Trialkylsulfonium- and trialkylselenoniumhydroxides are pyrolytic alkylation reagents that derivatize acidic compounds quantitatively inside the injector of the gas chromatograph. Trimethyl-sulfoniumhydroxide and Triethylsulfoniumhydroxide, the analogues of selenium respectively are stable in cool methanol solution for at least 6 months. The reagents are easy to handle and the byproducts formed are very volatile. Therefore the application of ternary sulfonium- and selenoniumhydroxides is equivalent or even superior to the use of the well known quartary ammoniumhydroxides.