| Popis: |
The potentiometric titration (PT) method has been applied for the first time to investigate the stability of L-ascorbic acid (H2Asc) and to determine its degradation products in aqueous solutions. The presented electrochemical procedures can be considered to be a fast, simple and inexpensive way to control the stability of H2Asc in a regular analytical practice as well as in the chemical and pharmaceutical industries. Experimental data as well as modeling suggest that the enolic form of 2,3-diketogulonic acid predominates in a solution as the main product of dehydroascorbate (DHA) degradation. Furthermore, the PT results supported by conductometric measurements (CM) and electrospray ionization mass spectrometry (ESI/MS) data enable us to propose the putative mechanism of the H2Asc decomposition. Moreover, it has been proven that among different types of investigated electrolytes (KNO3, KClO4 and KSCN), the thiocyanate ions (SCN-) reveal the stabilizing effect against the degradation of H2Asc. Thus, the presence of SCN- in the H2Asc solution is proposed as an alternative way for some organic solvents earlier used. Finally, a new paraffin-protection-layer procedure has been recommended for studying as well as storage of the solutions comprising components sensitive to external factors (e.g. O2, CO2) and to evaporation. |
