title: [Solubility behavior of four diastereomeric salts and two amino acids in near-critical CO2].
abstract: OBJECTIVE
  To establish a suitable condition for extraction of phenylalanine (Phe), 5-hydroxytryptophan (5-OH-Trp) and four diastereomeric salts, (1R,2S)-ephedrine- (2S,3S)-tartaric acid, (1R,2S)-ephedrine-(2R,3R)-tartaric acid, (1S,2S)-pseudoephedrine-(2S,3S)-tartaric acid, (1S,2S)-pseudoephedrine- (2R,3R)-tartaric acid in supercritical fluid extraction and to assess the solubilities of Phe, 5-OH-Trp and the four diastereomeric salts in CO2.
  
  
  METHODS
  Single-pass method and HPCE.
  
  
  RESULTS
  The solubilities of Phe, 5-OH-Trp and the four diastereomeric salts in CO2 were determined over temperature and pressure ranges of 25-50 degrees C and 6.32-34.03 MPa respectively. The experimental results showed that the solubilities of Phe, 5-OH-Trp and the four diastereomeric salts do not increase with density of CO2. There existed a maximum in the critical region of CO2.
  
  
  CONCLUSIONS
  The dramatically high solubilities in the pressure of 6.32-7.78 MPa show a critical behavior, which can be explained by critical characteristic through thermodynamics analysis. The results suggest that the separation of Phe, 5-OH-Trp and the four diastereomeric salts is more efficient in critical region of CO2.
authors.affiliation: Department of Pharmacy, Changhai Hospital, Second Military Medical University, Shanghai 200433, China. gaolh2002@sohu.com
authors.forename: Li-hong
authors.initials: LH
authors.lastname: Gao
authors.forename: Hong-lai
authors.initials: HL
authors.lastname: Liu
authors.forename: Shui-hong
authors.initials: SH
authors.lastname: Chai
authors.forename: Yi-feng
authors.initials: YF
authors.lastname: Cai
authors.forename: Li-li
authors.initials: LL
authors.lastname: Liu
authors.forename: Yu-tian
authors.initials: YT
authors.lastname: Wu
mesh_terms: D006916:5-Hydroxytryptophan / Q000737:chemistry*; D004809:Ephedrine / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D011312:Pressure; D012995:Solubility; D013237:Stereoisomerism; D013644:Tartrates / Q000737:chemistry*; D013696:Temperature
chemical_list: D013644:Tartrates; D010649:Phenylalanine; D006916:5-Hydroxytryptophan; D004809:Ephedrine; C029768:tartaric acid