pressurized Hot water Extraction technique/natural products notes/easy explained

Описание: Pressurized Hot Water Extraction (PHWE), also known as subcritical water extraction or superheated water extraction, is a "green" and efficient extraction technique that utilizes hot water under high pressure to extract various compounds from a wide range of matrices. It's considered a green method because water is a non-toxic, readily available, and inexpensive solvent, reducing the need for harmful organic solvents.

How it Works:
The core principle behind PHWE is the alteration of water's physicochemical properties under elevated temperature and pressure. Here's a breakdown:

Temperature and Pressure: Water is heated above its atmospheric boiling point (100
∘
C) but below its critical point (374
∘
C and 22.1 MPa). The pressure applied keeps the water in a liquid state, preventing it from boiling even at these high temperatures. Typical operating conditions range from 100−160
∘
C and 2−12 bar, though higher temperatures and pressures can be used.

Changes in Water Properties:

Polarity: As temperature increases, the dielectric constant of water decreases, making it less polar. This allows it to dissolve a wider range of compounds, including less polar ones that are typically extracted with organic solvents.

Viscosity and Surface Tension: Both viscosity and surface tension of water decrease at higher temperatures, allowing it to penetrate the sample matrix more effectively and facilitate better mass transfer of the target compounds.

Diffusivity: The self-diffusivity of water increases, enhancing the rate at which analytes can move from the sample matrix into the solvent.

Extraction Process:

Sample Preparation: The sample is typically placed in an extraction cell (often made of corrosion-resistant material).

Solvent Delivery: Hot water is pumped into the extraction cell at a desired pressure.

Heating and Pressurization: The cell containing the sample and solvent is heated to the desired temperature and pressurized.

Extraction: The sample is kept in contact with the pressurized hot water for a specific period (static extraction time). This allows the target compounds to dissolve into the water.

Dynamic Extraction (Optional): In some setups, fresh solvent is continuously flowed through the cell for a predetermined dynamic extraction time, rinsing the sample and carrying dissolved compounds away.

Collection and Cooling: The extracts are then collected and rapidly cooled, often in an ice bath, to prevent degradation of the extracted compounds.

Separation: After extraction, the extracts can be further processed, often using techniques like chromatography (HPLC, GC-MS) to analyze and quantify the extracted compounds.PHWE (most common abbreviation)

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