Acids, cyclodextrin effect columns

Determination of enantiomeric purity. Three mL of the solution was diluted in 50 mL of acetone and treated with 0.3 g of potassium permanganate and 0.32 g magnesium sulfate to effect oxidation of the product aldehydes to their respective acids. The mixture was stirred at room temperature for 30 minutes after which time the solvent was removed under reduced pressure. The residue was extracted three times with 50 mL of hot water. The three aqueous solutions were then combined, filtered, and washed with 50 mL of chloroform. The aqueous layer was acidified with hydrochloric acid to a pH of 2 and then extracted with 50 mL of chloroform. The chloroform was removed in vacuo and the resulting residue dissolved in 0,5 mL of toluene. This solution was analyzed by GC on a chiral /3-cyclodextrin column which separated the two enantiomers of the resulting 2-arylpropanoic acid. This analysis indicated a 91 9 ratio of the S and R enantiomers for an ee of 82%. 

Today, there are a number of effective chiral stationary phases suitable for GC, some based on amino acid derivatives, some on polysiloxane polymers and some, probably the more popular, based on cyclodextrin derivatives. Very few chiral columns, if any, are packed, the vast majority being open tubular columns having various lengths and an I.D. that ranges from about 250 pm or 320 pm There has, however, been a recent trend to smaller diameter columns cf. 125 pm) to achieve higher efficiencies and even shorter analysis times. 

The inclusion complex formations between the cyclodextrins and the mandelic acid enantiomers were evaluated. The effects of various factors such as the composition of the mobile phase, concentration of cyclodextrins and the column temperature on the retention and the enantioselectivity were studied. 

The effects of various factors, such as the organic modifier, different ODS C18 columns and the concentration of the hydrox5rpropyl-j3-cyclodextrin, were investigated. The chiral mobile phase was composed of methanol or acetonitrile and 0.5% tilethylammonium acetate buffer at pH 3.0 added with 25 mmol l of hydrox5rpropyl-j3-cyclodextrin. Triethylammonium acetate is a volatile buffering agent. It is prepared from equimolar quantities of triethylamine and acetic acid. Baseline separations could be reached for all race-mates. 

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