Due to the better understanding of the processes taking place at the surface of the stationary phases, the number of ion-exchange materials for ion chromatography (IC) has increased tremendously over recent years. As a result, the multitude of commercially available columns today with their different selectivities for anion and cation chromatography is almost confusing. Hence, the aim of this article is to describe the different principles determining selectivity and ion-exchange capacity and to classify the various ion-exchange materials accordingly. To ensure a fair comparison of these columns, the selectivity differences are illustrated by showing separations of standards rather than individual samples. Keywords Ion chromatography · Stationary phases · Support materials · Inorganic anions and cations · Organic anions and cations Anion exchangersPolymer-based anion exchangers Styrene/divinylbenzene copolymers, polymethacrylate, and polyvinyl resins are the most important organic polymers that are used as substrate materials in the manufacturing process for polymer-based anion exchangers.

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Sulfur vapor has been investigated by Raman spectroscopy in a wide temperature and pressure range (300 to 900°C, 0.05 to 0.5 MPa for overheated vapor and 0.007 to 1.65 MPa for saturated vapor). At least eight different species have been observed through their characteristic Raman lines. Well separated Raman lines have been selected for the observation of the change in vapor composition with temperature: symmetrical bending modes for the cyclic species Sg, S7, and S6 and stretching modes for the chain-like species SJ and S2. There are indications for the presence of two conformational isomers of S4, and in addition a new species has been discovered by its resonance Raman line at 635 em -1 which is tentatively assigned to chain-like molecules S. (n > 4) of helical conformation. Several relationships between the thermodynamic properties of the vapor and the Raman measurements are proposed, e.g., the determination of the temperature at which the molar fraction Xi is maximum for the overheated vapor at constant pressure; estimation of the x.lx; ratios using solution measurements of the Raman cross section for the molecules Sg, S7, S6. A careful comparison of these results with the values deduced from Rau's model results in good agreement for the behavior of most of the species apart from S7 which is underestimated in Rau's model. S7 is the dominating species in saturated sulfur vapor above 600 K until S2 takes over at ca. 1000 K.

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The vapor pressures of 24 esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5trichlorophenoxyacetic acid (2,4,5-T) have been determined using gas-liquid chromatography over the temperature range 170°to 300°C. These data were extrapolated to 25°C. in order to provide field temperature (25°C.) data for use as a criterion of herbicide volatility. The 25°C. data support the previous gage of volatility-that a phenoxy ester with five or less carbons in the ester portion is highly volatile-and indicate that the phenoxy-type herbicides with a vapor pressure greater than 1.5 X 10~4 mm. of Hg at 25°C. should be classified as "highly volatile."The volatility of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5trichlorophenoxy acetic acid (2,4,5-T) varies greatly with the alcohol portion of the molecule. Therefore, some of these compounds must be used with extreme caution, since they tend to vaporize and drift to adjacent areas following application.Laboratory methods for evaluating this volatility have been helpful and several have been proposed based upon bioassay techniques (2, 4, 7 7, 74) with sensitive plants.