Alternative Green Solvents and
Hyphenated Techniques
Alternative green solvents
▪ Subcritical water
▪ Supercritical fluids
▪ Bio-based solvents
▪ Surfactant-based solvents
▪ Deep eutectic solvents
▪ Ionic liquids
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Subcritical water
= liquid water at temperature and pressure below its critical point (TC = 374.15 °C,
PC = 22.1 MPa)
= pressurized hot water extraction = superheated water extraction = pressurized
liquid extraction
▪ dielectric constant, viscosity, surface tension; diffusion coefficient
▪ similar to ACN, MeOH, or EtOH
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Pressurized liquid extraction (PLE)
Supercritical fluids
= substances at temperature and pressure above their critical points
▪ permeability of the solvents
▪ CO2 (TC = 31 °C, PC = 74 bar), rarely EtOH or water
▪ energy demanding
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Supercritical fluid extraction (SFE)
Bio-based solvents
= solvents produced from biomass with a renewable origin (crops, forest products)
▪ bio-ethanol, bio-acetone, D-limonene, glycerol, ethyl lactate, ...
▪ cheap, accessible
▪ limited application
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Surfactant-based solvents
= solvents that decrease the surface tension
▪ aqueous solvents with the addition of surfactants generate micelles,
microemulsions, hexagonal phases, or vesicles
▪ Triton, Tween, …
▪ cheap, highly efficient, and user-friendly
▪ incompatibility with some instruments (LC or GC)
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Deep eutectic solvents
= a combination of hydrogen bond acceptor and hydrogen bond donor
▪ cholinium-based solvents, organic acids, aminoacids, …
▪ low volatility, low vapour pressure, high tunability, non-flammability, chemical
and thermal stability, and possibility to dissolve inorganic and organic compounds
▪ some of them are toxic
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Ionic liquids
= compounds completely composed of ions with melting points below 100 °C
▪ typically consists of organic cation and organic or inorganic anion
▪ low volatility, low vapour pressure, high tunability, non-flammability, chemical
and thermal stability, and possibility to dissolve inorganic and organic compounds
▪ some of them are toxic
ARMENTA, Sergio, et al. Alternative green solvents in sample preparation. Green Analytical Chemistry,
2022, 1: 100007. DOI: 10.1016/j.greeac.2022.100007
Ionic liquids
Alternative green solvents
Hyphenated techniques
= an analytical techniques in which a chromatographic technique(s) and spectroscopic
technique(s) are coupled for separation and identification purposes
LC-MS
GC-MS
CE-MS
LC-NMR
Chiral LC-CD-NMR