1、Designation: E 355 96 (Reapproved 2007)Standard Practice forGas Chromatography Terms and Relationships1This standard is issued under the fixed designation E 355; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. 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 practice covers primarily the terms and relation-ships used in gas elution chromatography. However, most ofthe terms shou
3、ld 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 Techniques2.1 Gas Chromatography, abbreviated as GC, comprises allchromatographic methods i
4、n 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 thedistribution of the components of a sample between the mobileand stationary phases, causi
5、ng 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 liquid as the stationary phase, which acts as a solvent forthe sample components.2.3 G
6、as-Solid Chromatography, abbreviated as GSC, uti-lizes an active solid (adsorbent) as the stationary phase.2.4 Gas Elution Chromatography utilizes a continuous in-ert gas flow as the carrier gas and the sample is introduced asa gas or a liquid with a finite volume into the carrier gas stream.If the
7、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 sample vapor isinstantaneously replaced by a continuous stream of carrier gascont
8、aining 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 displace a lessstrongly held solute from the stationary phase which in turndispl
9、aces 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 column temperature is held constantduring the passage of the sample components throug
10、h theseparation column.2.8 Programmed Temperature Gas Chromatograp-hy (PTGC), is the version of the technique in which thecolumn temperature is changed with time during the passage ofthe sample components through the separation column. Inlinear PTGC the program rate is constant during analysis.Isoth
11、ermal intervals may be included in the temperatureprogram.2.9 Programmed Flow, Pressure, or Velocity Gas Chroma-tography is the version of the technique in which the carriergas flow, pressure, or velocity is changed during analysis.2.10 Reaction Gas Chromatography is the version of thetechnique in w
12、hich 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 col-umn differs from that of the original sample, or between thecolumn and the
13、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 chromatography in which the original sample isdecomposed by heat to more volatile
14、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 vaporization of the introduced liquidsamples prior to their passage through the column. Sam
15、pleintroduction 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 of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the
16、direct responsibility of Subcom-mittee E13.19 on Separation Science.Current edition approved March 1, 2007. Published March 2007. Originallyapproved in 1968. Last previous edition approved in 2001 as E 355 - 96 (2001)1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
17、n, PA 19428-2959, United States.3.1.1 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 into thecolumn. The sample vaporizes as the column section contain-ing the liquid heats up after in
18、jection.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 Fv. The ratio of the total inlet flow (Fv+ Fc)tothe column flow ( Fc) is called the split ratio (s
19、):s 5Fv1 FcFc(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 injectionperiod is typically one minute. The split vent flow is reestab-lished afterward usually for the remain
20、der 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, or direct mode.3.1.6 A Retention Gap, is a section of tubing insertedbetween the inlet and the ana
21、lytical 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 theretention gap is deactivated but not coated.3.2 Columns, consist of tubes that contain the stati
22、onaryphase 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, have unobstructed centralgasflow channels.3.2.2.1 Wall-Coated Open-Tubular Columns, abbreviatedWCOT
23、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 present on the tubewall but still maintain the unobstructed central gas-flowchannel. This porous soli
24、d 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 chemical means from thewall.3.2.2.3 Support-Coated Open-Tubular Columns, abbrevi-ated SCOT columns, ref
25、er 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 components in the carrier gas emerging from thecolumn.3.3.1 Differential Concentration Detectors, meas
26、ure 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 components at the detector.3.3.3 Integral Detectors, measure the accumulated quantityof sample componen
27、t(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 componentsfrom the mobile phase eluting from GC columns.4. Reagents4.1 Carrier Gas is the Mobile P
28、hase 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 sample components by dissolving or adsorbingthem, or both. Inert materials that merely provide ph
29、ysicalsupport 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 support or the innercolumn wall and causes the separation of the sample compo-nents by differences
30、 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 achieved.4.3 The Solid Support is the inert material that holds thestationary (liquid) phase in in
31、timate 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 wall of the columnitself, or a combination of these.4.4 The Column Packing consists of all the mate
32、rial 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 when thecolumn packing consists only of the liquid phase plus the solidsupport. It is usually ex
33、pressed as weight percent of liquidphase present in the column packing:Liquid2phase loading, wt%5amount of liquid phase!3100amount of liquid phase 1 amount of solid support!(2)4.5 Solutes are the introduced sample components that aredelayed by the column as they are eluted through it by thecarrier g
34、as.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 obtainedwith differential and integral detectors for an unretainedsubstance and one other component a
35、re shown in Fig. 1.5.2 The definitions in this paragraph apply to chromato-grams obtained directly by means of differential detectors or bydifferentiating the records obtained by means of integraldetectors. The Baseline is the portion of the chromatogramrecording the detector response in the absence
36、 of solute orsolvent emerging from the column. A Peak is the portion of thechromatogram recording the detector response while a singleE 355 96 (2007)2component is eluted from the column. If two or more samplecomponents emerge together, they appear as a single peak. ThePeak Base, CD in Fig. 1, is an
37、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 peakbase measured in the direction of detector response is the PeakHeight. Retention dimensions parall
38、el 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 tothe inflection points (= 60.7 % of peak height) is the PeakWidth at Inflection Points, wi. The reten
39、tion 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 of thepeak base KL intercepted by the tangents drawn to theinflection points on both sides of the
40、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 detectors. As sample compo-nents pass through the detector the baseline is displacedcumulatively.
41、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 detector response, is the StepHeight, NM.6. Retention Parameters6.1 Retention parameters are listed
42、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. 1can be used to illustrate some of these parameters:Gas holdup time = OARetention time = OBAdjusted
43、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)i/(AB)sPeak resolution =2OB!j OB!1KL!i1 KL!j=OB!j OB!iKL!jSubscripts i, j, and s refer to any ea
44、rlier 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 stationary phase composition indifferent apparatus and for different conditions of columnlength, diameter, and
45、 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)the amount and mode of deposition of the liquid phase, may bevaried also. While the solid support is commonly assumed tobe inert, of
46、ten this is not so. The physical disposition of theliquid phase may also affect retention values (1).2Conse-quently, all components of the column packing and theprocedure for combining them must be fully specified to enableother workers to prepare identical compositions.7.2 Retention in gas-liquid c
47、hromatography can be ex-pressed on an absolute basis in terms of the partition coefficientor specific retention volume of a substance (tacitly assuming an2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.FIG. 1 Typical Chromatogram.E 355 96 (2007)3inert
48、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 the retent
49、ion 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 DpPaDp=pi poRelative column pres
