Analytica Chimica Acta, 225 (1989) 409-414 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 409 zyxwvu Short Communication QUANTITATION OF p- AND m-METHYLSTYRENES BY LIQUID CHROMATOGRAPHY AND 13C NUCLEAR MAGNETIC RESONANCE SPECTROMETRY S.S. YANG, M.E. GANGODA and R.K. GILPIN* Department of Chemistry, Kent State University, Kent, OH 44242 (U.S A.) (Received 31st October 1988) Summary. The molar ratio of p- and m-methylstyrene in mixtures is determined by liquid chro- matography and i3C NMR spectrometry. In the former instance, separation and quantitation are achieved using an adamantyl-modified column with a mobile phase of ethanol/water (30 + 70, v/ v) containing 0.01 M &.zyclodextrin. In the latter instance, a ‘H-decoupled i3C NMR technique is described for the determination of the positional isomers. The results obtained by both methods are self-consistent, with a standard deviation for the molar ratio of the para and meta isomers of less than k 0.01. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Owing to shortages of benzene during the period following World War II, methylstyrene was developed as a possible substitute for styrene because tol- uene instead of benzene could be used as the starting material [ zyxwvutsrqponmlkji 11. Although this attempt ceased because of the rapid development of techniques for ben- zene preparations, methylstyrene continues to be used today in copolymers and as a specialty monomer for paint, varnish and polyester preparations. The methylstyrene marketed usually consists of a mixture of zyxwvutsrqponmlkjihgfedcba paru and metu isomers. The analysis of mixtures of these isomers is often difficult [ 2-41. In the current study, two alternative methods using liquid chromatography (LC ) and 13Cnuclear magnetic resonance (NMR) spectrometry were developed to de- termine the molar ratio of p- and m-methylstyrene in mixtures. In the LC method, separation of the isomers was achieved on a column packed with adamantyl-modified silica. The adamantyl surface has been shown to have enhanced performance for basic compounds that interact strongly with resid- ual silanols [ 51 and its selectivity has been found to be similar to that of certain non-polar surfaces (Cs, C1s, etc.) [ 61. The adamantyl surface has shown good chromatographic properties in the analysis of cough/cold preparations [ 71. The mobile phase used was ethanol/water (30+ 70) containing 0.01 M j?- cyclodextrin (CD ). Cyclodextrins have been used as mobile-phase modifiers for the separations of positional and geometrical isomers in a number of in- stances [&lo]. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0003-2670/89/$03.50 0 1989 Elsevier Science Publishers B.V.