INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY ANALYTICAL CHEMISTRY DIVISION COMMISSION ON ANALYTICAL NOMENCLATURE RECOMMENDATIONS ON NOMENCLATURE FOR CHROMATOGRAPHY RULES APPROVED 1973 LONDON BUTTERWORTHS ANALYTICAL CHEMISTRY DIVISION COMMISSION ON ANALYTICAL NOMENCLATURE RECOMMENDATIONS ON NOMENCLATURE FOR CHROMATOGRAPHY RULES APPROVED 1973 Nearly ten years ago the Division of Analytical Chemistry approved 1 a set of recommendations for the nomenclature of Gas Chromatography . Since then the Commission on Nomenclature has bccn endeavouring to producc a unificd nomenclature applicable to all forms of scparation processes, and proposals have now been made for Liquid-Liquid Distri­ 3 bution2 and for Ion Exchangc . In the present proposals prcpared for the Commission by Dr D. Ambrose, Professor E. Bayer and Professor 0. Samuelson, the work has becn extcnded to all forms of chromatography. For the sake ofuniformity, compromises have inevitably had tobe made, as a result ofwhich, for example, there are somc changes from the recommenda­ tions in Rcf. 1. Account was taken, in the drafting, of other relevant pro­ posals4-7. It is rccommended that quantities should be expressed in the units (or their multiples or submultiplcs) of the International System of Units, or in 8 the units approved for use with the International System ; in particular, that physical dimcnsions, e.g. of columns, should be so expressed. It is to . be noted that the symbol T relates to thermodynamic temperatures and should not be used to represent temperatures expressed on the Celsius 9 scale . 1 CHROMATOGRAPHY A method, used primarily for separation of the components of a sample, in which the components are distributed between two phases, one of which is stationary while the other moves. The stationary phase may be a solid, or a liquid supported on a solid, or a gel. The stationary phase may be packed in a column, spread as a layer, or distributedas afilm, etc.; in these definitions chromatographic bed is used as a general term to denote any of the different forms in which the stationary phase may be used. The mobile phase may be gaseous or liquid. 2 PRINCIPAL METHODS 2.1 Frontal chromatography A procedure for chromatographic Separation in which the sample (liquid or gas) is fed continuously into the chromatographic bed. 2.2 Elution chromatography A procedure for chromatographic separation in which an eluent (see ltem 8.6) is passed through the Chromatographie bed after the application of the sample. 447 NOMENCLATURE FOR CHROMATOGRAPHY 2.3 Displacement chromatography An elution procedure in which the eluent contains a compound more effectively retained than the components of the sample under examination. 3 CLASSIFICATION ACCORDING TO PHASES USED In this classification, the first word specifies the mobile phase and the second the stationary phase. A liquid stationary phase is supported on a solid. 3.1 Gas chromatography (GC) 3.1.1 Gas-liquid chromatography (GLC) 3.1.2 Gas-solid chromatography (GSC) 3.2 Liquid chromatography ( LC) 3.2.1 Liquid-liquid chromatography (LLC) 3.2.2 Liquid-solid chromatography (LSC) 3.2.3 Liquid--gel chromatography In gas chromatography the distinction between gas-liquid and gas-solid may be obscure because liquids are used to modify solid stationary phases, and because the solid supports for liquid stationary phases affect the chroma­ graphic process. For classification by the phases used, the term relating to the predominant effect should be chosen. Liquid-gel chromatography includes gel-permeation and ion-exchange chromatography. 4 CLASSIFICATION ACCORDING TO MECHANISMS 4.1 Adsorption chromatography Separation based mainly on differences between the adsorption affinities of the components for the surface of an active solid. 4.2 Partition chromatography Separation based mainly on differences between the solubilities of the components in the stationary phase (gas chromatography), or on differences between the solubilities of the components in the mobile and stationary phases (liquid chromatography). 4.3 Ion-exchange chromatography Separation based mainly on differences in the ion-exchange affinities of the components. 4.4 Permeation chromatography Separation based mainly upon exclusion effects, such as differences in molecular size and/or shape ( e.g. molecular-sieve chromatography) or in charge (e.g. ion-exclusion chromatography). The term gel-permeation 448 NOMENCLATURE FüR CHROMATOGRAPHY chromatography is widely used for the process when the stationary phase is a swollen gel. The term gel-filtration is not recommended. 4.5 Other mechanisms In addition to ltems 4.1 to 4.4, there exist many techniques based upon other mechanisms. Examples are Iigand-exchange, formation of Charge­ transfer complexes, and bio-specific sorption, e.g. formation of enzyme­ substrate and antigen-antibody complexes. Classification according to mechanism should be avoided unless the predominant mechanism is known. In many instances more than one mechanism is involved. 5 CLASSIFICATION ACCORDING TO TECHNIQUES USED All types of chromatography can be classified according to Section 3 by the phases used or according to Section 4 by mechanism, but the terms in this section specify techniques and may provide a more useful characteriza­ tion of the process. 5.1 Column chromatography (CC) 5.2 Open-tube chromatography (see ltem 8.4) 5.3 Paper chromatography (PC) 5.4 Thin-layer chromatography (TLC) Chromatography carried out in a layer of adsorbent spread on a support, e.g. a glass plate. 5.5 Filament chromatography 6 TERMS FOR SPECIAL TECHNIQUES 6.1 Temperature-programmed chromatography A procedure in which the temperature of the column is changed system­ atically during a part or the whole of the separation. 6.2 Flow-programmed chromatography A procedure in which the rate of flow of the mobile phase is changed systematically during apart or the whole of the separation. 6.3 Salting-out chromatography A procedure in which a non-sorbable electrolyte is added to the eluent to modify the distribution equilibria of the components to be separated. 6.4 Selective elution An elution procedure in which a specific eluent is used, e.g. a complexing agent that forms stable non-sorbable complexes with one or a group of the compounds to be separated, but affects the other components only to a negligible extent. 449 NOMENCLATURE FOR CHROMATOGRAPHY 6.5 Stepwise elution An elution procedure in which two or more eluents of different com­ position are used in succession to elute the componen ts in a single Chromato­ graphie run. 6.6 Gradient elution An elution procedure in which the eluent composition is changed con­ tinuously. 6. 7 Two-dimensional chromatography A procedure applied in paper chromatography and thin-layer chromato­ graphy in which the components are caused first tomigratein one direction, and subsequently in a direction at right angles to the first one. The two elutions are usually carried out with different eluents. 6.8 Reversed-phase chromatography A term of historical interest in liquid~liquid chromatography rcferring to an elution procedure in which the stationary phase is non-polar, e.g. papcr treated with hydrocarbons or silicones. 7 TERMS RELATING TO THE METHOD IN GENERAL 7.1 Chromatogram A graphical or other presentation of detector response, effluent concentra­ tion, or other quantity used as a measure of eftluent concentration, versus effluent volume or time. The term is also applied to the layer or paper aftcr separation has occurred. 7.2 Elution curve A chromatogram, or part of a chromatogram, recordcd whcn elution techniques are used. 7.3 Chromatograph (verb) Toseparate by chromatography. 7.4 Chromatograph (noun) The assembly of apparatus for carrying out Chromatographie separation. 7.5 Elute To chromatograph by elution chromatography. This term is prcfcrred to the term develop, which has been used in paper chromatography and thin-layer chromatography. The process of elution may continuc until thc components have left the Chromatographie bed. 7.6 Extract To recover a compound from a Chromatographiezone by trcatment with a solvent. 450 NOMENCLATURE FOR CHROMATOGRAPHY 7.7 Zone A region in a Chromatographie column or layer where one or more com­ ponents of thc sample are located. 7.8 Spot A zone in paper and thin-layer chromatography of approximatcly circular appearance. 7.9 Starting point or line The point or line on a Chromatographie layer where the substance to be chromatographed is applied. 7.10 Baseline The portion of a chromatogram recorded when only eluent or carrier gas emergcs from the column. 7.11 Peak The portion of a differential chromatogram (See ltem 8.20) recording the detector response or eluate concentration (See Item 8.18) while a component emerges from the column (Figure 1). Ifseparation is incomplete, two or more components may appear as one unresolved peak. 7.12 Elution band Synonymous with peak. 7.13 Tailing Asymmetry of a peaksuch that, relative to the baseline, the front is steeper than the rear. In paper chromatography and thin-layer chromatography, the distortion of a zone showing a diffuse region behind the zone in the dircction of flow. 7.14 Fronting Asymmetry of a peak such that, relative to the baseline, the front is less steep than therear. In paperchromatography and thin-layerchromatography, the distortion of a zone showing a diffuse region in front of the zone in the direction of flow. 7.15 Step (on an integral chromatogram) The portion of an integral chromatogram (See ltem 8.21) recording the amount of a component, or the corresponding change in the signal from the detector as the component emerges from the column (Figure 1). 7.16 Step height (on an integral chromatogram) The distance (KL, Figure 1), perpendicular to the time or volume axis, through which the baseline moves as the result of a step on an integral chromatogram (See Item 8.21). 7.17 Interna) standard A compound added to a sample in known concentration, for example, for 451 NOMENCLATURE FOR CHROMATOGRAPHY (o) A c, p I __..___,.-L (b) -~-------- -K Figure 1.