I want to find adsorption isotherm for Hexadecyl Trimethyl Ammonium Bromide (HTAB) on Glass-beads (90-150 micron). Using UV I have found a peak for HTAB at around 195 nm and its calibration curve is quite reproducible. My problem is when I put HTAB and Glass-Beads together. The final peak of supernatant represents a concentration higher than the initial one. I checked for any peak interference that may come from Glass-Beads at the same wavelength, but I found no peak. Do you have any idea?
I already encountered the same problem when trying to quantify adsorbed phenolic molecules. We thought that the vessels and/or the adsorbents were contaminated with some substances which were escaping in the solution during the experiments, and whose UV absorption peak was close to what was expected. Extensive washing (Soxhlet extraction with solvent) of all materials removed the problem.
Alain
First I doubt very much that UV is applicable for determining concentration of the HTA ions. Likely, what you measure is the bromide. Bromide will exhibit negative adsorption, i.e. its concentration near surface of glass beads is less than in the bulk. Maybe in addition surfactant solubilizes and disperses surface contamination.
At the wavelength you are suggesting the quality of the glass has to very good and cleanliness impecable. Also alot organic materials will absorb at 190 nm. I would be using some other technique to quantify the absorption. Apart from elemental analysis, maybe FTIR would be good way forward.
the traditional way of determining absorption by this type of surfactants is two-phase titration or accordingly spectrophotometric determination of the complex formed. Analysis with ion selective electrodes would be easy to perform.
No you don!t use,because it is a colorless substance.So it should be converted a complex one to make suitable for UV adsorption,i.e. by using picric acıd at a basic medium.
Bromide absorbs at 195 nm. The HTA does not have aromatic groups that absorb in the UV region. You might measure the carbon contents of HTA solutions after adsorption to the glass beads. Chromic acid could be used to decompose the HTA in the solutions if you do not have access to a carbon analyzer. Oxidation of HTA will reduce the Cr (+6) in chromic acid to Cr (+3). A UV visible spectrometer can be used to measure the Cr(+3) formed. Chromic acid is prepared from sulfuric acid and potassium dichromate. Old methods to measure the organic matter content of soils used chromic acid. Chromic acid is not as commonly used any more because of the toxicity of Cr(+6).
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