Electrophoretic study of nitrofurantoin in aqueous suspensions. Effect of the addition of a polymeric thickener.

The electrophoretic mobility of nitrofurantoin (based on the microelectrophoresis method) has been studied in dilute dispersions of the drug. Specifically, the effect of NaCl, CaCl2 and AlCl3, pH, and a thickener, Carbopol 934, was determined. The electrophoretic mobility (mu) increases in absolute terms when the pH is raised between 3 and 9, although mu remains negative in this pH range. The variation of absolute mobility ([mu[) with NaCl concentration shows a pronounced maximum for a concentration of about 10(-4) M. However, when the concentration of CaCl2 in the medium is increased, [mu[ decreases steadily. The effect of AlCl3 concentration on the mobility is markedly influenced by the pH of the dispersing medium although a general trend is observed for mu to become more positive with increasing concentration of the salt. Finally, Carbopol 934 appears to impart an extra negative charge to the nitrofurantoin surface, since higher negative mobilities were measured in the presence of the polymer.