The relationship between Osmolarity and Osmolality of Infusion Solutions of Monosaccharides

Concentration of Osmotically active solutes plays a key role in an acceptance of parenteral infusions by patients. It is generally recommended that labels of infusions should list osmolarity (osmol/l). However, osmometer can only read osmolality (osmol/kg). The conversion of the experimental readings to the declared osmotic concentration wants to study the relationship between osmolality and osmolarity. The conversion factor defined as ratio of the solution molarity and its molality was introduced to convert osmolality to osmolarity. Unfortunately, the conversion factor changes with dilution. In this work, the total molal volume of the solute in aqueous solution, which is not influenced by the solution concentration, was used instead for aqueous solutions of monosaccharides. The method allowing estimation of the solute molal volume from its molal weight and true powder density was demonstrated. Finally, the original equation employing true density of the powder was recommended for conversion osmolality to osmolarity.