ASTM E1747-95(2005)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 2005)
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 priate safety and health practices and determine the applica-
bility of limitations prior to use.
1.1 Thisguidedefinespuritystandardsforcarbondioxideto
ensure the suitability of liquefied carbon dioxide gas for use in
2. Referenced Documents
SFE and SFC applications (see Guide E1449 for definitions of
2.1 ASTM Standards:
terms).This guide defines quantitation, labeling, and statistical
D2504 Test Method for Noncondensable Gases in C and
standards for impurities in carbon dioxide that are necessary
Lighter Hydrocarbon Products by Gas Chromatography
for successful SFE or SFC laboratory work, and it suggests
D2820 Test Method for C Through C Hydrocarbons in the
methods of analysis for quantifying these impurities.
Atmosphere By Gas Chromatography
1.2 Thisguideisprovidedforusebyspecialtygassuppliers
D3670 Guide for Determination of Precision and Bias of
who manufacture carbon dioxide specifically for SFE or SFC
Methods of Committee D22
applications.SFEorSFCCO productsofferedwithaclaimof
D3686 Practice for Sampling Atmospheres to Collect Or-
adherence to this guide will meet certain absolute purity and
ganic Compound Vapors (Activated Charcoal Tube Ad-
contaminantdetectabilityrequirementsmatchedtotheneedsof
sorption Method)
current SFE or SFC techniques. The use of this guide allows
D3687 Practice for Analysis of Organic Compound Vapors
differentSFEorSFCCO productofferingstobecomparedon
Collected by the Activated Charcoal Tube Adsorption
an equal purity basis.
Method
1.3 This guide considers contaminants to be those compo-
D4178 Practice for Calibrating Moisture Analyzers
nentsthateithercausedetectorsignalsthatinterferewiththose
D4532 Test Method for Respirable Dust in Workplace
of the target analytes or physically impede the SFE or SFC
Atmospheres
experiment.
E260 Practice for Packed Column Gas Chromatography
1.4 The values stated in SI units are to be regarded as
E355 Practice for Gas Chromatography Terms and Rela-
standard. No other units of measurement are included in this
tionships
standard.
E594 Practice 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
E697 PracticeforUseofElectron-CaptureDetectorsinGas
responsibility of the user of this standard to establish appro-
Chromatography
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 Sept. 1, 2005. Published September 2005. Originally
the ASTM website.
approved in 1995. Last previous edition approved in 2000 as E1747–95(2000).
Withdrawn. The last approved version of this historical standard is referenced
DOI: 10.1520/E1747-95R05.
on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1747 – 95 (2005)
E1449 Guide for Supercritical Fluid Chromatography CO , such as small particles and high-boiling solutes, are
Terms and Relationships detrimental to both SFE and SFC applications. Species repre-
E1510 Practice 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 P-1 Safe Handling of Compressed Gases in Contain- considered acceptable.
ers
4. Purity Specifications for SFE or SFC Grade CO
CGA V-7 Standard for Hydrogen Piping Systems at Con-
4.1 This guide proposes the following minimum purity
sumer Locations
specifications for CO for each of the classes of contaminants,
CGA P-9 The Inert Gases: Argon, Nitrogen and Helium 2
based on the demands of currently practiced SFE or SFC
CGAV-7 Standard Method of Determining Cylinder Valve
techniques.
Outlets Connections for Industrial Gas Mixtures
4.1.1 Liquid-Phase Contaminants Specification:
CGA P12 Safe Handling of Cryogenic Liquids
4.1.1.1 SFE grade carbon dioxide is intended to be used as
G6 Carbon Dioxide
anextractionsolventfromwhichasignificantconcentrationof
HB-3 Handbook of Compressed Gases
self-containedcontaminatesispossiblebecauserelativelylarge
3. Classification
(>50g)amountsofcarbondioxidemaybeused.Becauseeach
3.1 This guide covers the following four different classes of impurity cannot be identified, a known amount of internal
compounds: referencecompounds(forexample,HDandHCB)willbeused
3.1.1 Liquid-Phase Contaminants—Thesearematerialsdis- during the analysis to quantify contaminants on a relative
solved in the CO liquid phase that can be volatilized below weight basis. Total contaminant levels will be expressed in ng
300°C and resolved chromatographically using a gas chroma- of contaminant per g of CO and defined as that amount of
tography (CG) column; and detected by either a flame ioniza- impurity that will produce a detector signal at the “typical”
tion (FI) or electron capture (EC) detector (D). Species detection limits for an FID or ECD found in 1.0 g of CO .The
representative of this class include moderate (100 to 600) 1-g amount of carbon dioxide was selected as a convenient
molecular weight hydrocarbons and halocarbons (oils and mass from which the chemist could relate carbon dioxide
lubricants). contamination levels with the amount of carbon dioxide
required for his/her analysis by a simple ratio.
NOTE 1—Liquid-phase contaminant levels are defined in terms of the
4.1.1.2 SFC grade carbon dioxide is intended to be used as
lowestlimitofdetectorresponse(LLDR) forFIDsorECDsonly,because
a mobile phase material transferred directly from a chromato-
they are the primary detectors used with SFE or SFC techniques.
graphic column to a detector (FID or ECD) without pre-
However, the purification procedures used by the gas supplier to remove
FID- and ECD-responsive contaminants are assumed to be effective for concentration (see Practice E355).Accepted internal reference
contaminants responsive to other (for example, NPD, MS, IR, UV, etc.)
compounds (for example, HD and HCB) will be used as
detectors.
surrogate contaminants. Contaminant levels will be expressed
Because a wide variety of contaminants are found in liquid-phase CO
in ng of contaminant per g of CO and will be defined as that
as a consequence of its source, full speculation of every impurity by the
amount which will produce a detector signal 20 times greater
gas supplier is impractical. All liquid-phase contaminants are therefore
than the “typical” detection limit for FID and 25 times greater
quantified relative to two representative internal primary reference stan-
than an ECD at the lowest detectable limit for a single peak.A
dards: hexadecane (HD or C H ) for the FID and hexachlorobenzene
16 34
(HCB or C Cl ) for the ECD. Contaminant limits are defined on a mass
6 6 total of 200 times the lowest detectable limit will be set for all
basis for single peaks and for the sum of all detector responses.
contaminants for a specific detector.
3.1.2 Moisture—Although water is sparingly (<0.1 % 4.1.1.3 When specifying a FID response for SFE, the
maximumamountofanyonecontaminant(thatis,onepeakin
weight) soluble in liquid-phase CO , more than 10 ppm of
moisture may result in physical interference resulting from ice the chromatogram) will be 1 ng/g of liquid-phase CO . This is
equivalent to 1 ppb on a mass basis, or 1 ppb w/w. The
formation during SFC or SFE applications. A maximum limit
of 1 ppm of water in the carbon dioxide will be considered maximum amount of all FID-responsive contaminants (that is,
the sum of all peaks in the chromatogram) will be 10 ng/g of
acceptable.
liquid-phase CO or 10 ppb w/w. Contaminant concentrations
3.1.3 Gas-Phase Contaminants—Gaseous, noncondensible
are expressed in terms of the equivalent response for hexade-
moleculesreleaseduponvaporizationofliquidCO mayactas
cane, the internal standard, regardless of the actual identity of
interferencesduringSFCapplications;thisislessofaproblem
the contaminant.
inSFEapplications.Speciesrepresentativeofthisclassinclude
4.1.1.4 When specifying an FID response for SFC, the
oxygen and light hydrocarbons, such as methane, ethane, and
generally accepted LLDR for a FID is 0.25 6 0.1 ng for a
propane.Acombinedmaximumconcentrationinthegasphase
singlecomponentwithasignal-to-noiseratioof3:1.Therefore,
of 10 ppm will be considered acceptable.
“20” 30.25 ng=5 ng to the detector (one peak), and
3.1.4 Nonvolatile—Materials that leave a nonvolatile (boil-
“200” 30.25 ng=50 ng total detector response. If all 5 ng of
ing point >250°C) residue following the vaporization of liquid
the contaminant comes from1gof liquid-phase carbon
dioxide,thesinglecomponentimpuritylevelwouldbe50ppb.
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
This assumes that1gof carbon dioxide arrives at the detector
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
Poole, C. F., and Poole, S. K., Chromatography Today , Elsevier, 1991, p. 86. at one time, and the density of the CO is 1 g/mL. Under
E1747 – 95 (2005)
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
amount of all ECD-responsive contaminants (that is, the sum member group of specialty and bulk gas suppliers, publishes
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 V-7,
expressed in terms of the equivalent response for hexachlo-
CGA P-9, CGAV-7, CGAP12, G6, and HB-3.
robenzene, the internal standard, regardless of the actual
6. Representative Analysis Method for Liquid-Phase
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
molecule. Therefore, the total concentration of a single ECD
the most critical to the success of an SFE or SFC experiment.
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
4.1.2 Higher-Purity Materials—The specifications and detectability and statistical requirements recommended in this
methodologyproposedinthisguidecanbeusedtocertifyCO guide.
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
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 6.2.2 Apparatus:
specified. 6.2.2.1 Gas Chromatograph—The procedure requires a gas
chromatograph equipped with both an FID and an ECD. The
4.1.2.1 Minimum-purity CO contains a total of 10 ng of
LLDR for the FID must be 0.25 ng 6 0.1 ng of HD at a
FID-responsivecontaminantspergofCO (10ppbw/w),with
signal-to-noise ratio of 3:1. The LLDR for the ECD must be
no single FID-responsive contaminant greater than 1 ng/g (1
0.05ng 60.02ngHCB.Thedetectorsarejoinedtothecolumn
ppbw/w).Higher-specificationCO ,forexample,maycontain
using a “Y” separator and are back-pressure split at a 10:1
a total of 1 ppb w/w of FID-responsive contaminants, with no
FID-ECD ratio (see Practices E260 and E1510).
single contaminant greater than 0.1 ppb w/w.
(1) Also, the gas chromatograph must be equipped to
4.1.2.2 Gassuppliersarefreetomanufacturematerialswith
accommodateanexternalthermaldesorptionandcryofocusing
purity specifications as stringent as they choose. SFC and SFE
unit, and it must be configured for wi
...