LC/MS has been proposed to solve the problem of the inability of conventional GC/MS to analyze molecules considered either thermally labile of low volatility or high polarity. Over the last decade, many techniques including direct liquid introduction interfaces, mechanical transport dev ices, thermospray, particle beam interfaces, electrospray and ionspray have evolved to find practical application in LC/MS. For direct comparision of these different methods, a number of important criteria can facilitate the discussion of their relative strengths and weakness, the structure, eluant capacity, and choice of ionization method. The applications of LC/MS are also introduced.