ASTM D7151-05

Standard Test Method for Determination of Elements in Insulating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)

SIGNIFICANCE AND USE
This test method covers the rapid determination of 12 elements in insulating oils, and it provides rapid screening of used oils for indications of wear. Test times approximate several minutes per test specimen, and detectability is in the 10-100 μg/kg range.
This test method can be used to monitor equipment condition and help to define when corrective action is needed. It can also be used to detect contamination such as from silicone fluids (via Silicon) or from dirt (via Silicon and Aluminum).
This test method can be used to indicate the efficiency of reclaiming used insulating oil.
SCOPE
1.1 This test method describes the determination of metals and contaminants in insulating oils by inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific elements are listed in Table 1. This test method is similar to Test Method D 5185, but differs in methodology, which results in the greater sensitivity required for insulating oil applications.
1.2 This test method uses oil-soluble metals for calibration and does not purport to quantitatively determine insoluble particulates. Analytical results are particle size dependent, and low results are obtained for particles larger than several micrometers.
1.3 This test method determines the dissolved metals (which may originate from overheating) and a portion of the particulate metals (which generally originate from a wear mechanism). While this ICP method detects nearly all particles less than several micrometers, the response of larger particles decreases with increasing particle size because larger particles are less likely to make it through the nebulizer and into the sample excitation zone.
1.4 This test method includes an option for filtering the oil sample for those users who wish to separately determine dissolved metals and particulate metals (and hence, total metals).
1.5 Elements present at concentrations above the upper limit of the calibration curves can be determined with additional, appropriate dilutions and with no degradation of precision.
1.6 The values stated in SI (metric) units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2005
• ICS: 29.040.10 - Insulating oils
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.03 - Analytical Tests

Relations

• Referred By: ASTM D117-22 - Standard Guide for Sampling, Test Methods, and Specifications for Electrical Insulating Liquids
• Effective Date: 01-May-2005

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7151 − 05
StandardTest Method for
Determination of Elements in Insulating Oils by Inductively
Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
This standard is issued under the fixed designation D7151; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and to determine the
1.1 This test method describes the determination of metals
applicability of regulatory limitations prior to use.
and contaminants in insulating oils by inductively coupled
plasma atomic emission spectrometry (ICP-AES). The specific
2. Referenced Documents
elements are listed in Table 1. This test method is similar to
2.1 ASTM Standards:
Test Method D5185, but differs in methodology, which results
C1109 Practice for Analysis of Aqueous Leachates from
in the greater sensitivity required for insulating oil applica-
Nuclear Waste Materials Using Inductively Coupled
tions.
Plasma-Atomic Emission Spectroscopy
1.2 This test method uses oil-soluble metals for calibration
D923 Practices for Sampling Electrical Insulating Liquids
and does not purport to quantitatively determine insoluble
D1744 Test Method for Water in Liquid Petroleum Products
particulates.Analytical results are particle size dependent, and
by Karl Fischer Reagent
low results are obtained for particles larger than several
D2864 Terminology Relating to Electrical Insulating Liq-
micrometers.
uids and Gases
D4307 Practice for Preparation of Liquid Blends for Use as
1.3 Thistestmethoddeterminesthedissolvedmetals(which
Analytical Standards
may originate from overheating) and a portion of the particu-
D5185 TestMethodforDeterminationofAdditiveElements,
late metals (which generally originate from a wear mecha-
Wear Metals, and Contaminants in Used Lubricating Oils
nism). While this ICP method detects nearly all particles less
and Determination of Selected Elements in Base Oils by
than several micrometers, the response of larger particles
Inductively Coupled Plasma Atomic Emission Spectrom-
decreases with increasing particle size because larger particles
etry (ICP-AES)
are less likely to make it through the nebulizer and into the
sample excitation zone.
3. Terminology
1.4 This test method includes an option for filtering the oil
3.1 Definitions for general terms may be found in Termi-
sample for those users who wish to separately determine
nology D2864.
dissolved metals and particulate metals (and hence, total
3.2 Definitions of Terms Specific to This Standard:
metals).
3.2.1 Babington-type nebulizer—a device that generates an
1.5 Elementspresentatconcentrationsabovetheupperlimit
aerosol by flowing a liquid over a surface that contains an
of the calibration curves can be determined with additional,
orifice from which gas flows at a high velocity.
appropriate dilutions and with no degradation of precision.
3.2.2 inductively-coupled plasma (ICP)—a high-
1.6 The values stated in SI (metric) units are to be regarded
temperature discharge generated by flowing an ionizable gas
as the standard. The inch-pound units given in parentheses are
through a magnetic field induced by a load coil that surrounds
for information only.
the tubes carrying the gas.
1.7 This standard does not purport to address all of the
3.2.3 linear response range—the elemental concentration
safety concerns, if any, associated with its use. It is the
range over which the calibration curve is a straight line, within
the precision of the test method.
This test method is under the jurisdiction of ASTM Committee D27 on
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
mitteeD27.03 on Analytical Tests. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved May 1, 2005. Published June 2005. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7151-05. the ASTM website.
Eisentraut, K. J., Newman, R. W., Saba, C. S., Kauffman, R. E., and Rhine, W. Withdrawn. The last approved version of this historical standard is referenced
E., Analytical Chemistry, Vol 56, 1984. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7151 − 05
A
TABLE 1 Elements Determined and Suggested Wavelengths
corrections, all concentrations must be within the previously
Element Wavelength, nm
established linear response range of each element listed in
Aluminum 308.22, 396.15, 309.27
Table 1.
Cadmium 226.50. 214.44
6.1.1 Spectral interferences can usually be avoided by
Cobalt 228.62 231.16
judicious choice of analytical wavelengths. When spectral
Copper 324.75
Iron 259.94, 238.20
interferences cannot be avoided, the necessary corrections
Lead 220.35
should be made using the computer software supplied by the
Nickel 231.60, 227.02, 221.65
ICP manufacturer or the empirical method given in Test
Scandium 361.38
Silicon 288.16, 251.61
Method C1109 or by Boumans.
Silver 328.07
6.1.2 Interference correction factors can be negative if
Sodium 589.59
off-peak background correction is employed for an element.A
Tin 189.99, 242.95
Tungsten 239.71
negative correction factor can result when an interfering line is
Yttrium 371.03
encountered at the background correction wavelength rather
Zinc 206.20, 202.55, 213.86, 334.58, 481.05
than at the peak wavelength.
A
These wavelengths are only suggested and do not represent all possible
choices.
6.2 Viscosity Effects—Differences in the viscosities of the
test specimen solutions and standard solutions can cause
differences in the uptake rates.These differences can adversely
affect the accuracy of the analysis. The effects can be reduced
3.2.4 profiling—a technique that determines the wavelength
for which the signal intensity measured for a particular analyte by using a peristaltic pump to deliver solutions to the nebulizer
or by the use of internal standardization, or both.
is a maximum.
3.2.5 wear metal—an element introduced into the oil by
6.3 Particulates—Theuseofaninternalstandardwillreveal
wear of oil-wetted parts.
when particulates cause flow problems. Use of a Babington-
type high-solids nebulizer helps to minimize plugging of the
3.2.6 dissolved metal—a metallic element in the oil which
nebulizer.Also, the specimen introduction system can limit the
will pass a 0.45 µ filter.
transport of particulates, and the plasma can incompletely
4. Summary of Test Method
atomize larger particulates, thereby causing low results.
4.1 A weighed portion of a thoroughly homogenized insu-
6.4 Solvent Moisture—Excessive moisture (>30 mg/kg) in
lating oil is diluted 2.5:1 by weight with kerosine or other
the kerosine used for dilution can cause poor recovery of some
suitable solvent. Standards are prepared in the same manner.
elements. This can be minimized by checking each lot of
Aninternalstandardisaddedtothesolutionstocompensatefor
kerosineformoisturecontentusingTestMethodD1744andby
variations in test specimen introduction efficiency. The solu-
analyzing all diluted standards and test specimens within 24 h
tions are introduced to the ICP instrument by a peristaltic
of preparation.
pump. If free aspiration is used, an internal standard must be
used. By comparing emission intensities of elements in the test 7. Apparatus
specimen with emission intensities measured with the stan-
7.1 Balance, top loading, with automatic tare, capable of
dards, the concentrations of elements in the test specimen are
weighing to 0.001g, capacity of at least 150 g. A balance with
calculated.
a capacity of at least 250 g is required if preparing the Internal
Standard according to 10.2.
5. Significance and Use
7.2 Inductively Coupled Plasma Atomic Emission
5.1 This test method covers the rapid determination of 12
Spectrometer—Either a sequential or simultaneous spectrom-
elements in insulating oils, and it provides rapid screening of
eter is suitable, if equipped with a quartz ICP torch and RF
used oils for indications of wear. Test times approximate
generator to form and maintain the plasma. Suggested wave-
several minutes per test specimen, and detectability is in the
lengths for the determination of the elements in insulating oil
10-100 µg/kg range.
are given in Table 1.
5.2 This test method can be used to monitor equipment
7.3 Nebulizer—Use the nebulizer recommended by the ICP
condition and help to define when corrective action is needed.
manufacturer.ABabington-type high-solids nebulizer may be
It can also be used to detect contamination such as from
useful if samples contain high solids. This type of nebulizer
silicone fluids (via Silicon) or from dirt (via Silicon and
reduces the possibility of clogging and minimizes aerosol
Aluminum).
particle effects.
5.3 Thistestmethodcanbeusedtoindicatetheefficiencyof
7.4 Peristaltic Pump—A peristaltic pump is required to
reclaiming used insulating oil.
provide a constant flow of solution. The pump tubing must be
able to withstand at least 6 h exposure to the dilution solvent.
6. Interferences
6.1 Spectral—Check all spectral interferences expected
from the elements listed in Table 1. Follow the ICP manufac-
Boumans, P. W .J. M., “Corrections for Spectral Interferences in Optical
turer’s operating guide to develop and apply correction factors
Emission Spectroscopy with Special Reference to the RF Inductively Coupled
to compensate for the interferences. To apply interference Plasma,” Spectrochimica Acta, 1976, Vol 318, pp. 147-152.
D7151 − 05
Viton tubing is typically used with hydrocarbon solvents, and 10. Internal Standardization
poly (vinyl chloride) tubing is typically used with methyl
10.1 Theinternalstandardprocedurerequiresthateverytest
isobutyl ketone.
specimen solution have the same concentration of an internal
7.5 Solvent Dispenser, (optional) — A solvent dispenser standard element that is not present in the original specimen.
calibrated to deliver the required weight of dilution solvent is Specimen to specimen changes in the emission intensity of the
very useful. This dispenser should have at least 1 % accuracy internal standard element can be used to correct for variations
inthetestspecimenintroductionefficiency,whichisdependent
and 0.1 % precision.
on the physical properties of the test specimen.
7.6 Internal Standard Dispenser , (Optional) —Adispenser
calibrated to deliver the required weight of internal standard 10.2 Internal Standard Solution —Weigh 25.0 6 0.1g of
solution is very useful. This dispenser should have at least 1 % 2000 µg/g scandium-in-oil (or cobalt- or yttrium-in-oil) stan-
accuracy and 0.1 % precision. dard into a 500-mL Erlenmeyer flask. Add kerosine to make a
total of 250 6 1 g. Mix this solution thoroughly and transfer to
7.7 Specimen Solution Containers , nominal 30 mL (1 oz.),
the reservoir for the internal standard container or dispenser.
glass or plastic vials, with screw caps or snap-top caps.
The concentration of the internal standard is not required to be
200 µg/g. However, the concentration of the internal standard
8. Reagents and Materials
element should be at least 100 times its detection limit.
8.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
11. Sampling and Sample Handling
all reagents conform to the specifications of the Committee on
11.1 Laboratory samples must be taken in accordance with
Analytical Reagents of the American Chemical Society where
6 the instructions in Practices D923.
such specifications are available. Other grades may be used,
11.2 It is important to homogenize the insulating oil in the
provided it is first ascertained that the reagent is of sufficiently
high purity to permit its use without introducing a significant sample container in order to obtain a representative test
specimen. Mix the insulating oil sample vigorously by invert-
source of error.
ing several times.
8.2 Base Oil—U.S.P.Whiteoiloranymineraloilthatisfree
of analytes and having a viscosity at room temperature as close 11.3 (Optional) To separately determine the dissolved met-
als and particulate metals, filter the oil sample through a 0.45
as possible to that of the samples to be analyzed.
µ filter. The particles on the filter paper must then be dissolved
8.3 Internal Standard—Oil-soluble scandium, cobalt, or
or digested by a technique not addressed by this test method.
yttrium is required when the internal standardization option is
selected.
12. Preparation of Test Specimens and Standards
8.4 Organometallic Standards—Multi-element standards,
12.1 All test specimens and standards must be mixed
containing3.0and10.0µg/gofeachelement,canbepurchased
thoroughly when diluted with kerosine and the internal stan-
or prepared from the individual concentrates. Refer to Practice
dard.Theymustallbepreparedfromthesamebatchofinternal
D4307 for a procedure for preparation of multicomponent
standard. All prepared solutions must be analyzed within 24 h
liquid blends. When preparing multi-element standards, an
of preparation.
ultrasonicbathisrecommendedtoensurethatcompletemixing
is achieved. It is highly recommended to purchase the stan- 12.2 Blank—Prepare a blank by adding 6.00 6 0.02 g base
oil, 1.00 6 0.01 g internal standard solution, and 8.00 6 0.03
dards because of the difficulty in preparing multi-element
standards. g kerosine to a 30-mL polyethylene or glass vial.
8.5 Dilution Solvent—Reagent grade kerosine is recom- 12.3 Working Standard—Prepare a calibration standard by
adding 6.00 6 0.02 g of the 10 µg/g multi-element standard,
mended as a dilution solvent.Another solvent (such as toluene
or xylene) may be used if it is free of all analytes and 1.00 6 0.01 g internal standard solution, and 8.00 6 0.03 g
completely dissolves all standards and samples. kerosine to a 30-mL polyethylene vial.
12.4 Check Standard—Prepare a QC check standard by
9. Hazards
adding 6.00 6 0.02 g of the 3.0 µg/g multi-element standard,
1.00 6 0.01 g internal standard solution, and 8.00 6 0.03 g
9.1 Kerosine is classified as a combustible liquid and must
kerosine. Other concentrations may be used for the check
be kept away from all ignition sources. If the ICPis allowed to
standard as long as they are not prepared from the 10 µg/g
operate unattended, equipment malfunctions could cause leak-
standard used for calibration.
age of kerosine.
12.5 Test Spe
...