Abstract
Air-assisted liquid–liquid microextraction (AALLME) is a procedure for sample preparation that has high recoveries and high preconcentration factors while using a small amount of extractants. This procedure has gained widespread acceptance among scientists due to a variety of advantages, including its easiness, being cheap, green, and available in most laboratories. The current review has focused on the analysis of medicines and organic compounds using various modes of AALLME. The use of various extractants and support factors were developed in many modes of AALLME. A review of literature revealed that the procedure is used as a powerful and efficient approach for extracting medicals and organic compounds. This review explained 12 different types of AALLME methods. The findings on the modifications of AALLME modes that have been published are summarized. Future directions are also being discussed.
Graphical abstract
Abbreviations
- [C6MIM] [PF6]
-
1-hexyl-3-methylimidazolium hexafluorophosphate
- [P14,6,6,6] PF6
-
tri-hexyl (tetradecyl) phosphonium hexafluorophosphate
- AA-DLLME-OPS
-
air-assisted dispersive liquid–liquid microextraction procedure with organic-phase solidification
- AA-LDS-LLME-SFOD
-
air-assisted, low-density solvent-based liquid–liquid microextraction and solidified floating organic droplets
- AA-LLME-SFDES
-
air-assisted liquid–liquid microextraction based on solidification of floating deep eutectic solvent
- ASEME-SFO
-
air-assisted surfactant-enhanced emulsification liquid–liquid microextraction/solidification of floating organic droplets
- BE
-
back extraction
- ChCl
-
chloromethylene
- DESs
-
deep eutectic solvents
- DLLME
-
dispersive liquid–liquid microextraction
- EMAC
-
ethyl methyl ammonium chloride/pivalic acid
- EVA-DLLME
-
gas-controlled deep eutectic solvent-based evaporation-assisted dispersive liquid–liquid microextraction
- GC-ECD
-
gas chromatography with electron capture detector
- GC-FID
-
gas chromatography with flame ionization detection
- GC-FPD
-
gas chromatography-flame photometric detection
- GC-MS
-
gas chromatography–mass spectrometry
- GCT–DES–EVA–DLLME
-
gas-controlled deep eutectic solvent-based evaporation-assisted dispersive liquid–liquid microextraction
- HMIMNTF2
-
1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide
- HPLC-MS/MS
-
high-performance liquid chromatography–tandem mass spectrometry
- IL-AALLME
-
ionic liquid-based air-assisted liquid–liquid microextraction
- IP-AALLME
-
ion-pair air-assisted liquid–liquid microextraction
- LC-MS/MS
-
liquid chromatography tandem mass spectrometry
- LPME
-
liquid phase microextraction
- OS-AALLME
-
one-step air-assisted liquid–liquid microextraction
- OS-FAALLME
-
organic solvent-free air-assisted liquid–liquid microextraction
- SAALLME
-
salt- and air-assisted liquid–liquid microextraction
- SDME
-
single-drop microextraction
- SPME
-
solid phase microextraction
- TAALLME
-
tandem air-agitated liquid–liquid microextraction
- TNO
-
5,6,7,8-tetrahydro-5,5,8,8-tetramethylnaphthalen-2-ol
- UHPLC-PDA
-
ultra-high-performance liquid chromatographic with PDA detection developed and validated
- USE-AALLME
-
ultrasound-enhanced air-assisted liquid–liquid microextraction
- VAALLME
-
vortex-assisted-air liquid–liquid microextraction
- VALLE-AALLME
-
vortex-assisted liquid–liquid extraction/air-assisted liquid–liquid microextraction
1 Introduction
Sample preparation is a vital task before conducting an analytical study. It is usually done to remove interferences and nontarget substances from the test, or to fit the sample’s properties to the needs of certain analytical equipment. Preconcentration is essential, especially when the analytes are very small [1,2,3]. To overcome these challenges, one simple method is to separate the analytes from the real sample. Historically, solvent extraction methods were a favorite approach for the separation of various analytes in several matrixes [4,5]. Because of the low preconcentration factors and extensive use of toxic organic solvents, there has been a growing need to displace them with alternative approaches [6,7,8]. Solvent extraction procedure has now been surpassed by solid phase extraction (SPE), which eliminates the major disadvantages of solvent extraction. The sorbent adsorbed analytes onto a cartridge during most SPE methods. The adsorbed particles are eluted with a useful organic liquid and analyzed using an effective methodology. SPE cartridges also have some drawbacks, such as being costly and non-reusable. To address this challenge, the most recent research has concentrated on separation-based minimization using two types of microextraction: solid phase microextraction (SPME) and liquid phase microextraction (LPME) [9,10,11]. According to the methodologies and solvents utilized, there are three main forms of LPME (Figure 1).
Classification of LPME and AALLME modes.
1.1 Single-drop microextraction (SDME)
The SDME was the first liquid–liquid microextraction procedure invented. It is focused on the analyte distribution between a tiny drop of extractant deposited at the tip of a micro syringe needle and an aqueous solution. A drop of an insoluble separating phase (less than 10 µL) is injected from a syringe into a fluid (direct immersion-single drop microextraction) or gaseous test media (headspace-single drop microextraction). The single drop is pulled into the micro syringe after multiple extractions and transmitted to an analytical device for analyte measurement. The intended analytes are isolated from the test in the pending drop. Passive diffusion and recoveries are mainly influenced by analyte partition coefficients. The SDME types have challenges such as unstable drops and low drop volume [25].
1.2 Hollow fiber liquid–liquid microextraction (HF-LPME)
Pedersen-Bjergaard and Rasmussen advanced HF-LPME to address SDME’s drop instability [26]. The analytes are isolated first into an assisting liquid membrane maintained in the holes of a hydrophobic fibrous HF and then into an acceptor solvent placed within the fiber canal. The extractor liquid is covered in microliters within the lumen of a fibrous HF under this method, so it is not in direct contact with an aqueous solution. The feature of this technique is that the sample can be vigorously stirred without losing the analyte because it is manually protected. Prior to analysis, the HF is drenched in a suitable immiscible liquid, causing the organic layer to become adsorbed in the HF pores. A small layer of appropriate solvent, approximately less than 20 µL, forms within the HF’s wall. The HF is then loaded into a sample tube containing the desired aqueous solution. The test is stirred extensively to speed up the extraction. The analytes are subsequently extracted from the water system by passing them through the organic layer in the HF’s pores and into an acceptor liquid within its lumen. The HF’s single-use design removes the possibility of sample carry (15%). It was effectively implemented in the real vegetable samples. Long extraction times (0.5–1.5 h) are a drawback of HF-LPME, particularly for super molecules and biomolecules [27].
1.3 Dispersive liquid–liquid microextraction (DLLME)
To solve these problems, DLLME was introduced in 2006 [14]. DLLME is a rapid, economical, and easy approach that has been used to determine a variety of chemicals in a variety of samples. However, methods have been employed to improve the classic DLLME. Because of its low solvent volumes and high effective parameters, it has been developed to remove organic molecules and metals from the matrix. Chloroform and dichloromethane are the most widely known extraction solvents in traditional DLLME, both of which are highly volatile and dangerous [11,12,13,14,15,16].
Recent developments include ultrasonic assisted with DLLME [17], vortex assisted with DLLME [18], microwave assisted with DLLME [19], and air-assisted liquid–liquid microextraction (AALLME) [20]. In this situation, the purpose was to diminish or remove DLLME’s dispersive liquids. Vortexing or sonication improves the mass transfer rate of the analytes into the extractant by increasing the surface contact between them and the organic layer. The fundamental LPME and AALLME models are shown graphically in Figure 1.
In 2012, air was used as a component to improve the microextraction procedure. This is a low-cost, environmentally friendly option that can considerably improve the extraction efficiency. The AALLME is simpler, greener, economical, and quicker to use when compared to traditional or modified DLLME approaches. The AALLME technique is explained in only one review. Its main focus was on the basic principles and analytical instruments [21].
This study aims to provide a recent review of the use of AALLME for the detection of organic and medicinal materials in various matrices such as biological fluids, food, and water. The reviewed analytical characteristics are highlighted, and the tables with current applications of conventional and modified AALLME modes are supplied. AALLME sample preparation foundations, practical limitations, and future developments are briefly discussed. The literature search was conducted using the terms “Air-Assisted liquid–liquid Micro-Extraction,” “AAMLLE,” and “Organic and Medical Compounds” as descriptors in the Scopus, Springer, and Science Direct indexes, and the analysis was limited to studies published in the last 10 years (from 2012). According to our information, it is the first overview of the modified AALLME modes. This involves the extraction of medicines and organic compounds from different samples.
1.4 The general AALLME basics
The general procedure of AALLME was explained in Figure 2. In 2012, AALLME was initially used to analyze phthalate esters in aqueous solutions [20]. This approach was analogous to DLLME in that it did not require the use of an organic layer to disperse an extracted liquid into the test solution. Using a syringe fitted with a needle, an extract phase at 1 mL concentration was dispersed into the test solution by conducting sucking and dispersing cycles repeatedly. Despite the absence of a dispersing solvent, this technique considerably enhanced the contact area of the extractant with the test solution. The viscosity and interfacial tension of the extractant were shown to be the two most important factors in LPME procedures. These factors regulate both the extractant droplet size and the mass transfer rate of the analytes at the same time. Aspirating dispersion cycles transform the extraction solvent into very small droplets, greatly increasing the contact area of the test solution with the extractant [22].
Basic AALLME schematic design.
The AALLME method works in a similar way to batch extraction. In two different hydrodynamic situations, the many-batched extraction procedure is applied. The extractant and the aqueous layer are not actively agitated in the first place, and the contact between the two phases is flattened, with diffusion determining the solutes’ mobility ratio. In this case, the equilibrium condition is achieved after almost 2–3 h. Every second, the extractant and test solution are agitated for a predetermined amount of time, and diffusion-controlled mass transfer is supplanted by convective mass transfer. As a result, there is a large effective area. During the aspirating and dispersing cycles in AALLME, there is a lot of turbulence in the solutions, and the mass transfer of the solutes is mostly regulated by the convective process (Figure 2).
The rate law [21] for convective mass transfer can be explained using equation (1):
where N A denotes an analytes molar mass flux, K C is the convective mass transfer constants, and ΔC A is the variation in concentrations between the aqueous and organic phases.
The physicochemical characteristics of the organic solvent and aqueous solution are intricately connected to K C. The significant factors of K C, as determined by dimensional analysis and experiment, are viscosity, density, momentum, and the circular radius of the extractant. It is worth noting that K C and circular radius are inversely connected, with a large K C resulting from small spherical radii. Because AALLME creates very small droplets of extractant in the solution, it is only normal that K C is larger than in other approaches.
The number of steps in which the combination of extractant and test solution is sucked into an injector and pumped out into the glass vial should be tuned to increase the mass transfer rate of the solutes and the procedure’s recovery (R).
Recovery (R)
where C of is the final concentration of analytes in the organic solvent, and it was measured from an appropriate calibration graph achieved by directly injecting the standards into an experimental platform. C aqf and C aqi are the final and initial analytes’ quantities in the water, respectively; V o and V aq are the volumes of two phases [23,24].
2 Recent modified AALLME applications for extraction of medicines and organic compounds
The AALLME advanced microextraction method was used to determine analytes from aqueous and extractant phases by centrifuging them away from the standard solution. The separation solvent had to meet certain conditions, such as being low in solubility in water, being capable of extracting the substances, and creating a specific density that was different from the standard solution. Many kinds of solvents (ionic liquids [ILs], organic solvent free, ion-pair liquids, surfactants, chloroform, deep eutectic solvents [DESs], and solidified floating organic solvents [SFO]) have been used as extractants in AALLME (Figure 3). DES has been the most used with the AALLME technique, followed by chloroform, 1-dodecanol, n-octanol, and chloromethylene (ChCl). Figure 3 explains the types of extractants and their percentages according to the collected references and information in Tables 1–3.
The most used extractants in the AALLME procedure.
The applications of traditional AALLME for separation and determination of dyes and medical materials
| Analytes | Extractant | LOD | RSD% | EF | Detector | Sample | Recovery % | Linearity | Ref. |
|---|---|---|---|---|---|---|---|---|---|
| Azoxystrobin, diethofencarb, and pyrimethanil | 30 µL | 0.08, 0.16, and 0.25 µg L−1 | 6.8–9.3 | 145–178 | HPLC | Water, juice samples | 72.3–108.0 | — | [32] |
| 1-Octanol | |||||||||
| 6 Fluoroquinolone | 900 µL Chloroform | 5–10 µg kg−1 | 4.5–7.4 | — | HPLC-UV | Milk powder, eggs | 72–115 | 25–1,000 µg kg−1 | [39] |
| Aristolochic acid I | Chloroform | 0.16 ng mL−1 | 0.66 | 316 | HPLC-UV | Urine, flour, and aristolochiaceae fruit | — | 0.16–1,000 ng mL−1 | [40] |
| Bisphenols | n-Octanol | 0.2–0.7 µg L−1 | 4.4–14.1 | HPLC | Disposable lunch boxes | 80–106 | 1–100 µg L−1 | [46] | |
| 20 Endocrine-disrupting compounds | 40 µL | 0.03–0.80 ng g−1 | 1.1–14.5 | — | HPLC-MS/MS | Fish | 78.2–118.6 | 5–20 ng g−1 | [49] |
| 1-Undecanol | |||||||||
| Bisphenols, parabens, benzophenones, triclosan, triclocarban | 750 μL | 0.01–0.08 ng mL−1 | ≤15 | — | LC-MS/MS | Urine | — | 1–20 ng mL−1 | [50] |
| 1,2-dichloroethane | |||||||||
| 3-Monochloropropane-1,2-diol | 39 μL ChCl-acetic acid (DES) | 0.26 ng g−1 | 3.2 | — | GC-MS | Refined edible oils | — | 0.88–1,000 ng g−1 | [57] |
| Acetic acid | 32 µL Butylchloroformate | 9.63 | 3.43–6.21 | 415 | GC–FID | Fruit juices | 72–93 | 10.8–5,000 ng mL−1 | [58] |
| Propionic acid | 6.21 | 370 | |||||||
| Butyric acid | 5.74 | 360 | |||||||
| Valeric acid | 5.22 | 395 | |||||||
| Caproic acid | 3.23 ng mL−1 | 465 | |||||||
| Benzophenone-type UV filters | DL-menthol/decanoic acid (DES) | 0.05–0.2 ng mL−1 | 1.9–5.6 | HPLC-DAD | Aqueous samples | 88.8–105.9 | 0.5–1,000 | [59] | |
| 1H-Benzotriazole,5-methyl-1H-Benzotriazole and 5-chloro-1H-benzotriazole | 1-Hexanol | 0.8–1.4 | 3.0–7.8 | 43–87 | HPLC-UV | Water | 73−116 | 0.005–10 | [60] |
| Chlordiazepoxide, Alprazolam, and Lorazepam | 300 µL Chloroform | 0.7–2.9 µg L−1 | 0.9–3.1 | — | HPLC-UV | Water, tablets, juice, plasma, and urine | 81.2, 92.1, 90.1 | 800–1,100 µg L−1 | [62] |
| Organophosphorus pesticide | 16 µL Chloroform | 0.02–0.6 µg L−1 | 0.4–9.9 | — | GC-FPD | Fruit juice | 79–113 | 0.5–100 µg L−1 | [64] |
| Polycyclic aromatic hydrocarbons | — | 0.015–0.05 ng mL−1 | 327–773 | GC-FID | Hookah water | 33–77 | — | [67] | |
| Sudan I, II, III, IV, and Orange G | 77 μL [C6MIM][PF6] | 3.9–84.8, 0.013–3.1, 33–39, and 0.13–0.15 μg mL−1 | 4.5–5.6 | 33–39 | HPLC-UV | Human fluids | 86–91.7 | 0.013–3.1 µg mL−1 | [34] |
The application of AADLLME for extraction of medical and organic compounds
| Analytes | Extractant | LOD | RSD% | EF | Mode | Detector | Sample | Recovery % | Linearity | Ref. |
|---|---|---|---|---|---|---|---|---|---|---|
| Deoxynivalenol | Chloroform | 23.6 µg L−1 | 4.7 | — | AADLLME | HPLC-DAD | Rice | — | 5–500 µg L−1 | [43] |
| Aflatoxins | 250 µL Chloroform | 0.13–0.68 ng g−1 | ≤14.2 | — | AADLLME | HPLC-FLD | Rice | 76.0–109.3 | 0.08–10 ng g−1 | [48] |
| Benzoic acid and sorbic acid | 70 µL Menthol | 0.03, 0.02 mgL−1 | 3–6, 4–8 | 17.1, 16.2 | AADLLME-OPS | HPLC-UV | Beverages and soy sauce samples | 93–105, 96–101 | 0.1–150, 0.05–100 mg L−1 | [63] |
| Metronidazole, meropenem, ciprofloxacin, linezolid, piperacillin | 30 µL 1-Dodecanol | 0.001–0.08 μg L −1 | ≤9.87 | 87–121 | AADLLME-SFO | UHPLC-PDA | Human plasma | — | 0.005–0.25 μg L −1 | [52] |
| Pyrethroid pesticides | 95 μL ChCl: butyric acid (DES)/140 µL Chloroform | 9–21 ng L–1 | 3.2–5.4 | 623–690 | GCT–DES–EVA-DLLME | GC-MS | Fruit juices | 83–92 | 69–5,00,000 ng L–1 | [56] |
| Albendazole chloramphenicol trimethoprim, enrofloxacin, oxitetracycline, and nicarbazin | 1–50 μL dichloromethane, 2–160 μL dichloromethane, 1840 μL acetonitrile | 0.011–1.46 | — | — | AADLLME-SFO DLLME | HPLC | Egg | — | 0.35–9.36 | [61] |
| Auramine O | 3 mL methanol/1% acetic acid | 0.01 μg g−1 | 1.8–6.2 | — | AA-IL-DLLME | HPLC-UV/Vis | Solid bean | 83.5–104.8 | 0.05–50 μg g−1 | [55] |
| Carotenoids | 40 μL 1-dodecanol | 0.04 µg mL−1 | 7.92 | — | AA-LDS-LLME-SFOD | HPLC | Fruit juices | 93.6–101.5 | 0.2–30 µg mL−1 | [41] |
The applications of different modes of AALLME for extraction of dyes and medicines
| Analytes | Extractant | LOD | RSD% | EF | Mode | Detector | Sample | Recovery % | Linearity | Ref. |
|---|---|---|---|---|---|---|---|---|---|---|
| Aniline p-Toluidine | 65 µL | 3.0 | 4.2 | 890 | AALLME-SFO-DES | GC-SM | Wastewater water | 89 | 11–2000000 | [69] |
| ChCl: n-butyric acid | 6.0 | 3.9 | 940 | 94 | 23–2000000 | |||||
| p-Chloroaniline | 1.8 | 3.3 | 920 | 92 | 6–2000000 | |||||
| p-Anisidine | 2.4 | 860 | 86 | 9–2000000 | ||||||
| 4-tert-Butyl aniline | 5.3 ng L−1 | 2.6 | 790 | 79 | 18–2000000 ng L−1 | |||||
| Benzophenone salicylate ultraviolet filters | 65 μL | 0.045–0.54 μg L −1 | 3.6 | 41–50 | AALLME-SF-DES | HPLC | Water | 87.5–105.8 | 0.15–800 μg L−1 | [51] |
| DES (3 fatty acids) | ||||||||||
| Bisphenols | 100 μL | 0.16–0.75 μg L−1 | ≤6.9 | 15–18 | AALLME-SF-DES | HPLC-UV | Tea | 82.0–116.6 | 0.5–400 μg L−1 | [53] |
| Polycyclic aromatic hydrocarbons | DES | |||||||||
| 7 Fungicide residues | 30 µL 1-undecanol | 0.02–0.25 µg L−1 | 2.3–13.0 | — | AALLME-SFO | GC-ECD | Juice samples | 72.6–114.0 | 0.3–500 µg L−1 | [66] |
| Amitriptyline imipramine | 14 µL 1-dodecanol | 5.0 | 4.8 | 731 | AALLME-SFO | GC-FID | Plasma, wastewater | 73 | 15–2,000 | [70] |
| 7.0 ng mL−1 | 7.7 | 682 | 68 | 20–2,000 ng mL−1 | ||||||
| Clozapine | 50 μL | 0.92, 0.99 ng mL−1 | — | 241–247 | ASEME-SFO | HPLC-UV | Plasma, urine | ≥96.5 | 5–500 ng mL−1 | [37] |
| 1-undecanol | ||||||||||
| Methadone | 100 µL | 0.7 µg L−1 | ≤6 | 270 | DES-AAELLME | GC-FID | Plasma, urine | 98.4–101.2 | 2–8,000 µg L−1 | [68] |
| ChCl:TNO (1:2) DES | ||||||||||
| Rare ginsenosides | Choline chloride/phenol | 10.2–137.8 ng mL−1 | 1.2–4.5 | — | DES-AALLME | HPLC | Kang’ai injection | 91.3–106.7 | 0.25–100 ng mL−1 | [47] |
| 5 Fungicides | 40 µL | 0.4–1.8 µg mL−1 | 4.2–6.2 | — | IL-AALLME | HPLC-UV | Juice samples | 74.9–115.4 | 2–400 µg L−1 | [35] |
| HMIMNTF2 | ||||||||||
| 6 Benzoylureas | 30 μL 1-dodecanol/10 μL [P14,6,6,6]PF6 | 0.01–0.1 μg L−1 | 1.8–4.4 | 144–187 | IL-AALLME-SFOD | HPLC-UV | Water, honey samples | 84–109.2 | 0.5–500 μg mL−1 | [36] |
| Phthalic, iso-phthalic, and terephthalic acids | Tri-butyl amine-toluene | 0.09–0.24 ng mL−1 | 8.4 | 443–491 | IP-AALLME | HPLC | Aqueous solutions | 88–98 | 0.5–500 ng mL−1 | [42] |
| Phytosterols | EMAC: pivalic acid (DES) | 0.73–1.5 ng g –1 | ≤9.3 | 385–450 | LLE–SAALLME | GC–FID | Cow milk, butter, animal oil | 77–90 | 2.5–5,000 ng g –1 | [54] |
| o,m,p-Phthalic acids | Dimethyl sulfoxide | 0.11–0.29 ng mL−1 | 3.2–5.9 | 406–489 | OS-FAALLME | HPLC-DAD | Oil | 81–97 | 0.28–1,000 ng mL−1 | [44] |
| β-naphthol, naphthalene and anthracene | Acetonitrile | 4.25, 8.34 and 0.22 ng mL−1 | 4.8- 7.2 | 24–65 | SAALLME | HPLC | Aqueous solution | 92.0–99.0 | 1–1,000 ng mL−1 | [38] |
| Diclofenac, ibuprofen, and mefenamic acid | 37 µL | 0.1–0.3 ng mL−1 | ≥7.7 | 80–104 | TAALLME-BE | HPLC-UV | Wastewater, plasma | — | 0.5–4,000 ng mL−1 | [31] |
| 1,2-dichloroethane | ||||||||||
| Naproxen, diclofenac, and ibuprofen | 80 µL Chloroform | 0.20–0.52 ng mL−1 | 3.4–7.1 | 390–470 | AALLME-BE | HPLC | Human fluids | 78–94 | 2–10,000 ng mL−1 | [30] |
| Salicylic acid | 30 µL n-octanol | 1.0 | — | 135 | USE-AALLME | GC-FID | Urine | 94–103 | 0.4–1,000 µg L−1 | [65] |
| Diclofenac and ibuprofen | 1.0 | 125 | ||||||||
| 0.1 µg L−1 | 115 | |||||||||
| Bisphenol A, B | 5 mL n-hexane/14 µL Ammonia | 0.54–0.82 ng mL−1 | 5–6 | 4,050–4,300 | VAALE-AALLME | HPLC-VWC | Canned doogh | 81–86 | 1.5–100 ng mL−1 | [45] |
| β-naphthol, naphthalene, and anthracene | 500 μL | 10, 5, 0.5 ng mL−1 | <5.0 | 29, 40 and 62 | VAALLME | HPLC-UV | Water, wastewater | 97.0–102.0 | 2–2,000 ng mL−1 | [33] |
| Octanol/cyclohexane (50:50 v/v) | ||||||||||
| Valproic acid and 3-heptanone | 20 µL Chloroform | 0.010 | ≤9 | 56 ± 3 | VAALLME | GC-FID | Plasma | 19 ± 1 | 0.2–100 | [74] |
| 51 ± 2 | ||||||||||
| 0.057 mg L–1 | 17 ± 0.5 | 0.04–100 mg L−1 | ||||||||
| Morin complex | 500 µL 1-dodecanol/THF | 3.5 µg L–1 | 3.1 | 120 | SUPRAS-AA-LLME | UV-Vis | Fruit and beverage | 93–104 | 10–800 µg L–1 | [79] |
Recently, the AALLME procedure has been used with different extractants due to its more sensitive modes. And the combination with other procedures produced 11 new modes, as follows:
The traditional air-assisted liquid–liquid microextraction (AALLME)
The air-assisted dispersive liquid–liquid microextraction (AADLLME) procedure
The air-assisted liquid–liquid microextraction coupled with solidification of floating organic droplets (AALLME-SFO) procedure
Air-assisted liquid–liquid microextraction coupled with deep eutectic solvent (AA-LLME-DES) procedure
Vortex-assisted-air liquid–liquid microextraction procedure (VAALLME)
Ionic liquid-based air-assisted liquid–liquid microextraction (IL-AALLME) procedure
Ion-pair air-assisted liquid–liquid microextraction (IP-AALLME) procedure
One-step air-assisted liquid–liquid microextraction (OS-AALLME) procedure
Organic solvent-free air-assisted liquid–liquid microextraction (OS-FAALLME) procedure
Salt- and air-assisted liquid–liquid microextraction (SAALLME) procedure
Tandem air-agitated liquid–liquid microextraction (TAALLME)
Ultrasound air-assisted liquid–liquid microextraction (US-AALLME)
This review shows the traditional AALLME has been used the most, followed by AALLME-SFO, AALLME-DES, and AADLLME. The different modes of the AALLME and their percentages are depicted in Figure 4 and Tables 1–3.
The various modes of the air-assisted liquid–liquid microextraction procedure.
2.1 The traditional AALLME applications
The AALLME is a modern edition of the DLLME procedure. In the absence of a dispersing liquid, this technique requires a much smaller amount of extractant. Attempting to suck and repeatedly putting the mixture of aqueous phase and extracted liquid into a conical tube with a syringe resulted in fine organic droplets. After the phases were extracted, centrifugation was employed to separate analytes [20,28]. In other studies, the AALLME method was utilized to remove azoxystrobin, diethofencarb, and pyrimethanil from juice and aqueous samples. A lighter-than-water organic solvent (30 µL 1-octanol) was used for separation in this technique, as well as a narrow-neck tube to make extraction solvent collection easier [77]. This approach did not require the use of a centrifuge. The time spent for pretreating the samples is minimal (90 s). The lack of a disperser, in particular, improved extraction efficiency. As a result, the proposed process is quick, easy, and eco-friendly [32]. The major characteristics of the described approaches are stated in Table 1.
2.2 Air-assisted dispersed liquid–liquid microextraction (AADLLME)
In the DLLME technique, a different concept for dispersing tiny extractant drops throughout the test solution has recently been established. Air bubbles can assist you in doing this. The extract is withdrawn into the syringe with a little air and pumped out into the tubes for predefined cycles in the AA-LLME process, resulting in a turbid mixture with the extract scattered as tiny drops in the aqueous medium. Air was used as a component to improve the microextraction procedure. This is a low-cost, environmentally friendly option that can considerably improve the extraction efficiency. To create a turbid solution, air-assisted dispersion was employed instead of the dispersive liquid in a typical DLLME. The removal of the dispersive solvent can aid in the transfer of analytes into the extraction solvent’s tiny droplets. Economic benefits, easiness, speed, high recoveries, and nontoxicity are all features of using the AA-DLLME approach in the analysis of medications and organic compounds in real samples [52,61]. By periodically extracting the mixture containing the aqueous sample and a few microliters of solvent, a stable dispersion is created injecting the solvent into the syringe and then forcing it down the tube. As a result, the extraction solvent may become dispersed without the use of a dispersant liquid [48,70].
For the first time, an organic solvent-free AALLME approach was used to extract ortho-phthalic, meta-phthalic, and para-phthalic acids from edible oil. A basic solution and the oil test combination are repeatedly aspirated and injected into a funnel-bottom centrifuge tube to create the turbid solution. After centrifugation, the sediment layer is directly identified by HPLC-DAD [43]. GCT–DES–EVA–DLLME is a novel EVA–DLLME form that has been created by using nitrogen gas. Bifenthrin, phenothrin, tetramethrin, cyhalothrin, permethrin, and cypermethrin were measured in fruit juices using this approach. The suggestion was easy, dependable, and effective. LODs were obtained at 9–21 ng L–1 [56]. Table 2 lists other research with analytical characteristics.
2.3 Air-assisted liquid–liquid microextraction coupled with solidification of floating organic droplets (AALLME-SFO)
A tiny volume of organic phase is moved into the aqueous phase in most AALLME, and the mixture is then repetitively withdrawn into a needle and injected into a tube. Drug molecules transfer into the organic phase via the bolus flow created during the water-soluble sample withdrawal and ejection system [70,71,72]. New technologies are overcoming the extraction solvent challenges [41,52]. This method uses an organic phase with a lower density and a melting temperature of between 10 and 30°C. The extractants can be solidified after separation by exposing them to low temperatures. This allows them to be removed as droplets of floating solvent by the centrifugation method [66]. The approach has the benefit of combining the dispersive and extraction procedures into a single glass syringe. As a result, no dispersive liquids are used, which cuts down on extraction time. Furthermore, after solidification, the organic layer may be easily removed from the aqueous solution [61,69,72]. The procedure’s suitability as a beneficial alternative for the evaluation of actual food and environmental samples is further supported by its great results in actual analysis. Tables 2 and 3 contain many applications of SFO and AALLME for preconcentration of medicines.
Researchers developed a technique that uses the solidification of float organic droplets (SFO-AALLME) to extract benzoylurea pesticides from water sources and honey samples. [P14,6,6,6] PF6 and 1-dodecanol were used as extraction solvents in this approach. Because the employed ILs had a lower density than water, solidification was performed to remove the foggy state [36]. Another article that has been extracted is clozapine from biofluids by using surfactants in the SFO-AALLME technique. To speed up the mass transfer rate of the clozapine into the extractant, sodium dodecyl sulfate was added as a surfactant [37].
2.4 Air-assisted liquid–liquid microextraction using deep eutectic solvent as extractants (AALLME-DES)
DESs are described as a fluid eutectic mixture containing two or more chemicals having a low melting temperature. The DESs are currently receiving a lot of interest as a possible replacement for traditional organic solvents. The DESs are made up of a H-bond acceptor (HBA) and a H-bond donor (HBD) that is suited for the environment. HBA is typically made up of quaternary ammonium salt and choline chloride (ChCl) [68,69]. There are major benefits, including volatility, excellent thermal stability, and conductivity. DESs are also inexpensive, readily available, and harmless. The DES synthetic procedure is also quite simple [51,56]. More critically, because of the safe and environmentally friendly components, some of which can even be made with food-grade substances, DESs are deemed to be naturally nontoxic. Because of the wide range of HBA and HBD available, the physicochemical features of DESs can be tailored to meet the needs of a wide variety of industries [29].
As a result, for the analysis of rare ginsenosides in KA injection, the AALLM-DSE process was created. The goal of this research is to extract ginsenosides from KA injections and quantify their levels. Magnetic nanoparticles were also used to swiftly and efficiently extract the DES droplets from the solution. The water-soluble extraction solvents in this study were DESs (ChCl and phenol). The polarity of the aqueous phase was adjusted with the emulsified solvent (tetrahydrofuran). A small amount of N2 was added to produce a rather thorough emulsification step [47,71].
In other studies, the phthalates esters [75,76,77,78], amitriptyline and imipramine [73], and valproic acid and 3-heptanone [74] have all been determined using AALLME paired with GC. Due to the use of DES, this approach did not require the use of a centrifuge and was also environmentally benign. Table 3 shows many applications of AALLME with DES as green extractants.
2.5 Ionic liquid used in air-assisted liquid–liquid microextraction (IL-AALLME)
ILs are distinguished by their low vapor pressure, high thermal stability, ability to dissolve different chemical species, and low aqueous solubility. They are classified as environmentally benign and relatively safe solvents. Another significant benefit of ILs is the ability to mix and match cations and anions to get the necessary physicochemical properties. As a result, ILs are frequently referred to as modeling solvents. The IL-based AALLME approach has received a lot of interest because of these benefits [35]. Also, ILs can act as both an extraction solvent and a surfactant during the separation process. They are reducing the interfacial tension between two immiscible liquids through adsorption at the liquid–liquid interface [36]. The isolation of phthalic acid, iso-phthalic acid, and terephthalic acid in aqueous systems was very sensitive. This has been advanced by utilizing ion-pair air-assisted liquid–liquid microextraction (IP-AALLME) with a low-density extractant coupled with an HPLC-DAD detector. In this procedure, an aqueous test solution is mixed with tri-butyl amine (as an ion-pair agent) and toluene (as an extractant). By aspirating and spreading the mixture with a syringe needle, tiny organic-phase droplets are generated. After that, the generated ion-pairs are isolated into toluene, centrifuged, and the collected layer is transferred into a microtube and evaporated to dryness at 25°C below the nitrogen stream [42,78].
2.6 Coupled air-assisted liquid–liquid microextraction procedure with other methods
The evaluation of B-naphthol, naphthalene, and anthracene in the wastewater sample was then done using a vortex assisted-air liquid–liquid microextraction (VAALLME) technique in a limited bore tube. The extraction liquid in this process was a lighter organic solvent than water. There was no need for centrifugation because the air bubbles increased the extraction solvent collection [33]. Other studies [45,71] were reported in Table 1. The illegal azo-based dyes and their major metabolites were extracted using the ultrasonic-enhanced air-assisted liquid–liquid microextraction (US-AALLME) process. The procedure was conducted without the use of organic solvents, and ILs were considered suitable extractants [34].
The microdetermination of naproxen, diclofenac, and ibuprofen medications from plasma and urine was reported using a combination of back extraction and air-assisted liquid–liquid microextraction (AALLME-BE) techniques. Chloroform was used as an extractant. The analytes were separated into a hydrophobic layer and then back-extracted into an alkaline medium [30,77]. A tandem TAALLME was utilized to extract diclofenac, ibuprofen, and mefenamic acid (NSAIDs), and a response surface approach was employed to optimize the factors. A second application of AALLME was employed to extract drugs by using 1,2-dichloroethane (37 µL) as extractant and coupled with back-extraction in pH = 10.01 in 2 min [31,78].
A novel supramolecular solvents (SUPRAS)-based AALLME for the separation and extraction of Morin in fruit and beverage tests that is simple, fast, and environmentally friendly. The use of an alkanol-based nanostructure of supramolecular (500 µL 1-dodecanol/THF) increases the effectiveness of the microextraction method. Additionally, the analytical time is significantly reduced [79].
A new on-site sample preparation procedure for forest water tests has recently been introduced. A synthetic DES (1:2 of DL-menthol to citric acid) with excellent stability and extraction efficiency was produced and employed as an extractant. At first, AALLME was used to create an array device. Without the use of electricity, up to six tests were conducted on-site in 20 min [80].
3 Views for the future
It is envisaged that the creation of an automated AALLME approach as an economical microextraction technology will take off in common analysis in the future. Special equipment and extraction tubes must be developed for this project. Other forms of extractants (nanomaterials, surfactants, magnetic liquids, and biomolecules) are used because they are more effective. Green approaches will emerge for other modified AALLME modes. Various extraction techniques, such as point cloud extraction, will be combined with this method (CPE-AALLME) to be greener and faster. Another topic to examine in the coming years is the development of AALLME procedures that do not require the use of centrifuges. Future scope is more selective and sensitive when modified AALLME is used. The use of the AALLME method will increase significantly, not only in analytical chemistry but also in various industries in biological and medical fields, as well as environmentally sustainable industries.
Conclusion
The current review serves as an introduction to the modified AALLME approach, its basis, and applications. An overview of the advancements, uniqueness, and principles of liquid-phase microextraction (SDME, HF-LLME, and DLLME) is presented. AALLME’s various modes are discussed. The extraction solvents (SFO, IP, ILs, and DESs) utilized in AALLME were evaluated in terms of extraction capability and procedure efficiency. AALLME has been used to extract a variety of analytes, including organic substances and medical analytes. Easy assembly, the novelty of the extraction phase, and flexibility with most analysis instruments are all features of AALLME-based procedures. This approach to sample preparation is easy, inexpensive, effective, and environmentally friendly. It also assumes that numerous analytes have high EFs. These approaches are rising in popularity, and future innovations, modifications, and enhancements are expected. Quick sample preparation time (relative to SPME, SDME, and HF-LPME), high precision, reliability, and selectivity are only a few of the benefits of this technology. Furthermore, the AA-LLME technique is a viable alternative method for extracting organic compounds due to its simple operation, which requires no specialist equipment, quick extraction time, and inexpensive cost.
Acknowledgments
The authors gratefully acknowledge financial support from the Gifted Najaf’s Students School.
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Funding information: Authors state no funding involved.
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Author contributions: E.A.A. – conceptualization, data curation, writing – review and editing, project administration, supervision; H.S.A.A. – formal analysis, funding acquisition, data curation; M.S.G. – writing – original draft, visualization, software; E.H.B.A – investigation, methodology, resources.
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Conflict of interest: The authors state that they do not have any conflicts of interest.
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Ethical approval: The conducted research is not related to either human or animal use.
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