Application of Microgel as a Sorbent for Bisphenol Analysis in Liquid Food Samples

Featured Application

The synthesized microgels can become a cost-effective sorbent for the removal of bisphenols from an aqueous medium.

Abstract

Bisphenols are well-known endocrine disruptors that can easily migrate from plastic and can containers to food. Due to the complicated matrix and ultra-low concentrations of bisphenols in food, samples require extensive preparation before instrumental analysis. In this paper, an environmental sensitive microgel was employed as a sorbent for the preconcentration of four bisphenols, bisphenol A (BPA), bisphenol B (BPB), bisphenol E (BPE) and bisphenol F (BPF), from liquid food samples. Liquid chromatography with fluorescence detection (LC-FLD) was used for the quantification of bisphenols. By applying microgel solid-phase extraction procedure, the limits of detections achieved in liquid food samples can be lowered to 0.9 µg·L⁻¹ for BPF and BPA, 2.3 µg·L⁻¹ for BPE and 2.9 µg·L⁻¹ for BPB. Only 5 mg of microgel was sufficient to achieve good recoveries (70.5–109%) with precision (RSD 0.21–5.01%, n = 3) for different analyzed liquid food samples spiked at concentration levels of 50 µg·L⁻¹. In five out of twelve of the analyzed samples (pineapple, mandarin, peach, mushroom and pickles), they were contaminated with BPA, and the determined concentration was in the range of 6.2–22 µg·L⁻¹; however, these results are below the specific migration limit (SML) set for BPA (50 µg·kg⁻¹).

1. Introduction

Food contamination might be one of the most common methods of hazardous substances being ingested into a human body. One of the sources of food contamination is inadequate packaging, which may result in the migration of chemical compounds [1]. Among these substances are bisphenols, which are often employed in the production of polycarbonate and epoxy resins. These materials are often used to manufacture plastic bottles, internal coating of cans, food containers and microwave oven dishes [2]. BPA release from polycarbonate is explained by two different processes: diffusion-controlled release of residual BPA present in the polymer and hydrolysis, decomposition overtime at the polymer’s surface [3]. Special attention should be also paid to plastics marked with recycling codes 3 (polyvinyl chloride) or 7 (other types), as they might be made with BPA or its analogue [4]. Bisphenols are becoming well known as they appear to be aggressive endocrine disruptors, and they can easily migrate from plastic and can containers to food [5]. Endocrine disrupting compounds (EDC) disrupt proper functioning of endogenous hormones by mimicking their actions, which results in interferences with synthesis, transport and metabolism of steroid hormones [6]. Bisphenol A is linked to a variety of reproductive and cardiovascular diseases [4,7,8] and the development of many types of cancer (including lung, breast and prostate cancer) [9,10]. For this reason, since January 2011, the manufacture of baby bottles containing BPA is prohibited in European Union, while, since September 2018, the specific migration limit from plastic packaging for BPA was reduced to 50 µg·kg⁻¹ [11]. These restrictions regarding the use of BPA in plastic containers result in the replacement of BPA with its alternatives. Unfortunately, many of them are also bisphenols with estrogenic activity (BPB, BPS, BPE and BPF) [12,13,14]. As it has also been stated in a review article written by Chen et al. [15], although the estimated daily intake rates of bisphenols might be low, the potential additive or synergistic effects produced by a mixture of bisphenol analogues may be dangerous to human health and should be considered in epidemiological studies assessments. Due to these facts, when evaluating the safety of compounds for consumer use, it is essential to consider entire classes instead of individual compounds [16].

Several reviews carefully described analytical methods and sample preparation used for the determination of bisphenols in food [17,18,19,20]. Chromatographic methods such as gas chromatography (GC) or high-performance liquid chromatography (LC) with mass spectrometry are the most often used for the determination of bisphenols. However, due to the complicated matrix and ultra-low concentrations of bisphenols in food [11], samples often require extensive preparation before instrumental analysis. The majority of preconcentration methods used for the extraction of bisphenols from food are based on solid-phase extraction (SPE) [18,21] or microextraction techniques [22,23], where molecularly imprinted polymers (MIP) were often used as selective sorbents.

One of the novel alternatives of cost-effective sorbent are microgels [24], as their porous structure provides advantages, such as strong mechanical strength and large specific surface area, which can uptake a high concentration of the analyte [25]. As was stated by Naseem et al. [26], a major attribution of the usage of microgels is their ability to regenerate and be reused for several cycles. Recently, a few papers presented microgels, which were dedicated as a sorbent for BPA extraction. Du et al. [27] synthesized a polyethylene glycol diacrylate (PEGDA) hydrogel microsphere via reverse emulsion/UV light polymerization and applied it for the enrichment of BPA in spiked water samples. By applying 10 mg of hydrogel for spiked river samples, they achieved 91% recovery, which confirmed the application of hydrogel in real samples [27]. A powdered and activated carbon embedded chitosan-polyvinyl alcohol composite (PAC/CS/PVA) hydrogel was presented by Zhou et al. [24]. They fabricated both hydrophobic/hydrophilic bifunctional sorbents for the removal of sulfamethoxazole and bisphenol A from water. The adsorption performance of PAC/CS/PVA hydrogel was investigated under different typical water matrices, which resulted in the conclusion that ions, such as Cu²⁺, Cl⁻ and SO₄²⁻, had an insignificant effect on the adsorption of bisphenol. Unfortunately, until now, no paper presented the application of microgel for bisphenols sorption in complex food samples.

In a previous article [28], we described the synthesis and characterization of environmental sensitive microgel, which showed very good sorption for bisphenols. Therefore, this paper investigates the application of the microgel as a novel sorbent for the preconcentration of four common bisphenols (Figure 1). The extraction procedure was optimized and used on food samples, which might be exposed to bisphenol contamination due to the package in which they were stored. To the best of our knowledge, it is the first report about the application of microgels as sorbents for bisphenols preconcentration in complex samples. Various factors affecting adsorption and desorption steps for the preconcentration of BPF, BPE, BPA and BPB were investigated and optimized. Finally, the developed procedure was employed to determine these analytes in different liquid food samples.

2. Materials and Methods

2.1. Reagents

Solvents and standards used were of analytical grade. Methanol and acetonitrile were from Merck (Darmstadt, Germany, https://www.merckgroup.com/en). Bisphenol A (BPA, 99% analytical purity), bisphenol F (BPF, 99.7% analytical purity), bisphenol E (BPE, 98% analytical purity) and bisphenol B (BPB, 98% analytical purity) were purchased from Sigma-Aldrich (Steinheim, Germany, https://www.sigmaaldrich.com). Di(ethylene glycol) methyl ether methacrylate (MEO₂MA), ethylene dimethacrylate (EGDMA), oligo(ethylene glycol) methyl ether methacrylate (OEGMA), acrylic acid (AA) and ammonium persulfate (APS) were obtained from Sigma-Aldrich (Steinheim, Germany, https://www.sigmaaldrich.com). Supelclean™ ENVI-18 SPE cartridges were purchased from Sigma-Aldrich (Steinheim, Germany, https://www.sigmaaldrich.com), and Affinimip^® cartridges were purchased from Affinisep (Petit-Couronne, France, https://www.affinisep.com/). Water was purified by using a Milli-Q Plus system from Merck Millipore (Millipore, Bedford, MA, USA, http://www.millipore.com/). Sample workup and preparation were exclusively performed with gloves and bisphenol-free laboratory ware. Stock solutions of standards were prepared at a concentration of 1 g·L⁻¹ in water/methanol (90:10, 10 mL) and were stored in the refrigerator until use. Working solutions for calibration were developed as a standard mix by dilution of the stock solutions with water and were used immediately before analysis.

2.2. Synthesis of Microgel

The microgel was synthesized by precipitation polymerization and it consisted of the main monomer MEO₂MA, two co-monomers OEGMA and AA and EGDMA was used as a linker. All ingredients were dissolved in 60 mL of deionized water. The total concentration of monomers in the reaction mixture was set to 70 mM (81 mol% of MEO₂MA, 10 mol% of OEGMA, 7 mol% of AA and 2 mol% of EGDMA), and 17 mg of APS was added later to the solution. Synthesis was carried out in a 250 mL three-neck flask equipped with a reflux condenser, inlet and outlet of inert gas and a magnetic stirrer. For 30 min, the mixture was purged with argon, and then the temperature was increased to initiate the polymerization process by thermal decomposition of the initiator (APS). The reaction was carried out under an argon blanket for 6 h, and the stirring rate was set at 250 rpm during the entire polymerization process. After synthesis, the products were dialyzed with 5 L of water for one week at room temperature, and water was changed daily.

2.3. Apparatus—HPLC Determination of Bisphenols

Apparatus for sample preparation was a tube rotator RL-2002 from J.W. Electronic (Warsaw, Poland) and an MPW-55 centrifuge from MPW Medical Instruments (Warsaw, Poland). HPLC analysis was performed on Merck/Hitachi HPLC System (Darmstadt, Germany) equipped with a vacuum degasser, a gradient pump, an autosampler and a fluorescence detector. The data were collected and evaluated by using Merck chromatographic software D-7000. Chromatographic separation was performed on a reversed-phase SunFire™ C18 column (2.5 µm × 4.6 mm × 75 mm).

Column temperature was kept at 30 °C, and injection volume was 5 μL. For all HPLC analyses, an isocratic program (70% A, 30% B) was used at a flow rate of 1.5 mL·min⁻¹ by combining solvent A (water with formic acid, 2 mmol) and solvent B (acetonitrile). Fluorescence detection was carried out at 230 nm excitation wavelength and 316 nm emission wavelength.

The method performance was assessed in terms of linearity, limits of detection and analytical instrumental repeatability. Six-point calibration curves were constructed using standard mixtures of the analytes. Linearity testing indicated a linear response for the method for the concentration range from 0.001 to 1 mg·L⁻¹ with an R² value 0.9996 for BPF, R² value 0.9994 for BPE, R² value 0.9992 for BPA and R² value 0.9969 for BPB, respectively. The limits of detection achieved for the LC-FLD method were determined to be 5 µg·L⁻¹ for BPF, 12 µg·L⁻¹ for BPE, 4 µg·L⁻¹ BPA and 15 µg·L⁻¹ for BPB, respectively. Repeatability was determined as the RSD of three consecutive injections of the same sample.

2.4. Solid-Phase Extraction Procedure

In order to apply our microgel for the preconcentration of bisphenols and calculate the recoveries, we needed to achieve complete sorption of all investigated bisphenols. To optimize the SPE method, the influence of microgel dosages (1, 2.5 and 5 mg) and the effect of the concentration of BPA (0.01–1 mg·L⁻¹) were investigated. After applying the microgel into microcentrifuge tubes containing 1 mL of the standard aqueous solution of bisphenols, the mixtures were shaken continually in a tube rotator at 20 °C for 30 min. After the microgel was separated by centrifugation (2 min, 14,000 rpm), the concentration of bisphenols in the supernatant was determined by the LC-FLD method.

The desorption of bisphenols from the microgel matrix was investigated by testing various elution solvents needed for the complete elution of all the analytes from the microgel sorbent. Different compositions of methanol/water mixtures were tested for the evaluation of clean-up efficiency. After each sorption (5 mg of microgel, 50 µg·L⁻¹ of a standard mixture of four bisphenols) the microgel was washed with deionized water to check the retention of bisphenols and the next step was eluting bisphenols with the appropriate organic solvent.

2.5. Analysis of Food Samples

Food samples were taken from local markets in Warsaw, Poland. The analyzed samples included the liquid part of food and drinks: coated cans (mandarin, peach, two cans of pineapple, mushroom, figs, fruits in syrup and energy drink); polycarbonate bottle (mineral water); plastic packages marked with 7 recycle codes (pickles and sour cabbage); and tap water. The liquid part of each sample was filtered (0.45 µm), the pH was measured and then the liquid was kept at 4 °C before extraction. All the food samples were measured in their own pH (

Table 1. Recoveries of BPF, BPE, BPA and BPB in different liquid food samples spiked with 50 µg·L⁻¹ of a standard mixture of four bisphenols using microgel as a sorbent for preconcentration. Data are means with RSD (n = 3).

Sample	Packaging Type	pH of the Sample	BPF	BPE	BPA	BPB
			Recovery [%] ± RSD
Tap water	-	6.9	75.2 ± 1.76	84.6 ± 0.66	106 ± 0.91	109 ± 2.06
Mineral water	Polycarbonatebottle	5.2	81.0 ± 2.34	86.8 ± 4.34	85.8 ± 3.21	90.9 ± 4.54
Sour cabbage	Package no 7	3.4	77.1 ± 5.01	88.5 ± 0.83	90.0 ± 1.11	102 ± 0.21
Energy drink	Can	3.5	80.9 ± 1.23	75.2 ± 4.36	73.2 ± 3.74	95.4 ± 4.22
Pineapple	Can	3.6	75.4 ± 3.09	84.9 ± 3.41	109 ± 0.76	104 ± 1.17
Figs	Can	3.7	70.5 ± 0.54	77.5 ± 0.95	101 ± 1.48	83.8 ± 1.66
Fruits in syrup	Can	3.8	71.2 ± 1.71	72.4 ± 1.22	101 ± 1.91	108 ± 1.54

). The pH of the samples was not adjusted, as our microgel showed stability in the sorption of all bisphenol under pH 9 [28]. For each extraction, 1 mL of sample was used, and five milligrams of microgel was added. The extraction procedure was made on liquid food samples and liquid food samples spiked with a standard mixture of four bisphenols (50 µg·L⁻¹). All mixtures were then shaken in a tube rotator at 20 °C for 30 min. After separation from the mixtures, the microgel sorbent was washed with 500 µL of distilled water, and then bisphenols were eluted with 200 µL of 80% methanol and water solution. Afterwards, all collected samples (the effluent, water after washing and elution solvent after preconcentration) were analyzed by LC-FLD. The recovery (R) was calculated with the following equation:

$$R=\frac{C_{exp}}{C_{theor}}·100\%$$

where $C_{exp}$ is the experimental concentration of bisphenols after preconcentration, and $C_{theor}$ is the theoretical concentration, which should be obtained. Extraction repeatability was calculated as the standard deviation (SD) of three replicates.

2.6. Comparison of Microgel with Commercial SPE Cartridges

Two different commercial SPE cartridges—Supelclean™ ENVI-18 (500 mg) and Affinimip^® (100 mg)—were chosen to compare their sorption performance with the synthesized microgel. The ENVI-18 cartridge has a polymerically bonded octadecyl sorbent, which is dedicated for extracting and concentrating pollutants from aqueous environmental samples. The Affinimip^® cartridge has a molecularly imprinted polymer sorbent that is dedicated for the extraction of bisphenol A or closely related structures and has been already used for bisphenols preconcentration from food samples [29,30].

3. Results

3.1. Characterization of Microgel Sorbent

Polymer particles were characterized by transmission (TEM) and scanning electron microscopy (SEM) measurements and, in the dried state, they had regular spherical morphology, with an average particle diameter of approximately 100 nm. The influence of various parameters affecting the sorption of bisphenols on the microgel sorbent (pH, contact time, temperature and adsorption isotherm) was investigated and carefully discussed in the previous paper [28]. The results showed that the temperature and pH of the sample did not affect the sorption in a rather wide range (20–60 °C) and had a pH lower than 9. An analysis of experimental sorption data indicated that the sorption of bisphenols was characterized by a pseudo-second-order kinetic model and the data fitted well the Langmuir adsorption model. The maximum adsorption capacity obtained for bisphenols was in the range from 55 mg·g⁻¹ for BPF to 160 mg·g⁻¹ for BPB. The microgel was stable for up to five adsorption recycles without an obvious decrease in removal efficiency. What is more is that the possible generation of secondary pollutants, which may leach from the microgel, was also monitored by using LC-FLD [28].

3.2. Effect of the Amount of Microgel

In order to achieve the maximum quantitative recovery in the extraction of bisphenols, different amounts of microgel were tested. Therefore, 1, 2.5 and 5 mg of microgel were applied for the sorption of different concentrations of BPA. Figure 2 illustrates that the more microgel sorbent was applied, the higher concentration of BPA was adsorbed. Although our poly(MEO₂MA) microgel had a large adsorption capacity (Q_max in the range of 55 to 159 mg·g⁻¹ for all tested bisphenols [28]), 1 mg of microgel was not sufficient for the total sorption of even the smallest concentration of BPA. The amount of 5 mg of the microgel provided the best sorption of BPA, which remained above 95% in the range from 0.025 to 1 mg·L⁻¹, while for 2.5 mg the sorption for the concentration higher than 0.025 mg·L⁻¹ gradually decreased to 90%. As our goal was to use the microgel for the sorption of several bisphenols, 5 mg of microgel sorbent was selected for further experiments.

3.3. Desorption

The elution solvent must be capable of disrupting all retentive interactions between the analyte and sorbent but not too strong as to remove tightly bound contaminants. One milliliter of pure methanol was sufficient to obtain a complete desorption for all the analyzed bisphenols, which were adsorbed on the microgel. However, when 100% organic solvent is injected into liquid chromatography, the peaks for analytes become broad and asymmetric; this is why the different compositions of methanol and water were also studied for bisphenols removal. In order to obtain a 5-fold preconcentration of 1 mL of the sample, 200 µL of each methanol/water mixture was tested for the elution of all bisphenols. As presented in Figure 3, 80% of MeOH (80/20 methanol and deionized water) obtained the best desorption efficiency for all four bisphenols. This is why it was selected as the optimum elution solvent for further extraction studies.

3.4. Extraction of Bisphenols from Food Samples

Based on the above results, poly(MEO₂MA) microgel was employed as a sorbent for selective extraction of BPF, BPE, BPA and BPB from liquid food samples. Preliminary research with sample preparation of solid parts of food was performed with liquid organic solvents. When organic extracts were applied directly into microgel, it resulted in very poor retention of bisphenols. On the other hand, the evaporation of the organic solvents caused some loss of bisphenols. For that reason, only liquid samples were chosen for further studies.

As listed in Table 1, very good recoveries with the relative standard deviations (RSD) of 0.21–5.01% were obtained for all liquid food samples spiked with 50 µg·L⁻¹ mixture of bisphenols. Slightly poorer recoveries (70.5–84.9%) were obtained for BPF and BPE in fruit canned samples, which were caused by the weaker retention of these bisphenols, as around 10% of the spiked concentration of BPF and BPE were found in the effluent of each spiked food sample. Due to the relatively high complexity of food samples such as those tested, in some cases, the peaks from bisphenols were overlapped by the peak from the matrix, which made it impossible to assess recovery; this happened for the determination of BPB in mushroom or peach sample.

In five of the analyzed samples (pineapple, peach, mandarin, mushroom and pickles), the recovery for BPA was significantly higher than 110%, which resulted in the conclusion that they might be contaminated with BPA. Further experiments with the preconcentration of food extracts (without spiking) confirmed our suspicions. Figure 4 presents the LC-FLD chromatograms of the following: (A) liquid pineapple sample after the microgel preconcentration (visible peak for BPA, t_R = 6.39 min); (B) is the chromatogram of the liquid pineapple sample before the preconcentration procedure; and (C) presents the chromatogram of liquid pineapple sample spiked with 0.5 mg·L⁻¹ of four analyzed bisphenols, where the retention times were as follows: 3.03 min (BPF), 4.39 min (BPE), 6.36 min (BPA) and 11.2 min (BPB). After the extraction procedure, the detected and calculated concentration of bisphenol A was 6.2 µg·L⁻¹ for pineapple, 8.5 µg·L⁻¹ for mandarin, 11 µg·L⁻¹ for mushroom, 12 µg·L⁻¹ for pickles and 22 µg·L⁻¹ for peach (

Table 2. The detected concentration of bisphenol A in liquid food samples after the extraction procedure.

Analyte	Pineapple	Mandarin	Mushroom	Peach	Pickles
	C [µg·L−1]
BPA	6.2 ± 0.9	8.5 ± 0.4	11 ± 0.4	22 ± 2.0	12 ± 1.2

). These results are below the migration limits set for BPA (50 µg·kg⁻¹) [31].

3.5. Comparison of Microgel with SPE Cartridges

Both SPE procedures for Supelclean™ ENVI-18 and Affinimip^® cartridges were taken from the producer’s application notes with slight modifications (

Table 3. Solid-phase extraction methods used for preconcentration of fruits in syrup.

Sorbent	Microgel (5 mg)	ENVI-18 (500 mg)	Affinimip® (100 mg)
Conditioning	-	5 mL of MeOH 1 5 mL of H2O	3 mL of 2% FA 2/MeOH 3 mL ACN 3 3 mL H2O
Loading	1 mL of fruits in syrup spiked with 50 µg·L−1	10 mL of fruits in syrup spiked with 50 µg·L−1	10 mL of fruits in syrup spiked with 50 µg·L−1
Cleaning	0.5 mL of H2O	5 mL of 5/95 ACN/H2O	5 mL of 5/95 ACN/H2O
Elution	0.2 mL of 80% MeOH	2 mL of 80% MeOH	2 mL of 80% MeOH

¹ MeOH—methanol; ² FA—formic acid; ³ ACN—acetonitrile.

). The suggested cleaning mixture has a higher concentration of organic solvent, which throughout the extraction procedure resulted in eluting bisphenols from the sorbent of both cartridges. This is why the cleaning mixture was changed to 5/95 ACN/H₂O. The amount of 10 mL of filtered extract from fruits in syrup (without dilution) was spiked with 50 µg·L⁻¹ standard solution of BPB, BPE, BPF and BPA, and then it was introduced into the SPE cartridge. Following the application of the extract, cartridges were washed with 5 mL of 5/95 acetonitrile/water mixture, and each sample was eluted with 2 mL of 80% of methanol/water mixture. The experiments for microgel were performed in 2 mL microcentrifuge tubes; for that reason, the amount of the loading sample and elution solvent must be smaller in comparison to SPE cartridges. After preconcentration, all collected samples were analyzed by LC-FLD, and recoveries were calculated.

As presented in Figure 5, both cartridges showed very good recoveries (101.3–115.6% for Affinimip^® and 98.5–112.8% for Supelclean™ ENVI-18) for preconcentration of 10 mL of fruits in syrup spiked with 50 µg·L⁻¹ standard solution of investigated bisphenols. However, the Supelclean™ ENVI-18 cartridge was easily clogged with the matrix of the food sample, which prolonged the SPE procedure. The recoveries obtained for our microgel SPE procedure were comparable (from 71.2 to 108.3% for all bisphenols). However, lower recoveries (71.2–72.4%) obtained for BPE and BPF were caused by weaker retention of both bisphenols on microgel as small amounts were found in the effluent. In order to verify the results obtained on the microgel, all the samples where BPA was found (mandarin, pineapple, mushroom, peach and pickles) were also preconcentrated by using Affinimip^® cartridge, and the results were consistent with each other. For example, by using Affinimip^® cartridge for preconcentration, the determined amount of BPA in pickles was 10.9 µg·L⁻¹ and 19.8 µg·L⁻¹ for peach. These results differ only by less than 10% to the concentrations determined after microgel extraction (Table 2).

4. Discussion

For the very first time, the microgel was used as a sorbent in the preconcentration of bisphenols from complicated liquid matrices. The optimized microgel-SPE procedure with further analysis with LC–FLD allowed for 5-fold preconcentration of food samples and obtaining an LOD down to 0.9 ng·mL⁻¹ for BPF and BPA, 2.3 ng·mL⁻¹ for BPE and 2.9 ng·mL⁻¹ for BPB. The high extraction efficiency of microgel for different complex matrices suggests that the developed poly(MEO₂MA) microgel might be the effective solution for sample preparation in routine analysis of trace BPF, BPE, BPA and BPB. The application of microgel as sorbent resulted in discovering trace concentrations of BPA in five out of the twelve of the analyzed liquid food samples (mandarin, pineapple, peach, pickles and mushroom). The results of the cleanup and the obtained recoveries are comparable to commercial cartridges. Moreover, compared to different methods reported in the literature (listed in

Table 4. Comparison of our method of preconcentration of bisphenols to others.

Analyte(s)	Sample	Sample Preparation	Determination	LOD [µg·L−1]	Ref.
BPF, BPA	honey	MIP	LC-DAD	BPF, BPA 2.0	[32]
BPB, BPA	peeled canned tomatoes	(I). Strata C18 (II). Florisil SPE cartridges	LC-UV/FLD	BPB 0.7 BPA 1.1	[33]
BPB, BPA	tuna	LLE	LC-FLD	BPA 1.3 BPB 3.0	[34]
BPB, BPE BPF, BPA BPS	plastic packed baby food	(I). LLE (II). C18 and PSA SPE cartridges	GC-MS/MS	BPF 0.1 BPB, BPE, BPA, BPS 0.3	[12]
BPF, BPA, BPB	canned energy drinks	Affinimip® cartridge	UHPLC-FLD	BPB, BPF, BPA 0.2	[29]
BPF, BPE, BPA, BPB	energy drink, liquid from can (pineapple, mandarin, figs)	Microgel	LC-FLD	BPF, BPA 0.9 BPE 2.3 BPB 2.9	This work

) the obtained limit of detection for BPF and BPA was lower than others who used classical liquid chromatography.

It should be noted that the consideration of analyzing bisphenols from a quality assurance perspective require quantitation of bisphenols in both solid and liquid parts of food products. This was also confirmed in the work of Tzatzarakis et al. [35], where higher amounts of bisphenol A were found in solid parts than liquid part of canned food. This is why further studies are necessary for optimizing bisphenols extraction procedure from solid parts of food. On the other hand, considering all the above benefits, the authors hope that this study would be beneficial for the further development and application of microgel sorbents.