Continuous subcritical water extraction

Richter, P., B. Sepulveda, R. Oliva, K. Calderon, and R. Seguel (2003). Screening and determination of pesticides in soil using continuous subcritical water extraction and gas chromatography-mass spectrometry. J. Chromatogr. A, 944 169-177. 

Gamiz-Gracia, L. and de Castro, M.D.L. (2000) Continuous subcritical water extraction of medicinal plant essential oil comparison with conventional techniques. Talanta 51(6), 1179-1185. 

Luque-Garcia, J. L. and Luque de Castro, M. D., Coupling continuous subcritical water extraction, filtration, preconcentration, chromatographic separation and UV detection for the determination of chlorophenoxy acid herbicides in soils, J. Chromatogr. A, 959, 25-35, 2002. 

Ayala, R.S., Luque de Castro, M.D. (2001). Continuous subcritical water extraction as a useful tool for isolation of edible essential oils. Food Chemistry, Vol.75, pp. 109-113, ISSN 0308-8146... 

Jimenez-Carmona, R.S. Ubera, J.L. Luque de Castro, M.D. (1999). Comparison of continuous subcritical water extraction and hydrodistillation of marjoram essential oil, Journal of Chromatography A, Vol.855, pp.625-632, ISSN 0021-9673... 

Gamiz-Gracia and de Castro (2000) devised a subcritical extractor equipped with a three-way inlet valve and an on/off outlet valve to perform subcritical water extractions in a continuous manner for the isolation of fennel essential oil. The target compounds were removed from the aqueous extract by a single extraction with 5 ml hexane, determined by gas-chromatography-flame ionization and identified by mass spectrometry. This extraction method is superior to both hydrodistillation and dichloromethane manual extraction in terms of rapidity, efficiency, cleanliness and the possibility of manipulating the composition of the extract. 

D from soils. Subcritical water extraction in continuous mode at a flow rate of 1 ml/min... 

Chlorophenoxy acids Soil (postcolumn) HPLC/intrinsic properties UV-spectrophotometry 10-50 mg I extraction/inline filtration/solid-phase extraction Continuous subcritical water... 

Principles and Characteristics Water is an interesting alternative for an extraction fluid because of its unique properties and nontoxic characteristics. Two states of water have so far been used in the continuous extraction mode, namely subcritical (at 100 °C < T < 374 °C and sufficient pressure to maintain water in the liquid state) and supercritical (T>374°C, p>218 bar). Unfortunately, supercritical water is highly corrosive, and the high temperatures required may lead to thermal degradation of less stable organic compounds. However, water is also an excellent medium for extraction below its critical temperature [412], Subcritical water exhibits lower corrosive effects. 

Fernandez-Perez, V., M.M. Jimenez-Carmona, and M.D. Luque de Castro. 2001. Continuous liquid-liquid extraction using modified subcritical water for the demetalisation of used industrial oils. Anal. Chim. Acta 433 47-52. 

The special features of the uses of supercritical water justify dealing with them in a separate section. No commercially available or laboratory-made extractor can operate in a continuous manner under the conditions required by supercritical water. In fact, most of the few reported applications allegedly involving supercritical water extraction actually used subcritical water conditions with not more than two extractions in the supercritical state this can readily be inferred from the equipment used — stainless steel SF extractors can hardly withstand the drastic conditions needed for work with supercritical water. As a... 

Three distinct processes were experimentally studied a coupled process for deacidi%ing and enriching the plqrtosterol content of rice bran oil (RBO) by continuous countercurrent colnitmar fiactionation, a scale up of a coupled supercritical fluid extraction (SFE)/ supercritical fluid chromatogr hy (SFC) process for the enrichment of phytosterol in com bran oil, and a unit process involving the snbcritical water extraction of berry substrates. The e q)erimental aspects of the first two processes are described in the literature (36, 37), and will not be repeated here. Research is currently underw to couple the described process below with other unit processes involving both subcritical water and siq)ercritical carbon dioxide. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

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