Importance of injection solution composition for LC-MS-MS methods

For the first time, the influence of the injection solution composition on the quality of LC-MS-MS methods, in terms of column efficiency and peak sha pe, was systematically investigated. Various types of compounds, including polar ionic acidic, polar ionic basic and non-polar neutral compounds, were prepared in different solutions ranging from 100% water to 100% acetonitri le, Different volumes of these solutions were injected onto either C-18 or silica columns connected to tandem mass spectrometry. The mobile phases con sisted of acetonitrile, water, and small amounts of volatile acid or buffer . On silica columns, the influence of injection solution on the peak shape and column efficiency was straightforward. The sharpest peaks and the highe st column efficiency were obtained with 100% acetonitrile as the injection solvent. On C-18 columns, this type of influence was less clear due to the dual retention mechanism of the bonded phase and of the residual silanol gr oups. On C-18 column, retention due to residual silanol groups was signific ant even with a mobile phase containing less than 50%, acetonitrile. Poor p eak shape was observed when the injection solution had a stronger eluting s trength than mobile phase, particularly for early eluting peaks, (C) 2001 E lsevier Science B.V. All rights reserved.