Gas Chromatographic Determination of Small Amount of Impurities in Naphthalene

Abstract

n the commercial reagent grade naphthalene were carried out by gas chromatographic method. Benzo[ b ]thiophene and 2-methylnaphalene, contained as a relatively large amount of impurities in the naphthalene were detected directly with flame ionization detector (FID). Benzo[ b ]thiophene whose con centration in the naphthalene being lower than 20 ppm could be directly determined with flame photometric detector (FPD) up to 1 ppm.
To the naphthalene, whose impurity concentration being lower than the limit of detection of FID or FPD, the preconcentration technique by rapid zone melting was applied and additional 9 impurities, such as indan, indene, tetralin, 1-methylindene, 1-methylnaphthalene, 2-methyl benzo[ b ]thiophene, quinoline, 2, 6-dimethylnaphalene and biphenyl, were identified by gas chromatography-mass spectrometry.
The commercial spec ial grade naphthalene containing ca. 0.5% impurities was purified by zone melting method and recrystallization. Rapid zone melting conditions for concentration of impurities and purification of the naphthalene were evaluated and the best condition was found as follows: rotation speed is 125 Hz, alternating period of rotation is 0.4 sec and zone travel rate is 60 cm/hr. For the naphthalene containing large amount of impurities, rapid zone melting after recrystallization was found to be effective.