ELECTROSPRAY MASS-SPECTROMETRY - ETHYLENE-GLYCOL AS A SOLVENT AND ITSEFFECTS ON ION DESORPTION

Ethylene glycol solutions of gramicidin S, myoglobin and tetrabutylamm onium bromide were analysed by means of electrospray mass spectrometry and their spectra were compared with those of aqueous solutions. The evaporation of water and ethylene glycol droplets, initially at room o r elevated temperature, in air at room temperature was modelled. It wa s found that under conditions where a water droplet's radius would shr ink by approximately 30%, an ethylene glycol droplet shrinks negligibl y. Further, droplets that are initially hot (such as those that are ej ected from a heated electrospray needle) cool very rapidly owing to ev aporation and heat loss to ambient air, and subsequently evaporate muc h like droplets that are initially at room temperature. For gramicidin S, the ion abundances in ethylene glycol as solvent were approximatel y 200 times lower than those in water under room temperature operating conditions. In experiments where the spray probe was heated to approx imately 100-degrees-C to reduce the viscosity of ethylene glycol, the gramicidin response difference between the solvents decreased to about a factor of 40. Similar trends were observed for myoglobin and the te trabutylammonium ion. The gramicidin abundances in ethylene glycol, re lative to those in water, are orders of magnitude too large to be acco unted for using the conventional solvent evaporation model. It is spec ulated that decreasing the viscosity increases the velocity of ions dr ifting in ethylene glycol towards the solution/air interface and incre ases the total number of analyte ions desorbed at the Taylor cone duri ng electrospray.