title: ATR-FTIR characterization of transport properties of benzoic acid ion-pairs in silicone membranes.
abstract: A novel technique based on Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to study the transport of benzoic acid ion-pairs/salts in silicone membranes. The benzoic acid ion-pairs were prepared using various counter-ions with different degrees of lipophilicity, e.g. triethylamine (TA), diethylamine (DE), tert-butylamine (t-BA), 2-amino-2-methyl-propanol (AMP), and 2-amino-2-methyl-propanediol (AMPD). Silicone membrane, treated or untreated with propylene glycol (PG), was placed on the surface of a ZnSe crystal and the transport solution was applied to the upper surface of the membrane. A mathematical model, based on Fick's second law describing the build up of permeant concentration at the membrane/crystal interface with time was applied to determine diffusion coefficients. Absorption due to the acid (1700 cm(-1)) or benzoate anion (1555 cm(-1)) was observed at different regions without the interference from PG or silicone membrane. Benzoate anion, a charged species, was observed to permeate the membrane. The permeation of benzoate anion from sodium benzoate and polar ion-pairs of AMP and AMPD was very low in contrast to their high-saturated concentrations in PG as compared to the t-BA ion-pair. This indicated that benzoate anion preferentially permeates the membrane as an ion-pair rather than a single anion; otherwise its permeation should correspond to its concentration in PG instead of the lipophilicity of the ion-pairs. Additionally, the diffusion coefficient values of benzoic acid and benzoate anions through the treated and untreated membranes were not statistically different.
authors.affiliation: Faculty of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand. tvimon@ratree.psu.ac.th
authors.forename: Vimon
authors.initials: V
authors.lastname: Tantishaiyakul
authors.forename: Narubodee
authors.initials: N
authors.lastname: Phadoongsombut
authors.forename: Wibul
authors.initials: W
authors.lastname: Wongpuwarak
authors.forename: Jatupit
authors.initials: J
authors.lastname: Thungtiwachgul
authors.forename: Damrongsak
authors.initials: D
authors.lastname: Faroongsarng
authors.forename: Kamonthip
authors.initials: K
authors.lastname: Wiwattanawongsa
authors.forename: Yon
authors.initials: Y
authors.lastname: Rojanasakul
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry*; D019817:Benzoic Acid / Q000737:chemistry*; D008567:Membranes, Artificial; D010539:Permeability; D012828:Silicones; D017550:Spectroscopy, Fourier Transform Infrared; D013678:Technology, Pharmaceutical
chemical_list: D000935:Antifungal Agents; D008567:Membranes, Artificial; D012828:Silicones; D019817:Benzoic Acid