarodnem standardu, se nanašajo na odkrivanje in ugotavljanje specifičnih aditivov v neuporabljenih in uporabljenih mineralnih izolacijskih oljih. Metode odkrivanja se lahko uporabijo za ocenjevanje, ali mineralno izolacijsko olje vsebuje aditiv, ki ga navaja proizvajalec. Metode ugotavljanja se uporabljajo za količinsko določevanje aditivov, za katere je znano, da so prisotni, ali ki so bili predhodno odkriti z ustrezno metodo odkrivanja.

General Information

Status
Published
Publication Date
22-Jul-2010
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
14-Jul-2010
Due Date
18-Sep-2010
Completion Date
23-Jul-2010

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Nachweis und Bestimmung spezifizierter Additive in Isolierflüssigkeiten auf Mineralölbasis (IEC 60666:2010)Détection et dosage d'additifs spécifiques présents dans les huiles minérales isolantes (CEI 60666:2010)Detection and determination of specified additives in mineral insulating oils (IEC 60666:2010)29.040.10Izolacijska oljaInsulating oilsICS:Ta slovenski standard je istoveten z:EN 60666:2010SIST EN 60666:2010en01-september-2010SIST EN 60666:2010SLOVENSKI

STANDARDSIST HD 415 S1:19991DGRPHãþD
SIST EN 60666:2010
EUROPEAN STANDARD EN 60666 NORME EUROPÉENNE
EUROPÄISCHE NORM July 2010

CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2010 CENELEC -

All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60666:2010 E
ICS 17.220.99; 29.040.10 Supersedes HD 415 S1:1981
English version
Detection and determination of specified additives
in mineral insulating oils (IEC 60666:2010)

Détection et dosage d'additifs spécifiques présents dans les huiles minérales isolantes (CEI 60666:2010)

Nachweis und Bestimmung spezifizierter Additive in Isolierflüssigkeiten
auf Mineralölbasis (IEC 60666:2010)

This European Standard was approved by CENELEC on 2010-07-01. CENELEC 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 Central Secretariat or to any CENELEC 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 CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.

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

SIST EN 60666:2010

EN 60666:2010 - 2 - Foreword The text of document 10/803/FDIS, future edition 2 of IEC 60666, prepared by IEC TC 10, Fluids for electrotechnical applications, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60666 on 2010-07-01. This European Standard supersedes HD 415 S1:1981. The main changes with respect to HD 415 S1:1981 are listed below: – a change in the title from “Detection and determination of specified anti-oxidant additives in insulating oils” to “Detection and determination of specified additives in mineral insulating oils”. The previous edition only addressed the detection and determination of anti-oxidant additives, with particular regard to the DBPC, phenolic inhibitors and anthranilic acid; – more advanced methods for the determination of such anti-oxidant additives; – new Annexes B and C which provide methods for the determination of two additives different from the anti-oxidants. In particular, Annex B contains a method for the determination of the concentration in used and unused insulating mineral oils of passivators of the family of derivatives of benzotriazole. Annex C contains a method for the qualitative identification of pour point depressants used in some commercially available paraffinic oils to improve their low temperature properties. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent rights. The following dates were fixed: – latest date by which the EN has to be implemented

at national level by publication of an identical
national standard or by endorsement
(dop)
2011-04-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)

2013-07-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 60666:2010 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated: [3] IEC 60422 NOTE

Harmonized as EN 60422. [5] IEC 61198 NOTE
Harmonized as EN 61198. __________ SIST EN 60666:2010
- 3 - EN 60666:2010 Annex ZA
(normative)

Normative references to international publications with their corresponding European publications

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.

NOTE

When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.

Publication Year Title EN/HD Year

IEC 60296 - Fluids for electrotechnical applications - Unused mineral insulating oils for transformers and switchgear EN 60296 -

IEC 60475 - Method of sampling liquid dielectrics - -

ISO 5725 Series Accuracy (trueness and precision) of measurement methods and results - -

SIST EN 60666:2010
SIST EN 60666:2010

IEC 60666Edition 2.0 2010-04INTERNATIONAL STANDARD NORME INTERNATIONALEDetection and determination of specified additives in mineral insulating oils

Détection et dosage d’additifs spécifiques présents dans les huiles minérales isolantes

INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE VICS 17.220.99, 29.040.10 PRICE CODECODE PRIXISBN 978-2-88910-244-0

® Registered trademark of the International Electrotechnical Commission

Marque déposée de la Commission Electrotechnique Internationale ® SIST EN 60666:2010 colourinside

– 2 – 60666 © IEC:2010 CONTENTS FOREWORD...........................................................................................................................4 INTRODUCTION.....................................................................................................................6 1 Scope...............................................................................................................................7 2 Normative references.......................................................................................................7 3 Methods for the determination of anti-oxidant additives....................................................7 3.1 Determination of phenolic and amine-based antioxidants by infrared (IR) spectrophotometry – Method A................................................................................7 3.1.1 Introductory remark.....................................................................................7 3.1.2 Equipment, materials and solvents..............................................................8 3.1.3 Sample preparation.....................................................................................8 3.1.4 Calibration...................................................................................................8 3.1.5 Analysis.......................................................................................................9 3.1.6 Calculation..................................................................................................9 3.1.7 Precision...................................................................................................10 3.1.8 Repeatability.............................................................................................10 3.1.9 Reproducibility...........................................................................................10 3.1.10 Report.......................................................................................................10 3.2 Determination of 2,6-di-tert-butyl-para-cresol by IR spectrophotometry –

Method B...............................................................................................................10 3.2.1 Calibration.................................................................................................11 3.2.2 Sample test – New or used oil...................................................................11 3.2.3 Precision...................................................................................................11 3.2.4 Repeatability.............................................................................................11 3.2.5 Reproducibility...........................................................................................11 3.2.6 Report.......................................................................................................12 3.3 Determination of 2,6-di-tert-butyl-para-cresol (DBPC) by high performance liquid chromatography (HPLC)...............................................................................12 3.3.1 Introductory remark...................................................................................12 3.3.2 Materials and equipment...........................................................................12 3.3.3 Reagents and solvents..............................................................................12 3.3.4 Solid-liquid extraction................................................................................12 3.3.5 Analysis of the extract...............................................................................12 3.3.6 Calculation................................................................................................13 3.3.7 Precision...................................................................................................13 3.3.8 Repeatability.............................................................................................13 3.3.9 Reproducibility...........................................................................................13 3.3.10 Report.......................................................................................................13 3.4 Determination of phenolic inhibitors by gas chromatography – Mass spectrometry (GC-MS)...........................................................................................14 3.4.1 Summary of method..................................................................................14 3.4.2 Example of instrument parameters............................................................14 3.4.3 GC accessories.........................................................................................14 3.4.4 Calibration standard solutions...................................................................14 3.4.5 Internal standard solutions........................................................................14 3.4.6 Preparation of samples and calibration standards......................................15 3.4.7 Analytical procedure..................................................................................15 3.4.8 Calculation of results.................................................................................15 3.4.9 Precision...................................................................................................16 SIST EN 60666:2010

60666 © IEC:2010 – 3 –

3.4.10 Report.......................................................................................................16 Annex A (informative)

Detection of anti-oxidant additives by thin layer chromatography (TLC)....................................................................................................................................17 Annex B (informative)

Analysis method for determination of passivators in mineral oils by high performance liquid chromatography (HPLC).............................................................22 Annex C (informative)

Determination of pour point depressants by gel permeation chromatography....................................................................................................................30 Bibliography..........................................................................................................................32

Figure A.1 – Typical infrared spectrum to determine DBPC content......................................19 Figure A.2 – Typical infrared spectrum with 0,3 % DBPC......................................................20 Figure A.3 – Typical HPLC chromatogram to determine DBPC content.................................21 Figure B.1 – UV spectra of TTAA (in blue) and BTA (in red)..................................................26

Table B.1 – Examples of separation conditions.....................................................................26 Table B.2 – Repeatability......................................................................................................29 Table B.3 – Reproducibility...................................................................................................29

SIST EN 60666:2010
– 4 – 60666 © IEC:2010 INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
DETECTION AND DETERMINATION OF SPECIFIED
ADDITIVES IN MINERAL INSULATING OILS

FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60666 has been prepared by IEC technical committee 10: Fluids for electrotechnical applications. This second edition cancels and replaces the first edition, published in 1979, and constitutes a technical revision. The main changes with respect to the previous edition are listed below: – a change in the title from “Detection and determination of specified anti-oxidant additives in insulating oils” to “Detection and determination of specified additives in mineral insulating oils”. The previous edition only addressed the detection and determination of anti-oxidant additives, with particular regard to the DBPC, phenolic inhibitors and anthranilic acid; – more advanced methods for the determination of such anti-oxidant additives; – new Annexes B and C which provide methods for the determination of two additives different from the anti-oxidants. In particular, Annex B contains a method for the determination of the concentration in used and unused insulating mineral oils of passivators of the family of derivatives of benzotriazole. Annex C contains a method SIST EN 60666:2010

60666 © IEC:2010 – 5 –

for the qualitative identification of pour point depressants used in some commercially available paraffinic oils to improve their low temperature properties. The text of this standard is based on the following documents: FDIS Report on voting 10/803/FDIS 10/807/RVD

Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be

• reconfirmed, • withdrawn, • replaced by a revised edition, or • amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.

SIST EN 60666:2010

– 6 – 60666 © IEC:2010 INTRODUCTION General caution, health, safety and environmental protection This International Standard does not purport to address all the safety problems associated with its use. It is the responsibility of the user of the standard to establish appropriate health and safety practices and determine the applicability of regulatory limitations prior to use. The mineral oils which are the subject of this standard should be handled with due regard to personal hygiene. Direct contact with eyes may cause slight irritation. In the case of eye contact, irrigation with copious quantities of clean running water should be carried out and medical advice sought. Some of the tests specified in this standard involve the use of processes that could lead to a hazardous situation. Attention is drawn to the relevant standard for guidance. This standard involves mineral oils, chemicals and used sample containers. The disposal of these items should be carried out in accordance with current national legislation with regard to the impact on the environment. Every precaution should be taken to prevent the release into the environment of mineral oil. SIST EN 60666:2010

60666 © IEC:2010 – 7 –
DETECTION AND DETERMINATION OF SPECIFIED
ADDITIVES IN MINERAL INSULATING OILS

1 Scope The methods described in this International Standard concern the detection and determination of specified additives in unused and used mineral insulating oils.

The detection methods may be applied to assess whether or not a mineral insulating oil contains an additive as specified by the supplier. The determination methods are used for the quantitative determination of additives known to be present or previously detected by the appropriate detection method. 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. IEC 60296, Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear IEC 60475, Method of sampling liquid dielectrics ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results 3 Methods for the determination of anti-oxidant additives

3.1 Determination of phenolic and amine-based antioxidants by infrared (IR) spectrophotometry – Method A 3.1.1 Introductory remark This method determines the amount of 2,6-di-tert-butyl-para-cresol (DBPC) in unused and used mineral oils by measurement of the infrared absorption at the (O–H) stretching frequency of hindered phenols. It can also be used to determine the amount of 2,6-di-tert-butyl-phenol (DBP), but does not discriminate between them. The previous test method in the first edition of IEC 60666 described a procedure for the determination of specific antioxidants using IR techniques. This test method was satisfactory with new oils, where no oxidation by-products interfere with the antioxidant. However, this method was less satisfactory for used oils because oxidation by-products may modify the IR baseline, making the detection and quantification of the antioxidants difficult. To overcome this problem, a procedure for preparing a reference oil to be used as a baseline was described. Unfortunately, this procedure was difficult to perform, was time-consuming and did not ensure that the new baseline matched adequately that of the oil to be analysed, because the content of some components of the baseline oil and the analysed oil could be quite different. This new method describes a procedure for preparing reference, antioxidant-free oils by solid phase extraction (SPE) using silica gel. SIST EN 60666:2010

– 8 – 60666 © IEC:2010 3.1.2 Equipment, materials and solvents The following materials and reagents are used: – FT-IR or double-beam IR spectrometer having matched 1 mm sodium chloride cells (other materials are accepted provided they do not absorb IR radiation in the range 3 000 cm–1 to 3 800 cm–1); – 5 ml or 10 ml round-bottom flasks; – 5 ml or 10 ml beakers; – rotary evaporator; – silica gel cartridges (1 g or 2 g size is satisfactory); – n-pentane, analytical grade. 3.1.3 Sample preparation Into a beaker pour 1 g of the oil to be analysed for antioxidants, add 2 ml of analytical grade n-pentane and mix thoroughly. Filter the solution through a silica gel cartridge and recover the eluate in a round-bottom flask. Evaporate the n-pentane in the rotary evaporator.

Take a portion large enough to completely fill one IR cell of the oil that remains in the flask, fill one IR cell and put it on the reference beam of the spectrometer.

Fill a second IR cell with the oil to be analysed, which has not been submitted to the filtration process, and insert it on the analytical beam of the spectrometer. Record the IR spectrum as described in 3.1.5. 3.1.4 Calibration Prepare standard calibration solutions by dissolving weighed amounts of DBP or DBPC inhibitor in weighed amounts of antioxidant-free oil, prepared if necessary from the oil sample under test using the procedure in 3.1.3 (larger cartridges and amounts of oil will be necessary). The maximum life of the standard solution shall be six months. NOTE The calibration solutions may be prepared using an unused, inhibitor-free oil, provided the base oil is known to be the same as that under test. The oil should be tested by this procedure to ensure that no inhibitor is detectable. This alternative should not be used where the oil under test is heavily aged. Prepare at least five calibration solutions, covering the range 0,02 % to 0,50 % inhibitor by mass. Intermediate standards may be prepared if necessary when the approximate concentration of inhibitor in the sample is known. The absorbance (at 3 650 cm–1 for DBPC) of the calibration solutions is recorded as described in 3.1.5 and a calibration curve of absorbance against per cent inhibitor content produced. The calibration should be a straight line passing through the origin, according to the Beer-Lambert law of absorption:

KCDIIA==o10log
where SIST EN 60666:2010
60666 © IEC:2010 – 9 –
A is the absorbance; Io is the intensity of incident radiation; I

is the intensity of transmitted radiation; K is the extinction coefficient (constant for (O-H) of DBPC); C is the concentration of DBPC in percentage by mass; D is the cell path-length. Since K and D are constant for this determination, A is directly proportional to C. 3.1.5 Analysis 1. FT-IR instrument Check the equipment. The quality tests should be performed according to the manufacturer’s recommendations. 2. Double-beam IR spectrophotometer Prepare two matched liquid cells with path-lengths of 1 mm and sodium chloride windows. Fill both cells with the base oil and, with one cell in the sample beam and the other in the reference beam of the spectrometer and check that the IR spectrum between 3 800 cm–1 and 3 400 cm–1 is a straight line. Record the percentage transmittance (95 % – 100 %). Exchange the cells, i.e. transfer the cell in the sample beam to the reference beam and the cell in the reference beam to the sample beam. Repeat the spectrum acquisition and again ensure a straight line of approximately 95 % to 100 % transmittance is obtained. If the above conditions are not obtained, clean and polish or reject windows that have an absorbance in this region, and repeat the process until a matched pair of cells is obtained. These are then used for all the determinations. Test solutions 1. FT-IR instrument Fill the cell with the oil to be analysed and record the IR spectrum (A) at the appropriate wavelength. Repeat using the inhibitor-free reference oil and subtract this result from spectrum A to produce a spectrum with a linear baseline.

2. Double-beam IR spectrophotometer. Take a portion of the inhibitor-free reference oil in the flask, completely fill an IR cell and place it in the path of the reference beam of the spectrometer. Completely fill a second IR cell with the oil to be analysed and place it in the analytical beam of the spectrometer. Record the IR spectrum at the appropriate wavelength (in the range 3 500 cm–1

to 3700 cm–1 for DBPC). 3.1.6 Calculation Measurement of absorbance

1. FT-IR instrument Record the absorbance at the position of maximum peak height for the sample and for the inhibitor-free reference oil. SIST EN 60666:2010

– 10 – 60666 © IEC:2010 Subtract the reference oil spectrum from the sample oil spectrum and quantify the result by reference to calibration curves. 2. Double-beam IR spectrophotometer (see Figure A.1) Draw a base line as nearly as possible between 3 610 cm–1 and 3 680 cm–1 and record the percentage transmittance (Io) at which the base line crosses the 3 650 cm–1 line. Record the percentage transmittance at the tip of the peak at 3 650 cm–1 (I), then: IIo106503log A= The percentage DBPC equivalent to A3 650 is read from the calibration graph. Alternatively, automatic determination by the spectrometer may be used. 3.1.7 Precision The repeatability and reproducibility limits were established in accordance with the ISO 5725 series. 3.1.8 Repeatability The difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the values shown below by only 1 case in 20: – unused and used oils – 15 %, which can be calculated as (x1+x2)/2 × 0,15, where x1 and x2 are the results of the two replicates.

NOTE The repeatability values for oils only apply where the result is above 0,05 % DBPC in oil. 3.1.9 Reproducibility The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the values shown below by only 1 case in 20: – unused oils: for DBPC concentrations ≤ 0,1 %, the reproducibility is 0,02 % – absolute value; – unused oils: for DBPC concentrations > 0,1 %, the reproducibility is 45 %, which can be calculated as (x1+x2)/2 × 0,45, where x1 and x2 are the results of the two replicates;

– used oils – 45 %, which can be calculated as (x1+x2)/2 × 0,45, where x1 and x2 are the results of the two replicates.

NOTE The reproducibility values for used oils only apply where the result is above 0,05 % DBPC in oil.

3.1.10 Report Report the concentration of phenolic and amine-based antioxidants in % to the nearest 0,01 %. 3.2 Determination of 2,6-di-tert-butyl-para-cresol by IR spectrophotometry –

Method B For routine analysis of oils in service, a procedure, modifying 3.1 by the following changes, may be used. SIST EN 60666:2010

60666 © IEC:2010 – 11 –

3.2.1 Calibration Prepare one liquid cell with a path length of 0,2 mm and equipped with sodium chloride windows. Fill the cell with a mineral transformer oil without inhibitor (0 % inhibito

...

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