ASTM E1747-95(2011)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: E1747 − 95 (Reapproved 2011)
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 and health practices and determine the applica-
1.1 Thisguidedefinespuritystandardsforcarbondioxideto
bility of limitations prior to use.
ensure the suitability of liquefied carbon dioxide gas for use in
SFE and SFC applications (see Guide E1449 for definitions of
2. Referenced Documents
terms).This guide defines quantitation, labeling, and statistical
2.1 ASTM Standards:
standards for impurities in carbon dioxide that are necessary
D2504Test Method for Noncondensable Gases in C and
for successful SFE or SFC laboratory work, and it suggests
Lighter Hydrocarbon Products by Gas Chromatography
methods of analysis for quantifying these impurities.
D2820Test Method for C Through C Hydrocarbons in the
1.2 Thisguideisprovidedforusebyspecialtygassuppliers
Atmosphere by Gas Chromatography (Withdrawn 1993)
who manufacture carbon dioxide specifically for SFE or SFC
D3670Guide for Determination of Precision and Bias of
applications. SFE or SFC carbon dioxide (CO ) products
Methods of Committee D22
offered with a claim of adherence to this guide will meet
D3686Practice for Sampling Atmospheres to Collect Or-
certain absolute purity and contaminant detectability require-
ganic Compound Vapors (Activated Charcoal Tube Ad-
mentsmatchedtotheneedsofcurrentSFEorSFCtechniques.
sorption Method)
TheuseofthisguideallowsdifferentSFEorSFCCO product
D3687Practice for Analysis of Organic Compound Vapors
offerings to be compared on an equal purity basis.
Collected by the Activated Charcoal Tube Adsorption
1.3 This guide considers contaminants to be those compo-
Method
nentsthateithercausedetectorsignalsthatinterferewiththose
D4178Practice for Calibrating Moisture Analyzers
of the target analytes or physically impede the SFE or SFC
D4532Test Method for Respirable Dust in Workplace At-
experiment.
mospheres Using Cyclone Samplers
E260Practice for Packed Column Gas Chromatography
1.4 The values stated in SI units are to be regarded as
E355PracticeforGasChromatographyTermsandRelation-
standard. No other units of measurement are included in this
ships
standard.
E594Practice for Testing Flame Ionization Detectors Used
1.5 This standard does not purport to address all of the
in Gas or Supercritical Fluid Chromatography
safety concerns, if any, associated with its use. It is the
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 Nov. 1, 2011. Published December 2011. Originally the ASTM website.
approved in 1995. Last previous edition approved in 2005 as E1747–95(2005). The last approved version of this historical standard is referenced on
DOI: 10.1520/E1747-95R11. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1747 − 95 (2011)
E697Practice for Use of Electron-Capture Detectors in Gas 3.1.4 Nonvolatile—Materials that leave a nonvolatile (boil-
Chromatography ing point >250°C) residue following the vaporization of liquid
E1449Guidefor Supercritical FluidChromatographyTerms 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
example, silica). A maximum concentration of 1 ppm will be
2.2 CGA Publications:
considered acceptable.
CGA G-5.4Standard for Hydrogen Piping Systems at Con-
sumer 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
anextractionsolventfromwhichasignificantconcentrationof
3. Classification
self-containedcontaminatesispossiblebecauserelativelylarge
3.1 This guide covers the following four different classes of (>50g)amountsofcarbondioxidemaybeused.Becauseeach
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 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
5 required for his/her analysis by a simple ratio.
lowestlimitofdetectorresponse(LLDR) forFIDsorECDsonly,because
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.
compounds (for example, HD and HCB) will be used as
Because a wide variety of contaminants are found in liquid-phase CO
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
than an ECD at the lowest detectable limit for a single peak.A
basis for single peaks and for the sum of all detector responses.
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
maximumamountofanyonecontaminant(thatis,onepeakin
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
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
interferencesduringSFCapplications;thisislessofaproblem
are expressed in terms of the equivalent response for
inSFEapplications.Speciesrepresentativeofthisclassinclude
hexadecane, the internal standard, regardless of the actual
oxygen and light hydrocarbons, such as methane, ethane, and
identity of the contaminant.
propane.Acombinedmaximumconcentrationinthegasphase
4.1.1.4 When specifying an FID response for SFC, the
of 10 ppm will be considered acceptable.
generally accepted LLDR for a FID is 0.25 6 0.1 ng for a
singlecomponentwithasignal-to-noiseratioof3:1.Therefore,
“20” × 0.25 ng = 5 ng to the detector (one peak), and
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
“200”×0.25 ng=50 ng total detector response. If all 5 ng of
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
Poole, C.F., and Poole, S.K., Chromatography Today , Elsevier, 1991, p. 86. the contaminant comes from1gof liquid-phase carbon
E1747 − 95 (2011)
dioxide,thesinglecomponentimpuritylevelwouldbe50ppb. 4.1.4.3 Total Gas-Phase Hydrocarbons Specification—The
This assumes that 1 g of carbon dioxide arrives at the detector maximum amount of total gas-phase hydrocarbons (THCs)
at one time, and the density of the CO is 1 g/mL. Under acceptable is 5 ppm (mole or volume basis), expressed as
typical SFC conditions of ;400 atm and 75°C, less than 0.1 g methane.
4.1.5 Nonvolatile Contaminants Specification—The maxi-
of CO actually reaches the FID when using a 0.25 mm inside
diameter column with a 15-s wide peak. Therefore, the mum amount of nonvolatile residue acceptable is 1 mg/g of
CO or 1 ppm (w/w).
contamination level acceptable for SFC applications would be
less than 16 ppb on an absolute basis for a single peak (see 4.1.6 Specification Summary—Proposed minimum specifi-
cations for SFE and SFC CO are summarized in Table 1.
Practice E594).
4.1.1.5 ECD Detector—For SFE, the maximum amount of
5. Gas Handling and Safety
any one contaminant (that is, one peak in the chromatogram)
will be 0.2 ng/g of liquid-phase CO . This is equivalent to 0.2
5.1 The safe handling of compressed gases and cryogenic
ppb w/w, or 200 ppt w/w, on a mass basis. The maximum
liquidsforuseinchromatographyistheresponsibilityofevery
amount of all ECD-responsive contaminants (that is, the sum laboratory. The Compressed Gas Association, Inc. (CGA), a
of all peaks in the chromatogram) will be 2 ng/g of liquid-
member group of specialty and bulk gas suppliers, publishes
phase CO or 2 ppb w/w. Contaminant concentrations are the following guidelines to assist the laboratory chemist in
expressed in terms of the equivalent response for establishing a safe work environment: CGA P-1, CGA G-5.4,
hexachlorobenzene, the internal standard, regardless of the CGA P-9, CGAV-7, CGA P-12, G-6, and HB-3.
actual identity of the contaminant (see Practice E697).
6. Representative Analysis Method for Liquid-Phase
4.1.1.6 For SFC applications, the ECD is >5 times more
Contaminants
sensitive than the FID, assuming two halogen atoms per
molecule. Therefore, the total concentration of a single ECD
6.1 Contaminants dissolved in the liquid phase of CO are
impurity is proposed to be 1 ng/g of CO or 1 ppb. The total
2 the most critical to the success of an SFE or SFC experiment.
amount of ECD impurities considered acceptable is 10 ng/g of
Theliteratureprovidesawidevarietyofanalyticalmethodsfor
CO or 10 ppb.
2 detectingliquid-phasetracecontaminants,anyofwhichcanbe
used by gas suppliers as long as the method can achieve the
4.1.2 Higher-Purity Materials—The specifications and
methodologyproposedinthisguidecanbeusedtocertifyCO detectability and statistical requirements recommended in this
guide.
materials with higher-purity specifications. To certify such
materials, gas suppliers must vary (increase) the quantity of
6.2 Adsorbent Concentration Method—Outlined below is a
CO collected and adjust the quantity of internal standard used
representative method for liquid-phase contaminants, referred
for calibration. Contaminant concentrations are expressed in
to as the adsorbent concentration method.
terms of the equivalent responses for the internal standards
6.2.1 The method is included to develop the quantitation
recommended above and reported on a mass basis relative to
and statistical calculations discussed in Section 8; however,
the mass of CO collected. The applicable detector must be
this guide does not mandate its use.
specified.
6.2.2 Apparatus:
4.1.2.1 Minimum-purity CO contains a total of 10 ng of
6.2.2.1 Gas Chromatograph—The procedure requires a gas
FID-responsivecontaminantspergofCO (10ppbw/w),with chromatograph equipped with both an FID and an ECD. The
no single FID-responsive contaminant greater than 1 ng/g (1
LLDR for the FID must be 0.25 ng 6 0.1 ng of HD at a
ppbw/w).Higher-specificationCO ,forexample,maycontain signal-to-noise ratio of 3:1. The LLDR for the ECD must be
a total of 1 ppb w/w of FID-responsive contaminants, with no
0.05ng 60.02ngHCB.Thedetectorsarejoinedtothecolumn
single contaminant greater than 0.1 ppb w/w. using a “Y” separator and are back-pressure split at a 10:1
FID-ECD ratio (see Practices E260 and E1510).
4.1.2.2 Gassuppliersarefreetomanufacturematerialswith
...