Commercially available7LiOH was used for collecting volcanic gas samples on the island of Vulcano, Southern Italy, to determine trace elements by NAA. The high -background activity, which is induced when NaOH solutions are used as collecting agents was avoided in this way. While several elements (Cl, Br, I, As) could be determined in the collected samples, activation products of impurities in7LiOH produced considerable -background and this prevented the determination of other trace elements. An ion-exchange procedure for reducing impurities in7LiOH solutions, in particular of Hg, Ta and W, was then developed and is described here. This procedure, supplemented by steps to eliminate interference from18F in the irradiated samples due to small amounts of6Li in the7LiOH employed will allow very sensitive determinations of further trace elements in volcanic gases.