Table 2.
Selected examples of microextraction of bioactive compounds in liquid sorbents.
| Extraction format/methodology | Target analytes/sample | Method description/LOD | References |
|---|---|---|---|
| LLME | Caffeine/tea, coffee | 20 mg tea leaves powder + 20 mL EtOH/10 mL water (beaker, pH adjusted to 2.5); stirring (40 min, 45°C); supernatant decantated and filtered (0.45 μm); 1.0 mL extracted sample in 2:1 EtOH/water mixture (conical glass test tube); 150 μL DCM rapidly injected to form three solvents mixture; 20 s high speed vortex; add 300 μL water; vigorous shake, rest to obtain two phases; caffeine sedimented (bottom organic phase of DCM); centrifugation (5,000 rpm, 4 min)/0.05 μg mL−1 | (81) |
| VA-LLME | Phenolic acids/honey, iced tea, coffee drinks | Sample solution (pH 1.5–1.8, 10 mL volumetric flask); propyl acetate: pentanol: hexanol (1:2:1.5, v/v/v, 400 μL) vortex extraction (45 s, 2,500 rpm); rest 1 min; transfer top layer (~200 μL) to centrifuge tube (0.5 mL) containing 40 μL KOH (0.02 M); vortex (60 s, 2,500 rpm); collect aqueous fraction (bottom layer); HPLC analysis/0.05–0.68 μg L−1 | (82) |
| VA-LLME | Hydrophilic phenols/olive oil | 5 mL oil samples diluted to 5 mL (hexane) + 100 μL 1 M HCl; 2 min vortex; 10 min 4,000 rpm centrifugation; 40 μL acidic aqueous phase (lower phase) analyzed by differential pulse voltammetry (DPV) using SPCEs/0.022 mg L−1 | (83) |
| SHS-LLME/DLLME | Piperine/pepper | Sample grinding; 0.10 g + 5.0 ml ACN 45% (v/v); 1 min vortex; 2 min 6,000 rpm; filtration; 3.0 mL saturated NaCl (Salting-out extraction – SOE); 1 min vortex; 2 min 6,000 rpm; 50 μL SOE diluted to 4.0 mL (deionized water); 1.5 mL SHS + 1.0 mL 20 M NaOH, 10 s vortex; recover switched-off SHS layer; dilute 50% prior HPLC-DAD analysis/0.2-0.6, 0.7–2.0 μg mg−1 | (84) |
| LLME (US and salt-assisted) | Oleuropein/olive oil | 0.01 g + 10 mL extraction solvents mixture (phosphate buffer, with variable pH, ACN, and THF); US (25°C); 5 min 4,000 rpm centrifugation; 1 mL liquid phase + NaCl (salting out); 10 μL organic phase HPLC analysis/0.5 μg mL−1 | (85) |
| Ball mill-assisted DES-based extraction | Tanshinones/Salvia miltiorrhiza Bunge | Oven-dried, sliced, and crushed samples (0.05 g) mixed with DES (1.0 mL) in 2.0 mL Lysing Matrix D tubes (1.4 mm ceramic spheres, 1.1 g); centrifugation; LC-MS analysis | (86) |
| DES-LLME | Caffeine/soft drinks | 1 mL sample; 50 μL THF (aprotic solvent); 50 μL DES (choline chloride–phenol); HPLC-UV analysis/0.03 μg mL−1 | (87) |
| DES-LLME | Quercetin/wine, foods | Ground dried (5 g) and liquid (3 mL) samples + 10 mL MeOH; 40 min US extraction (RT); filtration/6.1 μg L−1 | (88) |
| DES-LLME | Rare ginsenosides/Kang'ai injection | 8 mL sample + 400 μL DES in glass test tube; add 150 mg inorganic salt; shake to obtain homogeneous solution; add 400 μL THF (turbidity is observed); add 150 mg Fe3O4; inject N2 (to obtain homogenous turbid droplets and make the magnetic nanoparticles absorb the droplets simultaneously); collect nanoparticles (magnet); washed thoroughly (little amount EtOH); concentrate to 200 μL; filtration (0.22 μm PTFE); HPLC analysis/10.2–137.8 ng mL−1 | (89) |
| DES-LLME | Curcumin/food, herbal tea | Curcumin standards + phosphate buffer (2 mL, pH 4) in 50 mL centrifuge tube; 400 μL DES (ChCl: Phenol, 1:4) as water-miscible extraction solvent injected rapidly into solution to form homogeneous solution; THF (400 μL, emulsifier) injected into solution; cloudy solution (formation of insoluble self-aggregates) was obtained; US (2 min) to homogenize DES droplets in the aqueous phase (curcumin extraction); centrifugation (4,500 rpm, 5 min); discard top water phase; DES rich-phase containing curcumin completed to 1 mL with EtOH; curcumin concentration determined by UV (425 nm)/2.86 μg L−1 | (90) |
| DES-DLLME | Phenylpropanoids/vegetable oils | 2 mL oil samples + 2 mL n-hexane; 45 μL PhAA/TMG in 200 μL isopropanol (dispersing solvent) rapidly added; 10 s vortex; 5,000 g centrifugation (5 min); 5 μL DES solution UHPLC analysis/0.07–0.01 μg mL−1 | (91) |
| DLLME (OS vs. DES) | Phytosterols/cow milk | 2.0 mL milk sample; 1.0 or 1.25 mL ACN (OS-DLLME or DES-DLLME, respectively); 30 s vortex; 4 min 4,000 rpm centrifugation; supernatant phase (0.8 mL) + 70 μL CCl4, mix; 3 min 4,000 rpm centrifugation; bottom phase evaporated (N2 stream); ACN (95%, v/v) reconstitution; HPLC-UV analysis/0.3–0.9, 0.09–0.32 ng mL−1 | (92) |
| NADES-LLME | Polyphenols/Greek medicinal plants | Pulverized material (0.1 g) + NADES (80% v/v, 10 mL), manual vigorous shaking; US extraction (80°C, 90 min, 140 w); centrifugation (15,000 rpm, 10 min); dilution 1:20 distilled water; spectrometric analysis | (93) |
| NADES-LLME | Anthocyanins/Catharanthus roseus | Samples (50 mg) + NADES (1.5 ml); stirred (40°C, 30 min); centrifugation (1,300 rpm, 20 min), filtration (0.45 μm filter); dilution (1:2, 3%FA); HPLC-DAD analysis | (94) |
| DLLME/SULLE | Phenolics/plums (Prunus domestica L.) | DLLME: 10 mg dry leaves into Eppendorf tube + 1 mL extraction medium; 200 μL EtAc + 100 μL ACN fast injection; cloudy solution centrifugation; injection (30 s); rest 1 min, 5 min 12,000 × g centrifugation; 100 μL top layer evaporated (N2 stream); 50 μL mobile phase resuspension, US (5 min); 20 μL HPLC analysis. SULLE: 10 mg dry leaves + 200 μL water + 400 μL ACN; gentle shaking (30 s); 200 μL sugar solution rapidly injected, 1 min vortex; phase separation centrifugation (5 min 12,000 × g); 250 μL top layer dried (N2 stream); 50 μL mobile phase resuspension, US (5 min); 20 μL HPLC analysis. | (95) |
| DLLME (several variations)/SULLE | harpagoside, phenolics/Harpagophytum procumbens root, food supplements | 50 mg ground roots (40 mesh) + 5 mL water (or 10% NaCl, NADES, IL, glucose or 1% β-cyclodextrin and HP-β-cyclodextrin); 30 s gentle shaking, 600 μL EtAc (extraction solvent) + 500 μl ACN (dispersive solvent); 30 s vortex, 2 min rest (10 min US for UA-DLLME); 4 min 1,500 rpm centrifugation; recover 350 μL top layer; dry (N2 stream); 50 μL resuspension (7% ACN, v/v, 3% acetic acid), 20 μL HPLC analysis. | (96) |
| DLLME | Phytosterols/functional foods, medicinal herbs | Sample (2 mL) + 4 mL water (5 mL glass centrifuge tube); fast mixture injection - 250 μL EtOH (dispersant) + 70 μL bromocyclohexane (extractant); vortex (10 s), US (2 min, 40 KHz); centrifugation (2.5 min, 13,457 × g); sedimented phase transferred to another vial, dry (N2 stream); add 120 μL CSR + 50 μL CMPI + 50 μL DMAP ACN; sealed vial radiated (750 W microwave reactor, 5 min, 60°C); dilute resulting solution with 4.0 mL water (5 mL centrifuge tube); add 70 μL bromobenzene (extractant) + 220 μL ACN (dispersant); vortexed (20 s), US (2 min); centrifugation (2.5 min, 13,457 × g); recover bromobenzene (bottom phase); UHPLC-MS/MS analysis/0.005–0.015 ng mL−1 | (97) |
| DLLME | Tocopherol/bovine milk | 1.0 mL milk sample + 9.0 mL EtOH (containing ascorbic acid, 5 g/L) heating (78°C, 30 min, 10 min intervals shake); ice-cooling, centrifugation (5 min, 4,500 rpm); 1.0 mL supernatant + 200 μL chloroform rapidly injected into 5 mL ultrapure water; cloudy solution centrifuged (5 min, 4,500 rpm); organic phase centrifuged again (10 min, 13,500 rpm), HPLC-PDA analysis/0.01 μg mL−1 | (98) |
| DLLME | Flavonols, organosulfurs, inulin/garlic, foods | 600 μL chloroform (extraction solvent) + 1 mL ACN (dispersive solvent) injected into sample solution; centrifugation (3 min, 2,000 rpm); chloroform phase dried (N2 stream); MeOH reconstitution (500 μL); HPLC-DAD analysis/0.14–2.15 μg mL−1 | (99, 100) |
| DLLME | Melatonin and trans-resveratrol/Wine | 2 mL centrifuged sample + 7 mL ultrapure water; 1.500 μL ACN (disperser) + 300 μL chloroform (extracting solvent) + 1.500 mg NaCl (ionic strength); mix 1 min; 5 min centrifugation; evaporate the organic phase (N2 steam); re-dissolution (150 μL phosphate buffer (40 mM), pH 3/ACN (80/20, v/v); HPLC-FLD analysis/0.07, 7.68 ng mL−1 | (101) |
| In-syringe DLLME | Caffeine/coffee | 1,500 μL sample + (1,225 μL MeOH + 225 μL DCM extraction); 20 s stirring, repeat; extract water dilution, filtration, HPLC-UV analysis/0.46 μg mL−1 | (102) |
| DLLME | Caffeine/tea; energy drinks | 2 mL sample + 8 mL deionized water; 1 min shaking; pH adjusted to 3; + 1.5 g NaCl; mix vigorously; + 450 μL EtOH (disperser) + 80 μL 1-octanol (extraction solvent); 1 min mixing; 6,000 rpm (5 min) centrifugation; 20 μL upper phase HPLC-UV analysis/0.9 ng mL−1 | (103) |
| DES-HS-SDME | Terpenes/spices | 50 mg sample (20 mL HS vial); 10 μL-GC microsyringe containing DES introduced in the HS of the sample vial: DES pushed down the microsyringe to form 1.5 μL drop at the needle tip; incubation (80°C, 90 min); DES drop withdrawn into the microsyringe, disposed in 250 μL insert and weighed; GC-MS analysis/0.47–86.40 μg g−1 | (104) |
| M-ILs-SDME | Ascorbic acid (AA)/orange juice | 8 mg M-ILs dissolved in a single EtOH droplet (1.0 μL); place on surface of 2 mL phosphate buffer (0.10 M, pH 6.0) containing AA (1.50– 40.0 nM); mixture gently stirred (15 min); AA extracted into M-ILs phase small volume; M-ILs-rich phase collected (strong magnet out the wall of the solution-containing tube, supernatant decanted). M-ILs phase EtOH dilution (3 μL); transfer onto the TiO2-NPs/CPE surface; 2 μL Nafion casted on the electrode; solvent evaporation (RT)/0.43 nM | (105) |
| IL-UAE | Liquiritin, liquiritin apioside, isoliquiritin, isoliquiritin apioside, glycyrrhizic acid/licorice | 1.0 g licorice powder (pulverized, 30 mesh sieves) + 10 mL ILs (several mixtures); US extraction; centrifugation; filtration; HPLC analysis/0.002-0.067 μg mL−1 | (106) |
| USAEME | Bioactive compounds/Saffron | 79.6 mg saffron sample; 1.1 mL H2O (extraction solvent); 18.6 min sonication 62.7 μL chloroform (pre-concentration solvent); RP-HPLC-DAD analysis | (107) |
| HF-LPME | Quercetin/tomato, onion | 1 g crushed, dried sample (6 h, 60°C); 10 mL 25% HCl (80°C, water 30 min, separately); filtration; dilution to 100 mL double distilled deionized water; 10 mL sample (pH 7.5) + 25 μL CTAB + 1-octanol; 30 min 900 rpm stirring, RT/0.1 ng mL−1 | (108) |
| HF-LPME | Hesperidin, honokiol, shikonin, magnolol, emodin, β,β′-dimethylacrylshikonin/TCM | Hollow-fiber segment first immersed in organic solvent to fill the solvent in the fiber lumen and wall pore; then the fiber was again immersed into NaCl solution to cover a thin salt membrane on the fiber wall pore filling organic solvent/0.6–12 ng mL−1 | (109) |
| DES-HF-LPME | Caffeic acid, cinnamic and p-hydroxycinnamic acids, ferulic acid/ TCM | 0.7 mL sample diluted to 7 mL (NaCl 20%, w/v), pH 2 (HCl); DES-immersed fibers (15 min) lumens filled with the 85% DES (MeOH) submerged; 40 min extraction (800 rpm stirring, 55°C); recover the analyte-enriched extractant from fibers lumen; flush lumens with 20 μL MeOH; combine fractions; 30 s vortex; 20 μL HPLC analysis/0.1-03 ng mL−1 | (110) |
| OIS-LPME | Alkaloids/TCM | 9 mL sample (pH 9) + pentanol/octanol (6:4, v/v) + NaCl (20% w/v) immobilized on permutite surface to form oil-in-salt double membranes; 30 min extraction (25°C, 500 rpm stirring); 50 μL MeOH permutite elution (30 s shaking); 20 μL HPLC analysis/0.1 ng mL−1 | (111) |
| BT-OIS-LPME | Magnolol, honokiol/TCM | 5 mL sample solution + conditioned ballpoint tip; 30 min 1,200 rpm extraction (RT); ballpoint tip cavity (enriched acceptor phase) rinsing (20 μL MeOH); 20 μL HPLC analysis/0.4, 0.6 ng mL−1 | (112) |
| DES-FSME | Curcuminoids/rhizoma turmeric tea | 20 mg sample + 0.8 mL of pH 2 HCl; dilution to 8.0 mL (water); 1,100 rpm stirring, 10 min extraction (40°C); add 70 μL DES, mix; rest 5 min; 6 min deep freezing (-20°C); collect solidified droplets; 1:1 MeOH dilution of melted droplets (RT); HPLC analysis/0.2–1 ng mL−1 | (113) |
| FSME | Myricetin, quercetin, isorhamnetin, chrysin, kaempferide/TCM | 1.0 g sample; 10 min soaking 40 mL MeOH; 30 min US; 30 min herbal extract reflux with 5 mL 25% HCl; 10 min 3,500 rpm centrifugation; adjust supernatant 50 mL; dilute 20 × 6 mL extract + 40 μL dispersed solution of fibroin/dodecanol, 1,200 rpm stirring, 40 min extraction; rest 5 min; 6 min deep freezing (-20°C); collect solidified droplets; 40 μL MeOH elution of melted droplets (RT); 15 min 10000 rpm centrifugation; 10 μL supernatant HPLC-DAD analysis/0.2–1 ng mL−1 | (114) |
| FSME | Caffeic, ferulic, p- and hydroxycinnamic acids/ TCM | 10 mL sample (pH 3) + 70 μL graphene/dodecanol (0.25 mg mL−1) dispersion; 30 min extraction (1,000 rpm stirring); rest 5 min; 6 min deep freezing (-20°C); collect solidified droplets; 40 μL MeOH elution of melted droplets (RT); 15 min 10,000 rpm centrifugation; 10 μL supernatant HPLC-DAD analysis/0.1–2 ng mL−1 | (115) |
| HF-EKE | Caffeine and GA/coffee | 5 g coffee + 3 ml water (different pHs), mixed and compacted into an EK cell (65 mm in length, 30 mm internal diameter); cathodic and anodic HFs dipped in 2-nitrophenyl octyl ether containing 5% di-(2-ethylhexyl) phosphate and 1-octanol, respectively. The two HFs (50 ml extraction solvent—-water with different pHs) placed at the ends of the sample compartment; sample solutions collected every 30 min (Hamilton syringe); US bath extraction with various voltages (5–30 V) and times (0.5–5 h); HPLC-PDA analysis. | (116) |
AA, Ascorbic acid; ACN, acetonitrile; APCI-MS, atmospheric-pressure chemical ionization mass spectrometry; BT-IOS-LPME, Ballpoint tip-protected oil-in-salt liquid-phase microextraction; CMPI, 2-Chloro-1-Methyl Pyridinium Iodide; CSR, 4′-Carboxy-substituted rosamine; DAD, diode-array detection; DCM, dichloromethane; DES, deep eutectic solvents; DLLME- dispersive liquid-liquid microextraction; DMAP, 4-dimethylaminopyridine; EtAc, ethyl acetate; EtOH, ethanol; FA, formic acid; FSME, floating solidification microextraction; GA, gallic acid; GC-MS, gas chromatography-mass spectrometry; HF-EKE, hollow fiber electrokinetic extraction; HF-LPME, hollow-fiber liquid-phase microextraction; HS, headspace; ILs, ionic liquids; IOS-LPME, oil-in-salt liquid-phase microextraction; LC-MS, liquid chromatography mass spectrometry; LE, liquid extraction; LLME, liquid-liquid microextraction; M-SPE, magnetic solid-phase extraction; M-ILs-SDME, magnetic ionic liquids single drop microextraction; ME, microextraction; MeOH, methanol; NADES, natural deep eutectic solvents; OS, organic solvents; PLE, pressurized liquid extraction; SHS, Switchable-hydrophilicity solvent; SULLE, sugaring-out assisted liquid-liquid extraction; TCM, traditional Chinese medicine; THF, Tetrahydrofuran; US, ultrasonication; USAEME, ultrasonic assisted emulsification microextraction; VA, vortex assisted.