Subcritical water chromatography: A green approach to high‐temperature liquid chromatography

Abstract

At temperatures and pressures lower than 374 degrees C and 218 atm, subcritical water has widely tunable properties such as dielectric constant, surface tension, viscosity, and dissociation constant achieved by simply adjusting the temperature with a moderate pressure to keep water in the liquid state. At elevated temperatures, water acts like a weak polar organic solvent. Thus, subcritical water has been used as a green eluent to replace hazardous solvents commonly used as organic modifiers in RPLC. Subcritical water chromatography (SBWC) is capable of separating polar, moderately polar, and even some nonpolar analytes. Most of these low molecular weight solutes are stable at elevated temperatures during a chromatographic run. Some new packing materials are also quite stable and robust at mild temperatures ranging from 80 to 150 degrees C. Advantages of SBWC include the elimination of hazardous organic solvents used in traditional RPLC, rapid analysis time, improved selectivity, temperature-dependent separation efficiency, temperature-programmed elution, and compatibility with both gas- and liquid-phase detectors. In this paper, the technical aspects as well as the applications of SBWC are reviewed. Topics addressed in this review include the unique characteristics of subcritical water, analytes separated by SBWC, packing materials tested for SBWC, the application of GC and LC detection techniques in SBWC, SBWC instrumentation development, temperature effects on SBWC separation, and models developed for separation in SBWC.

Current challenges in compound-specific stable isotope analysis of environmental organic contaminants

“…In addition, increasing the temperature of the mobile and stationary phase may modulate the solubility and, therefore, the retention of compounds. The static permittivity of water decreases with temperature, rendering its eluent strength similar to that of a methanolwater mixture [129]. Consequently, temperature gradients can replace organic solvent gradients.…”

Conversion of Japanese red pine wood (Pinus densiflora) into valuable chemicals under subcritical water conditions

“…In addition, the dissociation constant of water at temperatures of 200-300°C is three orders of magnitude greater than that of ambient water, which may also contribute to the reactivity of subcritical water with certain organic compounds. 18 Also subcritical water is an environmentally safe and non-toxic solvent. The presence of water at high temperatures as a reactant leads mainly to hydrolysis reactions, that is, the conversion of biomass to sugars.…”

Possibilidades e limitações no uso da temperatura em cromatografia líquida de fase reversa

“…A constante dielétrica (ε) da água diminui de 80, em temperatura ambiente, para valores de até 20 a 300 o C. [37][38][39] Assim, o uso da água como FM em altas temperaturas pode simular as propriedades de uma mistura da água com modificadores orgânicos. O uso de FM 100% aquosa é um exemplo de química verde, livre do alto custo na aquisição e no descarte de solventes orgânicos, e possibilita a detecção no UV em baixos comprimentos de onda ou acoplamento com o detector por ionização em chama (Flame Ionization Detector, FID).…”

“…O uso de FM 100% aquosa é um exemplo de química verde, livre do alto custo na aquisição e no descarte de solventes orgânicos, e possibilita a detecção no UV em baixos comprimentos de onda ou acoplamento com o detector por ionização em chama (Flame Ionization Detector, FID). [37][38][39][40] A seletividade em cromatografia empregando água super aquecida como fase móvel (Super Heated Water Chromatography, SHWC) é C na coluna XBridge C18 (150 x 4,6 mm, dp 5 μm) a uma vazão de 4 mL/min. Desta forma a técnica de SHWC é especialmente atrativa na análise de solutos polares que são fracamente retidos em modo reverso de eluição.…”