Surfactant elemental analyses

Analysis and Fate of Surfactants in the Aquatic Environment Sample Preparation for Trace Element Analysis Non-destructive Microanalysis of Cultural Heritage Materials Chromatographic-mass spectrometric food analysis for trace determination of pesticide residues... 

To further characterize the effect of the ammonia hydrothermal treatment, we compared elemental analysis data and 1R spectra before and after ammonia hydrothermal treatment to quantitatively disclose the role of counterion between the silica framework and surfactants. In Table 2, the N/C molar ratio of the mesoporous materials prior to the ammonia hydrothermal treatment is nearly twice of that after the treatment. Moreover, the IR band at 1383 cm 1, which arises from the N03 stretch bending mode, completely disappears after ammonia hydrothermal treatment [20], These results verify that the existence of nitrate counterion (the nitrate/surfactant 1) between surfactant molecules and silica framework in the acid-made mesoporous materials. The bridging counterion N03 was completely removed after ammonia hydrothermal treatment. 

The pore diameter of the resulting materials, their specific surface area and mesopore volume depend on the size of attached ligands (see Table 1). The presence of bonded alkylsilyl groups (appropriate ratio C H) and a successful removal of all surfactant molecules and pyridine (complete absence of nitrogen) was shown by means of the elemental analysis. Table 1 contains also the surface coverage of the bonded ligands. 

TGA measurements showed that 90-95w% of the surfactant is extracted by this procedure. Elemental analysis, X-Ray diffraction and infrared analysis proved that the recrystallized extracted surfactant is identical to the original one, and we have re-used it several times without any decrease in the quality of the obtained MCM materials. 

Although AOT is also an anionic surfactant of the same type as DOLPA, haemoglobin cannot be transferred into the AOT reverse micellar phase, and most haemoglobin can be seen at the oil-water interface as a red precipitate. Adachi and Harada have reported that cytochrome c precipitated as a cytochrome c-AOT complex at low concentrations of AOT [7]. It was found that this precipitate is likewise the AOT-haemoglobin complex (AOT/haemoglobin = 120 1) from the results of elemental analysis [8]. These results indicate that the difference in the extraction ability of DOLPA and AOT might depend on the hydrophobicity of the surfactants provided to the hydrophilic proteins. 

For colloids with a physically adsorbed surfactant or cca, the adsorption isotherm is important. The adsorbant concentration on the particle surface can be measured by infrared spectroscopy using diffuse reflectance and by ESCA. Absolute concentrations are difficult to determine with ESCA on "rough" surfaces, and a calibration point is required with other techniques. The change of the concentration of adsorbant in solution after adsorption on the colloid surfaces can be detected by elemental analysis of supernatant with plasma emission or atomic absorption if adsorbant contains specific element(s). When colloids are sterically stabilized, the effectiveness of the stabilization can be evaluated with solvent-nonsolvent techniques and with temperature studies ( 25,26). 

Elemental analysis (EA) is a convenient method for determination of copolymer and blend composition if one homopolymer contains an element not present in the second one. For example, EA can be properly used to quantify nitrogen in copolymers containing acrylonitrile units and oxygen in polymeric surfactants such as poly(oxy-alkylene). Therefore, for a binary system, every element can be balanced according to the following equation ... 

The N alkylacrylamides were copolymerized with acrylamide via micellar copolymerization using sodium dodecylsulfate as the surfactant and potassium persulfate as the free-radical initiator. Monomer feed mole ratios were varied from 0.25 99.75 to 0.75 99.25 N-alkylacrylamide acrylamide. Following reaction, the polymers were purified by precipitation in acetone, dialysis, and lyophilization. Elemental analysis confirmed the absence of surfactant in the copolymers. 

Elemental analysis is useful only in the analysis of unknowns. Because the range of elements that occur in surfactants is limited the following tests are usually all that are necessary. It may safely be assumed that carbon, hydrogen and oxygen are present. Nitrogen, sulphur and phosphorus are the only other non-metals of interest. 

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