1、Designation: E 1747 95 (Reapproved 2005)Standard Guide forPurity of Carbon Dioxide Used in Supercritical FluidApplications1This standard is issued under the fixed designation E 1747; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 sup
3、ercritical 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
4、 impurities 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 diox
5、ide toensure the suitability of liquefied carbon dioxide gas for use inSFE and SFC applications (see Guide E 1449 for definitions ofterms). This guide defines quantitation, labeling, and statisticalstandards for impurities in carbon dioxide that are necessaryfor successful SFE or SFC laboratory work
6、, and 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 CO2products offered with a claim ofadherence to this guide will meet certain absolute
7、purity andcontaminant detectability requirements matched to the needs ofcurrent SFE or SFC techniques. The use of this guide allowsdifferent SFE or SFC CO2product offerings to be compared onan equal purity basis.1.3 This guide considers contaminants to be those compo-nents that either cause detector
8、 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 thesafety concerns,
9、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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 2504 Test Method for Noncondensable Gases i
10、n C3andLighter Hydrocarbon Products by Gas ChromatographyD 2820 Test Method for C Through C5Hydrocarbons in theAtmosphere By Gas Chromatography3D 3670 Guide for Determination of Precision and Bias ofMethods of Committee D22D 3686 Practice for Sampling Atmospheres to Collect Or-ganic Compound Vapors
11、(Activated Charcoal Tube Ad-sorption Method)D 3687 Practice for Analysis of Organic Compound VaporsCollected by the Activated Charcoal Tube AdsorptionMethodsD 4178 Practice for Calibrating Moisture AnalyzersD 4532 Test Method for Respirable Dust in WorkplaceAtmosphereE 260 Practice for Packed Column
12、 Gas ChromatographyE 355 Practice for Gas Chromatography Terms and Rela-tionshipsE 594 Practice for Testing Flame Ionization Detectors Usedin Gas or Supercritical ChromatographyE 697 Practice for Use of Electron-Capture Detectors in1This guide is under the jurisdiction of ASTM Committee E13 on Molec
13、ularSpectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-tography.Current edition approved Sept. 1, 2005. Published September 2005. Originallyapproved in 1995. Last previous edition approved in 2000 as E 1747 95 (2000).2For referenced ASTM standards, visit the ASTM website,
14、 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Unit
15、ed States.Gas ChromatographyE 1449 Guide for Supercritical Fluid ChromatographyTerms and RelationshipsE 1510 Practice for Installing Fused Silica Open TubularCapillary Columns in Gas Chromatographs2.2 CGA Publications:4CGA P-1 Safe Handling of Compressed Gases in Contain-ersCGA V-7 Standard for Hydr
16、ogen Piping Systems at Con-sumer LocationsCGA P-9 The Inert Gases: Argon, Nitrogen and HeliumCGA V-7 Standard Method of Determining Cylinder ValveOutlets Connections for Industrial Gas MixturesCGA P12 Safe Handling of Cryogenic LiquidsG6 Carbon DioxideHB-3 Handbook of Compressed Gases3. Classificati
17、on3.1 This guide covers the following four different classes ofcompounds:3.1.1 Liquid-Phase ContaminantsThese are materials dis-solved in the CO2liquid phase that can be volatilized below300C and resolved chromatographically using a gas chroma-tography (CG) column; and detected by either a flame ion
18、iza-tion (FI) or electron capture (EC) detector (D). Speciesrepresentative of this class include moderate (100 to 600)molecular weight hydrocarbons and halocarbons (oils andlubricants).NOTE 1Liquid-phase contaminant levels are defined in terms of thelowest limit of detector response (LLDR)5for FIDs
19、or ECDs only, becausethey are the primary detectors used with SFE or SFC techniques.However, the purification procedures used by the gas supplier to removeFID- and ECD-responsive contaminants are assumed to be effective forcontaminants responsive to other (for example, NPD, MS, IR, UV, etc.)detector
20、s.Because a wide variety of contaminants are found in liquid-phase CO2as a consequence of its source, full speculation of every impurity by thegas supplier is impractical. All liquid-phase contaminants are thereforequantified relative to two representative internal primary reference stan-dards: hexa
21、decane (HD or C16H34) for the FID and hexachlorobenzene(HCB or C6Cl6) for the ECD. Contaminant limits are defined on a massbasis for single peaks 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
22、particles and high-boiling solutes, aredetrimental to both SFE and SFC applications. Species repre-sentative of this class include nonchromatographicable hydro-carbons or halocarbon oils, greases, and inorganic particles (forexample, silica). A maximum concentration of 1 ppm will beconsidered accept
23、able.4. Purity Specifications for SFE or SFC Grade CO24.1 This guide proposes the following minimum purityspecifications for CO2for each of the 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 car
24、bon dioxide is intended to be used asan extraction solvent from which a significant concentration ofself-contained contaminates is possible because relatively large(50 g) amounts of carbon dioxide may be used. Because eachimpurity cannot be identified, a known amount of internalreference compounds (
25、for example, HD and HCB) will be usedduring the analysis to quantify contaminants on a relativeweight basis. Total contaminant levels will be 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 FI
26、D 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 dioxidecontamination 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
27、used asa mobile phase material transferred directly from a chromato-graphic column to a detector (FID or ECD) without pre-concentration (see Practice E 355).Accepted internal referencecompounds (for example, HD and HCB) will be used assurrogate contaminants. Contaminant levels will be expressedin ng
28、 of contaminant per g of CO2and will be defined as thatamount which will produce a detector signal 20 times greaterthan the “typical” detection 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
29、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, 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-respo
30、nsive contaminants (that is,the sum of all peaks in the chromatogram) will be 10 ng/g ofliquid-phase CO2or 10 ppb w/w. Contaminant concentrationsare 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
31、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 of 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 fro
32、m1gofliquid-phase carbondioxide, the single component impurity level would be 50 ppb.4Available from Compressed Gas Association, Inc., 1725 Jefferson DavisHighway, Arlington, VA 22202-4100.5Poole, C. F., and Poole, S. K., Chromatography Today, Elsevier, 1991, p. 86.E 1747 95 (2005)2This assumes that
33、 1 g of carbon dioxide arrives at the detectorat one time, and the density of the CO2is 1 g/mL. Undertypical SFC conditions of ;400 atm and 75C, 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 acceptabl
34、e for SFC applications would beless than 16 ppb on an absolute basis for a single peak (seePractice E 594).4.1.1.5 ECD DetectorFor SFE, the maximum 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
35、/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 liquid-phase CO2or 2 ppb w/w. Contaminant concentrations areexpressed in terms of the equivalent response for hexachlo-robenzene, the internal standard, rega
36、rdless of the actualidentity of the contaminant (see Practice E 697).4.1.1.6 For SFC applications, the ECD is 5 times moresensitive than the FID, 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 totalamoun
37、t of ECD impurities considered acceptable is 10 ng/g ofCO2or 10 ppb.4.1.2 Higher-Purity MaterialsThe specifications andmethodology proposed in this guide can be used to certify CO2materials with higher-purity specifications. To certify suchmaterials, gas suppliers must vary (increase) the quantity o
38、fCO2collected and adjust the quantity of internal standard usedfor calibration. Contaminant concentrations are expressed interms of the equivalent responses for the internal standardsrecommended above and reported on a mass basis relative tothe mass of CO2collected. The applicable detector must besp
39、ecified.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 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 nos
40、ingle contaminant greater than 0.1 ppb w/w.4.1.2.2 Gas suppliers are free to manufacture materials withpurity specifications as stringent as they choose. SFC and SFEpractitioners may use the purity reporting standards definedhere as a basis for needs assessment and product comparison.No “grading” no
41、menclature is recommended in this guide.4.1.3 Moisture SpecificationThe maximum amount ofmoisture acceptable in the carbon dioxide is 1 ppm (mole 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 reduc
42、e the risk ofinadvertent contamination, certain gas-phase contaminantsshould be specified and controlled.4.1.4.2 Oxygen (or Oxygen/Argon) SpecificationThemaximum amount of oxygen (or unresolved oxygen/argon)acceptable is 5 ppm (mole or volume basis).4.1.4.3 Total Gas-Phase Hydrocarbons Specification
43、Themaximum amount of total gas-phase hydrocarbons (THCs)acceptable is 5 ppm (mole or volume basis), expressed asmethane.4.1.5 Nonvolatile Contaminants SpecificationThe maxi-mum amount of nonvolatile residue acceptable is 1 mg/g ofCO2or 1 ppm (w/w).4.1.6 Specification SummaryProposed minimum specifi-
44、cations for SFE and SFC CO2are summarized in Table 1.5. Gas Handling and Safety5.1 The safe handling of compressed gases and cryogenicliquids for use in chromatography is the responsibility of everylaboratory. The Compressed Gas Association, Inc. (CGA), amember group of specialty and bulk gas suppli
45、ers, publishesthe following guidelines to assist the laboratory chemist inestablishing a safe work environment: CGA P-1, CGA V-7,CGA P-9, CGA V-7, CGA P12, G6, and HB-3.6. Representative Analysis Method for Liquid-PhaseContaminants6.1 Contaminants dissolved in the liquid phase of CO2arethe most crit
46、ical to the success of an SFE or SFC experiment.The literature provides a wide variety of analytical methods fordetecting liquid-phase trace contaminants, any of which can beused by gas suppliers as long as the method can achieve thedetectability and statistical requirements recommended in thisguide
47、.6.2 Adsorbent Concentration MethodOutlined below is arepresentative method for liquid-phase contaminants, referredto as the adsorbent concentration method.6.2.1 The method is included to develop the quantitationand statistical calculations discussed in Section 8; however,this guide does not mandate
48、 its use.6.2.2 Apparatus:6.2.2.1 Gas ChromatographThe procedure requires a gaschromatograph equipped with both an FID and an ECD. TheLLDR5for 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 col
49、umnusing a “Y” separator and are back-pressure split at a 10:1FID-ECD ratio (see Practices E 260 and E 1510).(1) Also, the gas chromatograph must be equipped toaccommodate an external thermal desorption and cryofocusingTABLE 1 Proposed Minimum Specifications for SFE and SFCCO2ContaminantMaximum SingleConcentrationTotalConcentrationLiquid-phase (SFE)FID responsive 1 ppb w/w 10 ppb w/wECD responsive 0.2 ppb w/w 2 ppb w/wLiquid-phase (SFC)FID responsive 5 ppb w/w 50 ppb w/wECD responsive 1 ppb w/w 10 ppb w/wMoisture . 1 ppm m/mGas phaseOxygen . 5 ppm m/mTHC . 5 ppm m/mNon
