ASTM E544-99(2004)
(Practice)Standard Practices for Referencing Suprathreshold Odor Intensity
Standard Practices for Referencing Suprathreshold Odor Intensity
ABSTRACT
These practices are designed to outline two preferred procedures for referencing the odor intensities of any odorous material in the suprathreshold region on the ASTM Odor Intensity Referencing Scale. The method by which the reference odorant vapors are to be presented for evaluation by a panel of at least eight independent judgments is specified, but the manner by which the test sample is presented will depend on the nature of the sample, and is not defined herein. The methods, where a geometric progression scale with a ratio of 2 is recommended, are generally done by comparing the odor intensity of the sample to the odor intensities of a series of concentrations of the reference odorant 1-butanol (n-butanol). The two procedures differ in the method by which the diluted 1-butanol vapors are prepared. In Procedure A (dynamic scale method), a dynamic-dilution apparatus is used. This is equipped with a series of sniffing ports from which constant concentrations of 1-butanol emerge at constant volumetric flow rates in air. In Procedure B (static-scale method), a series of Erlenmeyer flasks containing known concentrations of 1-butanol in water is used.
SCOPE
1.1 These practices are designed to outline a preferred means for referencing the odor intensities of a material in the suprathreshold region.
1.2 The general objective is to reference the odor intensity rather than other odor properties of a sample.
1.3 These practices are designed to reference the odor intensity on the ASTM Odor Intensity Referencing Scale of any odorous material. This is done by a comparison of the odor intensity of the sample to the odor intensities of a series of concentrations of the reference odorant, which is 1-butanol (n-butanol).
1.4 The method by which the reference odorant vapors are to be presented for evaluation by the panelists is specified. The manner by which the test sample is presented will depend on the nature of the sample, and is not defined herein.
1.5 Test sample presentation should be consistent with good standard practice () and should be explicitly documented in the test report.
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 determine the applicability of regulatory limitations prior to use. See for specific safety data.
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Designation:E544–99(Reapproved 2004)
Standard Practices for
Referencing Suprathreshold Odor Intensity
This standard is issued under the fixed designation E544; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 These practices are designed to outline a preferred 3.1 ASTM odor intensity referencing scale—series of
means for referencing the odor intensities of a material in the 1-butanol dilutions used to establish which concentration
suprathreshold region. exhibits an odor intensity matching that of the sample.
1.2 The general objective is to reference the odor intensity 3.2 concentration—series of concentrations of 1-butanol in
rather than other odor properties of a sample. odorless air, nitrogen, or the water diluent, made to specific
1.3 These practices are designed to reference the odor reference dilutions which serve as the reference scale, volume
intensity on the ASTM Odor Intensity Referencing Scale of basis, of 1-butanol diluted air or in water. In the latter case, the
anyodorousmaterial.Thisisdonebyacomparisonoftheodor temperature of the solution during the test should be reported.
intensity of the sample to the odor intensities of a series of 3.3 dynamic scale—referencescaleinwhichvapordilutions
concentrations of the reference odorant, which is 1-butanol arepreparedbycontinuousmixingofvaporsof1-butanolwith
(n-butanol). anodorlessgas,suchasair,toyieldconstantdilutionsofvapor
1.4 The method by which the reference odorant vapors are in the gas.
tobepresentedforevaluationbythepanelistsisspecified.The 3.4 panelists—individuals who compare the odor intensity
manner by which the test sample is presented will depend on of the sample to the reference scale. These individuals should
the nature of the sample, and is not defined herein. be able to do this with a consistency described in 5.5.
1.5 Testsamplepresentationshouldbeconsistentwithgood 3.5 perceived (sensory) odor intensity—intensity of an odor
standard practice (1) and should be explicitly documented in sensation which is independent of the knowledge of the
the test report. odorant concentration.
1.6 This standard does not purport to address all of the 3.6 sample—material in any form exhibiting an odor that
safety concerns, if any, associated with its use. It is the needs to be measured.
responsibility of the user of this standard to establish appro- 3.7 static scale—reference scale in which dilutions of
priate safety and health practices and determine the applica- 1-butanolinwaterarepreparedinflasksandpresentedforodor
bility of regulatory limitations prior to use. SeeAnnexA1 for intensity comparison from the flasks.
specific safety data. 3.8 suprathreshold odor intensity—perceived (sensory) in-
tensity of the odor in that intensity region in which the odor is
2. Referenced Documents
clearly experienced.
2.1 ASTM Standards:
4. Summary of Practice
D1292 Test Method for Odor in Water
4.1 Thereferenceodorantusedtogenerateanodorintensity
scale is 1-butanol (n-butanol). The reasons for its selection are
ThesepracticesareunderthejurisdictionofASTMCommitteeE18onSensory
summarized in Appendix X1. A geometric progression scale
Evaluation of Materials and Products and are the direct responsibility of Subcom-
mittee E18.04 on Fundamentals of Sensory. witharatioof2isrecommended,thatis,ascaleinwhicheach
Current edition approved Dec. 1, 2004. Published December 2004. Originally
reference dilution differs in its 1-butanol concentration from
approved in 1975. Last previous edition approved in 1999 as E544–99. DOI:
the preceding dilution by a factor of 2.
10.1520/E0544-99R04.
4.2 Two procedures, A and B, are described in these
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
these recommended practices.
recommended practices. They differ in the method by which
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the diluted 1-butanol vapors are prepared.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E544–99 (2004)
NOTE 1—The relationships between the odor intensity of 1-butanol
absorption of water which will lower the vapor pressure of
concentrations in air and in water have not been evaluated. Translation of
1-butanol, and will result in a lower odorant concentration at
Procedure B data to the numerical values of Procedure A is not possible
the sniffing ports.
at this time.
5.2.3 Anadequateconcentrationrangeformostapplications
4.2.1 In Procedure A, hereafter referred to as the dynamic
is between 5 and 2000 ppm of 1-butanol in air. Above 2000
scale method, a dynamic-dilution apparatus is used. This is
ppm, the odor intensity is too strong for accurate judgment.
equipped with a series of sniffing ports from which constant
Below 5 ppm, the odor is too close to the threshold limit for
concentrationsof1-butanolemergeatconstantvolumetricflow
panelists to make accurate judgments.
rates in air.
5.2.4 The temperature of 1-butanol in the saturation tube
4.2.2 InProcedureB,hereafterreferredtoasthestatic-scale
shouldbenotedatthestartandkeptconstantduringthetest.It
method, a series of Erlenmeyer flasks containing known
should be within the range of comfortable room temperatures.
concentrations of 1-butanol in water is used.
5.2.5 The rate of dynamic delivery of air carrying diluted
4.3 The odor of the sample is matched, ignoring differences
1-butanol vapor from sniffing ports should be 160 6 20
in odor quality, against the odor intensity reference scale of
mL/min from a port with a cross-section of 400 to 500 mm ,
1-butanol by a panel yielding at least eight independent
resulting in a nominal linear flow rate of 300 mm/min. A rate
judgments. Panelists report that point in the reference scale
that is too slow allows the stimulus to be diluted with
which, in their opinion, matches the odor intensity of the
increasing amounts of room air.Arate that is too fast creates a
unknown.
mechanical sensation in the nose which complicates the odor
4.4 The independent judgments of the panelists are aver-
intensity judgment.
aged geometrically (see 7.4) with respect to the 1-butanol
5.2.6 An example of a dynamic dilution apparatus, called a
concentrations of the indicated matching points. Results are
dynamic olfactometer, is diagrammed in Fig. X1.1 and its
reported as an odor intensity, in parts per million, of 1-butanol
operation is explained, in Appendix X4.
inair(ProcedureA)orwater(ProcedureB)ontheASTMOdor
5.3 Reference Concentrations:
Intensity Referencing Scale. When water is used as a diluent,
the temperature of the reference scale solutions during the test 5.3.1 This practice is intended to establish, on a continuous
must be reported. ppm1-butanolscale,thatppmvaluewhichbestcorrespondsin
itsodorintensitytotheodorintensityofthesample.Sincesuch
4.5 The odor intensity equivalent values which are obtained
a scale is technically difficult, the one designed consists of a
may then be used to compare the relative intensities of sample
seriesofdiscreteconcentrationpointsatsniffingportscontinu-
groups.Thesevaluesarereferencevaluesandarenotrelatedto
ously delivering known concentrations of 1-butanol vapor in
the odor intensities by a simple proportionality coefficient (see
air.
8.2).
5.3.2 A geometric progression scale of concentrations is
5. ProcedureA—Dynamic-Scale Method
used, in which each reference port differs in its 1-butanol
concentrationfromtheprecedingportbyafactorof2.Itwould
5.1 Reagents:
have been desirable to select and always use the same ppm
5.1.1 1-butanol (n-butanol), the reference odorant, with
values for the same ports, however, this would require very
required purity 99+mol% by gas chromatography. Also shall
complex flow adjustment systems. Although the ppm values
be free of strong odorous impurities.
delivered by the scale ports change with temperature, they
5.1.2 Diluent—Nonodorous room or cylinder air.
remain in the same ratio to each other, and thus still permit the
5.2 Preparation of Dynamic Scale:
intensity equivalence point to be easily found.
5.2.1 Prepare the 1-butanol airflow mixtures in an olfacto-
5.3.3 The scale points are arranged systematically, in the
meter apparatus as follows: Pass air over an expanded surface
order of increasing concentrations, and are numbered in
of 1-butanol in order to produce a saturated vapor at a known
ascending integers, from 1 for the lowest concentration of
ambient temperature.Temperatures should be ambient in order
1-butanol.
to avoid condensation in the airflow lines. Air becomes
5.3.4 The matching points normally used are the scale
saturated (98+%) at flow rates up to 60 mL/min when passed
points, or positions between the scale points, but can also be
overasurfaceof1-butanolthatis120mmlongby10mmwide
those points beyond either end of the scale.
in a 13-mm inside diameter glass tube which is held in a
5.4 Test Room—The test room must be well-ventilated,
horizontal position. Saturated vapor prepared by bubbling air
essentially odor-free, and comfortable. In order to avoid bias,
through 1-butanol is less desirable since the bubbles burst at
waiting panelists should not observe or learn the judgments of
the surface and produce droplets. In such methods of vapor
thepanelistcurrentlymatchingtheodorintensityofthesample
generation,glasswoolfilter,operatingatthesametemperature
to the scale (1, 2).
as the 1-butanol liquid sample, must be used to remove the
droplets. Obtain concentrations of vapor below saturation by 5.5 Odor Panel:
diluting the saturated vapor with additional volumes of air.
5.5.1 Number—The number of panelists should be eight or
5.2.2 If air, such as pumped ambient air which contains more, to permit elementary statistical tests on their judgments.
watervaporisused,replacethe1-butanolinthesaturationtube A smaller number of panelists may be used with replicate
every 2 to 3 h; otherwise it will become diluted by the judgments to increase the total to eight or more. It is important
E544–99 (2004)
when obtaining replicate data that all bias is removed. Precau- 5.6.9 Panelists may differ in the amount of time required to
tions such as separate sessions and recoding are recommended render a judgment. The panelist should be allowed to proceed
(1). ataratecomfortabletohim.Asmanyassixteststimulicanbe
handled by a panel of nine in a 1-h session.
5.5.2 Selection—Special training is not needed but precau-
tions must be taken in the selection of the panelists (3). An
6. Procedure B—Static-Scale Method
individual with insufficient sensitivity to detect the odor of 10
6.1 The reference odorant is 1-butanol, (see 5.1.1). The
ppm of 1-butanol in air should not be a panelist. Also, some
diluent is distilled water that is odor-free.
individuals have been observed to experience difficulty in
matching odor intensities. Prospective panelists can be
NOTE 2—If diluent other than water is used, equivalent ppm (vol/vol)
screenedbyhavingthemrepeatedlymatchtheodorintensityof values will not exhibit matching odor intensities because of differences in
molecular weights, densities, and the activity coefficients of 1-butanol in
a known concentration of 1-butanol vapor to the 1-butanol
different solvents. Use of other solvents is therefore not recommended.
reference scale. Those whose standard deviation in repeated
testing exceeds 1.5 scale steps should not be used in the panel. 6.2 Follow the procedures outlined in Section 5, except for
Periodic retesting of panelists may be advisable. 5.2.
6.3 Preparation of Static Scale:
5.6 Judgment Procedure:
6.3.1 Prepare solutions of 1-butanol in water, using pipets
5.6.1 Panelists are instructed on the nature of the 1-butanol
and volumetric flasks, following the usual laboratory proce-
odor intensity reference scale. They are told that the ports are
dures for solution preparation.
numbered beginning with No. 1, which represents the weakest
6.3.2 Procedure—Place the reference sniffing solutions into
odorandthattheodorsincreasesystematicallyinintensitywith
standard 500-mL wide-mouth, conical Erlenmeyer flasks (see
increasing port identification numbers.
Test Method D1292). The volume of solution should be 200
5.6.2 Panelists are instructed to smell the unknown sample
mLand should be replaced by new solutions after a maximum
andthentosmellthescale,beginningwithitsweakestend,and
period of 2 h. Between sniffings, cover the top of each flask
match the unknown to the scale, ignoring differences in the
withaluminumfoilinordertoassureequilibrationbetweenthe
odor quality. They are permitted to check and recheck the
solution and the air head-space above it. The flasks should be
unknownagainstthescaleanynumberoftimesandshouldnot
gentlyshakenbyeachpanelistpriortoeachsniffinginorderto
be hurried or biased by others in any manner.
assure equilibrium.
5.6.3 Panelists are advised that they may report one of the
6.3.3 The temperature of the reference solutions during the
scale points as the best match, or else may report that the best
test should be ambient, and should be noted and kept constant
match occurs between two adjacent points, for example, the
during the test.
unknown is stronger than scale point No. 7, but weaker than
6.3.4 Theodorthresholdof1-butanolinwateris2.5ppmat
scale point No. 8.
21°C (5). The useful concentration range for the static scale is
5.6.4 Panelists should be advised that the odor may also be
above this value but does not extend to the solubility limit of
weakerthantheweakestpointofthescale,orstrongerthanthe
7.08% of 30°C (70 800 ppm) (6). At concentrations close to
strongest point of the scale.
the solubility limit, excess 1-butanol may separate from the
5.6.5 When his judgment is within scale limits, the panelist
solution with temperature change. If this occurs the odor
should make sure that the selected position is a good match,
becomes equivalent to that of pure 1-butanol.
that is, that the next lower concentration of 1-butanol indeed
6.3.5 Considerable latitude as to the selection of concentra-
smells weaker than the unknown, and that the next higher
tions is allowed. To go from the saturation point to the
concentration indeed smells stronger.
threshold requires 16 flasks, assuming that each succeeding
5.6.6 Panelistsreportthematchingpointintermsoftheport
mix is one half of the preceding c
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