IEC 60666:2010

IEC 60666 ®
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Detection and determination of specified additives in mineral insulating oils

Détection et dosage d’additifs spécifiques présents dans les huiles minérales
isolantes
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IEC 60666 ®
Edition 2.0 2010-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Detection 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
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 17.220.99, 29.040.10 ISBN 978-2-88910-244-0
– 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).
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

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

– 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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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

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.
– 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.

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.

– 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
–1
materials are accepted provided they do not absorb IR radiation in the range 3 000 cm
–1
to 3 800 cm );
– 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.
–1
The absorbance (at 3 650 cm 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:
I
o
A = log = KCD
I
where
60666 © IEC:2010 – 9 –
A is the absorbance;
I is the intensity of incident radiation;
o
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
–1
reference beam of the spectrometer and check that the IR spectrum between 3 800 cm and
–1
3 400 cm 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
–1 –1
IR spectrum at the appropriate wavelength (in the range 3 500 cm to 3700 cm 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.
– 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)
–1 –1
Draw a base line as nearly as possible between 3 610 cm and 3 680 cm and record the
–1
percentage transmittance (I ) at which the base line crosses the 3 650 cm line.
o
–1
Record the percentage transmittance at the tip of the peak at 3 650 cm (I), then:
I
o
A = log
3 650 10
I
The percentage DBPC equivalent to A is read from the calibration graph.
3 650
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 (x +x )/2 × 0,15, where x and
1 2 1
x 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 (x +x )/2 × 0,45, where x and x are the results of the two replicates;
1 2 1 2
– used oils – 45 %, which can be calculated as (x +x )/2 × 0,45, where x and x are the
1 2 1 2
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.
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 % inhibitor calibration solution)
and measure the IR spectrum.
Prepare at least 3 calibration solutions by adding DBPC inhibitor to achieve concentrations
between 0,1 % and 0,4 %.
Measure the IR spectrum of each calibration solution.
–1
Measure the heights of the inhibitor characteristic peaks at approximately 3 650 cm (see
Figure A.2).
Construct the calibration line: height of the peak as a percentage of transmission ~
concentration of DBPC as mass per cent in oil.
3.2.2 Sample test – New or used oil
Fill and drain the calibrated cell with the test oil 3 times.
Fill the cell and measure the IR spectrum.
Measure the height of the inhibitor characteristic peak as a percentage of transmission by
visual examination, in the same way as during the calibration procedure (see Figure A.2).
From the peak height, read the mass per cent of inhibitor in the oil sample under test using
the calibration line.
3.2.3 Precision
The repeatability and reproducibility limits for method B have been established to be the same
as for Method A.
3.2.4 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,
under normal and correct operation of the test method, exceed the values shown below by
only 1 case in 20:
– unused and used oils – 15 %.
NOTE The repeatability values for oils only apply where the result is above 0,05 % DBPC in oil.
3.2.5 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 %;
– used oils – 45 %.
NOTE The reproducibility values for used oils only apply where the result is above 0,05 % DBPC in oil.

– 12 – 60666 © IEC:2010
3.2.6 Report
Report the concentration of 2,6-di-tert-butyl-para-cresol (DBPC) in % to the nearest 0,01 %.
3.3 Determination of 2,6-di-tert-butyl-para-cresol (DBPC) by high performance liquid
chromatography (HPLC)
3.3.1 Introductory remark
This method determines the amount of 2,6-di-tert-butyl-para-cresol (DBPC) in unused and
used mineral oils by using high-performance liquid chromatography after sample preparation
using solid phase extraction technique.
3.3.2 Materials and equipment
The following materials and equipment are used:
– HPLC with a UV or a diode array UV detector;
– column – an example of column found satisfactory is C , 3,9 mm × 300 mm with 5 μm
coating thickness;
– pre-column – C , 5 μm;
– cartridges – 0,6 g to 1 g of silica;
– syringe filter – PTFE, maximum pore-size 0,5 μm (optional).
3.3.3 Reagents and solvents
Reagents shall comprise:
– methanol, HPLC grade;
– water, HPLC grade;
– n-pentane, HPLC grade.
3.3.4 Solid-liquid extraction
Weigh between 0,25 g and 0,5 g of oil sample to an accuracy of 0,01 g and dissolve it in
2,5 ml of n-pentane.
Rinse a new silica cartridge with 3 ml of n-pentane and discard the eluate. While the silica is
still wet, immediately pass the sample solution through the cartridge under a slight vacuum at
a maximum flow of 3 ml/min. Discard eluate.
Dry the cartridge by suction maintaining the vacuum for at least 10 min.
Stop the vacuum and elute the absorbed material with the same eluent to be used in the
chromatographic analysis.
Collect the first 5 ml in a 5 ml volumetric flask.
It may be advantageous to filter this solution through a syringe filter when transferring it to a
vial.
Transfer the eluate to a suitable vial for analysis by HPLC.
3.3.5 Analysis of the extract
The following conditions have been used:

60666 © IEC:2010 – 13 –
Mobile phase: Isocratic conditions
Eluent: Levels between 100 % methanol and methanol containing up to 40 % of
water (volume/volume) have been used.
Injection volume: 10 μl to 20 μl
Flow rate: 1 ml/min
Temperature: Isothermal at a temperature between 30 °C and 40 °C
Peak detection: About 276 nm to 278 nm with a retention time from about 3 min to 10 min
depending on elution conditions.
See Figure A.3 for an example of the chromatogram.
3.3.6 Calculation
Peak areas or peak heights of the sample are compared with calibration standards prepared
as in 3.1.4.
Plot a calibration curve of peak heights or peak areas against per cent inhibitor content. Read
on the calibration curve the percentage of DBPC in the sample.
3.3.7 Precision
The repeatability and reproducibility limits were established in accordance with the ISO 5725
series.
3.3.8 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,
under normal and correct operation of the test method, exceed the values shown below by
only 1 case in 20:
– unused and used oils – 15 %.
NOTE The repeatability values for oils only apply where the result is above 0,05 % DBPC in oil.
3.3.9 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, under 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 %;
– used oils – 45 %.
NOTE The reproducibility values for used oils only apply where the result is above 0,05 % DBPC in oil.
3.3.10 Report
Report the concentration of 2,6-di-tert-butyl-para-cresol (DBPC) in % to the nearest 0,01 %.

– 14 – 60666 © IEC:2010
3.4 Determination of phenolic inhibitors by gas chromatography – Mass spectrometry
(GC-MS)
3.4.1 Summary of method
Solvent containing an internal standard (the dimethyl ester of phthalic acid) is added to the oil
and to suitable calibration standards containing known amounts of 2,6-di-tert-butyl-phenol
(DBP) and of 2,6-di-tert-butyl-para-cresol (DBPC). Samples and standards are injected on the
GC (split injection) using mass spectrometric detection. Ion chromatograms of m/z = 191, 205
and 163 are used for the quantitation of DBP, DBPC and the internal standard, respectively.
This method is applicable to all mineral oils, including such used oils where the IR
spectrophotometric methods may suffer from interferences. Because of the high sensitivity of
this method it can also be used to ascertain the absence of inhibitor in uninhibited oils.
3.4.2 Example of instrument parameters
Split injection: 1 μl injected, with a split ratio of 200:1, at 275 °C
Carrier gas: Helium
Column head pressure: Constant flow mode, 1,2 ml/min
Column: 5 % phenyl- 95 % dimethyl-polysiloxane, 30 m, 0,25 mm,
0,25 μm or equivalent
GC temperature program: Start at 120 °C, hold for 1 min, increase 10 ºC/min until DBPC
has eluted, then increase at 50 °C/min to 300 °C. Hold at 300 °C
until the baseline is restored.
MS settings: EI+, 70 eV, trap temperature 150 °C, manifold temperature
80 °C, scan from m/z = 50 to 500, 3 scans per second to
establish retention times and identities (3.4.7). Start scanning at
3 min, stop scanning at 7 min or later.
3.4.3 GC accessories
Liner: Split injection liner
Syringe: 5 μl or 10 μl
Washing solvent: Toluene
3.4.4 Calibration standard solutions
Weigh about 0,28 g of DBPC and/or DBP into a 10 ml vial and record the weight to ± 0,001 g.
Add about 8 g mineral oil complying with IEC 60296 containing no inhibitor and record the
weight to ±0,01 g. Mix and stir with magnet until DBPC and DBP are dissolved, heating
slightly if required. Prepare a series of calibration standard solutions containing 0,02 %,
0,04 %, 0,1 %, 0,2 % and 0,4 % by weight of the calibration standard solution above, using
the same oil and mixing the solutions thoroughly.
The standards may be stored in darkness and cool conditions for maximum of 6 months.
3.4.5 Internal standard solutions
Solution 1: Weigh about 1,0 g dimethylphthalate into a 100 ml volumetric flask and record the
weight to ±0,001 g.
60666 © IEC:2010 – 15 –
Fill with toluene to 100 ml, record the weight and mix thoroughly.
Solution 2: Transfer 1 000 μl of internal standard solution 1 into a 100 ml volumetric flask, fill
up with toluene to 100 ml and mix thoroughly.
Do not store solution 2; it must be prepared for each set of analyses.
3.4.6 Preparation of samples and calibration standards
Add 100 μl of the sample(s) and of each of the series of calibration standard solutions into
separate vials, then add 1 000 μl of internal standard solution 2 and mix well. Analyse the
sample(s) and the calibration standard solutions.
3.4.7 Analytical procedure
Set up and tune the MS according to the manufacturer’s instructions.
Carry out a full scan for determination of the retention time and identification according to
target ions of DBPC, DBP and dimethylphthalate and a SIM method (selective ion monitoring)
for calibration and analysis.
NOTE For many mass spectrometers used as detectors, the ion chromatograms for quantitation can be extracted
from chromatographic runs with full MS scans and with sufficient signal-to-noise ratio. In such cases, it is not
necessary to run the MS in SIM mode. However, SIM might still be preferable in order to save on data storage
capacity.
3.4.8 Calculation of results
Integrate and note the area for the target ions on DBPC, DBP and dimethylphthalate and
calculate the RFx for each level of calibration standard:
RFx = [A /M ] / [A /M ]
IS IS C C
where
A is the area of the internal standard;
IS
M is the mass of the internal standard;
IS
A is the area of the compound;
C
M is the mass of the compound.
C
The RFx from calibration, internal standard areas and sample areas are used for calculation
of the inhibitor content. Use of a spreadsheet program is recommended.
C = [A /RFx] / [M /A ] × M
S S IS IS S
where
C is the content of the sample;
S
A is the area of the sample;
S
RFx is the reference factor from calibration;
M is the mass of the internal standard;
IS
A is the area of the internal standard;
IS
M is the mass of the sample.
S
– 16 – 60666 © IEC:2010
NOTE The method could be modified to include other sufficiently volatile phenolic inhibitors and also amine
inhibitors. Some diphenylamines have been used in the past in transformer oils and may possibly still be used by
some producers. However, BTA may decompose at the temperatures used in this method.
3.4.9 Precision
This method is capable of detecting anti-oxidants at trace levels or confirmation of absence of
these compounds and, while only a limited number of laboratories were involved in evaluation,
the precision is dependent principally on the dilution stage which can be easily evaluated by
each laboratory.
3.4.10 Report
Report the concentration of 2,6-di-tert-butyl-para-cresol (DBPC) in % to the nearest 0,01 %.

60666 © IEC:2010 – 17 –
Annex A
(informative)
Detection of anti-oxidant additives by thin layer chromatography (TLC)

NOTE This method may be used for screening or semi-quantitative purposes.
A.1 Summary of the method
The method described can be used to obtain a semi-quantitative estimation of DBPC when an
IR spectrophotometer, an HPLC or a GC-MS are not available. It gives a semi-quantitative
determination of the DBPC content, of new or used mineral oils in the range 0,01 % to 0,10 %
by mass, with differentiation between increments of 0,02 % by mass. It can also be used for
the range 0,10 % to 0,50 % by mass after suitable dilution of the oil.
A known amount of a mixture of oil and chloroform (1:1 volume) is applied into a silica gel
coated TLC aluminium sheet (sheet A). After the solvent has evaporated, sheet A is covered
with an identical sheet B, silica gel against silica gel.
Sheet A is then heated while sheet B, on which the inhibitor condenses, is simultaneously
cooled. Sheet B is then treated with phosphomolybdic acid and ammonia. The area of the
blue spot produced is proportional to the quantity of DBPC.
A.2 Reagents and solvents
The following reagents and solvents are used:
– phosphomolybdic acid 3,5 % in isopropanol, spray reagent for chromatography;
– chloroform, analytical grade;
– ammonia solution (25 % NH3, density at 20 °C: 0,91 g/cm );
– white oil or insulating oil, free of DBPC and other phenolic impurities according to the
method of detection.
A.3 Equipment
The following equipment shall be used:
– TLC aluminium sheets, silica gel coated, layer thickness 0,25 mm;
– 10 μl syringe;
– heating plate able to maintain a temperature of 125 °C ± 5 °C;
– device for measuring the temperature of the heating plate;
– metal box, water-tight and with a flat bottom, approximate dimensions 6 cm × 6 cm, height
7 cm to 10 cm;
– glass container with a tight cover, as used in TLC, approximate size 20 cm × 7 cm, height
20 cm (a conventional desiccator may also be used).

– 18 – 60666 © IEC:2010
A.4 Procedure
A.4.1 For DBPC concentrations of 0,01 % to 0,10 % by mass
Prepare standard solutions in white oil or in a DBPC-free insulating base oil, containing
0,01 %, 0,02 %, 0,05 % and 0,10 % by mass of DBPC.
Dilute the oil to be tested and the standard solutions with chloroform (one volume oil to one
volume chloroform).
Cut two TLC sheets (A and B) of size 6 cm × 6 cm. Divide these into areas of 1 cm by pencil
marks. Areas within 1 cm of the edge shall not be used.
Using the syringe, apply 10 μl of the oil-chloroform solution into the middle of one of the
1 cm areas on sheet A.
Proceed similarly with the standard solutions applying 10 μl in the middle of neighbouring
areas on sheet A.
Evaporate the chloroform by exposing the sheet in air at ambient temperature (approximately
2 min).
NOTE 1 It is important to remove completely the solvent as ascertained by elimination of the smell of chloroform.
Place on sheet A the second sheet B, silica gel against silica gel.
NOTE 2 With oils of higher aromatic content and particularly when using TLC plates of poor consistency, it has
been found that better differentiation at t
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