DRIFTS surface specificity

DRIFTs spectra of the Rh-LDH catalysts showed no change of the structure of the initial LDHs. Additionally, specific bands for the organic part of the complex (1260-1210 and 1450-1430 cm 1 for S=0 and Ar-P vibrations) were observed, providing confirmation of the presence of the exchanged Rh on the surface of the brucite-like layers without affecting the LDH structure. 

In summary, it is perfectly legitimate to design CWEs with solid-state internal contact and to expect electrochemical performance comparable to the conventional ISE. However, the design of the membrane/solid interface has to be done with the understanding of the electrochemical processes at such an interface. The problems include the drift scale with the surface area and the length of the internal contact, specifically with its parasitic capacitance and resistance. From this consideration alone, it can be concluded that such problems can be minimized by decreasing the... 

CONTENTS 1. Chemometrics and the Analytical Process. 2. Precision and Accuracy. 3. Evaluation of Precision and Accuracy. Comparison of Two Procedures. 4. Evaluation of Sources of Variation in Data. Analysis of Variance. 5. Calibration. 6. Reliability and Drift. 7. Sensitivity and Limit of Detection. 8. Selectivity and Specificity. 9. Information. 10. Costs. 11. The Time Constant. 12. Signals and Data. 13. Regression Methods. 14. Correlation Methods. 15. Signal Processing. 16. Response Surfaces and Models. 17. Exploration of Response Surfaces. 18. Optimization of Analytical Chemical Methods. 19. Optimization of Chromatographic Methods. 20. The Multivariate Approach. 21. Principal Components and Factor Analysis. 22. Clustering Techniques. 23. Supervised Pattern Recognition. 24. Decisions in the Analytical Laboratory. 

A closely related matter is the measurement and use of the flatband potential. The existing data show that for a silicon/electrolyte interface the flatband potential is specific to the given surface condition. Also, the flatband potential generally drifts due to the fact that the surface of silicon in electrolytes changes constantly with time. Also, it changes with application of potentials which is generally required for the determination of flatband potential. Therefore, any theory which assumes a fixed value of flat-band potential will be limited in its scope of validity. 

Spectra. The energy spectrum is collected from the particles emitted from all depths simultaneously using a silicon surface barrier detector, electronic amplifiers, an analog-to-digital converter and a multichannel analyzer. A reference pulse is fed into the electronics to monitor the stability of the system thus allowing corrections to be made should electronic drift occur during the course of the measurement. Specific systems are described in the references (1 -4,6,7,12-17). By using computer-based data acquisition systems, the depth profile can be displayed at the time of analysis. 

Use of surface speciation models for prediction of adsorption and transport requires specification of the mode of bonding and speciation of oxyanions on oxide surfaces. FTIR spectroscopy (especially ATR and DRIFT) offers the potential to establish symmetry of surface species, protonation, and determination of monodentate or bidentate bonding. Determination of surface speciation is greatly enhanced when the spectroscopic information is combined with measurements of electrophoretic mobility (EM), calculation of point of zero charge and proton balance measurements before and after adsorption. We review adsorption of phosphate, carbonate, boron, selenate and selenite on Fe and A1 oxides. New preliminary spectra and EM and proton balance information for arsenate and arsenite adsorption on amorphous Fe and A1 oxide suggest that HASO4 and H2ASO3 are the dominant surface species. 

Identification of the specific species of the adsorbed oxyanion as well as mode of bonding to the oxide surface is often possible using a combination of Fourier Transform Infrared (FTIR) spectroscopy, electrophoretic mobility (EM) and sorption-proton balance data. This information is required for selection of realistic surface species when using surface complexation models and prediction of oxyanion transport. Earlier, limited IR research on surface speciation was conducted under dry conditions, thus results may not correspond to those for natural systems where surface species may be hydrated. In this study we review adsorbed phosphate, carbonate, borate, selenate, selenite, and molybdate species on aluminum and iron oxides using FTIR spectroscopy in both Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) modes. We present new FTIR, EM, and titration information on adsorbed arsenate and arsenite. Using these techniques we... 

---