D2492

Designation: D 2492 – 90 (Reapproved 1998)
Standard Test Method for
Forms of Sulfur in Coal1
This standard is issued under the fixed designation D 2492; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method applies to the determination of sulfate
sulfur and pyritic sulfur in coal and calculates organic sulfur by
difference. This test method is not applicable to coke or other
carbonaceous materials. Monosulfides (pyrites and FeS2 are
disulfides) of iron and elements such as cadmium, lead,
vanadium, and zinc can be present in coal. In the range of 0 to
100 ppm, these monosulfides do not contribute significantly to
the total inorganic sulfide content.
1.2 The values stated in SI units are to be regarded as
standard.
1.3 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 appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D 1193 Specification for Reagent Water2
D 2013 Method of Preparing Coal Samples for Analysis3
D 3173 Test Method for Moisture in the Analysis Sample of
Coal and Coke3
D 3177 Test Methods for Total Sulfur in the Analysis
Sample of Coal and Coke3
D 3180 Practice for Calculating Coal and Coke Analyses
from As-Determined to Different Bases3
D 4239 Test Methods for Sulfur in the Analysis Sample of
Coal and Coke Using High-Temperature Tube Furnace
Combustion Methods3
E 832 Specification for Laboratory Filter Papers4
3. Summary of Test Method
3.1 Sulfate Sulfur:
3.1.1 Sulfate sulfur is extracted from the analysis sample
with dilute hydrochloric acid. The sulfate sulfur in the extract
is determined gravimetrically. Sulfates are soluble in hydro-
chloric acid, but pyritic and organic sulfur are not.
3.2 Pyritic Sulfur:
3.2.1 Pyritic sulfur is calculated as a stoichiometric combi-
nation with iron.
3.2.2 Methods:
3.2.2.1 Referee Method, which can be used in cases of
dispute or arbitration. The iron combined in the pyritic state is
extracted with dilute nitric acid from the coal residue remain-
ing after sulfate extraction (Note 1). The iron is determined by
atomic absorption techniques (Note 2).
NOTE 1—The sulfate extraction step also removes hydrochloric acid
soluble iron (nonpyritic iron) from the test specimen. A test specimen
separate from that used for the sulfate extraction could be used for the
nitric acid extraction of iron. In this case, both nonpyritic and pyritic iron
are extracted from the test specimen. Since there is evidence that for some
coals the extraction of nonpyritic iron by nitric acids falls short of the
amount extracted by hydrochloric acid,5,6
the use of a separate test
specimen for the nitric acid extraction of iron with subsequent correction
for the contribution of nonpyritic iron is not included in this test method.
NOTE 2—Round-robin testing of the coal samples used to generate data
for the precision statement in this test method indicates that plasma
emission techniques give results equivalent to those from atomic absorp-
tion analysis for the determination of iron. However, emission analysis is
highly susceptible to interferences from other analytes that may be
dissolved during the extraction of iron. Selection of a wavelength that is
free from interferences and linear over the range of iron anticipated for
emission analysis can require a detailed compositional analysis of the coal
mineral matter, thus limiting the practicality of this approach.
3.2.2.2 Alternative Method, which can be used in routine
practice or when the concerned parties agree on this test
method. The iron originally combined in the pyritic state can
be extracted with dilute hydrochloric acid from the ash
obtained by incinerating the coal residue remaining after
sulfate extraction. The iron is determined by atomic absorption
techniques (Note 2).
4. Significance and Use
4.1 This test method provides for a separation of coal-
associated sulfur into two commonly recognized forms: pyritic
and sulfate. Organic sulfur is calculated by difference. Results
obtained by the test method are used to serve a number of
interests, including the evaluation of coal preparation and
processing operations designed to reduce coal sulfur levels.
1
This test method is under the jurisdiction of ASTM Committee D-5 on Coal and
Coke and is the direct responsibility of Subcommittee D05.21 on Methods of
Analysis.
Current edition approved March 30, 1990. Published May 1990. Originally
published as D 2492 – 66 T. Last previous edition D 2492 – 84.
2
Annual Book of ASTM Standards, Vol 11.01.
3
4
5
Edwards, A. H., Daybell, G. N., and Pringle, W. J. S., “An Investigation into
Methods for the Determination of Forms of Sulfur in Coal,” Fuel, Vol 37, 1958, pp.
47–59.
6
Burns, M. S., “Determination of Pyritic Sulfur in Australian Coals,” Fuel, Vol
49, 1970, pp. 126–33.
1
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM

5. Analysis Sample
5.1 The analysis sample is that sample which has been
pulverized to pass No. 60 (250-µm) sieve as prepared in
accordance with Test Method D 2013. Moisture shall be
determined in accordance with Test Method D 3173 to permit
calculations to other than as-analyzed bases.
6. Sulfate Sulfur
6.1 Apparatus:
6.1.1 Balance, sensitive to 0.1 mg.
6.1.2 Crucibles, porcelain, platinum, alundum, or silica of
10- to 25-mL capacity for ignition of barium sulfate (BaSO4).
6.1.3 Hot Plate, electric or gas-heated with capability for
temperature control.
6.1.4 Muffle Furnace, electrically heated and capable of
regulating the temperature at 800 6 25°C for igniting BaSO4.
6.2 Reagents and Materials:
6.2.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit-
tee on Analytical Reagents of the American Chemical Society,
where such specifications are available.7
Other grades may be
used, provided that the reagent is of sufficiently high purity to
permit its use without lessening the accuracy of the determi-
nation.
6.2.2 Purity of Water—Unless otherwise indicated, refer-
ences to water shall be understood to mean reagent water
conforming to Specification D 1193, Type III.
6.2.3 Ammonium Hydroxide (14.9N, sp. gr. 0.90)—
concentrated aqueous ammonia.
6.2.4 Ammonium Hydroxide Solution 1.5N, (1 + 10)—Mix
one volume of concentrated aqueous ammonia with ten vol-
umes of water.
6.2.5 Barium Chloride Solution (100 g/L)—Dissolve 100 g
of barium chloride (BaCl2·2H2O) in water and dilute to 1 L.
6.2.6 Bromine Water (saturated)—Add an excess of bro-
mine to 1 L of water. (Caution—Store in a dark bottle and
keep in a hood.) (Solubility, 42 g/L.)
6.2.7 Ethanol, reagent grade, denatured.
6.2.8 Filter Paper—Unless otherwise indicated, references
to filter paper shall be understood to mean filter paper
conforming to Specification E 832.
6.2.9 Hydrochloric Acid, 12N (sp. gr. 1.19)—Concentrated
aqueous hydrochloric acid (HCl).
6.2.10 Hydrochloric Acid, 4.8N (2 + 3)—Mix two volumes
of concentrated aqueous hydrochloric acid (HCl, sp. gr. 1.19)
with three volumes of water.
6.2.11 Methyl Orange Indicator Solution, (0.02 g/100
mL)—Dissolve 0.02 g of methyl orange in 100 mL of hot
water.
6.2.12 Silver Nitrate Solution, (0.43 g/100 mL)—Dissolve
0.43 g of silver nitrate in 100 mL of water. Store in an amber
glass bottle.
6.3 Procedure:
6.3.1 Extraction—Weigh to the nearest 1 mg a 2- to 5-g test
specimen of analysis sample (Note 3) and transfer to a 250-mL
Erlenmeyer flask or beaker. Add 50-mL HCl (2 + 3) in small
increments while stirring to wet the coal thoroughly. A few
drops of ethanol added to the coal facilitates the wetting
process. Place on a hotplate and boil gently for 1⁄2 h. Carefully
filter the contents into a 400-mL beaker, using a Type II, Class
F filter paper. Wash the filter paper and contents with sufficient
small water washings to ensure the transfer of all HCl extract
to the beaker. Save the filter paper with extracted residue for
subsequent extraction of pyrites.
NOTE 3—It is practical to limit the sample weight to 2 g when the total
sulfur level is 2 % or above, to avoid handling an excessive amount of iron
in the pyritic extraction.
6.3.2 Add 5 mL of bromine water to the extract and boil for
at least 5 min to oxidize iron and expel excess bromide. Cool
to room temperature.
6.3.3 Precipitate the iron by slowly adding aqueous ammo-
nium hydroxide (sp. gr. 0.90) until a slight excess is present as
measured by pH indicator paper. Add 5 mL more with constant
stirring to coagulate the ferric hydroxide. Filter on a Type II,
Class E filter paper into a 400-mL or larger beaker. Wash the
filter paper several times with hot ammoniacal solution (6.2.4).
6.3.4 Precipitation—Add two or three drops of methyl
orange solution and neutralize the filtrate (6.3.3) by cautiously
adding aqueous HCl (sp. gr. 1.19) until the solution turns pink.
Add 1 mL in excess. Heat to boiling and, while stirring slowly,
add 10 mL of BaCl2 solution. Continue boiling gently for 10 to
15 min and allow to stand overnight at room temperature or for
4 h between 70 and 100°C covered with a watch glass. Filter
through a Type II, Class G filter paper and wash with
intermittent small washings of hot water until one drop of
silver nitrate solution produces no more than a slight opales-
cence when added to 8 to 10 mL of the filtrate.
6.3.5 Sulfate Blank—Prepare a sulfate blank following the
same procedure and using the same amounts of all reagents as
described in 6.3.1-6.3.4. Save the filter paper from 6.3.1 of the
blank test for the pyritic iron blank in 7.3.3.
6.3.6 Determination—Preignite crucibles (6.1.2) at 800 6
25°C for 30 min. Cool in a desiccator and weigh to the nearest
0.1 mg. Place the specimen filter paper from 6.3.4 and the
blank filter paper from 6.3.5 in separate preignited crucibles.
Fold the filter papers over loosely to allow free access of air.
Smoke the paper off gradually to prevent spattering. At no time
allow to burn with flame. After the filter paper is practically
consumed, raise the temperature to 800 6 25°C and maintain
for 1 h. Cool the crucibles in a desiccator until equilibrium is
reached. Weigh the crucibles and contents to the nearest 0.1
mg. Ignition is considered to be complete when the weight of
the crucible and contents do not change by more than 0.2 mg
after reheating at 800 6 25°C for 30 min.
6.4 Calculation:
6.4.1 Calculate the percentage of sulfate sulfur as follows:
Sulfate sulfur % 5 $@~S 2 Cs! 2 ~B 2 CB!# 3 13.735%/W (1)
where:
7
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD.
D 2492
2

S 5 weight of sample crucible plus ignited BaSO4 pre-
cipitate, g;
Cs 5 weight of sample crucible, g;
B 5 weight of blank crucible plus ignited sulfate blank, g,
CB 5 weight of blank crucible, g; and,
W 5 weight of test specimen used (6.3.1), g.
METHODS FOR PYRITIC SULFUR
7. Referee Method—Using Coal Residue Remaining
After Sulfate Extraction
7.1 Apparatus:
7.1.1 Atomic Absorption Spectrophotometer.
7.1.2 Balance, see 6.1.1.
7.1.3 Hot Plate, see 6.1.3.
7.2.1 Purity of Reagents, see 6.2.1.
7.2.2 Purity of Water, see 6.2.2.
7.2.3 Filter Paper, see 6.2.8.
7.2.4 Hydrochloric Acid, 12N (sp. gr. 1.19)—see 6.2.9.
7.2.5 Hydrochloric Acid, 4.8N (2 + 3)—see 6.2.10.
7.2.6 Hydrochloric Acid, 0.24N, (1 + 49)—Mix 1 volume of
concentrated aqueous hydrochloric acid (HCl, sp. gr. 1.19) with
49 volumes of water.
7.2.7 Iron Standard, (400 ppm)—Weigh 0.4000 g 6 0.1 mg
of clean, pure iron wire or 0.5179 g 6 0.1 mg of high purity
iron (III) oxide into a 250-mL beaker. Add 50 mL of HCl
(7.2.5) and cover with a watch glass. Heat until the solution
boils gently for 1⁄2h or until no visible particles are left.
Quantitatively transfer the contents to a 1000-mL volumetric
flask and dilute to the mark with water. Alternatively, an
appropriate commercially available iron standard with an
equivalent acid concentration may be used.
7.2.8 Lanthanum Solution—Dissolve 175 g of lanthanum
chloride (LaCl3) or 265 g of hydrated lanthanum chloride
(LaCl3·7H2O) in water and dilute to 1 L. Alternatively, slurry
115 g of lanthanum oxide (La2O3) in 200 mL of water. Slowly
add 200 mL of concentrated aqueous hydrochloric acid (HCl,
sp. gr. 1.19), while mixing continually with the flask under cold
water, to dissolve the oxide. Dilute to 1 L.
7.2.9 Nitric Acid, 2N (1 + 7)—Mix one volume of concen-
trated aqueous nitric acid (HNO3, sp. gr. 1.42) with seven
volumes of water.
7.3 Procedure:
7.3.1 Extraction—Transfer the filter paper and extracted
residue from 6.3.1 to a 250-mL Erlenmeyer flask. Slowly add
50 mL of HNO3 (1 + 7) with stirring, to ensure complete
wetting and to help disintegrate the filter paper. Either boil
gently for 30 min or let stand overnight at room temperature.
Filter the flask and contents through a Type II, Class F filter
paper into a 400- to 600-mL beaker. Wash the residue at least
six times with small increments of water, keeping the total
volume of filtrate between 100 and 200 mL.
7.3.2 Preparation of Test Solution—Transfer the filtrate
from 7.3.1 to a 200-mL volumetric flask and dilute to volume
with water. Transfer a 10-mL aliquot of the diluted filtrate to a
100-mL volumetric flask. Add 10 mL of lanthanum solution
(7.2.8) and dilute to volume with HCl (1 + 49). This is the test
solution.
7.3.3 Preparation of Blank Test—Perform a parallel blank
test following the same procedure and reagents as described in
7.3.1 and 7.3.2 using the filter paper generated in 6.3.1 of the
sulfate blank test.
7.3.4 Determination of Iron by Atomic Absorption:
7.3.4.1 Spectrometric Conditions—Suitable conditions for
the determination of iron are as follows:
Wavelength 248.3 nm (0- to 5-ppm Fe)
Wavelength 372.0 nm (5- to 100-ppm Fe)
Wavelength 344.1 nm (>100-ppm Fe)
Flame: air/acetylene (lean)
7.3.4.2 Preparation of Calibration Solutions—Prepare a set
of calibration solutions to cover the expected range of concen-
tration in the test solution (7.3.2) by transferring appropriate
volumes of the iron standard solution (7.2.7) to a series of
100-mL volumetric flasks. Add 10 mL of lanthanum solution
(7.2.8). Dilute to the mark with HCl (1 + 49).
7.3.4.3 Calibration—Measure the absorbance of the cali-
bration solutions (7.3.4.2) using the atomic absorption spec-
trometer (7.1.1) using the appropriate conditions (7.3.4.1). By
regression analysis, construct a calibration curve (Note 4) of
absorbance against iron content for the calibration solutions
(7.3.4.2).
NOTE 4—For guidance on appropriate procedures for construction of
calibration curve, see pages 72 to 78 of Wernimont.8
7.3.4.4 Determination of Iron in the Test Solution and Blank
Test—Measure the absorbance of the test solution (7.3.2) and
the blank test (7.3.3) using the same conditions as used for the
calibration solutions (7.3.4.3). Read the concentration of the
test solution and the blank test by reference to the calibration
curve (7.3.4.3).
7.4 Calculation:
7.4.1 Calculate the percentage of pyritic sulfur as follows:
Pyritic sulfur, % 5 @F 3 A 3 V 3 C 3 P 3 ~T 2 B!#/W (2)
where:
F 5 1.148, dimensionless, the stoichiometric ratio of sulfur
to iron in iron disulfide (FeS2);
A 5 20, dimensionless, the aliquot factor indicating pro-
portion of filtrate used to prepare the test solution in
7.3.2;
V 5 100 mL, the volume of the test solution from 7.3.2;
C 5 10−6
g/µg conversion factor from micrograms to
grams;
P 5 100, dimensionless, conversion factor from weight
fraction to percentage by weight;
T 5 concentration of iron in the test solution, µg/mL;
B 5 concentration of iron in the blank test, µg/mL; and
W 5 weight of the test specimen (6.3.1), g.
8. Alternative Method—Using Ash Remaining After
Incineration of Residue from Sulfate Extraction
8.1 Apparatus:
8.1.1 Atomic Absorption Spectrophotometer, see 7.1.1.
8.1.2 Balance, see 6.1.1.
8
Wernimont, G. T., “Use of Statistics to Develop and Evaluate Analytical
Methods,” AOAC, Arlington, VA, 1987.
D 2492
3

8.1.3 Crucibles, porcelain, platinum, alundum, or silica of
10- to 25-mL capacity for incineration of coal residue remain-
ing after sulfate extraction.
8.1.4 Hot Plate, see 6.1.3.
8.1.5 Muffle Furnace, electrically heated and capable of
regulating the temperature at 700 to 750°C for incineration of
the coal residue remaining after sulfate extraction.
8.1.6 Tongs, platinum tipped or tips covered with rubber
policemen.
8.2.1 Purity of Reagents—see 6.2.1.
8.2.2 Purity of Water—see 6.2.2.
8.2.3 Filter Paper—see 6.2.8.
8.2.4 Hydrochloric Acid, 12N (sp. gr. 1.19)—see 6.2.9.
8.2.7 Iron Standard, (400 ppm)—see 7.2.7.
8.2.8 Lanthanum Solution—see 7.2.8.
8.3 Procedure:
8.3.1 Ashing of Residue from Sulfate Extraction—Transfer
the filter paper and extracted residue from 6.3.1 to a crucible
(8.1.3). Place the crucible in a cold muffle furnace and heat
gradually at such a rate that the temperature reaches 95°C in 45
min. Hold at this temperature for 90 min (Note 5). Char the
coal without ignition (Note 6). Once charring is complete,
continue heating so that the temperature reaches 700 to 750°C
in another hour. Continue incineration for an additional 6 h or
until no unburned particles are observed. Remove the crucible
from the muffle furnace and allow to cool to room temperature.
NOTE 5—This hold step should prevent spattering of sample onto the
sides of the crucible. Material deposited on the sides of the crucible is not
dissolved by boiling in HCl.
NOTE 6—Residues from coals of anthracitic and bituminous rank, in the
majority of cases, can be charred without ignition by gradually raising the
temperature from 300 to 450°C over a period of 2 h. Residues from coals
of subbituminous and lignite rank, in the majority of cases, can be charred
without ignition by gradually raising the temperature from 200 to 450°C
over a period of 4 h. Ignition of the coal residue can result in localized
temperatures in the sample, which could result in the production of oxides
of iron such as Fe3O4, which would not dissolve in the digestion step
outlined in 8.3.2.
8.3.2 Digestion of Ash—Place the crucible on its side in a
250-mL beaker which contains 100 mL of HCl (2 + 3). Place
a stirring bar in the beaker and cover with a watch glass.
Transfer the beaker to a hot plate and heat to just below the
boiling point; maintain at this temperature for 1⁄2 h with gentle
stirring. Carefully remove the crucible with a set of tongs.
Immerse only tips of the tongs in the solution. Rinse the
crucible and tips of the tongs with deionized water, collecting
the washings in the beaker. Continue to heat the solution while
stirring until it boils moderately (Note 7) for a period of 1⁄2 h or
until no reddish particles are visible in the residue.
NOTE 7—If the solution does not reach the boiling point, the hydro-
chloric acid-soluble iron compounds may not dissolve completely.
8.3.3 Preparation of Test Solution—Filter the contents of
the beaker through a Type II, Class F filter paper into a 200-mL
volumetric flask. Wash the beaker, filter paper, and residue with
sufficient small water washings to ensure transfer of all the
hydrochloric acid extract to the volumetric flask. Dilute to the
mark with deionized water. Transfer a 10-mL aliquot of the
diluted filtrate to a 100-mL volumetric flask. Add 10 mL of
lanthanum solution (7.2.8, Note 8). Dilute to volume with HCl
(1 + 49). This is the test solution.
NOTE 8—Experimental tests have shown that addition of the lanthanum
solution to the hydrochloric acid extract from digestion of the ash is not
essential to the determination of pyritic iron. However, to permit com-
parison of results from the referee and alternative method on a common
calibration basis, the addition of the lanthanum solution is included.
8.3.4 Preparation of Blank Test—Perform a parallel blank
test following the same procedure and reagents as described in
8.3.1-8.3.3, using the filter paper generated in 6.3.1 of the
sulfate blank test.
8.3.5 Determination of Iron by Atomic Absorption—
Determine the iron content of the test solution (8.3.3) and blank
test (8.3.4) as described in 7.3.4.1-7.3.4.4.
8.4 Calculation—Calculate the percent by weight of pyritic
sulfur in the sample, according to Eq 2.
9. Organic Sulfur
9.1 When analyses are expressed on a common moisture
basis, the percentage of organic sulfur is obtained by subtract-
ing the sum of the percentages of sulfate sulfur and pyritic
sulfur from the percentage of total sulfur as determined by Test
Methods D 3177 or D 4239.
10. Report
10.1 Report the following information:
10.1.1 Date of the test,
10.1.2 Identification of sample tested,
10.1.3 Basis for expression of results,
10.1.4 The method used in the case of pyritic sulfur,
10.1.5 The instrumental conditions used for the determina-
tion of pyritic iron,
10.1.6 A note to the effect that organic sulfur is calculated
by difference,
10.1.7 Any unusual features noted during the determina-
tions, and
10.1.8 Any operation not included in the standard or re-
garded as optional.
11. Precision and Bias 9
11.1 Where applicable, these test methods are calibrated
with solutions that are similar in content of the constituent of
interest to that of the test solution.
11.2 Precision Statement for Sulfate Sulfur:
11.2.1 Repeatability—Results of consecutive determina-
tions performed on the same sample, in the same laboratory, by
the same operator, and using the same apparatus should not
differ by more than the following:
Sulfate Sulfur 0.02 % by weight (3)
11.2.2 Reproducibility—The means of the results of dupli-
cate determinations carried out by different laboratories, on
representative samples taken from the same bulk sample after
the last stage of reduction should not differ by more than the
following:
9
Supporting data are available from ASTM Headquarters. Request RR:D5-1009.
D 2492
4

Sulfate Sulfur 0.04 % by weight (4)
11.3 Precision Statement for Pyritic Sulfur:
11.3.1 Referee Method Using Coal Residue Remaining After
Sulfate Extraction—The relative precision of this test method
for the estimation of pyritic sulfur covers the concentration
range of 0.10 to 12.00 weight % on a dry basis.
11.3.1.1 Repeatability—The difference in absolute value
between two consecutive test results, calculated to a dry basis
(Practice D 3180), performed on two separate test specimens of
the same test unit of No. 60 (250-µm) coal sample in the same
laboratory, by the same operator, and using the same apparatus
should not exceed the repeatability interval I(r) by more than
5 % of such paired values (95 % confidence level). When such
a difference is found to exceed the repeatability interval, there
is reason to question one or both of the test results. The
repeatability interval is calculated using the following equa-
tion:
I~r! 5 0.09 X 1 0.08 (5)
where X is the average of the two test results.
NOTE 9—Eq 3 applies to the relative spread of a measurement that is
expressed as weight percent on a dry basis and is derived from statistical
evaluation of round robin results.
Example—Two separate test specimens yielded test results for pyritic
sulfur of 2.6 and 2.8 %. The average of the two test results is 2.7 %. The
calculated repeatability interval I(r) of 0.3 %. The difference between the
two test results is 0.2 % and does not exceed the I(r) of 0.3 %. Therefore,
these two test results are acceptable at the 95 % confidence level.
11.3.1.2 Reproducibility—The difference in absolute value
between test results, calculated to a dry basis (Practice
D 3180), carried out in different laboratories on representative
test units of No. 60 (250-µm) coal sample prepared from the
same bulk sample after the last stage of reduction, should not
exceed the reproducibility interval I(R) by more than 5 % of
such paired values (95 % confidence level). When such a
difference is found to exceed the reproducibility interval, there
is reason to question the test result from one or both of the
laboratories. The reproducibility interval is calculated using the
following equation:
I~R! 5 0.27 X 1 0.15 (6)
where X is the average of the test results from the two
separate laboratories.
evaluation of round robin results. For the purposes of the reproducibility
statement given in this standard, a laboratory test result consists of the
average of results conducted on two separate test specimens in the same
laboratory, which meet the repeatability requirements stipulated in
11.3.1.1.
Example—Two separate test specimens in one laboratory yielded test
results for pyritic sulfur that met the precision requirements for repeat-
ability and gave an average 8.0 % pyritic sulfur as the laboratory test
result. A laboratory test result of 10.0 % that met repeatability precision
requirements was obtained in another laboratory. The average of the two
laboratory test results is 9.0 %. The calculated reproducibility interval I(R)
is 2.6 %. The difference between the two test results is 2.0 % and does not
exceed the I(R) of 2.6 %. Therefore, these two laboratory test results are
acceptable at the 95 % confidence level.
11.3.2 Alternative Method—Using Ash Remaining After In-
cineration of Residue from Sulfate Extraction—The relative
precision of this test method for the determination of pyritic
sulfur covers the concentration range of 0.10 to 12.00 weight %
on a dry basis.
11.3.2.1 Repeatability—The difference in absolute value
between two consecutive test results, calculated to a dry basis
(Practice D 3180), performed on two separate test specimens of
the same test unit of No. 60 (250-µm) coal sample in the same
laboratory, by the same operator, and using the same apparatus,
should not exceed the repeatability interval I(r) by more than
5 % of such paired values (95 % confidence level). When such
a difference is found to exceed the repeatability interval, there
repeatability interval is calculated using the following equa-
tion:
I~r! 5 0.11 X 1 0.06 (7)
where X is the average of the two test results.
evaluation of round robin results.
Example—Two separate test specimens yielded test results for pyritic
sulfur of 4.4 and 4.8 %. The average of the two test results is 4.6 %. The
calculated repeatability interval I(r) is 0.6 %. The difference between the
two test results is 0.2 % and does not exceed the I(r) of 0.6 %. Therefore,
these two test results are acceptable at the 95 % confidence level.
11.3.2.2 Reproducibility—The difference in absolute value
between test results, calculated to a dry basis (Practice
D 3180), performed in different laboratories on representative
test units of No. 60 (250-µm) coal sample prepared from the
same bulk sample after the last stage of reduction, should not
exceed the reproducibility interval I(R) by more than 5 % of
such paired values (95 % confidence level). When such a
difference is found to exceed the reproducibility interval, there
reproducibility interval is calculated using the following equa-
tion:
I~R! 5 0.19 X 1 0.07 (8)
where X is the average of the test results from the two
separate laboratories.
evaluation of round robin results. For the purposes of the reproducibility
statement given in this standard, a laboratory test result consists of the
average of results conducted on two separate test specimens in the same
laboratory, that meet the repeatability requirements stipulated in 11.3.2.1.
Example—Two separate test specimens in one laboratory yielded test
results for pyritic sulfur that met the precision requirements for repeat-
ability and gave an average 5.0 % pyritic sulfur as the laboratory test
result. A laboratory test result of 7.0 % that met repeatability precision
requirements was obtained in another laboratory. The average of the two
laboratory test results is 6.0 %. The calculated reproducibility interval I(R)
is 1.2 %. The difference between the two test results is 2.0 % and exceeds
the I(R) of 1.2 %. Therefore, either one or both of the laboratory test
results are suspect at the 95 % confidence level.
11.4 Bias 9
11.4.1 Absolute Bias—Since no suitable certified reference
materials for sulphate or pyritic sulfur are currently available,
no statement on absolute bias can be made for this test method.
11.4.2 Relative Bias—Based on a matched paired compari-
son at the 95 % confidence level,8
the alternative method for
D 2492
5

the determination of pyritic sulfur was found to be biased high
with respect to the referee method, with the minimum detect-
able bias being 0.06 %.
The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connection
with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such
patent rights, and the risk of infringement of such rights, are entirely their own responsibility.
This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and
if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards
and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your
views known to the ASTM Committee on Standards, 100 Barr Harbor Drive, West Conshohocken, PA 19428.
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