Phosphoric acid ionization analyzed

Szepesi et al. reported an ion-pair separation of eburnane alkaloids on a chemically bonded cyanopropyl stationary phase. As counter-ion, di-(2-ethyl hexyl)phosphoric acid or (+)-10-camphorsulfonic acid were used in a mobile phase consisting of hexane - chloroform -acetonitrile mixtures (Table 8.8, 8.9). Because of the poor solubility of the latter pairing ion, diethylamine (Table 8.9) was added to the mobile phase. Addition of diethylamine considerably reduced the k1 of the alkaloids, due to suppression of the ionization of the alkaloids. However, due to the strong acidic character of the pairing ion, ion-pairs were still formed under these conditions. The camphorsulfonic acid containing mobile phases were found to be very useful for the separation of optical isomers (Table 8.10, 8.11, Fig.8.8) 6. It was also found that the selectivity of the system could be altered by choosing different medium-polarity solvents (moderator solvents) as dioxane, chloroform or tetrahydrofuran. The polar component of the solvent system affected peak shape. Based on these observations, a method was developed to analyze the optical purity of vincamine and vinpocetine. For the ana-... 

This is an important reagent in this method. Start with a good quality distilled (not de-ionized) water and distill it once again in an all-glass apparatus. Reflux the distillate, about one liter at a time, with 10 g of potassium persulphate KgSaGg and 1-2 ml of 85% phosphoric acid for 4 hr and then distill it into a receiver, protected from dust, rejecting the first 100 and last 200 milliliters. Store in a clean glass-stoppered bottle, which is never left open. This water, when analyzed as described below, should not contain more than 0.2 mg C/liter. 

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