Chemical speciation of N-(phosphonomethyl)glycine in solution and at mineral interfaces

• Published in: Surface and interface analysis Vol. 36; no. 8; pp. 1074 - 1077
• Main Authors: Ramstedt, Madeleine, Norgren, Caroline, Sheals, Julia, Shchukarev, Andrei, Sjöberg, Staffan
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2004; Wiley
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; cryogenics; Exact sciences and technology; goethite; manganite; phosphonomethylglycine; Physics; solid-liquid interface; XPS; Water; Liquid solid interface; pH value; phosphonomethylglycine; Nitrogen; Sorption; goethite; manganite; Vacuum techniques; Cryogenics; Protonation; XPS; solid-liquid interface; X-ray photoelectron spectra
• ISSN: 0142-2421; 1096-9918
• DOI: 10.1002/sia.1844

The chemical speciation of the zwitterionic compound N‐(phosphonomethyl)glycine (PMG) was studied in solution and at the mineral/water interface at different pH. Results from vacuum techniques such as XPS were compared with previously published conventional batch experiments. It was shown that by keeping the samples frozen during XPS analyses it was possible to keep a water interface. The frozen interface enables studies of the protonation of the nitrogen group which has previously been difficult using XPS. The protonation in frozen solutions was compared with literature data and the differences discussed. Furthermore, the speciation of PMG at the surface of manganite (γ‐MnOOH) and goethite (α‐FeOOH) was studied. It was found that at least one of the protonation constants for surface‐bound PMG differs significantly from the protonation constants in a pure PMG solution. The formation of different surface complexes is discussed together with differences between the sorption capacities of PMG onto the minerals studied. Copyright © 2004 John Wiley & Sons, Ltd.