A surfactant may be added to the loading medium to aid dispersal of the AM esters; it is typically used at a concentration of <0.1% (wt/vol). For loading, the required volumes of the DMSO stock solutions of the AM ester and of the surfactant should be premixed and then dispersed into aqueous medium for loading. If the loading medium is buffered with bicarbonate, then loading should be done under a 5% CO2 atmosphere to prevent alkalinization of the medium through loss of CO2.