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Two-dimensional thermal field-flow fractionation (2D-ThFFF) is a new instrumental technique devised for continuous fractionation of soluble macromolecules and particles. The sample mixture is introduced into a disc-shaped channel and the separated sample components are collected continuously from the channel outlets. The method is based on a two-dimensional fractionation mechanism with radial and tangential flow components in the channel. The effects of flow components and thermal gradient on the fractionation were studied in the separation of polystyrene samples of different molecular masses using cyclohexane or a binary solvent consisting of 25% ethylbenzene and 75% cyclohexane as carrier. The continuous separation of polystyrene samples was improved with increasing thermal gradient and with the use of slow radial and tangential flow rates. The technique can be applied to preparative continuous separation of macromolecules.

Instrumental techniques to analyse macromolecular and particulate materials have undergone rapid development in response to the need for high resolution, precise identification and characterization, and enrichment and collection for further analysis. Continuous two-dimensional field-flow fractionation (2D-FFF), which is described in this article, is a novel technique for separation and collection of macromolecules and particles. 2D-FFF is based on the conventional field-flow fractionation principle but with carrier flow in two-dimensions. This overview discusses the principle of the technique, describes the instrumentation and suggests potential applications and further extensions. An overview of the basic field-flow fractionation principle is presented.

This paper demonstrates the use of the first on‐line capillary electrophoresis instrument with continuously flowing electrolyte solutions and sequentially applied sample introduction. The system was used in on‐line determination of chloride, sulfate, and carbonate concentrations of process waters at a pulp mill. The module constructed for on‐line feeding of the solvents is described. Separations were performed in a pyromellitic acid‐hexamethonium hydroxide‐triethanol amine mixture at pH 7.7 with indirect‐UV detection at 254 nm. Two standard mixtures were used to show the repeatability of the analysis and to estimate the accuracy of the on‐line system. The analytes could be separated within 240 s. Sampling from a pulp machine could be accomplished on‐line at 6‐minute intervals. On‐line tests gave a limit of detection and a limit of determination in the low mg/L range.