Solvent and pH effects on fast and ultrasensitive 1,1′-oxalyldi(4-methyl)imidazole chemiluminescence

Abstract

Solvent and pH effects on fast and ultrasensitive 1,1′-oxalyldi(4-methyl)imidazole chemiluminescence (OD4MI–CL) were studied. The influences of these two factors on the complex OD4MI–CL reaction are discussed within a conceptual prototype for developing aqueous and non-aqueous capillary electrophoresis (ACE and NACE) devices with OD4MI–CL detection. The reaction channel length and OD4MI yield from the reaction between bis(2,4,6-trichlorophenyl) oxalate (TCPO) and 4-methylimidazole in the channel will be influenced by pH, water volume fraction, and cosolvent properties of the solution. Optimum OD4MI–CL efficiency is observed at pH 6.5 when 1-propanol, which has a low dielectric constant (ε = 20.8), is used as the NACE solvent in the separation channel. Water (ε = 80.1), the solvent in the ACE separation channel, acts similarly to a high dielectric constant organic solvent in NACE because the disadvantages normally associated with TCPO–CL reactions in water disappear due to the faster OD4MI–CL reaction versus OD4MI decomposition in aqueous solution. Therefore, it is expected that the OD4MI–CL detection system can be used in both NACE and ACE devices without requiring detector modifications. We also conclude that OD4MI–CL detection in NACE and ACE devices will be much more sensitive than the TCPO–CL detection used in current NACE devices.