Table 3.

The review of representative conditions for gallic acid isolation and analysis by HPLC, HPLTC, GC, and electrochemical methods in various solid and liquid matrix types.

Material	Sample Preparation	Analytical Conditions	Ref.
Tea samples, including fermented (black and red), semi-fermented (oolong), and non-fermented (green) teas of different geographical origins	Grinding of samples; triple maceration with 20 mL of 80% (v/v) methanol (MeOH) for 3 h and then twice with 20 mL of 80% (v/v) MeOH containing 0.15% HCl for 3 h; filtration of the obtained extracts	HPLC-DAD; C18 column (250 × 4.6 mm I.D, 5-μm); mobile phase: water-acetic acid, 97:3 v/v (A), MeOH (B); gradient elution program: 100% solvent A for 1 min, followed by a linear increase in solvent B to 63% in 27 min; flow rate: 1 mL L/min; detection: λ = 200–400 nm	[88]
Schinus terebinthifolius Raddi bark	Maceration in 40% ethanol (EtOH) over 5 days; extracts hydrolysis by refluxing for 1.5 h with 5% sulfuric acid, followed by LLE with 30 mL of ethyl acetate (EtAc) and concentration in a rotavapor	HPLC-DAD; C18 column (250 × 4.6 mm, 5 μm); mobile phase: ACN:H2O and MeOH:H2O at pH 2.7(adjusted with formic acid (HCOOH)); gradient elution I: organic phase changes from 5 to 80% for 20 min; gradient elution II: organic phase changes from 15 to 80% for 20 min; flow rate: 1 mL/min; detection: λ = 200–400 nm	[89]
Stem bark of Q. parviflora and Q. grandiflora	Maceration with a hydroalcoholic solution; complete evaporation of the solvents under reduced pressure at 40 °C	HPLC-UV; C18 column (250 × 4.6 mm., 5 μm); mobile phase: water (+0.05% trifluoroacetic acid [TFA]) as solvent A and MeOH (+0.05% TFA) as solvent B; gradient elution profile: 0–12 min (15–40% B); 12–14 min (40–74%) B; 14 -16 min (74–15%) B, 16–18 min (15% B); flow 0.8 mL/min; λ = 280 nm	[90]
Fresh fruit of Benincasa hispida (Bh)	Homogenization of pulps; low heating maceration with water at 60 °C for 30 min followed by drying for 2 days at 55–60 °C	HPLC-UV; LiChrospher 100 RP-18 (125 × 4 mm, 5-μm); mobile phase: 0.01 M potassium dihydrogen phosphate-ACN (85:15, v/v) at pH 3.2; flow 0.75 mL L/min.; detection: λ = 280 nm	[91]
Stem bark of Schinopsis brasiliensis Engl., Anacardiaceae	Hydroalcoholic maceration of dry powder material with water:EtOH mixture (30:70, v/v) for 72 h; drying of the obtained extract at 140 °C	HPLC-UV; Phenomenex Gemini NX C18 column (5-μm, 250 × 4.6 mm); mobile phase: 0.05% orthophosphoric acid (A): MeOH (B); gradient program: 90–10% B (10 min), 70–30% B (3 min), 40–60% B (5 min), 60–40% B (3 min), 80–20% B (3 min) and 90–10% B (6 min); flow 1 mL L/min; λ = 271 nm	[92]
Rhodiola kirilowii (Regel.) Maximroot Rhodiola rosea L. root	Extraction under reflux for 45 min with 70% MeOH with acetylsalicylic acid; evaporation of organic phase and dissolution in the mobile phase	UPLC-ESI MS/MS; C18 column (1.7 μm, 2.1 × 50 mm); mobile phase: MeOH (A), water (B); flow 0.35 mL L/min; isocratic elution: 95% of phase A; column temperature: 24 °C; ion source temperature: 100 °C; desolvation temperature: 300 °C; gas flow rate: desolvation gas: 700 L/h; cone gas: 10 L/h.	[28]
Herba Gei	Extraction under reflux with 30% EtOH in a water bath for 90 min; filtration of the obtained extract	HPLC-UV; C18 column (250 × 4.6 mm, 5 μm); column temperature: 30 °C; mobile phase: MeOH (B) -0.1% aqueous phosphoric acid (A); isocratic elution: (10% B, 90% A); flow rate 1 mL/min; λ = 273 nm	[93]
Syzygium polyanthum leaf	Maceration with water and MeOH; filtration; evaporation and dissolution of 10 mg of the aqueous and methanolic extracts in 1 mL of MeOH	HPLC-UV; C18 column (250 × 4.6 mm, 5 μm); mobile phase: 0.1% aqueous HCOOH (A) and ACN (B); gradient elution profile: 0–12 min with 15–25% B, 12–22 min with 25% B, 22–25 min with 25–15% B, and 25–30 min with 15% B; flow 1 mL/min; λ = 280 nm	[94]
Fruits mixture (Triphala): Amla (Phyllanthus emblica Linn.), Baheda (Terminalia belerica Roxb., Fam. Combretaceae), and Harde (Terminalia chebula Retz., Fam. Combretaceae)	Triple maceration with MeOH; combination of the obtained extracts; concentration at reduced temperature (50 °C) on rotavapor; filtration through a nylon filter	HPLC-UV; C18 column (250 × 4.6 mm, 5 μm); mobile phase: ACN (A) and o-phosphoric acid in water (0.3%) (B); gradient elution profile: 0–5 min with 90–88% B, 5–6 min with 88–86% B, 6–9.5 min with 86–80% B, 9.5–10.5 min with 80–79% B, 10.5–12 min with 79–78% B, 12–22 min with 78–76% B, and 22–30 min with 76–90% B; flow 0.8 mL/min; λ = 254 nm	[95]
European red oak (Quercus robur), North American white oak (Quercus alba), blocks	Grinding of the sample into fine dust; collecting of oak wood dust on the polycarbonate membrane filters; filter maceration with the MeOH/water mixture (80/20 v/v) for 60 min; evaporation of MeOH; LLE with EtAc–EtOH (95/5 v/v) and then evaporation and reconstitution in 0.07% HCOOH (100 μL, pH 2.7); filtration through a nylon filter	HPLC-UV; C18 column (150 × 4.6 mm, 5 μm); mobile phase: pH 2.7 HCOOH (A) and 0.07% HCOOH in MeOH (B); gradient elution: 100% (A) for 20 min, 100% to 20% in 5 min, 20% for 10 min, 20% to 100% in 5 min, and 100% for 20 min; flow 0.7 mL/min; λ = 270 nm	[96]
Human plasma and urine	Acid hydrolysis; maceration with EtAc; evaporation of organic phase; dissolution in the mobile phase	HPLC-UV; Chrospher 100 RP-18 column (5 μm; 120 × 4 mm); method 1: mobile phase (4.4 × 10−3 M phosphoric acid in water); flow 1 mL L/min; λ = 220 nm and 270 nm; method 2: mobile phase water–ACN (97.5:2.5, v/v) modified with 0.025% phosphoric acid; flow 1 mL L/min; λ = 220 nm and 270 nm	[97]
Ficus auriculata Lour. leaves (Roxburgh Fig)	UASE with the aqueous solvent at 37 kHz; centrifugation of the extract at 10000 rpm for 10 min; filtration using Whatman filter paper	HPLC-IR-UV-Vis; Shimpack C18 column (250 × 4.6 mm, 5 μm); mobile phase consisted of pure ACN (A) and 0.1% ortho-phosphoric acid in water (B) with a stable composition of 20% A and 80% B; flow 0.8 mL L/min	[98]
Triphala waste	Grinding of the dried sample into small particles; fermentation with Aspergillus niger; drying and milling of the fermented sample into powder; UASE with water (10–60 min, 40 kHz at 30 °C)	HPLC-UV; C18 column (250 × 4.6 mm, 5 μm); mobile phase: ACN (A) and acetic acid in water (0.1%) (B); gradient elution; flow 1 mL/min; λ = 280 nm	[99]
Fruit wines and grape wines of Papazkarasi-type cultivar	Removing the alcohol using a rotatory evaporator; lyophilization of residues; dissolution in water	HPLC-UV; C18 column (150 × 4.6 mm, 3.5 μm); mobile phase: 10 mM phosphoric acid as solvent A and MeOH as solvent B; gradient elution profile: 0–15 min (0–60% B), 15–20 min (60–80% B), 20–22 min (80–100% B), 22–27 min (100–0% B), and 27–32 min (0% B); flow 1 mL/min; λ = 214 nm	[100]
Camellia sinensis leaves	Maceration with hot water and then polyamide membrane separation; filtration with filter paper	HPLC-UV; C-18 column; mobile phase, consisting of 7% (v/v) solvent A (100% ACN) and 93% of solvent B (20 mM KH2PO4); flow 1 mL/min.	[101]
Aqueous solutions	Reactive extraction with tri-n-caprylylamine in hexanol (0.234 mol/L) at 25 °C; filtration through a syringe PVD filter	HPLC-DAD; Eclipse XDB-C18 column (250 × 4.6 mm, 5 µm); at 35 °C; mobile phase: ACN (10%) and 0.2 mole of the aqueous solution of acetic acid (90%); flow 1 mL/min; λ = 273 nm	[102]
Acacia arabica bark	Grinding; MASE and reflux extraction with 20% MeOH at T = 88 °C for 1–7 h; maceration in 20% MeOH for 12–30 h; centrifugation of the obtained extract	HPLC-UV; C18 column (150 × 4.6 mm, 5 μm); mobile phase: 0.025% o-phosphoric acid in water (A) and MeOH (B); gradient elution profile: 0–5 min, 20% B; 5.1–15 min, increasing gradually from 50% to 80% B; 15.1–18 min, 20% B; flow 1 mL/min; λ = 272 nm	[103]
Mixture of Vidanga (Embelia ribes Burm.), Amalaki (Emblica officinalis Geartn), Haritaki (Terminalia chebula Retz.), Nishotha or Trivrt- Root (Operculina turpethum Linn.), and Guda (Jeggary)	Maceration with MeOH; evaporation; reconstitution in MeOH	HPTLC with silica gel 60 F254 plates (10 × 10 cm, 0.2 mm thickness); mobile phase: toluene/EtAc/MeOH/HCOOH (5: 4: 0.5: 0.5, v/v); migration distance: 80 mm; λ = 254 nm	[104]
Amrtottara kvatha mixture containing fresh stem of Tinospora cordifolia (Willd.) Miers (Guduchi), dried fruit rind of Terminalia chebula Retz (Haritaki), and dried rhizome of Zingiber offficinale Roscoe (Shunti)	Maceration with boiling water; evaporation at 80 °C for 2 h; reconstitution of the residue in MeOH	HPTLC with silica gel 60 F254 plates (20 × 20 cm) with the aluminum sheet support; the mobile phase: toluene/EtAc/HCOOH (5/7/1, v/v/v); migration distance: 70 mm; λ = 254 nm and λ = 366 nm	[105]
Polyherbal tablets (Amalant and Sookshma Triphala Tablet) containing Embelica Officinalis	Extraction under reflux with 50 mL of MeOH; filtration of the obtained extract	HPTLC with silica gel 60 F254 plates (20 × 10 cm with 0.2 mm thickness); mobile phase: toluene/EtAc/HCOOH (6/3/1, v/v/v); distance: 60 mm; λ = 254 nm	[106]
Flower buds of Syzygium aromaticum (L.) Merr. & Perry (clove)	Extraction under reflux with MeOH; concentration of the obtained extract to a known volume	HPTLC with the silica gel 60 F254 plates (20 × 10 cm, 0.2 mm thickness); the mobile phase: toluene/EtAc/HCOOH (10.8 mL) (3:2:0.4, v/v); distance: 80 mm; λ = 280 nm	[107]
Selected polyherbal supplements	Maceration in MeOH enhanced by shaking for 4 hrs using a magnetic stirrer; filtration of the obtained extract	HPTLC with the aluminum backed TLC plate coated with the 0.2 mm layer of silica gel (10 × 10cm); mobile phase: toluene/EtAc/HCOOH (5:5:1, v/v/v); λ = 254 nm	[108]
Emblica officinalis fruit	Double maceration with MeOH for 24 h at 25 °C; filtration and concentration of the obtained extract	HPTLC with silica gel 60 F254 (4 × 10 cm); mobile phase: toluene/EtAc/HCOOH at the ratio (7/5/1, v/v/v); λ = 273 nm	[109]
Polyherbal formulation, psoriasis tablets with Azadirachta indica Linn., Curcuma longa Linn., Rubia cordifolia Linn., Tinospora cordifolia Willd., Acacia catechu Wild and others herbs	Distillation with MeOH; filtration; concentration of the obtained extract to a dry residue; reconstitution in MeOH	HPTLC with silica gel 60 F254 TLC plate (0.2 mm thickness); mobile phase: toluene/EtAc/formic acid (4.5: 3:0.2, v/v/v); λ = 366 nm	[110]
Eucalyptus leaves	Grinding of dried leaves; MASE with different solvents: n-hexane, DCM, EtAc, acetone, MeOH, MeOH/water (60:40, v/v); concentration and dissolution of the dry residue in MeOH.	HPTLC with silica gel 60 F254 plates (20 × 20 cm) with aluminum sheet support; mobile phase: EtAc/CHCl3/formic acid (50:50:3, v/v/v); migration distance: 30 mm; λ = 288 nm	[111]
Ceratonia siliqua wood	Maceration with MeOH/water mixture; evaporation; LLE of the aqueous phase with petroleum ether (2 × 25 mL), then with Et2O (2 × 25 mL), and finally with a mixture of Et2O:MeOH (9:1; 2 × 25 mL); hydrolysis with HCl (6 M) in MeOH (1:1, v/v) at 100 °C for 8 h; evaporation; reconstitution in water and evaporation again (four or five times); LLE with a mixture of Et2O:MeOH (9:1; 2 × 25 mL) and water (2 × 25 mL); derivatization with trimethylchlorosilane (TMCS) and bis-(trimethylsilyl)-trifluoracetamide (BSTFA) (1:3)	GC/MS; DB-1 fused silica capillary column (30 m × 0.25 mm I.D., 0.25 µm film thickness); carrier gas: helium; flow 1.5 mL/min; temperature of the injector: 280 °C; volume of sample: 1µL; split ratio: 1:10; temperature of the interface: 300 °C; column temperature program: oven equilibration time 1 min; initial temperature 90 °C for 2 min, then raised to 290 °C at a rate of 20°C/min and then 5 min at 290 °C, and then to 310 °C at a rate of 4 °C/min and kept for 10 min; ionization energy: 70 eV	[112]
Red wine samples	MSPD of wine samples (1.5 mL) acidified to pH 1.0 with 0.1 mL of 1 M solution of HCl and salted with 0.4 g of NaCl using 1.5 g of silica gel (70–230 mesh) as a dispersant and 5 mL of EtAc as the eluting solvent; evaporation of the extract; derivatization with 100 µL of BSTFA and pyridine (1 mL); the procedure gave mean recoveries between 87 and 109% with RSD < 9%	GC/MS in the selective ion monitoring (SIM) mode; the DB-5MS fused silica capillary column (30 m × 0.25 mm, 0.25 µm film thickness); carrier gas: helium; flow 2.5 mL/min; column head pressure 26.04 psi; temperature of the injector 320 °C; volume of sample 1 µL; split ratio 1:50; temperature of the interface 280 °C; column temperature program: oven equilibration time 1 min, initial temperature 120 °C for 3 min, then raised to 292 °C at a rate of 5 °C/min and then to 320 °C at a rate of 30 °C/min with a final isotherm of 2 min; ionization energy: 70 eV	[113]
Balsamic vinegar from Modena	Dilution of the sample with water (1:1); SPE 1) with 1 g diatomaceous earth cartridges using 6 mL of EtAc or n-butanol or isopentyl alcohol or 4-methylpentan-2-one; SPE 2) in the polyamidic SPE cartridge conditioned with 2 mL of MeOH and 2 mL of water and eluted with 3 mL of EtAc; evaporation; derivatization of 1 mL of sample reconstituted in 1 mL of DCM to ensure removal of water (azeotropic removal of water) with 300 µL of 1:1 BSTFA/pyridine at 70°C for 30 min.	GC/MS with the SIM mode; RTX-5MS fused silica capillary column (30 m × 0.25 mm, 0.25 µm film thickness); carrier gas: helium; flow 39 mL/min; temperature of the injector 260 °C; volume of sample 1µL; splitless mode; temperature of the interface 280 °C; column temperature program: oven equilibration time 1 min; initial temperature 90 °C for 1 min, then raised to 240 °C at the rate of 20 °C/min and then 240°C for10 min, then to 280 °C at a rate of 20 °C/min with a final isotherm of 1 min; ionization energy: 70 eV	[114]
Origanum dictamnus (dictamus), Eucalyptus globulus (eucalyptus), Origanum vulgare L. (oregano), Mellisa officinalis L. (balm mint), and Sideritis cretica (mountain tea)	Maceration of the dried sample (0.5 g) with 62.5% aqueous MeOH containing BHT (1 g/L); the addition of HCl (10 mL); sonication of the extraction mixture for 15 min and extraction under reflux at 90°C for 2 h; LLE with EtAc (3 × 10 mL); reduction of the organic phase and removing moisture with anhydrous Na2SO4; derivatization after the evaporation of the solvent with the mixture TMCS (100 µL) and BSTFA (200 µL) at 80 °C for 45 min.	GC/MS; capillary column low-bleed CP-Sil 8 CB-MS (30 m × 0.32 mm, 0.25 µm film thickness); carrier gas: helium; flow 1.9 mL/min; temperature of the injector 280 °C; volume of sample 1 µL; splitless mode; temperature of the interface 290 °C; column temperature program: oven equilibration time 1 min; initial temperature 70 °C then raised to 135 °C at 2 °C/min, kept for 10 min and then raised to 220 °C at 4 °C/min and kept for 10 min and up to 270 °C at a rate of 3.5 °C/min with a final isotherm of 20 min; ionization energy: 70 Ev	[115]
Wines from different regions of Poland	UASE-PMLS of 25 µL sample on 60 mg of MgSO4, used as the sample support, using 1 ml of ACN or DCM or EtAc or MeOH; exposition for 25 min in an ultrasound bath; evaporation of the extract to dryness; derivatization with a mixture of 1% TMCS in BSTFA (30 µL) at 35°C for 30 min	GC-MS; ZB-5 MS capillary column (30 m×0.25 mm, 0.25 µm film thickness); carrier gas: helium; flow 1 mL/min; temperature of the injector 240 °C; sample volume 2 µL; splitless mode; temperature of the interface 300 °C; column temperature program: 70 °C for 1 min, then increased to 280 °C at 10 °C /min and kept for 5 min; ionization energy: 70 eV	[116]
Blue Oak Plant	Hydrolysis of sample (1 g) with 10 mL of 3% HCl (v/v) at 110 °C for 4 h; maceration of hydrolyzed sample after its cooling with 5% EtOH in EtAc (100 mL) and 50 g of Na2SO4; evaporation of the extract to dryness; derivatization with TMCS after the solvent evaporation; LLE cleanup using back extraction with isooctane (1 mL) and water (1:1)	GC-MS; DB-1 capillary column (15 m × 0.53 mm, 0.1µm film thickness); carrier gas: helium; flow 7 mL/min; temperature of the injector 240 °C; sample volume 2 µL; splitless mode; temperature of the interface 280 °C; column temperature program: initial temperature 60 °C for 0.5 min, then raised to 110 °C at a rate of 5 °C/min, and then raised to 180 °C at 10 °C/min, and finally up to 275 °C at 30 °C/min with a final isotherm of 1 min; ionization energy 70 eV	[117]
Wastewater olive oil	LLME with EtAc (0.5 mL) of 2 mL of acidified samples (pH 3) saturated with NaCl; evaporation to dryness in the nitrogen stream; derivatization of the solid residue with 50 µL of a mixture of BSTFA and pyridine in EtAc as the silylation reagent (4:1:5, v/v/v)	GC/MS with the SIM mode; HP-5MS fused silica capillary column (60 m × 0.25 mm × 0.25µm film thickness); carrier gas: helium; flow 1 mL/min; temperature of the injector 250 °C; sample volume 1 µL; splitless mode; temperature of the interface 280 °C; column temperature program: oven equilibration time 1 min; initial temperature 90 °C for 1 min, then raised to 220 °C at 6 °C/min and then to 290 °C at 10 °C/min and kept for 1.23 min and finally to 310 °C at a rate of 40 °C/min and kept for 7.5 min; ionization energy 70 eV	[118]
Green tea sample	Maceration with water at pH3.0, adjusted with a phosphate buffer saline (PBS)	Differential pulse voltammetry with graphene modified glassy carbon electrode used as a working electrode, the saturated Ag/AgCl electrode and a Pt wire, which was used as a reference and counter electrode, respectively; potential window range from −0.4 to 1. 2 V; a scanning rate of 0.1 V·S−1; the stirring time −25 s at pH = 3(PBS)	[119]
Red wine	Unprepared samples	Differential pulse voltammetry win zinc oxide nanoparticles modified-carbon paste electrodeas working electrode, a KCl saturated Ag/AgCl as reference electrode, and a platinum wire as counter electrode; potential window range from 0 to 1. 2 V, a scanning rate of 0.1 V·S−1; the stirring time −25 s at pH = 2, adjusted with PBS	[120]
Green tea sample	Maceration with water	Differential pulse voltammetry with poly(glutamic acid): graphene modified electrode; potential window range from −0.8 to 2 V, a scanning rate of 0.1 V·S−1 at pH 5, adjusted with acetate buffer	[121]
Apple juice, lemon juice, peach juice, green tea, orange juice	Dilution of different beverage samples (5 mL) with 10 mL of phosphate buffer solution (0.1 mol/L, pH 7.0)	Amperometry with silver nanoparticle/delphinid in modified glassy carbon electrode. The experiments were carried out at a potential of 220 mV in a 0.1 mol/L phosphate buffer solution at pH 7.0	[122]
C. wightii (Commiphora mukul) known as Indianbdellium-tree, V. agnus-castus also called Vitex, C. sinensis (green tea)	UASE with water: EtOH mixture (30:70) at 25 °C at a constant frequency of 35 kHz for 30 min extracts; filtration through Whatman no. 1 filter paper	Differential pulse voltammetry with carbon paste electrode modified with carboxylated multi-walled carbon nanotubes; a potential window range from 0 to 0.9 V, a scanning rate of 0.148 V·s−1 and solution was 0.2 M PBS at pH 2.0	[123]
Apple peel, apple flesh, nettle	Maceration and dilution	Differential pulse voltammetry with a three electrode cell including modified or bare CPE, saturated calomel electrode and a platinum wire as working reference and counter electrodes, respectively; a potential window of 0.0–0.4 V; the scan rate was 40 mV s−1 and solution was phosphate buffer at pH 7.0	[124]
Fruit juice (e.g., orange, apple, and apricot juice)	Unprepared sample	Differential pulse polarography with dropping mercury electrode as a working electrode, a platinum counter electrode, and an Ag/AgCl (3 M NaCl) reference electrode; optimum conditions: 200–1000 μL of fruit juice samples pH 10.0, at the reduction (peak) potential of –160 mV, 2 s drop time, and 50 mV pulse amplitude	[125]