Effect of water addition to super/sub-critical fluid mobile-phases for achiral and chiral separations

Use of water as an additive in sub/supercritical fluid chromatography (SFC) is becoming more common. Water can significantly modify mobile-phase properties by increasing the polarity and also acting as an additional source of H-bonding - resulting in novel selectivities. Addition of water to SFC mobile-phases increases its solvating power allowing the technique to work with highly polar analytes previously thought to be out-of-scope. A lesser discussed but equally important consequence of water addition is the role it plays in modulating analyte interactions with the stationary-phase. These interactions can be beneficial in terms of having better peak shape, increased efficiency and lesser retention time. Early studies that used water in neat CO2 bear testimony to this observation. This review discusses all these aspects of incorporating water in SFC mobile-phases and aims to elucidate the topic for wider acceptance and further investigation. • Presence of water in SFC mobile-phases significantly alter retention behavior.• Early studies employed water with neat CO2 for stationary-phase modification.• Current studies use water with cosolvents for mobile-phase modification as well.• A discussion on advantages, pitfalls, gaps and possible future work is presented.