Flow sorption microcalorimetry

FIG. 5 Apparatus for flow sorption microcalorimetry simultaneously with flow frontal analysis sohd/hquid chromatography. L1-L6, solutions Dl, D2, degassers 7PV, electric seven-port valve PCI, PC2, personal computers MP, HPLC micropump PR, pressure regulator 6WV, six-way valve L, loop Tl, T2, thermostats TAM, microcalorimeter COL, column RID, refractive index detector SC, RID sample ceU RC, RID reference ceU A, amphfler FM, flowmeter W, waste. (Adapted from Ref. 35.)... 

Chapter 9, by Kiraly (Hungary), attempts to clarify the adsorption of surfactants at solid/solution interfaces by calorimetric methods. The author addresses questions related to the composition and structure of the adsorption layer, the mechanism of the adsorption, the kinetics, the thermodynamics driving forces, the nature of the solid surface and of the surfactant (ionic, nonionic, HLB, CMC), experimental conditions, etc. He describes the calorimetric methods used, to elucidate the description of thermodynamic properties of surfactants at the boundary of solid-liquid interfaces. Isotherm power-compensation calorimetry is an essential method for such measurements. Isoperibolic heat-flux calorimetry is described for the evaluation of adsorption kinetics, DSC is used for the evaluation of enthalpy measurements, and immersion microcalorimetry is recommended for the detection of enthalpic interaction between a bare surface and a solution. Batch sorption, titration sorption, and flow sorption microcalorimetry are also discussed. 

Further work by the author [42] compared the adsorption of PtCle and AuCU ions on a basic ion exchanger and a graphitised carbon adsorbent and has confirmed that flow adsorption microcalorimetry can rapidly determine the capacity and the kinetics of sorption of the ions on such adsorbents under dynamic conditions. The rate of sorption of the Pt and the Au ions was limited by their diffusion into the resin matrix and the high affinity of the resin for water. High surface area graphitic carbons suffer much less from these effects and appeared to be much more effective adsorbents. 

Sorption on ion exchangers produces marked heat effects when they sorb ions from aqueous solutions. The author used flow microcalorimetry to determine the heat effects caused by the sorption and desorption of ions and discovered that the heats of cation exchange on strongly acidic exchangers were generally very large, but very much dependant on the ion s valency [52]. 

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