title: pH of solution greatly affects sorption of ionizable compounds into low-density polyethylene film.
abstract: Sorption of ionizable compounds of pyridines and aromatic carboxylic acids into low-density polyethylene (LDPE) film was investigated as a function of pH ranging from 4 to 7. The sorptions for pyridines were increased with increasing pH. Within the range examined, pH 7 was observed to promote the highest degree of sorption. When the pH increased by one unit from 6 to 7, the sorptions for 2-propylpyridine and 2,4,6-trimethylpyridine were both increased approximately 3.8 and 10.5 times, respectively. At pH 4, the sorption for the pyridines entirely disappeared. In contrast, the sorptions for aromatic carboxylic acids increased with decreasing pH. Within the range examined, pH 4 was observed to promote the highest degree of sorption. The magnitude of sorption for pyridines and carboxylic acids apparently depended on the affinity (delta(c)) of these compounds for LDPE film. Another factor affecting the sorption at various pHs was the pK(a) of these compounds; the sorption greatly decreased with the ionization degree of these compounds. To elucidate the phenomena, the following thermodynamic sorption equation was applied: S = S(0)gamma exp[V(v){(delta(w) - delta(v))(2) - delta(c)(2))/RT}. The plots of ln S for pyridines vs the term of the equation gave an insufficient relationship (r = 0.519). In contrast, taking into account the ratio (chi(i)()) of concentration of un-ionized compound to total concentration, the improvement for the equation was made: S' = S/chi(i)() = S(0)gamma exp[V(v){(delta(w) - delta(v))(2) - delta(c)(2))/RT}. The plots of ln S' vs the term of the equation gave a better relationship (r = 0.884). Furthermore, the equation was also applicable for the sorption behavior of carboxylic acids into LDPE (r = 0.769).
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Hiroya
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Toshiro
authors.initials: T
authors.lastname: Matsui
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ohtsu
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Watanabe
authors.forename: Keiko
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Matsumoto
mesh_terms: D000327:Adsorption; D002264:Carboxylic Acids / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry*; D020959:Polyethylene / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012996:Solutions
chemical_list: D002264:Carboxylic Acids; D007477:Ions; D011725:Pyridines; D012996:Solutions; D020959:Polyethylene