The ratio of citric acid to D-isocitric acid can be used to distinguish authentic and adulterated fruit juices. To separate DL-isocitric acid enantiomers, we used ligand exchange CE. D-Quinic acid was used as a chiral selector ligand and Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions were used as the central ions of the chiral selector in the BGE. DL-Isocitric acid was found to be enantioseparated with the above metal ions except for Mn(II) ion. The optimum running conditions for the analysis of D- and L-isocitric acids along with citric acid, an isomer of isocitric acid, were found to be a BGE (pH 5.0) containing 30% ACN, 20 mM acetic acid, 20 mM NiSO(4), and 80 mM D-quinic acid. Under these conditions, DL-isocitric and citric acids in fruit juices were analyzed successfully.
Separation membranes are used in many fields ranging from medical science to industry, and much effort has been devoted to the development of new membranes with high qualities. [1][2][3] Recently, inorganic membranes have attracted much attention because of their superior mechanical strength, thermal stability and resistance to organic solvents. A variety of preparation and application methods of inorganic membranes have been reported. [4][5][6][7][8][9][10][11][12][13][14][15] Zeolites 4-8 and ceramics 9-14 are frequently used as sources of inorganic membranes. Zeolites are porous crystalline materials, which have a high surface area to volume ratio. Membranes made of zeolites are used for catalysts, 5 pervaporation 6,7 and high temperature separation of hydrocarbon isomer vapors. 8 Ceramics such as alumina are hard and heat-resistant materials made with nonmetallic minerals, and ceramic membranes for gas separation 13 and catalysts 14 have been synthesized.Mesoporous silica has also been adopted as a source material in the synthesis of inorganic membranes. 9,15 Mesoporous silica is an ordered material that has three different mesophases: lamellar, cubic and hexagonal. 16,17 In particular, the hexagonal mesophase possesses highly regular arrays of uniform-sized channels whose diameters are in the approximate range of 1 to over 10 nm depending on the surfactants and reaction parameters. Because of its porosity, high surface area, ordered pore arrangement and pore size uniformity, mesoporous silica has been the subject of many theoretical and applied studies. 18 For practical applications, the morphology of mesoporous silica is very important. The film is an ideal morphology for separation membranes, sensor 19,20 and optics. 21,22 Usually, mesoporous silica films are prepared on a flat substrate by dipor spin-coating methods. [23][24][25] However, in the case of hexagonal mesoporous silica, the channels are aligned parallel to the substrate surface, and transport of molecules across the film is not possible. In order to achieve separation, straight channels should be oriented perpendicular to the surface to transport molecules across the film. To solve this problem, instead of hexagonal mesoporous silica, some researchers have used cubic mesoporous silica to synthesize the inorganic membrane. 15,19 Recently, a porous anodic alumina membrane with a perpendicularly oriented silica-surfactant nanochannel assembly membrane (NAM) was synthesized. 26 The porous anodic alumina membrane has a packed array of columnar pores ranging from tens to hundreds of nanometers in diameter, and the channel direction of the columnar pores is perpendicular to the membrane.When a precursor solution containing cetyltrimethylammonium bromide (CTAB) surfactant and tetraethyl orthosilicate (TEOS) as a silica source is introduced into the alumina pores, highly ordered hexagonally arranged silica-surfactant nanochannels with pores of 3.4 nm diameter are assembled inside the alumina pores. The channel direction of mesoporous silica is predomi...
Nicotine (NC) and its related compounds (cotinine (CN), nornicotine (NN), anatabine (AT) and anabasine (AB)) were simultaneously enantioseparated by CE using a capillary with amino groups and sulfated beta-CD as a chiral selector. The optimum running conditions were found to be 30 mM acetate buffer (pH 5.0) containing 8% sulfated beta-CD with an applied voltage of +15 kV at 30 degrees C using direct detection at 260 nm. Using a capillary coated with amino groups, the EOF migrates toward the positive pole. However, when sulfated beta-CD was added to the BGE, it was found that the EOF migrated toward the negative pole due to ionic adsorption of sulfated beta-CD to amino groups on the capillary inner wall. All the cationic analytes migrated as anions, suggesting that they formed stable anionic complexes with sulfated beta-CD. With this system and a simple pretreatment with mini-cartridges, NC alkaloids in five cigarette samples were enantioseparated. As a result, each of the compounds except for CN was detected. In the case of NC, only (S)-NC was detected (more than 99.9%), but in the case of NN, AT and AB, the ratios of (S)-isomer to total isomers were in the ranges 58-70, 81-85 and 59-65%, respectively. On the other hand, only NC was detected in cigarette smoke and the ratio of (S)- and (R)-NCs was 96:4. The amounts of NC alkaloids in cigarettes suggest that the production of (R)-NC resulted from racemization due to the high temperature/burning of the cigarette.
The possibility of using porous anodic alumina membranes as a column for normal-phase high performance liquid chromatography was evaluated using phenol and toluene with mobile phases having different solvent compositions.
Chiral resolution of isoxanthohumol (IX) in beer samples was performed by hydroxypropyl-gamma-cyclodextrin-modified micellar electrokinetic chromatography. The optimum running conditions were found to be 20 mM phosphate buffer (pH 7.0) containing 45 mM hydroxypropyl-gamma-cyclodextrin and 100 mM sodium dodecyl sulfate with an effective voltage of +20 kV at 20 degrees C using direct detection at 210, 295, and 370 nm. IX was detected in 12 beer samples and the total levels of (+)- and (-)-IX ranged from 0.15 to 1.4 mg/L. But the amount of xanthohumol (XN) was below the detection limit (0.017 mg/L). Each level of (-)-IX was almost the same as that of (+)-IX, suggesting that IX was a racemic mixture in these beer samples. The racemization of IX in beer could be attributed to the production of a racemic mixture from XN during boiling and to the fact that IX enantiomers were easily interconverted.
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