Brønsted acidity in deep eutectic solvents and ionic liquids.

Despite the importance of ionic liquids in a variety of fields, little is understood about the behaviour of protons in these media. The main difficulty arises due to the unknown activity of protons in non-aqueous solvents. This study presents acid dissociation constants for nine organic acids in deep eutectic solvents (DESs) using standard pH indicator solutes. The pKIn value for bromophenol blue was found by titrating the DES with triflic acid. The experimental method was developed to understand the acid-base properties of deep eutectic solvents, and through this study it was found that the organic acids studied were slightly less dissociated in the DES than in water with pKa values between 0.2 and 0.5 higher. pKIn values were also determined for two ionic liquids, [Bmim][BF4] and [Emim][acetate]. The anion of the ionic liquid changes the pH of the solution by acting as a buffer. [Emim][acetate] was found to be more basic than water. It is also shown that water significantly affects the pH of ionic liquids. This is thought to arise because aqueous mixtures with ionic liquids form heterogeneous solutions and the proton partitions into the aqueous phase. This study also attempted to develop an electrochemical pH sensor. It was shown that a linear response of cell potential vs. ln aH+ could be obtained but the slope for the correlation was less than that obtained in aqueous solutions. Finally it was shown that the liquid junction potential between two reference electrodes immersed in different DESs was dependent upon the pH difference between the liquids.

Novel potentiometric sensors for determination of ondansetron hydrochloride in pure and dosage form.

A new and sensitive potentiometric method has been developed and characterized for four novel sensors responsive to ondansetron hydrochloride. The potentiometric sensor method includes advancement of ondansetron hydrochloride sensors using a membrane comprised of molybdophosphoric acid (MPA) and ondansetron as an electro-active material in a polyvinylchloride (PVC) matrix membrane plasticized with di-butyl phthalate (DBPH), ortho-nitrophenyloctyl ether (O-NPOE), di-octyl phthalate (DOPH), or di-butyl phosphate (DBP). The validity of sensors in the present work has been examined, and steady and reproducible responses were obtained over the concentration ranges of 7.3 × 10-5 to 1.0 × 10-2, 6.6 × 10-6 to 1.0 × 10-2, 1.0 × 10-5 to 1.0 × 10-2, and 2.0 × 10-5 to 1.0 × 10-2 M for DBPH-, O-NPOE-, DOPH-, and DBP-ondansetron, respectively. The sensors revealed Nernstian gradients of 59.61 ± 0.50, 57.71 ± 0.23, 53.01 ± 0.14, and 53.20 ± 0.35 mV per decade individually with pH ranges of 2.5-5.5 in DBPH and 3.5-5.0 in O-NPOE electrodes, and 4.0-5.5 for both individual DOPH and DBP plasticized film-based sensors. The time responses for the sensors were 30, 32, 31, and 29 s for DBPH-, O-NPOE-, DOPH-, and DBP-ondansetron, respectively. The developed sensors also exhibited high selectivity towards ondansetron hydrochloride against different interfering species of inorganic particles with long-term stability of approximately 41, 36, 18, and multiple days for the DBPH, O-NPOE, DOPH, and DBP electrodes.