Mobile proton condition

Figure 2 demonstrates the effects of adding octane sulfonic acid to the injection solvent for a reverse-phase separation of pyridinium and deoxypyri-dinium, components of collagen, in rat urine. These polyamine containing compounds are protonated and poorly retained under the usual acidic or neutral mobile-phase conditions. The sample preparation method is simple dilution and does not afford the removal of salts from the sample. Therefore if the analytes were inadequately retained the sensitivity, as well as the method accuracy, would suffer. As the concentration of octane sulfonic acid is increased to 50 mM (Fig. 2a), both the retention time and the peak response for the analytes improve significantly. Litde improvement is obtained at higher concentrations of octane sulfonic acid and retention is not strongly dependent on the injection volume (Fig. 2b). To protect the ion source from the fouling effects of octane sulfonic acid in the injection solvent, a timed divert valve was inserted before the ion source to shunt the excess ion pair reagents to waste during the first few minutes of each injection.

As mentioned earlier, the high-resolution H NMR spectra recorded here for static samples are linked to mobile water molecules but the dc relaxation (TSDC) is caused by mobile protons and other ions when condition of throughout percolation of ions (between two electrodes in a TSDC cell) is achieved on heating of a frozen system. Both dynamic phenomena are temperature dependent (Figure 1.210). 

In the range of reactant concentrations experimentally explored, the reaction is very sluggish if the initial pH of the solution is above 7, whereas when pH < 6, it very rapidly drops to pH 2. When operated in a CSTR, the reaction exhibits steady-state bistability, with pH differences between branches up to ApH 8), and does not lead to kinetic oscillations. However, in an OSFR, it was shown to display a diffusion-driven oscillatory instability because of the long-range activation of the free protons. But this instabihty can be quenched by weakly buffering the system with a low-mobility proton-binding species [58]. This condition is straightforwardly... 

This suggests that in solution there will be an acidity (pH) at which the amino acids will exist in the zwitterionic form, or have no net charge. The pH at which this occurs as a result of the proton condition is referred to as the isoionic point pL. Similarly, when it is observed that there is no net charge on the molecule within the system as judged by experimental conditions (i.e., no mobility during an electrophoresis experiment) the pH at which this occurs is referred to as the isoelectric point (p/J. For an aqueous solution of amino acids ... 

Because carotenes lack heteroatoms such as oxygen to which protons or sodium cations might attach, no ions are usually detected for these hydrocarbon compounds during ESI in positive mode, although protonated molecules and sodium adducts were observed for xanthophyUs under normal conditions with MeOH, MTBE, and H2O as a mobile phase from HPLC. Addition of a heptafluorobutanol oxidant at 0.1 or 0.5% produced abundant molecular ions of p-carotene with high reproducibility. Substitution of MeOH for acetonitrile produced similar limits of detection. ... 

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