Vacuum-assisted headspace single-drop microextraction: Eliminating interfacial gas-phase limitations

Area of Science:

• Analytical Chemistry
• Separation Science
• Environmental Analysis

Background:

• Headspace single-drop microextraction (HS-SDME) traditionally assumes liquid-phase control, neglecting gas-phase mass transfer limitations.
• Existing HS-SDME protocols operate at atmospheric pressure, potentially limiting extraction efficiency due to unaddressed interfacial gas constraints.

Purpose of the Study:

• To investigate and demonstrate the presence of gas-phase limitations in HS-SDME.
• To propose and validate the use of reduced headspace pressures to mitigate these limitations and accelerate extraction.
• To model the pressure dependence of HS-SDME by decoupling evaporation and analyte uptake steps.

Main Methods:

• Developed a two-interfacial step model: evaporation (water-headspace) using two-film theory and analyte uptake (headspace-microdrop) using resistance model.
• Employed naphthalene, acenaphthene, and pyrene as model analytes with varying Henry's law constants.
• Performed HS-SDME experiments at reduced headspace pressures (down to 0.04 atm) and compared extraction times with standard atmospheric pressure conditions.

Main Results:

• Extraction times were significantly reduced for all model analytes at pressures below 1 atm.
• Reduced pressure accelerated naphthalene extraction, confirming gas-layer mass transfer influence even for volatile compounds.
• Gas-phase resistance was reduced by over 96% at 0.04 atm, demonstrating the effectiveness of vacuum in overcoming these constraints.

Conclusions:

• Gas-phase limitations are significant in HS-SDME and can be effectively overcome by reducing headspace pressure.
• The proposed model accurately describes the pressure dependence of HS-SDME, highlighting the interplay of interfacial steps.
• Reduced pressure HS-SDME offers a more efficient extraction method, with potential applications predicted using Henry's law constants.