Analysis of silyl derivatives of methylphosphonic acid esters by gas chromatography-mass spectrometry with atmospheric pressure photoionization

Using trimethylsilyl (TMS) and tert -butyldimethylsilyl (TBDMS) derivatives of methylphosphonic acid and methylphosphonic acid esters, a comparative study of two ionization methods, namely, atmospheric pressure photoionization (APPhI) and photochemical ionization (APCPhI), in gas chromatography/mass spectrometry has been performed. It has been shown that, in the case of APPhI, the mass spectra of TMS and TBDMS derivatives contained only peaks corresponding to [M + 73] + and [M + 115] + (or [M + Si(Me) 3 ] + and [M + Si( t Bu)(Me) 2 ] + ions, respectively, where M is the molecular mass of a respective TMS or TBDMS derivative of methylphosphonic ester). APCPhI mass spectra recorded in the presence of acetone as a reagent substance consisted of only peaks of [M + H] + and [M + M A + H] + ions (M A is acetone molecule). The corresponding detection limits for silylated derivatives in APPhI and APCPhI were 30–125 pg and 1.1–23 pg, respectively (depending on the analyte).