Table 1.

Properties of LPME techniques [1,3,8,9,10,11,12,13,15,16,17,18,25,32].

Technique	Solvent properties	Solvent volume	Sample preparation; other equipment	Mixing/ stirring	Extraction time	Typical analytes	Automation	Other considerations & modifications
SDME	immiscible with water; usually GC-compatible HS-SDME: low vapor pressure, also water; recent: ionic liquids	1–8 µL	GC syringe sample: filtration in DI-SDME; adjustment of ionic strength, T	DI-SDME: up to 600 rpm HS-SDME: higher rates	min. 1–15 min, usually longer	non-polar, semi-volatile or volatile (HS-SDME)	semi-automatic in dynamic mode; continuous flow ME (CF-ME) [34]	simple; ready-to-analyze extracts; modifications: dynamic mode possible in-needle or in-syringe; LLLME with back-extraction into droplet of 2nd immiscible solvent; exhaustive extraction by multiple HS-SDME [35]
HF-LPME	immiscible with water; compatible with HF material; low volatility & viscosity, e.g., toluene, n-octanol, also di-n-hexyl ether HF-LLLME: above valid for solvent in the HF wall; in the HF lumen: aqueous acceptor phase or ionic liquid or immiscible organic solvent	4–20 µL	small-diameter porous tube (fiber), usually polypropylene, one end sealed, other attached to syringe sample: adjustment of pH and ionic strength	vigorous stirring or vibration, microwaves	20–60 min (except for dynamic HF-LPME or EME)	non-polar; ionizable (in HF-LLLME)	yes, with autosampler; dynamic HF-LPME [36]; still each fiber manually prepared	applicable to »dirty« samples; modifications: dynamic HF-LPME [36]; solvent-bar microextraction (SBE) [37]; air in HF wall with aqueous solvent in lumen for volatile analytes [38]
DLLME	disperser solvent: miscible with water, e.g., acetone, methanol, ethanol, acetonitrile, THF; extraction solvent: ρsolv. > ρaq, e.g., C2Cl4, Cl-benzene, CH2Cl2, CHCl3, CCl4, ionic liquid; OR ρsolv. < ρaq, e.g., 1- or 2-dodecanol, 1-undecanol, hexadecane (Tmp ≈ room T), also cyclohexane, n-hexanol, tri-n-butyl-phosphate	Disp.s.: 0, 1–2 mL Extr.s.: 10–150 µL	centrifuge (ρsolv. > ρaq); ice bath or special extracting vessel (ρsolv. < ρaq); sample: filtration, adjustment of pH and ionic strength	not needed; ultrasound, vortex [9]	equilibration in few seconds; phase separation 1–20 min	non-polar	barely possible, although attempts [39]	modifications: temperature-controlled DLLME with ionic liquids, mixing and separation of phases at high/low T [40]