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Dr. Yu Yang is a Full Professor at East Carolina University. He received his Ph.D. from the University of Mainz, Germany in 1993. Dr. Yang's group is an international leader in the field of subcritical water research. His expertise includes subcritical water chromatography and extraction, organic solubility, and stability in subcritical water. Selected honors include UNC Board of Governors Distinguished Professor for Teaching Award, Achievement for Excellence in Research Award, and the Starter Grant Award from the Society for Analytical Chemists of Pittsburgh. Dr. Yang serves as the Editor-in-Chief for one journal and is on the editorial board for four other journals.
Subcritical water refers to high-temperature and high-pressure water. A unique and useful characteristic of subcritical water is that its polarity can be dramatically decreased with increasing temperature. Therefore, subcritical water can behave similar to methanol or ethanol. This makes subcritical water a green extraction fluid used for a variety of organic species. This review focuses on the subcritical water extraction (SBWE) of natural products. The extracted materials include medicinal and seasoning herbs, vegetables, fruits, food by-products, algae, shrubs, tea leaves, grains, and seeds. A wide range of natural products such as alkaloids, carbohydrates, essential oil, flavonoids, glycosides, lignans, organic acids, polyphenolics, quinones, steroids, and terpenes have been extracted using subcritical water. Various SBWE systems and their advantages and drawbacks have also been discussed in this review. In addition, we have reviewed co-solvents including ethanol, methanol, salts, and ionic liquids used to assist SBWE. Other extraction techniques such as microwave and sonication combined with SBWE are also covered in this review. It is very clear that temperature has the most significant effect on SBWE efficiency, and thus, it can be optimized. The optimal temperature ranges from 130 to 240 °C for extracting the natural products mentioned above. This review can help readers learn more about the SBWE technology, especially for readers with an interest in the field of green extraction of natural products. The major advantage of SBWE of natural products is that water is nontoxic, and therefore, it is more suitable for the extraction of herbs, vegetables, and fruits. Another advantage is that no liquid waste disposal is required after SBWE. Compared with organic solvents, subcritical water not only has advantages in ecology, economy, and safety, but also its density, ion product, and dielectric constant can be adjusted by temperature. These tunable properties allow subcritical water to carry out class selective extractions such as extracting polar compounds at lower temperatures and less polar ingredients at higher temperatures. SBWE can mimic the traditional herbal decoction for preparing herbal medication and with higher extraction efficiency. Since SBWE employs high-temperature and high-pressure, great caution is needed for safe operation. Another challenge for application of SBWE is potential organic degradation under high temperature conditions. We highly recommend conducting analyte stability checks when carrying out SBWE. For analytes with poor SBWE efficiency, a small number of organic modifiers such as ethanol, surfactants, or ionic liquids may be added.
Yan Cheng; Fumin Xue; Shuai Yu; Shichao Du; Yu Yang. Subcritical Water Extraction of Natural Products. Molecules 2021, 26, 4004 .
AMA StyleYan Cheng, Fumin Xue, Shuai Yu, Shichao Du, Yu Yang. Subcritical Water Extraction of Natural Products. Molecules. 2021; 26 (13):4004.
Chicago/Turabian StyleYan Cheng; Fumin Xue; Shuai Yu; Shichao Du; Yu Yang. 2021. "Subcritical Water Extraction of Natural Products." Molecules 26, no. 13: 4004.
In this work, a green extraction technique, subcritical water extraction (SBWE), was employed to extract active pharmaceutical ingredients (APIs) from an important Chinese medicinal herb, Salvia miltiorrhiza (danshen), at various temperatures. The APIs included tanshinone I, tanshinone IIA, protocatechualdehyde, caffeic acid, and ferulic acid. Traditional herbal decoction (THD) of Salvia miltiorrhiza was also carried out for comparison purposes. Reproduction assay of herbal extracts obtained by both SBWE and THD were then conducted on Caenorhabditis elegans so that SBWE conditions could be optimized for the purpose of developing efficacious herbal medicine from Salvia miltiorrhiza. The extraction efficiency was mostly enhanced with increasing extraction temperature. The quantity of tanshinone I in the herbal extract obtained by SBWE at 150 °C was 370-fold higher than that achieved by THD extraction. Reproduction evaluation revealed that the worm reproduction rate decreased and the reproduction inhibition rate increased with elevated SBWE temperatures. Most importantly, the reproduction inhibition rate of the SBWE herbal extracts obtained at all four temperatures investigated was higher than that of traditional herbal decoction extracts. The results of this work show that there are several benefits of subcritical water extraction of medicinal herbs over other existing herbal medicine preparation techniques. Compared to THD, the thousand-year-old and yet still popular herbal preparation method used in herbal medicine, subcritical water extraction is conducted in a closed system where no loss of volatile active pharmaceutical ingredients occurs, although analyte degradation may happen at higher temperatures. Temperature optimization in SBWE makes it possible to be more efficient in extracting APIs from medicinal herbs than the THD method. Compared to other industrial processes of producing herbal medicine, subcritical water extraction eliminates toxic organic solvents. Thus, subcritical water extraction is not only environmentally friendly but also produces safer herbal medicine for patients.
Brahmam Kapalavavi; Ninad Doctor; Baohong Zhang; Yu Yang. Subcritical Water Extraction of Salvia miltiorrhiza. Molecules 2021, 26, 1634 .
AMA StyleBrahmam Kapalavavi, Ninad Doctor, Baohong Zhang, Yu Yang. Subcritical Water Extraction of Salvia miltiorrhiza. Molecules. 2021; 26 (6):1634.
Chicago/Turabian StyleBrahmam Kapalavavi; Ninad Doctor; Baohong Zhang; Yu Yang. 2021. "Subcritical Water Extraction of Salvia miltiorrhiza." Molecules 26, no. 6: 1634.
In order to facilitate the development of the green subcritical water chromatography technique for vanillin and coumarin, the stability of the compounds under subcritical water conditions was investigated in this work. In addition, their extraction from natural products was also studied. The stability experiments were carried out by heating the mixtures of vanillin and water or coumarin and water at temperatures ranging from 100 °C to 250 °C, while subcritical water extractions (SBWE) of both analytes from vanilla beans and whole tonka beans were conducted at 100 °C to 200 °C. Analyte quantification for both stability and extraction studies was carried out by HPLC. After heating for 60 min, vanillin was found to be stable in water at temperatures up to 250 °C. While coumarin is also stable at lower temperatures such as 100 °C and 150 °C, it undergoes partial degradation after heating for 60 min at 200 °C and higher. The results of this stability study support green subcritical water chromatographic separation and extraction of vanillin and coumarin at temperatures up to 150 °C. The SBWE results revealed that the extraction efficiency of both analytes from vanilla beans and tonka beans is significantly improved with increasing temperature.
Ninad Doctor; Grayson Parker; Katie Vang; Melanie Smith; Berkant Kayan; Yu Yang. Stability and Extraction of Vanillin and Coumarin under Subcritical Water Conditions. Molecules 2020, 25, 1061 .
AMA StyleNinad Doctor, Grayson Parker, Katie Vang, Melanie Smith, Berkant Kayan, Yu Yang. Stability and Extraction of Vanillin and Coumarin under Subcritical Water Conditions. Molecules. 2020; 25 (5):1061.
Chicago/Turabian StyleNinad Doctor; Grayson Parker; Katie Vang; Melanie Smith; Berkant Kayan; Yu Yang. 2020. "Stability and Extraction of Vanillin and Coumarin under Subcritical Water Conditions." Molecules 25, no. 5: 1061.
Organic solvents are widely used in pharmaceutical and chemical industry for chromatographic separations. In recent years, subcritical water chromatography (SBWC) has shown ability in replacing hazardous organic solvents used in traditional high-performance liquid chromatography (HPLC). In this work, a pain killer—aspirin—and an antidiabetic drug—metformin HCl—were successfully separated on an XBridge C18 column using no organic solvents in the subcritical water chromatography mobile phase. Both traditional HPLC and subcritical water chromatography were used for comparison purposes. SBWC separation of metformin HCl and aspirin were achieved at 95 °C and 125 °C, respectively. The recovery for both active pharmaceutical ingredients (APIs) obtained by SBWC is 99% in comparing with the stated content of each drug. The relative standard deviation is less than 1% for SBWC assays developed in this work. This level of accuracy and precision achieved by SBWC is the same as that resulted by the traditional HPLC analysis.
Ninad Doctor; Yu Yang. Separation and Analysis of Aspirin and Metformin HCl Using Green Subcritical Water Chromatography. Molecules 2018, 23, 2258 .
AMA StyleNinad Doctor, Yu Yang. Separation and Analysis of Aspirin and Metformin HCl Using Green Subcritical Water Chromatography. Molecules. 2018; 23 (9):2258.
Chicago/Turabian StyleNinad Doctor; Yu Yang. 2018. "Separation and Analysis of Aspirin and Metformin HCl Using Green Subcritical Water Chromatography." Molecules 23, no. 9: 2258.
Ninad Doctor; Yu Yang. Destruction of Polychlorinated Biphenyls under Subcritical Water Conditions in the Presence of Hydrogen Peroxide or Sodium Hydroxide. International Journal of Chemical Engineering and Applications 2018, 9, 119 -122.
AMA StyleNinad Doctor, Yu Yang. Destruction of Polychlorinated Biphenyls under Subcritical Water Conditions in the Presence of Hydrogen Peroxide or Sodium Hydroxide. International Journal of Chemical Engineering and Applications. 2018; 9 (4):119-122.
Chicago/Turabian StyleNinad Doctor; Yu Yang. 2018. "Destruction of Polychlorinated Biphenyls under Subcritical Water Conditions in the Presence of Hydrogen Peroxide or Sodium Hydroxide." International Journal of Chemical Engineering and Applications 9, no. 4: 119-122.
Reverse phase liquid chromatography (RPLC) is a commonly used separation and analysis technique. RPLC typically employs mixtures of organic solvents and water or aqueous buffers as the mobile phase. With RPLC being used on a global scale, enormous quantities of organic solvents are consumed every day. In addition to the purchasing cost of the hazardous solvents, the issue of waste disposal is another concern. At ambient temperature, water is too polar to dissolve many organic substances. Therefore, although water is nontoxic it cannot be used to replace the mobile phase in RPLC since organic analytes will not be eluted. Subcritical water chromatography may be an alternative. The characteristics of water, such as polarity, surface tension, and viscosity, can be altered by manipulating water’s temperature, thus making it behave like an organic solvent. The aim of this study was to evaluate the feasibility of separation using water mobile phase and detection by an electrochemical (EC) detector. The classes of analytes studied were neurotransmitters/metabolites, nucleic acids/heterocyclic bases, and capsaicinoids. Both isothermal and temperature-programmed separations were carried out. The separation temperature ranged from 25 to 100 °C. For separations of all three classes of solutes, the retention time was decreased with increasing temperature, thus shortening the analysis time. The peaks also became narrower as temperature increased. The limit of detection of neurotransmitters/metabolites ranges from 0.112 to 0.224 ppm.
Heather Anderson; Yu Yang. Subcritical Water Chromatography with Electrochemical Detection. Molecules 2017, 22, 962 .
AMA StyleHeather Anderson, Yu Yang. Subcritical Water Chromatography with Electrochemical Detection. Molecules. 2017; 22 (6):962.
Chicago/Turabian StyleHeather Anderson; Yu Yang. 2017. "Subcritical Water Chromatography with Electrochemical Detection." Molecules 22, no. 6: 962.
Sema Akay; Berkant Kayan; Yu Yang. Solubility and Chromatographic Separation of 5-Fluorouracil under Subcritical Water Conditions. Journal of Chemical & Engineering Data 2017, 62, 1538 -1543.
AMA StyleSema Akay, Berkant Kayan, Yu Yang. Solubility and Chromatographic Separation of 5-Fluorouracil under Subcritical Water Conditions. Journal of Chemical & Engineering Data. 2017; 62 (4):1538-1543.
Chicago/Turabian StyleSema Akay; Berkant Kayan; Yu Yang. 2017. "Solubility and Chromatographic Separation of 5-Fluorouracil under Subcritical Water Conditions." Journal of Chemical & Engineering Data 62, no. 4: 1538-1543.
Ninad Doctor; Larry Yang; Yu Yang. Polychlorinated biphenyls degradation in subcritical water. 3RD INTERNATIONAL CONFERENCE ON CHEMICAL MATERIALS AND PROCESS (ICCMP 2017) 2017, 1879, 40003 .
AMA StyleNinad Doctor, Larry Yang, Yu Yang. Polychlorinated biphenyls degradation in subcritical water. 3RD INTERNATIONAL CONFERENCE ON CHEMICAL MATERIALS AND PROCESS (ICCMP 2017). 2017; 1879 ():40003.
Chicago/Turabian StyleNinad Doctor; Larry Yang; Yu Yang. 2017. "Polychlorinated biphenyls degradation in subcritical water." 3RD INTERNATIONAL CONFERENCE ON CHEMICAL MATERIALS AND PROCESS (ICCMP 2017) 1879, no. : 40003.
The goal of this work was to further validate the subcritical water chromatography (SBWC) methods for separation and analysis of preservatives through the evaluation of analyte stability in subcritical water.
B. Kapalavavi; R. Marple; C. Gamsky; Y. Yang. Studies on the stability of preservatives under subcritical water conditions. International Journal of Cosmetic Science 2015, 37, 306 -311.
AMA StyleB. Kapalavavi, R. Marple, C. Gamsky, Y. Yang. Studies on the stability of preservatives under subcritical water conditions. International Journal of Cosmetic Science. 2015; 37 (3):306-311.
Chicago/Turabian StyleB. Kapalavavi; R. Marple; C. Gamsky; Y. Yang. 2015. "Studies on the stability of preservatives under subcritical water conditions." International Journal of Cosmetic Science 37, no. 3: 306-311.
Brahmam Kapalavavi; John Ankney; Matthew Baucom; Yu Yang. Solubility of Parabens in Subcritical Water. Journal of Chemical & Engineering Data 2014, 59, 912 -916.
AMA StyleBrahmam Kapalavavi, John Ankney, Matthew Baucom, Yu Yang. Solubility of Parabens in Subcritical Water. Journal of Chemical & Engineering Data. 2014; 59 (3):912-916.
Chicago/Turabian StyleBrahmam Kapalavavi; John Ankney; Matthew Baucom; Yu Yang. 2014. "Solubility of Parabens in Subcritical Water." Journal of Chemical & Engineering Data 59, no. 3: 912-916.
Several high‐temperature liquid chromatography (HTLC) and subcritical water chromatography (SBWC) methods have been successfully developed in this study for separation and analysis of preservatives contained in Olay skincare creams. Efficient separation and quantitative analysis of preservatives have been achieved on four commercially available ZirChrom and Waters XBridge columns at temperatures ranging from 100 to 200°C. The quantification results obtained by both HTLC and SBWC methods developed for preservatives analysis are accurate and reproducible. A large number of replicate HTLC and SBWC runs also indicate no significant system building‐up or interference for skincare cream analysis. Compared with traditional HPLC separation carried out at ambient temperature, the HTLC methods can save up to 90% methanol required in the HPLC mobile phase. However, the SBWC methods developed in this project completely eliminated the use of toxic organic solvents required in the HPLC mobile phase, thus saving a significant amount of money and making the environment greener. Although both homemade and commercial systems can accomplish SBWC separations, the SBWC methods using the commercial system for preservative analysis are recommended for industrial applications because they can be directly applied in industrial plant settings.
Y. Yang; B. Kapalavavi; L. Gujjar; S. Hadrous; R. Marple; C. Gamsky. Industrial application of green chromatography - II. Separation and analysis of preservatives in skincare products using subcritical water chromatography. International Journal of Cosmetic Science 2012, 34, 466 -476.
AMA StyleY. Yang, B. Kapalavavi, L. Gujjar, S. Hadrous, R. Marple, C. Gamsky. Industrial application of green chromatography - II. Separation and analysis of preservatives in skincare products using subcritical water chromatography. International Journal of Cosmetic Science. 2012; 34 (5):466-476.
Chicago/Turabian StyleY. Yang; B. Kapalavavi; L. Gujjar; S. Hadrous; R. Marple; C. Gamsky. 2012. "Industrial application of green chromatography - II. Separation and analysis of preservatives in skincare products using subcritical water chromatography." International Journal of Cosmetic Science 34, no. 5: 466-476.
In this study, high-temperature liquid chromatographic (HTLC) and subcritical water chromatographic (SBWC) separations of sunscreens contained in skincare creams were achieved at temperatures ranging from 90 to 250°C. The columns employed in this work include a ZirChrom-DiamondBond-C18, a XTerra MS C18 and a XBridge C18 column. The quantity of methanol consumed by the greener HTLC sunscreen methods developed in this project is significantly reduced although the HTLC separation at this stage is not as efficient as that achieved by traditional HPLC. SBWC separation of sunscreens was also achieved on the XTerra MS C18 and the XBridge C18 columns using pure water at 230-250°C. Methanol was eliminated in the SBWC methods developed in this study.
B. Kapalavavi; C. Gamsky; R. Marple; Y. Yang. Separation of sunscreens in skincare creams using greener high-temperature liquid chromatography and subcritical water chromatography. International Journal of Cosmetic Science 2011, 34, 169 -175.
AMA StyleB. Kapalavavi, C. Gamsky, R. Marple, Y. Yang. Separation of sunscreens in skincare creams using greener high-temperature liquid chromatography and subcritical water chromatography. International Journal of Cosmetic Science. 2011; 34 (2):169-175.
Chicago/Turabian StyleB. Kapalavavi; C. Gamsky; R. Marple; Y. Yang. 2011. "Separation of sunscreens in skincare creams using greener high-temperature liquid chromatography and subcritical water chromatography." International Journal of Cosmetic Science 34, no. 2: 169-175.
In this work, chromatographic separation of niacin and niacinamide using pure water as the sole component in the mobile phase has been investigated. The separation and analysis of niacinamide have been optimized using three columns at different temperatures and various flow rates. Our results clearly demonstrate that separation and analysis of niacinamide from skincare products can be achieved using pure water as the eluent at 60 °C on a Waters XTerra MS C18 column, a Waters XBridge C18 column, or at 80 °C on a Hamilton PRP-1 column. The separation efficiency, quantification quality, and analysis time of this new method are at least comparable with those of the traditional HPLC methods. Compared with traditional HPLC, the major advantage of this newly developed green chromatography technique is the elimination of organic solvents required in the HPLC mobile phase. In addition, the pure water chromatography separations described in this work can be directly applied in industrial plant settings without further modification of the existing HPLC equipment.
Yu Yang; Zackary Strickland; Brahmam Kapalavavi; Ronita Marple; Chris Gamsky. Industrial application of green chromatography—I. Separation and analysis of niacinamide in skincare creams using pure water as the mobile phase. Talanta 2011, 84, 169 -174.
AMA StyleYu Yang, Zackary Strickland, Brahmam Kapalavavi, Ronita Marple, Chris Gamsky. Industrial application of green chromatography—I. Separation and analysis of niacinamide in skincare creams using pure water as the mobile phase. Talanta. 2011; 84 (1):169-174.
Chicago/Turabian StyleYu Yang; Zackary Strickland; Brahmam Kapalavavi; Ronita Marple; Chris Gamsky. 2011. "Industrial application of green chromatography—I. Separation and analysis of niacinamide in skincare creams using pure water as the mobile phase." Talanta 84, no. 1: 169-174.
In the first part of this study, the stability of five terpenes (alpha-pinene, limonene, camphor, citronellol, and carvacrol) under subcritical water conditions was investigated. The stability studies were carried out at four different temperatures (100, 150, 200, and 250 degrees C) with two different heating times (30 and 300 min). When water temperature was increased, the degradation of terpenes became more serious. Prolonged exposure time to each heating temperature also caused decreased terpene stability. The terpene recoveries were determined by conducting subcritical water extraction of sand spiked with terpenes. The recoveries are typically around 70 to 80% for extractions at 100 degrees C. Terpene recoveries were decreased with increasing water temperature due to poorer stability of terpenes. After the degradation and recovery studies, basil and oregano leaves were extracted using water at both 100 and 150 degrees C. The concentrations of each individual terpene in the water extract generally ranged from trace quantity to 65 microg terpene/g herb. However, the concentration of carvacrol in the oregano-water extract at 150 degrees C was found to be as high as 4270 microg carvacrol/g oregano.
Yu Yang; Berkant Kayan; Neval Bozer; Bryan Pate; Christopher Baker; Ahmet Murat Gizir. Terpene degradation and extraction from basil and oregano leaves using subcritical water. Journal of Chromatography A 2007, 1152, 262 -267.
AMA StyleYu Yang, Berkant Kayan, Neval Bozer, Bryan Pate, Christopher Baker, Ahmet Murat Gizir. Terpene degradation and extraction from basil and oregano leaves using subcritical water. Journal of Chromatography A. 2007; 1152 (1-2):262-267.
Chicago/Turabian StyleYu Yang; Berkant Kayan; Neval Bozer; Bryan Pate; Christopher Baker; Ahmet Murat Gizir. 2007. "Terpene degradation and extraction from basil and oregano leaves using subcritical water." Journal of Chromatography A 1152, no. 1-2: 262-267.
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.
Yu Yang. Subcritical water chromatography: A green approach to high-temperature liquid chromatography. Journal of Separation Science 2007, 30, 1131 -40.
AMA StyleYu Yang. Subcritical water chromatography: A green approach to high-temperature liquid chromatography. Journal of Separation Science. 2007; 30 (8):1131-40.
Chicago/Turabian StyleYu Yang. 2007. "Subcritical water chromatography: A green approach to high-temperature liquid chromatography." Journal of Separation Science 30, no. 8: 1131-40.