1、Designation: E1747 95 (Reapproved 2011)Standard Guide forPurity of Carbon Dioxide Used in Supercritical FluidApplications1This standard is issued under the fixed designation E1747; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe rapid commercial development of carbon dioxide for use in supercritical fluid extraction (SFE)and superc
3、ritical fluid chromatography (SFC) has hastened the need to establish common puritystandards to be specified by specialty gas suppliers. As a consequence of its isolation frompetrochemical side-streams or as a by-product of fermentation or ammonia synthesis, carbon dioxidecontains a wide range of im
4、purities that can interfere with analytical quantification or instrumentoperation. This guide is intended to serve as a guide to specialty gas suppliers for testing the suitabilityof carbon dioxide for use in SFC and SFE applications.1. Scope1.1 This guide defines purity standards for carbon dioxide
5、 toensure the suitability of liquefied carbon dioxide gas for use inSFE and SFC applications (see Guide E1449 for definitions ofterms). This guide defines quantitation, labeling, and statisticalstandards for impurities in carbon dioxide that are necessaryfor successful SFE or SFC laboratory work, an
6、d it suggestsmethods of analysis for quantifying these impurities.1.2 This guide is provided for use by specialty gas supplierswho manufacture carbon dioxide specifically for SFE or SFCapplications. SFE or SFC carbon dioxide (CO2) productsoffered with a claim of adherence to this guide will meetcert
7、ain absolute purity and contaminant detectability require-ments matched to the needs of current SFE or SFC techniques.The use of this guide allows different SFE or SFC CO2productofferings to be compared on an equal purity basis.1.3 This guide considers contaminants to be those compo-nents that eithe
8、r cause detector signals that interfere with thoseof the target analytes or physically impede the SFE or SFCexperiment.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thes
9、afety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2504 Test Method for Noncondensable Gas
10、es in C2andLighter Hydrocarbon Products by Gas ChromatographyD2820 Test Method for C Through C5Hydrocarbons in theAtmosphere By Gas Chromatography3D3670 Guide for Determination of Precision and Bias ofMethods of Committee D22D3686 Practice for Sampling Atmospheres to Collect Or-ganic Compound Vapors
11、 (Activated Charcoal Tube Ad-sorption Method)D3687 Practice for Analysis of Organic Compound VaporsCollected by the Activated Charcoal Tube AdsorptionMethodD4178 Practice for Calibrating Moisture AnalyzersD4532 Test Method for Respirable Dust in WorkplaceAtmospheres Using Cyclone SamplersE260 Practi
12、ce for Packed Column Gas ChromatographyE355 Practice for Gas Chromatography Terms and Rela-tionshipsE594 Practice for Testing Flame Ionization Detectors Usedin Gas or Supercritical Fluid ChromatographyE697 Practice for Use of Electron-Capture Detectors in GasChromatography1This guide is under the ju
13、risdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.19 on Separation Science.Current edition approved Nov. 1, 2011. Published December 2011. Originallyapproved in 1995. Last previous edition approved in 2005 as E1747
14、95 (2005).DOI: 10.1520/E1747-95R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last appro
15、ved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E1449 Guide for Supercritical Fluid ChromatographyTerms and RelationshipsE1510 Practice for Installing Fused Silica
16、Open TubularCapillary Columns in Gas Chromatographs2.2 CGA Publications:4CGA G-5.4 Standard for Hydrogen Piping Systems at Con-sumer LocationsCGA P-1 Safe Handling of Compressed Gases in Contain-ersCGA P-9 The Inert Gases: Argon, Nitrogen and HeliumCGA P-12 Safe Handling of Cryogenic LiquidsCGA V-7
17、Standard Method of Determining Cylinder ValveOutlets Connections for Industrial Gas MixturesG-6 Carbon DioxideHB-3 Handbook of Compressed Gases3. Classification3.1 This guide covers the following four different classes ofcompounds:3.1.1 Liquid-Phase ContaminantsThese are materials dis-solved in the
18、CO2liquid phase that can be volatilized below300C and resolved chromatographically using a gas chroma-tography (CG) column; and detected by either a flame ioniza-tion (FI) or electron capture (EC) detector (D). Speciesrepresentative of this class include moderate (100 to 600)molecular weight hydroca
19、rbons and halocarbons (oils andlubricants).NOTE 1Liquid-phase contaminant levels are defined in terms of thelowest limit of detector response (LLDR)5for FIDs or ECDs only, becausethey are the primary detectors used with SFE or SFC techniques.However, the purification procedures used by the gas suppl
20、ier to removeFID- and ECD-responsive contaminants are assumed to be effective forcontaminants responsive to other (for example, NPD, MS, IR, UV, etc.)detectors.Because a wide variety of contaminants are found in liquid-phase CO2as a consequence of its source, full speculation of every impurity by th
21、egas supplier is impractical. All liquid-phase contaminants are thereforequantified relative to two representative internal primary reference stan-dards: hexadecane (HD or C16H34) for the FID and hexachlorobenzene(HCB or C6Cl6) for the ECD. Contaminant limits are defined on a massbasis for single pe
22、aks and for the sum of all detector responses.3.1.2 MoistureAlthough water is sparingly (250C) residue following the vaporization of liquidCO2, such as small particles and high-boiling solutes, aredetrimental to both SFE and SFC applications. Species repre-sentative of this class include nonchromato
23、graphicable hydro-carbons or halocarbon oils, greases, and inorganic particles (forexample, silica). A maximum concentration of 1 ppm will beconsidered acceptable.4. Purity Specifications for SFE or SFC Grade CO24.1 This guide proposes the following minimum purityspecifications for CO2for each of th
24、e classes of contaminants,based on the demands of currently practiced SFE or SFCtechniques.4.1.1 Liquid-Phase Contaminants Specification:4.1.1.1 SFE grade carbon dioxide is intended to be used asan extraction solvent from which a significant concentration ofself-contained contaminates is possible be
25、cause relatively large(50 g) amounts of carbon dioxide may be used. Because eachimpurity cannot be identified, a known amount of internalreference compounds (for example, HD and HCB) will be usedduring the analysis to quantify contaminants on a relativeweight basis. Total contaminant levels will be
26、expressed in ngof contaminant per g of CO2and defined as that amount ofimpurity that will produce a detector signal at the “typical”detection limits for an FID or ECD found in 1.0 g of CO2. The1-g amount of carbon dioxide was selected as a convenientmass from which the chemist could relate carbon di
27、oxidecontamination levels with the amount of carbon dioxiderequired for his/her analysis by a simple ratio.4.1.1.2 SFC grade carbon dioxide is intended to be used asa mobile phase material transferred directly from a chromato-graphic column to a detector (FID or ECD) without pre-concentration (see P
28、ractice E355). Accepted internal referencecompounds (for example, HD and HCB) will be used assurrogate contaminants. Contaminant levels will be expressedin ng of contaminant per g of CO2and will be defined as thatamount which will produce a detector signal 20 times greaterthan the “typical” detectio
29、n limit for FID and 25 times greaterthan an ECD at the lowest detectable limit for a single peak. Atotal of 200 times the lowest detectable limit will be set for allcontaminants for a specific detector.4.1.1.3 When specifying a FID response for SFE, themaximum amount of any one contaminant (that is,
30、 one peak inthe chromatogram) will be 1 ng/g of liquid-phase CO2. This isequivalent to 1 ppb on a mass basis, or 1 ppb w/w. Themaximum amount of all FID-responsive contaminants (that is,the sum of all peaks in the chromatogram) will be 10 ng/g ofliquid-phase CO2or 10 ppb w/w. Contaminant concentrati
31、onsare expressed in terms of the equivalent response for hexade-cane, the internal standard, regardless of the actual identity ofthe contaminant.4.1.1.4 When specifying an FID response for SFC, thegenerally accepted LLDR for a FID is 0.25 6 0.1 ng for asingle component with a signal-to-noise ratio o
32、f 3:1. Therefore,“20” 3 0.25 ng = 5 ng to the detector (one peak), and“200” 3 0.25 ng = 50 ng total detector response. If all 5 ng ofthe contaminant comes from1gofliquid-phase carbondioxide, the single component impurity level would be 50 ppb.This assumes that1gofcarbon dioxide arrives at the detect
33、orat one time, and the density of the CO2is 1 g/mL. Under4Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5thFloor, Chantilly, VA 20151-2923, http:/.5Poole, C.F., and Poole, S.K., Chromatography Today , Elsevier, 1991, p. 86.E1747 95 (2011)2typical SFC conditions of ;400 atm and 75
34、C, less than 0.1 gof CO2actually reaches the FID when using a 0.25 mm insidediameter column with a 15-s wide peak. Therefore, thecontamination level acceptable for SFC applications would beless than 16 ppb on an absolute basis for a single peak (seePractice E594).4.1.1.5 ECD DetectorFor SFE, the max
35、imum amount ofany one contaminant (that is, one peak in the chromatogram)will be 0.2 ng/g of liquid-phase CO2. This is equivalent to 0.2ppb w/w, or 200 ppt w/w, on a mass basis. The maximumamount of all ECD-responsive contaminants (that is, the sumof all peaks in the chromatogram) will be 2 ng/g of
36、liquid-phase CO2or 2 ppb w/w. Contaminant concentrations areexpressed in terms of the equivalent response for hexachlo-robenzene, the internal standard, regardless of the actualidentity of the contaminant (see Practice E697).4.1.1.6 For SFC applications, the ECD is 5 times moresensitive than the FID
37、, assuming two halogen atoms permolecule. Therefore, the total concentration of a single ECDimpurity is proposed to be 1 ng/g of CO2or 1 ppb. The totalamount of ECD impurities considered acceptable is 10 ng/g ofCO2or 10 ppb.4.1.2 Higher-Purity MaterialsThe specifications andmethodology proposed in t
38、his guide can be used to certify CO2materials with higher-purity specifications. To certify suchmaterials, gas suppliers must vary (increase) the quantity ofCO2collected and adjust the quantity of internal standard usedfor calibration. Contaminant concentrations are expressed interms of the equivale
39、nt responses for the internal standardsrecommended above and reported on a mass basis relative tothe mass of CO2collected. The applicable detector must bespecified.4.1.2.1 Minimum-purity CO2contains a total of 10 ng ofFID-responsive contaminants per g of CO2(10 ppb w/w), withno single FID-responsive
40、 contaminant greater than 1 ng/g (1ppb w/w). Higher-specification CO2, for example, may containa total of 1 ppb w/w of FID-responsive contaminants, with nosingle contaminant greater than 0.1 ppb w/w.4.1.2.2 Gas suppliers are free to manufacture materials withpurity specifications as stringent as the
41、y choose. SFC and SFEpractitioners may use the purity reporting standards definedhere as a basis for needs assessment and product comparison.No “grading” nomenclature is recommended in this guide.4.1.3 Moisture SpecificationThe maximum amount ofmoisture acceptable in the carbon dioxide is 1 ppm (mol
42、e orvolume basis).4.1.4 Gas-Phase Contaminants Specification:4.1.4.1 Gas-phase contaminants generally do not impedeSFE or SFC experiments. However, to reduce the risk ofinadvertent contamination, certain gas-phase contaminantsshould be specified and controlled.4.1.4.2 Oxygen (or Oxygen/Argon) Specif
43、icationThemaximum amount of oxygen (or unresolved oxygen/argon)acceptable is 5 ppm (mole or volume basis).4.1.4.3 Total Gas-Phase Hydrocarbons SpecificationThemaximum amount of total gas-phase hydrocarbons (THCs)acceptable is 5 ppm (mole or volume basis), expressed asmethane.4.1.5 Nonvolatile Contam
44、inants SpecificationThe maxi-mum amount of nonvolatile residue acceptable is 1 mg/g ofCO2or 1 ppm (w/w).4.1.6 Specification SummaryProposed minimum specifi-cations for SFE and SFC CO2are summarized in Table 1.5. Gas Handling and Safety5.1 The safe handling of compressed gases and cryogenicliquids fo
45、r use in chromatography is the responsibility of everylaboratory. The Compressed Gas Association, Inc. (CGA), amember group of specialty and bulk gas suppliers, publishesthe following guidelines to assist the laboratory chemist inestablishing a safe work environment: CGA P-1, CGA G-5.4,CGA P-9, CGA
46、V-7, CGA P-12, G-6, and HB-3.6. Representative Analysis Method for Liquid-PhaseContaminants6.1 Contaminants dissolved in the liquid phase of CO2arethe most critical to the success of an SFE or SFC experiment.The literature provides a wide variety of analytical methods fordetecting liquid-phase trace
47、 contaminants, any of which can beused by gas suppliers as long as the method can achieve thedetectability and statistical requirements recommended in thisguide.6.2 Adsorbent Concentration MethodOutlined below is arepresentative method for liquid-phase contaminants, referredto as the adsorbent conce
48、ntration method.6.2.1 The method is included to develop the quantitationand statistical calculations discussed in Section 8; however,this guide does not mandate its use.6.2.2 Apparatus:6.2.2.1 Gas ChromatographThe procedure requires a gaschromatograph equipped with both an FID and an ECD. TheLLDR5fo
49、r the FID must be 0.25 ng 6 0.1 ng of HD at asignal-to-noise ratio of 3:1. The LLDR for the ECD must be0.05 ng 6 0.02 ng HCB.The detectors are joined to the columnusing a “Y” separator and are back-pressure split at a 10:1FID-ECD ratio (see Practices E260 and E1510).(1) Also, the gas chromatograph must be equipped toaccommodate an external thermal desorption and cryofocusingunit, and it must be configured for wide-bore, open-tubularcolumns and temperature programming up to 270C.(2) Any common detector recording device may be used,such as a computerized
