Gyoung Won Kang

RAPID DETERMINATION OF WATER-SOLUBLE B GROUP VITAMINS IN URINE BY GRADIENT LC/MS WITH A DISPOSABLE HOME-MADE MICROCOLUMN

ABSTRACT A rapid and simple analytical method without pretreatment, based on gradient LC/MS with a disposable microcolumn, has been developed to determine B group vitamins in urine. Urine samples were directly injected to the disposable home-made microcolumn. A 5 cm silica capillary with a sintered silica frit was placed in the microcolumn outlet. A 1/32 inch coupling union with graphite Vespel ferrules was used to give a safe and void volume free connection between the 5 cm capillary and a long capillary to the electrospray interface. The microcolumn can be emptied after being used for a series of urine samples, and repacked with fresh stationary phase. Healthy volunteers swallowed an overdose of vitamin pills, and the urine samples were collected 1,2,3,5, and 8 hours after swallowing. Vitamins immediately showed up in urine, hit the maximum, and disappeared swiftly. This technique is expected to have some application for clinical purposes.

Thermodynamic Study of Enantioseparation of Arylpropionic Acids with a Chiralcel OJ-H Stationary Phase

Abstract Enantioseparation data of ketoprofen, fenoprofen, and ibuprofen have been obtained and thermodynamically analyzed. The Chiralcel OJ column was used for chiral separation. The mobile phases were 100/0, 95/5, and 90/10 v/v% hexane/2‐propanol mixtures with 0.5% acetic acid. The capacity factors of the solutes were measured at 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C. The thermodynamic properties of solute transfer from the mobile to the stationary phase were critically analyzed in comparison with the thermodynamic properties obtained by the Chirex 3001 phase in methanol/water eluents. The well‐known enthalpic–entropic compensation is clearly valid for the systems studied in this research. The solute–Chiralcel OJ interactions of R‐ and S‐ibuprofen were found weaker than those of R‐ and S‐fenoprofen and ketoprofen, since ibuprofen is much less polar than others and subject to much weaker interactions with the stationary phase. Careful interpretation of the data revealed that the solute–Chiralcel OJ interaction is stronger than the solute–Chirex 3001 interaction. It is likely that the supramolecular structure of the Chiralcel OJ phase with chiral cavities provides more versatile functional and steric environments, to give stronger interactions and better chiral recognition and discrimination. There appeared extrema in the plots of ΔH 0 and ΔS 0 against eluent composition obtained in the Chiralcel OJ system. Adsorption of 2‐propanol to multiple sites with different priorities and different steric environments seems to cause such a phenomenon.

Thermodynamic Study of Enantioseparation of Arylpropionic Acids with the Chirex 3001 Stationary Phase

Abstract Enantioseparation data of ketoprofen, fenoprofen, and ibuprofen have been obtained and thermodynamically analyzed. The Chirex 3001 column was used for chiral separation. The mobile phases were 100/0, 90/10, 80/20, and 70/30 v/v% methanol/water mixtures with 0.02 M ammonium acetate, and 80/20 v/v% methanol/water with 0.005, 0.01, and 0.02 M ammonium acetate. The capacity factors of the solutes were measured at 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C. The thermodynamic properties of solute transfer from the mobile to the stationary phase were strongly dependent on mobile phase composition. The variations in solute transfer enthalpy (ΔH°) and entropy (ΔS°) were found to be primarily influenced by the cavity formation effect. The differential thermodynamic properties between the R‐ and S‐isomers were also computed. The absolute magnitudes of ΔΔH° and TΔΔS° were far smaller than those of ΔH° and TΔS°. The variation trend of ΔΔH° is very similar to that of TΔΔS°, and the differential free energy of transfer (ΔΔH°−TΔΔS°) is slightly negative and virtually invariant with respect to mobile phase composition. S‐profen isomers were found more retained in the Chirex 3001 column although, the difference in solute‐stationary phase interactions between the R‐ and S‐enantiomers is very low.

A simplified molecular mechanics calculation of enantioseparation of arylpropionic acids in chirex 3001 stationary phase

Abstract A very simplified molecular mechanics calculation approach is introduced. We simply used the most stable conformations of the CSP and R‐ and S‐enantiomers, and considered only 10–20 major CSP–solute configurations and determined the lowest energy of each configuration by manually placing the solute around the CSP on a trial and error basis and by letting the system be optimized. The simplified molecular mechanics calculation of this study is somewhat useful to predict retention orders or to catch a rough figure on how differential interactions take place.