Table 4.
Density separation and organic removal for MPs analysis in soil.
| No. | Order | Extraction (density separation; DS) | Organic removal (OR) | Filtration | Ref. | ||
|---|---|---|---|---|---|---|---|
| Solution | Procedure | Filter type | Drying conditions | ||||
| 1 | DS → OR | NaCl (1.19 g/cm3) | Add NaCl solution Ultrasonication for 2 min Stir for 30 min Settle for 24 h Repeat three times |
WPO (30% H2O2) at 50 °C for 72 h | 20 μm nylon net filter | Room temperature | (Liu et al., 2018) |
| 2 | DS → OR | NaCl (1.20 g/cm3) | 1. Add 160 mL of 27% NaCl solution Stir for 10 min Centrifuge at 3450 G for 30 min Filter supernatant using 0.45 μm membrane filter 2. Remove particles stuck to beaker walls by 27% NaCl and settle for 24 h Mix sample mixture at 800 rpm for 10 min Centrifuge at 3450 G for 30 min |
Wash particles from the filter and then treat them with 40–80 mL of 65% HNO3 at 90 °C for 48 h | 0.2 μm infrared transparent anodisc filter | N/A | (Scheurer and Bigalke, 2018) |
| 3 | OR → DS → OR | NaI (1.80 g/cm3) | Add 150 mL of NaI solution Centrifuge again Wash with NaI solution |
1. Pre-oxidation: WPO (10 mL of 35% H2O2 + 1 mL of 10% FeSO4) at 50 °C Add a few drops of butyl alcohol (if frothing was excessive) Add 1 mL of 10% FeSO4 (to decompose the H2O2) Add 30 mL of 0.5 M NaOH Store for 24 h Adjust to 150 mL using DI water Agitate for 20 min using ultrasonic Centrifuge at 2300 rpm for 10 min 2. Post-oxidation: WPO (2 mL of 35% H2O2) |
1 mm, 0.25 mm, 0.05 mm sieve | 80 °C | (Zhang and Liu, 2018) |
| 4 | DS only | 1. NaCl (1.20 g/cm3) 2. NaI (1.60 g/cm3) |
1. Use a continuous flow and floating separation apparatus Float using NaCl solution Clean residues in the sieve (300 mesh) were cleaned using water 2. Residues were floated using NaI solution Filter if it contained a large number of solid particles |
N/A | N/A | Air dry | (Zhou et al., 2018) |
| 5 | 1. OR → DS → OR 2. DS → OR |
1. NaCl (1.20 g/cm3), NaI (1.80 g/cm3), ZnCl2 (1.50 g/cm3) 2. Only using NaCl (1.20 g/cm3) |
1. Test three types of floatation solutions Add 200 mL of a solution Stir at 200 rpm for 1 h using a shaker Settle for 48 h and siphon out 100 mL of supernatant Add 100 mL of the same floatation solution Stir for 30 min and settle for 48 h Combine supernatants 2. Repeat steps but by only using NaCl solution |
1. Pre-oxidation: WPO (200 mL of 30% H2O2) If temperature remained stable, heating at 70 °C 2. Post-oxidation: WPO (30% H2O2 + H2SO4 (3:1, v/v)) |
20 μm nylon filter | Air dry | (Li et al., 2019) |
| 6 | DS → OR | NaCl (1.24 ± 0.05 g/cm3) | Add NaCl solution Stir for 30 min Settle for 24 h Repeat three times Filter with 20 →m |
Wash filter WPO (100 mL of 30% H2O2) at 65 °C at 80 rpm for 72 h |
20 μm nylon net filter | Room temperature | (Lv et al., 2019) |
| 7 | DS only | 1. DI water (1.0 g/cm3) 2. NaCl (1.20 g/cm3) 3. ZnCl2 (1.55 g/cm3) |
1. Add 20 mL of DI water stir at 21,000 rpm for 30 s Centrifuge at 2000 rpm for 15 min Filter supernatant using by 2–3 μm filter paper 2. Add 20 mL of NaCl Stir, centrifuge and filter the same way 3. Add 20 mL of ZnCl2 Stir 32,000 rpm for 30 s Centrifuge 2000 rpm for 15 min Filter the same way |
N/A | 2.5 μm cellulose filter paper | N/A | (Corradini et al., 2019) |
| 8 | DS → OR | NaBr (1.55 g/cm3) | Add NaBr solution Stir for 5 min Settle for 2 h Use automatic cycling device for 30 min Filter using a 20 μm filter |
WPO (30% H2O2) at 60 °C for 3 days | 20 μm membrane filter | N/A | (Liu et al., 2019b) |
| 9 | DS → OR | NaI | Add 200 mL of NaI solution Stir for 30 min Settle for 12 h Filter using a 7 μm glass fiber filter |
WPO (100 mL of 30% H2O2) for 12 h | 7 μm glass fiber filter | Room temperature |
(Huang et al., 2020) |
| 10 | DS → OR | DI water (1.0 g/cm3) | Leach soil specimens using pressurized water Add distilled water Shake for 30 s Precipitate for 5 min Repeat three times |
Oxidation using 10 mL of 98% H2SO4 Sonicate for 20 min Place in ice bath Dilute with distilled water |
Membrane filter paper | Dry at 50–60 °C | (Li et al., 2020) |
| 11 | DS → OR | 1. NaCl (1.20 g/cm3) 2. NaI (1.60 g/cm3) |
Disperse dried soil with (NaPO3)6 (0.5 mol/L) Add NaCl solution into beaker (flow rate 1.0 L/min) with air blowing at the bottom Collect the over-flow materials on a vibrating sieve (pore 50 μm) Settle residues on the sieve for 48 h in NaI solution Filter using a 5 μm cellulose nitrate filter Repeat three times |
WPO (30% H2O2) at 70 °C for 72 h | 20 μm glass fiber filter | N/A | (Zhou et al., 2020) |
| 12 | DS → OR | ZnCl2 (1.60 g/cm3) | Add ZnCl2 solution Settle for 6 h at room temperature Repeat three times |
WPO (30% H2O2) at 70 °C in water bath | N/A | Air dry | (Duan et al., 2020) |
| 13 | OR → DS | NaCl (30%; w/v) | Add 600 mL of NaCl solution Settle for 12 h |
WPO (50 mL of mixture (35% H2O2 + 0.5 M of ferrous sulfate)) at room temperature for 24–72 h | 300, 150, 50 μm sieve | N/A | (Rafique et al., 2020) |
| 14 | DS only | 1. DI water (1.0 g/cm3), 2. NaCl (1.20 g/cm3), 3. ZnCl2 (1.55 g/cm3) |
1. For visual identification, centrifuge 5 g of soil and 20 mL of DI water at 2000 rpm for 15 min Filter supernatant through a 2.5 μm filter paper Fill remaining sediments with 20 mL of NaCl Centrifuge at 21000 rpm for 30 s and filter supernatant a another time Fill remaining sediments with 20 mL of ZnCl2 Centrifuge last time and filter supernatant through the same filter used the previous two times 2. For FTIR microscope analysis, sonicate 1 g soil and 10 mL of ZnCl2 for 10 min Agitate at 2000 rpm for 15 s Shake for 20 min at 180 oscillations per min Before filtration, centrifuge for 10 min at 2500 rpm Filter supernatant through a 0.4 μm polycarbonate membrane filter Re-fill with ZnCl2 and underwent same step once again |
N/A | 1. 2.5 μm cellulose filter paper (for visual identification by optical microscope) 2. 0.4 μm polycarbonate membrane filter (for FTIR analysis) |
Dried at 40 °C for 12 h (for FTIR analysis) | (Corradini et al., 2021) |
| 15 | DS only | Tap water | Add tap water Stir and settle overnight |
N/A | 1 mm sieve (collect >1 mm size) | Dry at 60 °C for 24 h | (Katsumi et al., 2021) |
| 16 | DS → OR | ZnCl2 (1.70 g/cm3) | Add 500 mL of ZnCl2 solution Stir at 300 rpm for 5 min Settle for 24 h Repeat three times |
WPO (20 mL of 0.05 M FeSO4 and 3 mL of conc. H2SO4 and 20 mL of 30% H2O2) at 75 °C for 24 h Rinse with water and sieve using a 1 mm sieve |
0.45 μm membrane filter | Room temperature | (Choi et al., 2021) |
| 17 | OR → DS | ZnCl2:CaCl2 (2:1.4; 1.55–1.58 g/cm3) | 1. Filter digested supernatant through 20 μm sieve, afterward, visually sort and analyze the >1 mm particles 2. Fill digested remnant with density solution Filter supernatant through 20 μm sieve Sort >1 mm Repeat this process two more times 3. Perform density separation of the particles of <1 mm obtained from the first process and >20 μm obtained from the second process and filter supernatant finally |
WPO (200 mL of 30% H2O2) | 0.7 μm glass fiber filter | N/A | (Kim et al., 2021) |
| 18 | DS → OR | NaCl (1.19 g/cm3) | Shake soil samples at 150 rpm for 30 min with 300 mL of distilled water using an orbital shaker Settle for 24 h Repeat 3–4 times until no more observed floating extract Centrifuge the collected supernatant solution for 29 min at 1500 rpm Mix supernatant with 100 mL of NaCl solution for 15 min at 150 rpm and settle overnight Centrifuge supernatant for 10 min at 1500 rpm for 1 s |
WPO (100 mL of 30% H2O2) for 7 days at 25 °C | 0.45 μm cellulose nitrate filter | Room temperature |
(Ragoobur et al., 2021) |
| 19 | OR → DS | CaCl2 (1.40 g/cm3) | Centrifuge with CaCl2 solution for 10 min at a speed of 3700 min−1 Stain samples with Nile red |
Fenton reaction by adding 30 mL of 30% H2O2, 30 mL of iron catalyst for 1 h at 0 °C | Glass fiber filter | 60 °C | (Grause et al., 2022) |
| 20 | OR → DS | NaCl (1.20 g/cm3) | Add 100 mL of NaCl solution Stir for 1 min Settle for 1.5 h |
WPO (40 mL of 33% (w/v) H2O2) for 2 hat 60 °C Stir at 300 rpm |
50 μm stainless steel filter | N/A | (Pérez-Reverón et al., 2022) |