Monolithic　silica　capillary　columns　synthesized　following　a　three-level　design　were　evaluated　for　the　electrochromatographic　separation　of　acidic　and　neutral　compounds.　The　influences　of　four　factors　in　the　sol-gel　synthesis,　i.e.　the　concentrations　of　tetramethylorthosilicate　(TMOS)　and　PEG　in　the　starting　mixture,　the　gelation　temperature　and　the　silanization　modifying　time,　on　the　electrochromatographic　performance　of　the　resulting　C18-silica　capillary　monoliths　were　studied.　The　considered　responses　were　retention　factor,　resolution,　symmetry　factor,　column　efficiency,　electrokinetic　porosity　and　the　equivalent　length　of　the　monolith.　The　four　factors　were　varied　to　change　the　pore　structure　and　the　surface　coverage　with　octadecyl　moieties,　resulting　in　nine　stationary　phases.　The　retentive　properties　of　the　columns　were　initially　characterized　with　alkylbenzenes.　Next,　the　separation　for　acetylsalicylic　acid　(ASA)　and　its　related　compounds　was　optimized　and　used　to　evaluate　the　performance　of　the　nine　stationary　phases　considering　six　responses.　A　compromise　between　the　different　responses　was　found　around　higher　concentrations　of　tetramethylorthosilicate　and　PEG　with　a　lower　gelation　temperature　and　a　modifying　time　of　2　h.　Column　efficiencies　up　to　96　000　plates/m　and　resolutions　above　1.9　were　obtained　for　the　acetylsalicylic　acid　separation,　with　a　sufficient　EOF　to　yield　rapid　analysis,　which　showed　improvements　over　the　center-point　stationary　phase.　Copyright　©　2011　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.