1、Designation: E 1449 92 (Reapproved 2006)Standard Guide forSupercritical Fluid Chromatography Terms andRelationships1This standard is issued under the fixed designation E 1449; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r 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.1. Scope1.1 This guide deals primarily with the terms and relation-ships used in supercritical fluid chromatography.1.2 Sinc
3、e many of the basic terms and definitions also applyto gas chromatography and liquid chromatography, this guideis using, whenever possible, symbols identical to PracticesE 355 and E 682.2. Referenced Documents2.1 ASTM Standards:2E 355 Practice for Gas Chromatography Terms and Rela-tionshipsE 682 Pra
4、ctice for Liquid Chromatography Terms and Re-lationships3. Names of Techniques3.1 Supercritical Fluid Chromatography, abbreviated asSFC, comprises all chromatographic methods in which boththe mobile phase is supercritical under the conditions ofanalysis and where the solvating properties of the flui
5、d have ameasurable affect on the separation. Early work in the field wasperformed under a broader headingdense gas chromatogra-phy. Related work in the field uses subcritical or near-criticalconditions to affect separation.3.2 Separation is achieved by differences in the distributionof the component
6、s of a sample between the mobile andstationary phases, causing them to move through the column atdifferent rates (differential migration).3.3 In supercritical fluid chromatography, the pressure maybe constant or changing during a chromatographic separation.3.3.1 Isobaric is a term used when the mobi
7、le phase is keptat constant pressure. This may be for a specified time intervalor for the entire chromatographic separation.3.3.2 Programmed Pressure Supercritical Fluid Chroma-tography is the version of the technique in which the columnpressure is changed with time during the passage of the samplec
8、omponents through the separation column. Isobaric intervalsmay be included in the pressure program.3.4 In supercritical fluid chromatography, the temperaturemay be constant, or changing during a chromatographicseparation.3.4.1 Isothermal Supercritical Fluid Chromatography isthe version of the techni
9、que in which the column temperatureis held constant during the passage of the sample componentsthrough the separation column.3.4.2 Programmed Temperature Supercritical Fluid Chro-matography is the version of the technique in which thecolumn temperature is changed with time during the passage ofthe s
10、ample components through the separation column. Iso-thermal intervals may be included in the temperature program.3.5 In supercritical fluid chromatography, the density maybe constant or changing during the chromatographic separa-tion.3.5.1 Isoconfertic is a term used when the density of themobile ph
11、ase is kept constant for a specified time or for theentire chromatographic separation.3.5.2 Programmed Density Supercritical Fluid Chromatog-raphy is the version of the technique in which the columndensity is changed with time during the passage of the samplecomponents through the separation column.
12、 Isoconfertic inter-vals may be included in the density program.3.5.3 Flow Programming is a technique where the mobilephase linear velocity is changed during the chromatographicprocedure. However, with fixed orifice restrictors, flow pro-gramming is more complex requiring an increase in pressure toe
13、ffect an increase in linear velocity.1This guide is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-tography.Current edition approved Sept. 1, 2006. Published September 2006. Originallyapproved in 1992. Last prev
14、ious edition approved in 2000 as E 1449 92 (2000).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.1Copyright
15、ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.6 In supercritical fluid chromatography, the compositionof the mobile phase may be constant or changing during achromatographic separation.3.6.1 The term Isocratic is used when the composition o
16、fthe mobile phase is kept constant during a chromatographicseparation.3.6.2 The term Gradient Elution is used to specify thetechnique when a deliberate change in the mobile phasecomposition is made during the chromatographic procedure.Isocratic intervals may be included in the gradient program.4. Ap
17、paratus4.1 PumpsThe function of the pumps is to deliver themobile phase at a controlled flow rate to the chromatographiccolumn.4.1.1 Syringe Pumps have a piston that advances at acontrolled rate within a smooth cylinder to displace the mobilephase.4.1.2 Reciprocating Pumps have a single or dual cham
18、berfrom which mobile phase is displaced by reciprocating pis-ton(s) or diaphragm(s).4.2 Sample Inlet Systems represent the means for introduc-ing samples into the columns.4.2.1 Direct Injection is a sample introduction techniquewhereby the entire volume of sample is swept onto the head ofthe analyti
19、cal column. Its use is most prevalent in packedcolumn SFC.4.2.2 Split-Flow Injection introduces only a portion of thesample volume onto the analytical column so as to preventoverloading of the column in open tubular SFC. This isachieved by the use of a splitter tee or similar contrivance, suchthat t
20、he incoming slug of sample is divided between theanalytical column and a flow restrictor vented to waste. Theamount of sample deposited on the column is a function of theratio of the flow to the column versus the flow through thisrestrictor. This ratio can thus be adjusted for different samplesand c
21、olumn capacities.4.2.3 Timed-Split (Moving-Split) Injection achieves thesame end result as split-flow injection. The volume of sampleintroduced onto the column is governed by the rapid back-and-forth motion of an internal-loop sample rotor in a valve. Thetime interval between the two motions determi
22、nes the volumeof sample injected, with shorter times delivering smallervolumes.4.2.4 On-Line Supercritical Extraction is a means of di-rectly introducing a sample or portion of a sample into asupercritical fluid chromatograph. The sample is placed in anextraction cell and extracted with the supercri
23、tical fluid. Theextraction effluent containing the solutes of interest are ulti-mately transferred to the column by the action of switching orsampling valves. This can be accomplished with or withoutsolute focusing (that is, using a suitable trap such as acryogenic trapping).4.3 Columns consist of t
24、ubes that contain the stationaryphase and through which the supercritical fluid mobile phaseflows.4.3.1 Packed Column Supercritical Fluid Chromatography-uses an active solid or a liquid that is chemically bonded to asolid and packed into a column, generally stainless steel orfused silica; as the sta
25、tionary phase.4.3.2 Wall-Coated Open-Tubular Supercritical Fluid Chro-matography uses a liquid that is chemically bonded to the wallof an open-tubular column as stationary phase. Fused silicatubing columns, internal diameter (i.d.) 100 m, may shatterat pressures employed in SFC.Ahigh degree of cross
26、linking isdesirable to reduce stationary phase solubility in the mobilephase.4.4 Restrictors are devices employed to maintain the pres-sure in the chromatographic system. The pressure of thesupercritical fluid is usually reduced to ambient after passagethrough the restrictor.The mobile phase flow ra
27、te is determinedby the restrictor dimensions or operation. The restrictor isplaced before some types of detectors (for example, flameionization, mass spectrometer) and after other types of detec-tors (for example, UV).4.4.1 A Linear Restrictor is a length of small i.d. tubing ofuniform bore. Linear
28、restrictors are made of polyimidecoatedfused silica tubing, or stainless steel or other tubing of theappropriate diameter. The amount of restriction provided isdependent upon both the length and i.d. of the tubing.4.4.2 A Tapered Restrictor is a length of small i.d. tubingwhere one end has been redu
29、ced by drawing in a flame in thecase of fused silica tubing, or crimped in the case of metaltubing.4.4.3 An Integral Restrictor (1)3consists of a length offused silica tubing with one end closed by heating with amicrotorch. This closed end is then ground until a hole with thedesired initial linear v
30、elocity is obtained.4.4.4 A Converging-Diverging Restrictor (2) has the wall ofthe tubing collapsed slightly near one end forming a constric-tion. This constriction is similar to a venturi in profile and thepoint of smallest diameter is located about 1 to 2 mm from theend of the tubing.4.4.5 An Orif
31、ice is a type of restrictor which uses a metaldisk or diaphragm with an appropriately sized opening. Thistype normally requires an adapter or holder specifically de-signed to couple the device to a detector.4.4.6 A Porous Frit Restrictor4consists of a length of fusedsilica tubing containing a porous
32、 plug at one end.4.4.7 A Back Pressure Regulator consists of a diaphragmvalve which can be adjusted to control the pressure maintainedon its inlet (instrument) side. The outlet discharge pressure isnominally one atmosphere.4.5 Detectors are devices that respond to the presence ofeluted solutes in th
33、e mobile phase emerging from the column.Ideally, the response should be proportional to the mass orconcentration of solute in the mobile phase. Detectors may bedivided either according to the type of measurement or theprinciple of detection.4.5.1 Differential Concentration Detectors measure thepropo
34、rtion of eluted sample component(s) in the mobile phase3The boldface numbers in parentheses refer to the list of references at the endof this guide.4Cortez, H., Pfeiffer, C., Richter, B., and Stevens, T. U. S., Patent No. 4 793 920,1988.E 1449 92 (2006)2passing through the detector. The peak area is
35、 inverselyproportional to the mobile phase flow rate.4.5.2 Differential Mass Detectors measure the instanta-neous mass of a component within the detector per unit time(g/s). The area under the curve is independent of the mobilephase flow rate.5. Reagents5.1 Supercritical Fluid is a fluid state of a
36、substance inter-mediate between a gas and a liquid. A supercritical fluid maybe defined from the accompanying phase diagram (Fig. 1). Thesupercritical fluid region is defined by temperatures andpressures, both above the critical values. A subcritical fluid (orliquid) is a compound that would usually
37、 be a gas at ambienttemperature but is held as a liquid by the application ofpressure below its supercritical point.5.1.1 The Critical Temperature is the temperature abovewhich a substance cannot be liquefied or condensed no matterhow great the applied pressure.5.1.2 The Critical Pressure is the pre
38、ssure that would justsuffice to liquefy the fluid at its critical temperature.5.1.3 The Reduced Pressure is the ratio of the workingpressure to the critical pressure of the substance.5.1.4 The Reduced Temperature is the ratio of the workingtemperature to the critical temperature of the substance.5.1
39、.5 The Density of a supercritical fluid (the weight per unitvolume of the fluid) in chromatographic separations is calcu-lated from an empirical equation of state.5.2 A Modifier or co-solvent is a substance added to asupercritical fluid to enhance its solvent strength, usually byincreasing the polar
40、ity of the mobile phase, or binding to activesites on a stationary phase.5.3 The Stationary Phase is composed of the active immo-bile materials within the column that selectively retard thepassage of sample components. Inert materials that merelyprovide physical support or occupy space within the co
41、lumnsare not part of the stationary phase.NOTE 1Extremely porous stationary phases may exhibit exclusionphenomenon in addition to adsorptive interactions.5.3.1 An Interactive Solid is a stationary phase material withbulk homogeneity where the surface effects separation byadsorptive interactions. Exa
42、mples are silica and alumina.5.3.2 A Bonded Phase is a stationary phase that has beencovalently attached to a solid support. The sample componentspartition between the stationary and mobile phases whichresults in separation. Octadecylsilyl groups bonded to silica gelparticles and polydimethylsiloxan
43、e (or dimethyl polysiloxane)bonded to deactivated fused silica column wall representexamples for packed column and open tubular column phases,respectively.5.4 The Solid Support is the inert material that holds thestationary phase in intimate contact with the mobile phase. Itmay consist of porous or
44、impenetrable particles or granules orthe interior wall of the column itself, or a combination of these.5.5 The Column Packing consists of all the material used tofill packed columns, including the solid support and the bondedphase or the interactive solid.5.6 Solutes are the sample components that a
45、re introducedinto the chromatographic system and are transported by themobile phase and elute through the column. Some solutes maybe unretained.6. Readout6.1 A Chromatogram is a plot of detector response againsttime or effluent volume. Idealized chromatograms obtainedwith a differential detector for
46、 an unretained substance and oneother component are shown in Fig. 2.6.2 The definitions in 6.2.1-6.2.6 apply to chromatogramsobtained directly by means of differential detectors or indi-rectly by differentiating the response of integral detectors.6.2.1 ABaseline is that portion of a chromatogram whe
47、re nodetectable sample components emerge from the column.6.2.2 A Peak is that portion of a chromatogram where asingle detectable component, or two or more unresolveddetectable components, elute from the column.6.2.3 The Peak Base,CDinFig. 2, is the interpolation of thebaseline between the extremitie
48、s of a peak.6.2.4 The Peak Area, CHFEGJD in Fig. 2, is the areaenclosed between the peak and the peak base.6.2.5 Peak Height,EBinFig. 2, is the perpendiculardistance measured in the direction of detector response, fromthe peak base to peak maximum.6.2.6 Peak Widths represent retention dimensions par
49、allelto the baseline. Peak width at base or base width, KL in Fig. 2,is the retention dimension of the peak base intercepted by theFIG. 1 Phase Diagram FIG. 2 Typical ChromatogramE 1449 92 (2006)3tangents drawn to the inflection points on both sides of thepeak. Peak width at half height, HJ in Fig. 2, is the retentiondimension drawn at 50 % of peak height parallel to the peakbase. The peak width at inflection point, FG in Fig. 2,istheretention dimension drawn at the inflection points (+60.7 % ofpeak height) parallel to the peak base.7. Retention Parameters, Symbols, and Units7.
