Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

2004 ◽  
Vol 1036 (2) ◽  
pp. 183-188 ◽  
Author(s):  
An-Na Tang ◽  
Dong-Qing Jiang ◽  
Yan Jiang ◽  
Shan-Wei Wang ◽  
Xiu-Ping Yan
Keyword(s):  
Aqueous Solutions ◽  
Cloud Point ◽  
High Performance ◽  
Cloud Point Extraction ◽  
High Performance Liquid Chromatographic ◽  
Liquid Chromatographic

Free Energies of Adsorption of Dipeptides and 2,5-Piperazinediones on Silica from Neutral Aqueous Solutions as Estimated from High-Performance Liquid-Chromatographic Retention Data

1994 ◽  
Vol 59 (8) ◽  
pp. 1721-1728 ◽  
Author(s):  
Vladimir A. Basiuk ◽  
Taras Yu. Gromovoy
Keyword(s):  
Aqueous Solutions ◽  
High Performance ◽  
Equilibrium Constants ◽  
High Performance Liquid Chromatographic ◽  
Chromatographic Retention ◽  
Retention Data ◽  
Free Energies ◽  
Sorbate Molecule ◽  
Aliphatic Carbon ◽  
Liquid Chromatographic

The equilibrium constants (K) and free energies (-∆G) of adsorption of dipeptides and their cyclic derivatives, 2,5-piperazinediones, on silica from neutral aqueous solutions were calculated from their HPLC retention data on a silica gel column. For the majority of the dipeptides -∆G values were negative, ranging from -1 170 to 430 J mol-1, and K < 1, thus indicating a very weak adsorption. The 2,5-piperazinediones under study exhibited higher adsorbabilities (-∆G -1 070 + 3 030 J mol-1, K > 1) as compared to the respective dipeptides. The effect of the α-substituent structure on the adsorbability is analyzed. A linear dependence of -∆G on the number of aliphatic carbon atoms in a sorbate molecule was observed for the series of dipeptides and 2,5-piperazinediones derived from bifunctional aliphatic amino acids.

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