This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles

for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Designation: D4952 − 12 (Reapproved 2017)

Standard Test Method for

Qualitative Analysis for Active Sulfur Species in Fuels and
Solvents (Doctor Test)1
This standard is issued under the fixed designation D4952; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Scope 3. Summary of Test Method

1.1 This test method covers and is intended primarily for the 3.1 The sample is shaken with sodium plumbite solution, a
detection of mercaptans in motor fuel, kerosine, and similar small quantity of powdered sulfur added, and the mixture
petroleum products. This method may also provide information shaken again. The presence of mercaptans or hydrogen sulfide
on hydrogen sulfide and elemental sulfur that may be present in or both is indicated by discoloration of the sulfur floating at the
these sample types. oil-water interface or by discoloration of either of the phases.
1.2 The values stated in SI units are to be regarded as 4. Significance and Use
standard. No other units of measurement are included in this
standard. 4.1 Sulfur present as mercaptans or as hydrogen sulfide in
distillate fuels and solvents can attack many metallic and
1.3 This standard does not purport to address all of the
non-metallic materials in fuel and other distribution systems. A
safety concerns, if any, associated with its use. It is the
negative result in the doctor test ensures that the concentration
responsibility of the user of this standard to establish appro-
of these compounds is insufficient to cause such problems in
priate safety and health practices and determine the applica-
normal use.
bility of regulatory limitations prior to use.
1.4 This international standard was developed in accor- 5. Interferences
dance with internationally recognized principles on standard-
5.1 This test cannot be used if there are more than trace
ization established in the Decision on Principles for the
amounts of peroxides in the test sample. Peroxides can give a
Development of International Standards, Guides and Recom-
false positive results where mercaptans are at low level or not
mendations issued by the World Trade Organization Technical
even present.4
Barriers to Trade (TBT) Committee.
5.2 To check if peroxides are present in sufficient concen-
2. Referenced Documents tration to invalidate the test, shake 10 mL 6 0.5 mL of a fresh
2.1 ASTM Standards:2 portion of the sample with approximately 2 mL of the potas-
D1193 Specification for Reagent Water sium iodide solution, add two drops of the acetic acid solution,
D3227 Test Method for (Thiol Mercaptan) Sulfur in and two drops of the starch solution. If the aqueous layer turns
Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels a blue color, this confirms the presence of peroxides in
(Potentiometric Method) sufficient quantity to invalidate the test, and the test on this
2.2 Energy Institute Standards:3 sample should be discontinued. Proceed in accordance with
IP 30 Detection of Mercaptans, Hydrogen Sulfide, Elemental 5.4.
Sulfur, and Peroxides – Doctor Test Method 5.3 Alternatively, one may choose to perform a preliminary
Doctor Test. If a brown precipitate slowly forms, peroxide is
1
This test method is under the jurisdiction of ASTM Committee D02 on probably present. Proceed in accordance with 5.2 to confirm
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of presence of peroxides at sufficient quantity to invalidate the
Subcommittee D02.03 on Elemental Analysis.
Current edition approved May 1, 2017. Published June 2017. Originally test.
approved in 1989. Last previous edition approved in 2012 as D4952 – 12. DOI: 5.4 If interference from peroxides is confirmed, proceed to
10.1520/D4952-12R17.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or re-sample and retest. Ensure that sampling and handling
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM procedures for the new sample prevent UV light exposures as
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR, Brooks, B. T., “Sodium Plumbite or Doctor Test of Gasolines,” Industrial and
U.K., http://www.energyinst.org. Engineering Chemistry, Vol 16, No. 6, June 1924, p. 588.

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 D4952 − 12 (2017)
prescribed in 7.1. None of the normal refinery units or blending 7.2 It is preferable to collect the field samples using dark
processes producing spark ignition motor fuels are known to brown/amber bottles or metal cans, or if using clear glass
create peroxides under normal operating conditions. bottles to wrap them in foil or place in a light-tight box to
prevent UV light exposure.
6. Reagents and Materials
6.1 Purity of Reagents—Reagent grade chemicals shall be 7.3 The samples should be tested without delay upon receipt
used in all tests. Unless otherwise indicated, it is intended that in the laboratory before further chemical interactions take
all reagents conform to the specifications of the Committee on place.
Analytical Reagents of the American Chemical Society where
such specifications are available.5 Other grades may be used, 8. Procedure
provided it is first ascertained that the reagent is of sufficiently 8.1 Shake vigorously together in a test tube 10 mL of the
high purity to permit its use without lessening the accuracy of sample being tested and 5 mL of sodium plumbite solution for
the determination. about 15 s. Add a small amount of pure, sublimed flowers of
6.2 Purity of Water—Unless otherwise indicated, references sulfur so that practically all of it floats on the interface between
to water shall be understood to mean reagent water as defined the sample and the sodium plumbite solution after shaking.
by Types II or III of Specification D1193. Shake again for 15 s. Allow to settle and observe within 2 min.
NOTE 2—It is important to avoid adding more sulfur than will just cover
6.3 Doctor (Sodium Plumbite) Solution—(Warning— the interface. About 20 mg to 25 mg is the proper quantity, which can be
Poisonous and suspect carcinogen.) Dissolve approximately estimated with a little practice. If too much sulfur is added, any possible
125 g of sodium hydroxide (NaOH) in 1 L of reagent water. discoloration will be masked by the excess of sulfur.
Add 60 g of lead monoxide (PbO) and shake vigorously for
15 min, or let stand with occasional shakings for at least one 9. Interpretation of Results
day. Allow to settle and decant or siphon off the clear liquid. If 9.1 If the solution is discolored or if the yellow color of the
the solution does not settle clear, filter it through filter paper. sulfur film is noticeably masked, report the test as positive and
Keep the solution in a tightly sealed bottle and refilter before consider the sample as sour. If the sample remains unchanged
use if not perfectly clear. As an alternative, the lab may use a in color and the sulfur film is bright yellow or only slightly
commercially prepared solution that meets the requirements of discolored with gray or flecked with black, report the test as
the laboratory preparation. negative and consider the sample as sweet. If a brown
NOTE 1—Alternative volumes of the solution may be prepared or precipitate slowly forms, peroxide is probably present. Proceed
purchased, provided the final solution concentration is equivalent. in accordance with 5.2.
6.4 Sulfur—Pure, sublimed, stored in a closed container. NOTE 3—This examination must be made with extreme care. Some-
6.5 Potassium Iodide, approximately 100 g ⁄L Solution— times the sulfur layer will be only flecked with spots of gray or black, and
Dissolve approximately 1 g of potassium iodide in approxi- if there is any change in the color of either the sample or the Doctor
solution these spots will be difficult to detect.
mately 10 mL of water. Prepare fresh for each test.
NOTE 4—Strictly speaking, the test will not reject the sample on the
6.6 Acetic Acid, approximately 100 g ⁄L Solution—Add ap- basis of mercaptans only. The primary criterion for rejection is the
proximately 10 mL of glacial acetic acid to approximately appearance of the sulfur layer after shaking, and small amounts of
mercaptans will only discolor the sulfur. However, samples which contain
100 mL water.
mercaptans will also normally contain small amounts of sulfur in other
6.7 Starch Indicator, approximately 5 g ⁄L Indicator forms which will discolor the layers at the interface. The addition of pure,
Solution—Prepare fresh each time of testing. sublimed flowers of sulfur is required to indicate that a reaction of
mercaptan and sodium plumbite has occurred.
7. Sampling and Handling of Test Samples NOTE 5—When the sample contains appreciable amounts of hydrogen
sulfide, a heavy black precipitate may be formed during the initial shaking
7.1 Improper choice of clear glass sample bottles followed and before the addition of the sulfur. If such a precipitate is noted, the test
by exposure to sunlight or fluorescent lighting emitting UV may be stopped at that point and the sample reported as “Does not pass.”
wavelengths shorter than 550 nm in the laboratory can generate However, if this observation is at all doubtful, the test should be
peroxides in cracked gasolines as well as finished batches of continued. If the sample darkens before the addition of sulfur is made, this
indicates that the sample contains mercaptans and an excess of elemental
gasolines. Peroxides are generated in proportion to the head-
sulfur that is needed to drive the sample reaction with sodium plumbite.
space air volume and time of exposure.6 It has been reported
that peroxides can interfere with the Doctor Test—see 5.1. 9.1.1 The relationship between the appearance of the
sample and the type of sulfur is shown in Table 1.
5
Reagent Chemicals, American Chemical Society Specifications, American 9.2 If the doctor test is positive, mercaptan content may be
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory determined using Test Method D3227.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, 10. Precision and Bias
MD.
6
Supporting data (Jennings, R., and Kohler, D., “Sunlight and Air Exposure 10.1 No justifiable values of repeatability, reproducibility,
Effects on Octane Number or Cetane Number of Petroleum Product Samples,” April
or bias for this test method can be stated here because the test
2001) have been filed at ASTM International Headquarters and may be obtained by
requesting Research Report RR:D02-1502. Contact ASTM Customer Service at detects only the presence or absence of active sulfur species,
service@astm.org. such as hydrogen sulfide or mercaptan.

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 D4952 − 12 (2017)
TABLE 1 Relationship Between Sample and Sulfur
Appearance Type of Sulfur
Formation of a brown precipitate before addition of sulfur Peroxide is probably present; proceed in accordance with 5.2
Darkening of the sample before addition of sulfur Mercaptans and elemental sulfur present in sample
Black precipitate before addition of sulfur Appreciable amounts of hydrogen sulfide
Black color of sulfur after shaking Traces of hydrogen sulfide
Spots of discoloration in the sulfur layer, plus darkening of the sample Hydrogen sulfide absent; mercaptans or elemental sulfur, or both, present
Clear yellow Doctor solution; no discoloration of sulfur Hydrogen sulfide and elemental sulfur absent; traces of mercaptans present

11. Keywords
11.1 doctor test; hydrogen sulfide; kerosine; mercaptans;
motor fuel; sulfur

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