Subcritical Water Chromatography — An Economical and Green Separation Technique

Abstract

Subcritical water chromatography (SBWC) refers to a new reversed‐phase liquid chromatography (RPLC) technique where high‐temperature water is used as the sole mobile phase component. The major advantage of SBWC is the elimination of toxic mobile phase organic solvents required in traditional RPLC. These organic solvents are not only expensive in terms of purchasing price but also costly in their waste disposal. Therefore, the SBWC technique offers both economical and environmental benefits. Additional advantages of SBWC are fast analysis time; temperature‐dependent efficiency, selectivity, and resolution; temperature‐programmed elution; and ability to accommodate both gas‐ and liquid‐phase detectors. Most importantly, after years of academic studies, industry started paying attention to this economical and green separation technique. For example, Procter & Gamble has recently funded an SBWC project in developing green SBWC methods for the analysis of skincare products.

Synthesis and evaluation of NA-PHEMAH polymer for use as a new stationary phase in high-temperature liquid chromatography

“…In HTLC, a mixture of water and organic solvent(s) or pure water is used as the mobile phase. At elevated temperatures the water-organic solvent(s) mixture or pure water becomes a stronger solvent for reversed phase liquid chromatography separation due to the decreased dielectric constant with increasing temperature [1][2][3]. Thus, temperature can be regarded as an important parameter to enhance separation efficiency, speed up analysis, and manipulate the selectivity of a chromatographic separation [1][2][3][4].…”

“…At elevated temperatures the water-organic solvent(s) mixture or pure water becomes a stronger solvent for reversed phase liquid chromatography separation due to the decreased dielectric constant with increasing temperature [1][2][3]. Thus, temperature can be regarded as an important parameter to enhance separation efficiency, speed up analysis, and manipulate the selectivity of a chromatographic separation [1][2][3][4]. Although there have been a large number of research papers on HTLC published in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], the routine use of this technique is still not accepted in industry.…”

“…Most of these more thermally stable columns are packed with hybrid silica-or zirconia-based particles while fewer polymer columns are available for HTLC separations [1][2][3][4][5][6][7][8][9][10][11][12][13]. Polymer packings are preferred for HTLC separation due to their high stability at elevated temperatures.…”

Separation of sunscreens in skincare creams using greener high‐temperature liquid chromatography and subcritical water chromatography

“…Fortunately, the amount of organic solvents required in HPLC mobile phase can be significantly reduced by high‐temperature liquid chromatography (HTLC) [19–24]. Even better, separation of certain classes of organics has been achieved by subcritical water chromatography (SBWC) where high‐temperature water is used as the sole mobile‐phase component [25–45]. Obviously, hazardous organic solvents such as methanol and acetonitrile are eliminated from the SBWC mobile phase.…”

“…As most of the HTLC and SBWC publications up to date are limited to academic studies, it is important to develop HTLC methods that can later be adopted by industry. Our recent work on SBWC separation and analysis of niacin and niacinamide and preservatives clearly demonstrates that it is indeed feasible for industry to replace certain existing HPLC methods with the green SBWC ones [43–45].…”