ASTM E1747-95(2019)

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: E1747 − 95 (Reapproved 2019)
Standard Guide for
Purity of Carbon Dioxide Used in Supercritical Fluid
Applications
This standard is issued under the fixed designation E1747; 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.
INTRODUCTION
Therapidcommercialdevelopmentofcarbondioxideforuseinsupercriticalfluidextraction(SFE)
and supercritical fluid chromatography (SFC) has hastened the need to establish common purity
standards to be specified by specialty gas suppliers. As a consequence of its isolation from
petrochemical side-streams or as a by-product of fermentation or ammonia synthesis, carbon dioxide
contains a wide range of impurities that can interfere with analytical quantification or instrument
operation.Thisguideisintendedtoserveasaguidetospecialtygassuppliersfortestingthesuitability
of carbon dioxide for use in SFC and SFE applications.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 Thisguidedefinespuritystandardsforcarbondioxideto
mine the applicability of limitations prior to use.
ensure the suitability of liquefied carbon dioxide gas for use in
1.6 This international standard was developed in accor-
SFE and SFC applications (see Guide E1449 for definitions of
dance with internationally recognized principles on standard-
terms).This guide defines quantitation, labeling, and statistical
ization established in the Decision on Principles for the
standards for impurities in carbon dioxide that are necessary
Development of International Standards, Guides and Recom-
for successful SFE or SFC laboratory work, and it suggests
mendations issued by the World Trade Organization Technical
methods of analysis for quantifying these impurities.
Barriers to Trade (TBT) Committee.
1.2 Thisguideisprovidedforusebyspecialtygassuppliers
2. Referenced Documents
who manufacture carbon dioxide specifically for SFE or SFC
applications. SFE or SFC carbon dioxide (CO ) products
2.1 ASTM Standards:
offered with a claim of adherence to this guide will meet
D2504Test Method for Noncondensable Gases in C and
certain absolute purity and contaminant detectability require-
Lighter Hydrocarbon Products by Gas Chromatography
ments matched to the needs of current SFE or SFC techniques.
D2820Test Method for C Through C Hydrocarbons in the
TheuseofthisguideallowsdifferentSFEorSFCCO product
Atmosphere by Gas Chromatography (Withdrawn 1993)
offerings to be compared on an equal purity basis.
D3670Guide for Determination of Precision and Bias of
Methods of Committee D22
1.3 This guide considers contaminants to be those compo-
D3686Practice for Sampling Atmospheres to Collect Or-
nentsthateithercausedetectorsignalsthatinterferewiththose
ganic Compound Vapors (Activated Charcoal Tube Ad-
of the target analytes or physically impede the SFE or SFC
sorption Method)
experiment.
D3687Test Method for Analysis of Organic Compound
1.4 The values stated in SI units are to be regarded as
VaporsCollectedbytheActivatedCharcoalTubeAdsorp-
standard. No other units of measurement are included in this
tion Method
standard.
D4178Practice for Calibrating Moisture Analyzers
1.5 This standard does not purport to address all of the
D4532Test Method for Respirable Dust in Workplace At-
safety concerns, if any, associated with its use. It is the
mospheres Using Cyclone Samplers
1 2
This guide is under the jurisdiction of ASTM Committee E13 on Molecular For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Spectroscopy and Separation Science and is the direct responsibility of Subcom- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
mittee E13.19 on Separation Science. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 1, 2019. Published December 2019. Originally the ASTM website.
approved in 1995. Last previous edition approved in 2011 as E1747–95(2011). The last approved version of this historical standard is referenced on
DOI: 10.1520/E1747-95R19. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1747 − 95 (2019)
E260Practice for Packed Column Gas Chromatography interferencesduringSFCapplications;thisislessofaproblem
E355PracticeforGasChromatographyTermsandRelation- inSFEapplications.Speciesrepresentativeofthisclassinclude
ships oxygen and light hydrocarbons, such as methane, ethane, and
E594Practice for Testing Flame Ionization Detectors Used propane.Acombinedmaximumconcentrationinthegasphase
in Gas or Supercritical Fluid Chromatography of 10 ppm will be considered acceptable.
E697Practice for Use of Electron-Capture Detectors in Gas 3.1.4 Nonvolatile—Materials that leave a nonvolatile (boil-
Chromatography ingpoint>250°C)residuefollowingthevaporizationofliquid
E1449Guide for Supercritical Fluid ChromatographyTerms CO , such as small particles and high-boiling solutes, are
and Relationships detrimental to both SFE and SFC applications. Species repre-
E1510Practice for Installing Fused Silica Open Tubular sentative of this class include nonchromatographicable hydro-
Capillary Columns in Gas Chromatographs carbonsorhalocarbonoils,greases,andinorganicparticles(for
2.2 CGA Publications: example, silica). A maximum concentration of 1 ppm will be
CGA G-5.4Standard for Hydrogen Piping Systems at User considered acceptable.
Locations
4. Purity Specifications for SFE or SFC Grade CO
CGAP-1SafeHandlingofCompressedGasesinContainers
CGA P-9The Inert Gases: Argon, Nitrogen and Helium
4.1 This guide proposes the following minimum purity
CGA P-12Safe Handling of Cryogenic Liquids
specifications for CO for each of the classes of contaminants,
CGA V-7Standard Method of Determining Cylinder Valve
based on the demands of currently practiced SFE or SFC
Outlets Connections for Industrial Gas Mixtures
techniques.
G-6Carbon Dioxide
4.1.1 Liquid-Phase Contaminants Specification:
HB-3Handbook of Compressed Gases
4.1.1.1 SFE grade carbon dioxide is intended to be used as
an extraction solvent from which a significant concentration of
3. Classification
self-containedcontaminatesispossiblebecauserelativelylarge
3.1 This guide covers the following four different classes of
(>50 g) amounts of carbon dioxide may be used. Because each
compounds:
impurity cannot be identified, a known amount of internal
3.1.1 Liquid-Phase Contaminants—These are materials dis-
referencecompounds(forexample,HDandHCB)willbeused
solved in the CO liquid phase that can be volatilized below
2 during the analysis to quantify contaminants on a relative
300°C and resolved chromatographically using a gas chroma-
weight basis. Total contaminant levels will be expressed in ng
tography (CG) column; and detected by either a flame ioniza-
of contaminant per g of CO and defined as that amount of
tion (FI) or electron capture (EC) detector (D). Species
impurity that will produce a detector signal at the “typical”
representative of this class include moderate (100 to 600)
detection limits for an FID or ECD found in 1.0 g of CO .The
molecular weight hydrocarbons and halocarbons (oils and
1 g amount of carbon dioxide was selected as a convenient
lubricants).
mass from which the chemist could relate carbon dioxide
contamination levels with the amount of carbon dioxide
NOTE 1—Liquid-phase contaminant levels are defined in terms of the
lowestlimitofdetectorresponse(LLDR) forFIDsorECDsonly,because required for his/her analysis by a simple ratio.
they are the primary detectors used with SFE or SFC techniques.
4.1.1.2 SFC grade carbon dioxide is intended to be used as
However, the purification procedures used by the gas supplier to remove
a mobile phase material transferred directly from a chromato-
FID- and ECD-responsive contaminants are assumed to be effective for
graphic column to a detector (FID or ECD) without pre-
contaminants responsive to other (for example, NPD, MS, IR, UV, etc.)
concentration (see Practice E355).Accepted internal reference
detectors.
Because a wide variety of contaminants are found in liquid-phase CO compounds (for example, HD and HCB) will be used as
as a consequence of its source, full speculation of every impurity by the
surrogate contaminants. Contaminant levels will be expressed
gas supplier is impractical. All liquid-phase contaminants are therefore
in ng of contaminant per g of CO and will be defined as that
quantified relative to two representative internal primary reference stan-
amount which will produce a detector signal 20 times greater
dards: hexadecane (HD or C H ) for the FID and hexachlorobenzene
16 34
than the “typical” detection limit for FID and 25 times greater
(HCB or C Cl ) for the ECD. Contaminant limits are defined on a mass
6 6
basis for single peaks and for the sum of all detector responses.
than an ECD at the lowest detectable limit for a single peak.A
total of 200 times the lowest detectable limit will be set for all
3.1.2 Moisture—Although water is sparingly (<0.1 %
contaminants for a specific detector.
weight) soluble in liquid-phase CO , more than 10 ppm of
4.1.1.3 When specifying a FID response for SFE, the
moisture may result in physical interference resulting from ice
maximum amount of any one contaminant (that is, one peak in
formation during SFC or SFE applications. A maximum limit
the chromatogram) will be 1 ng/g of liquid-phase CO . This is
of 1 ppm of water in the carbon dioxide will be considered 2
equivalent to 1 ppb on a mass basis, or 1 ppb w/w. The
acceptable.
maximum amount of all FID-responsive contaminants (that is,
3.1.3 Gas-Phase Contaminants—Gaseous, noncondensible
the sum of all peaks in the chromatogram) will be 10 ng/g of
moleculesreleaseduponvaporizationofliquidCO mayactas
liquid-phase CO or 10 ppb w/w. Contaminant concentrations
are expressed in terms of the equivalent response for
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
hexadecane, the internal standard, regardless of the actual
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
Poole, C. F., and Poole, S. K., Chromatography Today, Elsevier, 1991, p. 86. identity of the contaminant.
E1747 − 95 (2019)
4.1.1.4 When specifying an FID response for SFC, the inadvertent contamination, certain gas-phase contaminants
generally accepted LLDR for a FID is 0.25 ng 6 0.1 ng for a should be specified and controlled.
singlecomponentwithasignal-to-noiseratioof3:1.Therefore, 4.1.4.2 Oxygen (or Oxygen/Argon) Specification—The
“20” × 0.25 ng = 5 ng to the detector (one peak), and maximum amount of oxygen (or unresolved oxygen/argon)
“200”×0.25 ng=50 ng total detector response. If all 5 ng of acceptable is 5 ppm (mole or volume basis).
the contaminant comes from1gof liquid-phase carbon 4.1.4.3 Total Gas-Phase Hydrocarbons Specification—The
dioxide,thesinglecomponentimpuritylevelwouldbe50ppb. maximum amount of total gas-phase hydrocarbons (THCs)
This assumes that 1 g of carbon dioxide arrives at the detector acceptable is 5 ppm (mole or volume basis), expressed as
at one time, and the density of the CO is 1 g/mL. Under methane.
typical SFC conditions of ;400 atm and 75°C, less than 0.1 g 4.1.5 Nonvolatile Contaminants Specification—The maxi-
of CO actually reaches the FID when using a 0.25 mm inside mum amount of nonvolatile residue acceptable is 1 mg/g of
diameter column with a 15 s wide peak. Therefore, the CO or 1 ppm (w/w).
contamination level acceptable for SFC applications would be 4.1.6 Specification Summary—Proposed minimum specifi-
less than 16 ppb on an absolute basis for a single peak (see cations for SFE and SFC CO are summarized in Table 1.
Practice E594).
5. Gas Handling and Safety
4.1.1.5 ECD Detector—For SFE, the maximum amount of
any one contaminant (that is, one peak in the chromatogram) 5.1 The safe handling of compressed gases and cryogenic
will be 0.2 ng/g of liquid-phase CO . This is equivalent to 0.2 liquidsforuseinchromatographyistheresponsibilityofevery
ppb w/w, or 200 ppt w/w, on a mass basis. The maximum laboratory. The Compressed Gas Association, Inc. (CGA), a
member group of specialty and bulk gas suppliers, publishes
amount of all ECD-responsive contaminants (that is, the sum
of all peaks in the chromatogram) will be 2 ng/g of liquid- the following guidelines to assist the laboratory chemist in
phase CO or 2 ppb w/w. Contaminant concentrations are establishing a safe work environment: CGA P-1, CGA G-5.4,
expressed in terms of the equivalent response for CGA P-9, CGAV-7, CGA P-12, G-6, and HB-3.
hexachlorobenzene, the internal standard, regardless of the
6. Representative Analysis Method for Liquid-Phase
actual identity of the contaminant (see Practice E697).
Contaminants
4.1.1.6 For SFC applications, the ECD is >5 times more
sensitive than the FID, assuming two halogen atoms per 6.1 Contaminants dissolved in the liquid phase of CO are
the most critical to the success of an SFE or SFC experiment.
molecule. Therefore, the total concentration of a single ECD
impurity is proposed to be 1 ng/g of CO or 1 ppb. The total Theliteratureprovidesawidevarietyofanalyticalmethodsfor
amount of ECD impurities considered acceptable is 10 ng/g of detectingliquid-phasetracecontaminants,anyofwhichcanbe
CO or 10 ppb. used by gas suppliers as long as the method can achieve the
detectability and statistical requirements recommended in this
4.1.2 Higher-Purity Materials—The specifications and
guide.
methodologyproposedinthisguidecanbeusedtocertifyCO
materials with higher-purity specifications. To certify such
6.2 Adsorbent Concentration Method—Outlined below is a
materials, gas suppliers must vary (increase) the quantity of
representative method for liquid-phase contaminants, referred
CO collected and adjust the quantity of internal standard used
2 to as the adsorbent concentration method.
for calibration. Contaminant concentrations are expressed in
6.2.1 The method is included to develop the quantitation
terms of the equivalent responses for the internal standards
and statistical calculations discussed in Section 8; however,
recommended above and reported on a mass basis relative to
this guide does not mandate its use.
the mass of CO collected. The applicable detector must be
2 6.2.2 Apparatus:
specified.
6.2.2.1 Gas Chromatograph—The procedure requires a gas
4.1.2.1 Minimum-purity CO contains a total of 10 ng of
chromatograph equipped with both an FID and an ECD. The
FID-responsive contaminants per g of CO (10 ppb w/w), with
LLDR for the FID must be 0.25 ng 6 0.1 ng of HD at a
no single FID-responsive contaminant greater than 1 ng/g (1
signal-to-noise ratio of 3:1. The LLDR for the ECD must be
ppbw/w).Higher-specificationCO ,forexample,maycontain
a total of 1 ppb w/w of FID-responsive contaminants, with no
TABLE 1 Proposed Minimum Specifications for SFE and SFC
single contaminant greater than 0.1 ppb w/w.
CO
4.1.2.2 Gas suppliers are free to manufacture materials with
Maximum Single Total
Contaminant
purity specifications as stringent as they choose. SFC and SFE
Concentration Concentration
practitioners may use the purity reporting standards defined
Liquid-phase (SFE)
FID responsive 1 ppb w/w 10 ppb w/w
here as a basis for needs assessment and product comparison.
ECD responsive 0.2 ppb w/w 2 ppb w/w
No “grading” nomenclature is recommended in this guide.
Liquid-phase (SFC)
4.1.3 Moisture Specification—The maximum amount of FID responsive 5 ppb w/w 50 ppb w/w
ECD responsive 1 ppb w/w 10 ppb w/w
moisture acceptable in the carbon dioxide is 1 ppm (mole or
Moisture . 1 ppm m/m
volume basis).
Gas phase
Oxygen . 5 ppm m/m
4.1.4 Gas-Phase Contaminants Specification:
THC . 5 ppm m/m
4.1.4.1 Gas-phase contaminants generally do not impede
Nonvolatile . 1 ppm w/w
SFE or SFC experiments. However, to reduce the risk of
E1747 − 95 (2019
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