1、Designation: E355 96 (Reapproved 2014)Standard Practice forGas Chromatography Terms and Relationships1This standard is issued under the fixed designation E355; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This practice covers primarily the terms an
3、d relation-ships used in gas elution chromatography. However, most ofthe terms should also apply to other kinds of gas chromatog-raphy and are also valid in the various liquid column chro-matographic techniques, although at this time they are notstandardized for the latter usage.2. Names of Techniqu
4、es2.1 Gas Chromatography, abbreviated as GC, comprises allchromatographic methods in which the moving phase isgaseous. The stationary phase may be either a dry granularsolid or a liquid supported by the granules or by the wall of thecolumn, or both. Separation is achieved by differences in thedistri
5、bution of the components of a sample between the mobileand stationary phases, causing them to move through thecolumn at different rates and from it at different times. In thisrecommended practice gas elution chromatography is implied.2.2 Gas-Liquid Chromatography, abbreviated as GLC, uti-lizes a liq
6、uid as the stationary phase, which acts as a solvent forthe sample components.2.3 Gas-Solid Chromatography, abbreviated as GSC, uti-lizes an active solid (adsorbent) as the stationary phase.2.4 Gas Elution Chromatography utilizes a continuous inertgas flow as the carrier gas and the sample is introd
7、uced as a gasor a liquid with a finite volume into the carrier gas stream. Ifthe sample is introduced as a liquid, it is vaporized in thesystem prior to or during passage through the separationcolumn.2.5 Gas-Frontal Chromatography is a technique in which acontinuous stream of carrier gas mixed with
8、sample vapor isinstantaneously replaced by a continuous stream of carrier gascontaining sample vapor at a different concentration. Theconcentration profile is therefore step-shaped at the columninlet.2.6 Gas-Displacement Chromatography employs a desor-bent as the carrier gas or in the carrier gas to
9、 displace a lessstrongly held solute from the stationary phase which in turndisplaces the next less strongly held one etc., causing thecomponents to emerge in the normal order, that is, least-to-most strongly absorbed.2.7 Isothermal Gas Chromatography is the version of thetechnique in which the colu
10、mn temperature is held constantduring the passage of the sample components through theseparation column.2.8 Programmed Temperature Gas Chromatography(PTGC), is the version of the technique in which the columntemperature is changed with time during the passage of thesample components through the sepa
11、ration column. In linearPTGC the program rate is constant during analysis. Isothermalintervals may be included in the temperature program.2.9 Programmed Flow, Pressure, or Velocity Gas Chroma-tography is the version of the technique in which the carrier gasflow, pressure, or velocity is changed duri
12、ng analysis.2.10 Reaction Gas Chromatography is the version of thetechnique in which the composition of the sample is changedbetween sample introduction and the detector. The reaction cantake place upstream of the column when the chemical compo-sition of the individual components passing through the
13、 col-umn differs from that of the original sample, or between thecolumn and the detector when the original sample componentsare separated in the column but their chemical composition ischanged prior to entering the detection device.2.11 Pyrolysis Gas Chromatography is the version of reac-tion gas ch
14、romatography in which the original sample isdecomposed by heat to more volatile components prior topassage through the separation column.3. Apparatus3.1 Sample Inlet Systems, represent the means for introduc-ing samples into the separation column, including the heatedzones permitting the vaporizatio
15、n of the introduced liquidsamples prior to their passage through the column. Sampleintroduction can be carried out by introduction of a liquid,solid, or gas into the carrier-gas stream. The sample may bevaporized before or after introduction into the column.1This practice is under the jurisdiction o
16、f ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.19 on Separation Science.Current edition approved May 1, 2014. Published June 2014. Originallyapproved in 1968. Last previous edition approved in 2007 as E355 96 (2007).DOI: 10.
17、1520/E0355-96R14.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 Direct Inlets, rapidly vaporize the sample prior toentering the column.All of the sample vapor enters the column.3.1.2 On-Column Inlets, introduce a liquid sample
18、into thecolumn. The sample vaporizes as the column section contain-ing the liquid heats up after injection.3.1.3 Split Inlets, rapidly vaporize the sample prior toentering the column. A defined fraction of the sample vaporenters the column; the remainder leaves the inlet through a ventat a flow rate
19、 Fv. The ratio of the total inlet flow (Fv+ Fc)tothe column flow (Fc) is called the split ratio (s):s 5Fv1FcFc(1)3.1.4 Splitless Injection, utilizes a split inlet wherein thesplit vent flow is blocked during the injection period such thatmost of the sample vapor enters the column. The injectionperio
20、d is typically one minute. The split vent flow is reestab-lished afterward usually for the remainder of the run.3.1.5 Programmed-Temperature Vaporizers (PTV), accept aliquid sample that vaporizes as the inlet system heats up afterinjection. A PTV may operate in either a split, splitless,on-column, o
21、r direct mode.3.1.6 A Retention Gap, is a section of tubing insertedbetween the inlet and the analytical column proper. Theretention gap may have an inner diameter different than theanalytical column. The retention gap has significantly lowerretaining power than the analytical column; in practice th
22、eretention gap is deactivated but not coated.3.2 Columns, consist of tubes that contain the stationaryphase and through which the gaseous mobile phase flows.3.2.1 Packed Columns, are filled with granular packing thatis kept in place by gas-permeable plugs at both ends.3.2.2 Open-Tubular Columns, hav
23、e unobstructed centralgasflow channels.3.2.2.1 Wall-Coated Open-Tubular Columns, abbreviatedWCOT columns, have the liquid phase coated directly on theinside, relatively smooth wall of the column tubing.3.2.2.2 Porous-Layer Open-Tubular Columns, abbreviatedPLOT columns, have a solid porous layer pres
24、ent on the tubewall but still maintain the unobstructed central gas-flowchannel. This porous solid layer can either act as an adsorbentor a support which in turn is coated with a thin film of theliquid phase, or both. The solid layer can either be deposited onthe inside tube wall or formed by chemic
25、al means from thewall.3.2.2.3 Support-Coated Open-Tubular Columns, abbrevi-ated SCOT columns, refer to those PLOT Columns where thesolid layer consists of the particles of a solid support whichwere deposited on the inside tube wall.3.3 Detectors, are devices that indicate the presence ofeluted compo
26、nents in the carrier gas emerging from thecolumn.3.3.1 Differential Concentration Detectors, measure the in-stantaneous proportion of eluted sample components in thecarrier gas passing through the detector.3.3.2 Differential Mass Detectors, measure the instanta-neous rate of arrival of sample compon
27、ents at the detector.3.3.3 Integral Detectors, measure the accumulated quantityof sample component(s) reaching the detector.3.3.4 Spectrometric Detectors, measure and record spectraof eluting components, such as the mass spectrum of theinfrared spectrum.3.4 Traps, are devices for recovering sample c
28、omponentsfrom the mobile phase eluting from GC columns.4. Reagents4.1 Carrier Gas is the Mobile Phase used to sweep or elutethe sample components through and from the column.4.2 The Stationary Phase is composed of the active immo-bile materials within the column that selectively delay thepassage of
29、sample components by dissolving or adsorbingthem, or both. Inert materials that merely provide physicalsupport for the stationary phase or occupy space within thecolumn are not part of the stationary phase.4.2.1 Liquid Stationary Phase is one type of stationaryphase which is dispersed on the solid s
30、upport or the innercolumn wall and causes the separation of the sample compo-nents by differences in the partitioning of the sample compo-nents between the mobile and liquid phases.4.2.2 An Active Solid is one that has ab- or adsorptiveproperties by means of which chromatographic separationsmay be a
31、chieved.4.3 The Solid Support is the inert material that holds thestationary (liquid) phase in intimate contact with the carrier gasflowing through it. It may consist of porous or impenetrableparticles or granules which hold the liquid phase and betweenwhich the carrier gas flows, or the interior wa
32、ll of the columnitself, or a combination of these.4.4 The Column Packing consists of all the material used tofill packed columns, including the solid support and the liquidphase or the active solid.4.4.1 The Liquid-Phase Loading describes the relativeamount of liquid phase present in a packed column
33、 when thecolumn packing consists only of the liquid phase plus the solidsupport. It is usually expressed as weight percent of liquidphase present in the column packing:Liquid 2 phase loading, wt% (2)5amount of liquid phase! 3100amount of liquid phase1amount of solid support!4.5 Solutes are the intro
34、duced sample components that aredelayed by the column as they are eluted through it by thecarrier gas.4.6 Unretained Substances are not delayed by the columnpacking.5. Gas Chromatographic Data5.1 A Chromatogram is a plot of detector response againsttime or effluent volume. Idealized chromatograms ob
35、tainedwith differential and integral detectors for an unretainedsubstance and one other component are shown in Fig. 1.5.2 The definitions in this paragraph apply to chromato-grams obtained directly by means of differential detectors or byE355 96 (2014)2differentiating the records obtained by means o
36、f integraldetectors. The Baseline is the portion of the chromatogramrecording the detector response in the absence of solute orsolvent emerging from the column. A Peak is the portion of thechromatogram recording the detector response while a singlecomponent is eluted from the column. If two or more
37、samplecomponents emerge together, they appear as a single peak. ThePeak Base, CD in Fig. 1, is an interpolation of the baselinebetween the extremities of the peak. The area enclosed betweenthe peak and the peak base, CHFEGJD in Fig. 1,isthePeakArea. The dimension BE from the peak maximum to the peak
38、base measured in the direction of detector response is the PeakHeight. Retention dimensions parallel to the baseline aretermed as the peak widths. The retention dimension of a lineparallel to the peak base bisecting the peak height andterminating at the inflexion points FG of the tangents drawn toth
39、e inflection points (= 60.7 % of peak height) is the PeakWidth at Inflection Points, wi. The retention dimension of a lineparallel to the peak base drawn to 50 % of the peak height andterminating at the sides HJ of the peak is the Peak Width atHalf Height,wh. The retention dimension of the segment o
40、f thepeak base KL intercepted by the tangents drawn to theinflection points on both sides of the peak is the Peak Width atBase or Base Width, wb.5.3 The following definitions apply to chromatograms ob-tained with integral detectors, or by integration of the recordsobtained by means of differential d
41、etectors. As sample compo-nents pass through the detector the baseline is displacedcumulatively. The change in baseline position as a singlesample component is eluted is a Step. The difference betweenstraight line extensions of the baselines on both sides of thestep, measured in the direction of det
42、ector response, is the StepHeight, NM.6. Retention Parameters6.1 Retention parameters are listed in Table 1. The interre-lations shown apply only to gas elution chromatographycolumns operated under constant conditions and for which thepartition coefficients are independent of concentration. Fig. 1ca
43、n be used to illustrate some of these parameters:Gas holdup time = OARetention time = OBAdjusted retention time = ABPartition (capacity) ratio = AB/OAPeak width at half height = HJPeak width at base = KLNumber of theoretical plates = 16 (OB/KL)2= v 5.54 (OB/HJ)2Relative retention = (AB)j/(AB)ior (AB
44、)i/(AB)sPeak resolution=2fs OBdj2s OBd1gs KLdi1s KLdj=sOBdj2sOBdisKLdjSubscripts i, j, and s refer to any earlier peak, any later peak,and a reference peak, respectively.7. Presentation of Isothermal Retention Data7.1 Retention values should be reported in a form that canbe applied for a specific st
45、ationary phase composition indifferent apparatus and for different conditions of columnlength, diameter, and inlet and outlet pressures, and fordifferent carrier gases and flow rate. When the solid support isinert, its particle-size range and distribution, and (within limits)FIG. 1 Typical Chromatog
46、ramE355 96 (2014)3the amount and mode of deposition of the liquid phase, may bevaried also. While the solid support is commonly assumed tobe inert, often this is not so. The physical disposition of theliquid phase may also affect retention values (1).2Consequently, all components of the column packi
47、ng and theprocedure for combining them must be fully specified to enableother workers to prepare identical compositions.7.2 Retention in gas-liquid chromatography can be ex-pressed on an absolute basis in terms of the partition coefficientor specific retention volume of a substance (tacitly assuming
48、 aninert solid support). Relative retentions are more convenientlydetermined, however, and they should be expressed relative toa substance which is easily available and emerges relativelyclose to the substance of interest.7.3 Retention index is another retention parameter. It isdefined relative to t
49、he retention of n-alkanes, and represents thenumber of carbon atoms, multiplied by 100, in a hypotheticaln-alkane that would have an identical retention.TABLE 1 Summary of Parameters, Symbols, Units, and Useful Relationships in Gas ChromatographyGC Parameter Symbol Unit Definition or Relation to Other ParametersAbsolute temperature of carrier gas T K C + 273.15 at point where gas flow rate is measuredAbsolute temperature of column TcKAbsolute ambient temperature TaKColumn inlet pressure piPaColumn outlet pressure PoPaPressure drop along the column pPap=pi poRelative column pre
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