Magnetic Solid Phase Extraction of Lead (II) and Cadmium (II) From Water Samples Using ZnO@Fe₃O₄ Nanoparticles Combined With Flame Atomic Absorption Spectrometry Determination

ABSTRACT

A new magnetic solid phase extraction method was developed utilizing magnetically enhanced zinc oxide (ZnO@Fe₃O₄) nanoparticles for the separation and enrichment of lead (II) and cadmium (II) before sample determination through flame atomic absorption spectrometry. The ZnO@Fe₃O₄ nanoparticles synthesized by the hydrothermal method were characterized by x‐ray diffraction, scanning electron microscopy, and energy‐dispersive x‐ray spectroscopy. The experimental factors like pH (6.0), eluent type and concentration (1 M nitric acid for lead (II), 1 M hydrochloric acid for cadmium (II)), adsorbent amount (150 mg for lead (II), and 200 mg for cadmium (II)), sample volume (5 mL), and extraction time (5 min for lead (II), and 10 min for cadmium (II)) were optimized. Under the optimization conditions, limits of detection of 2.36 and 7.86 µg/L for lead (II) and cadmium (II) were obtained with a wide concentration range from 50 to 5000 µg/L, respectively. The presented method was successfully applied to real water samples with spiked recoveries in the range of 99.2%–101% for lead (II) and 99.6%–100% for cadmium (II).

1. Introduction

Owing to economic development over the past decades, industrial productivity has increased, and human life has been significantly enriched. However, various problems, most notably water pollution, have also been brought about by this increase in productivity [1, 2]. The primary source of clean water pollution is wastewater contaminated with heavy metal ions, which negatively affects living organisms and seriously damages the ecosystem [3]. The release of wastewater also causes soil contamination and accumulation of heavy metal ions in the vegetation. It is known that heavy metal ions are very toxic, and they accumulate in living organisms, especially through the food chain and water, because they are not biodegradable [4]. Lead (II) (Pb (II)) and cadmium (II) (Cd (II)) are the most common types of heavy metal ions. They cause abnormalities in the organs of living organisms, even at very low levels. They seriously damage brain functions and cellular processes [5, 6, 7]. As a result, they can lead to many diseases, such as neurological, behavioral, and genetic disorders, cancer, liver disease, kidney problems, and even death [8, 9, 10]. Therefore, developing a rapid, sensitive, and reliable method to remove Pb(II) and Cd(II) ions from water samples is very important.

In the literature, some extraction techniques, such as liquid–liquid extraction [11], cloud point extraction [12], high‐pressure assisted extraction [13], and solid phase extraction (SPE) [14, 15, 16], were used for the elimination, separation, and enrichment of heavy metal ions. SPE is the most preferred among other extraction techniques, thanks to its features such as high sensitivity, less organic solvent consumption, low cost, and high concentration factors [17, 18, 19]. However, SPE has some limitations due to time‐consuming processes such as column passage and filtration steps [20, 21]. Recently, magnetic solid phase extraction (MSPE) has been preferred among the different SPE methods to make separation faster and easier without the additional filtration or centrifugation procedures to overcome these limitations [22]. The choice of suitable adsorbent is important in MSPE to develop an analytical procedure. The adsorbent used in the MSPE method is generally distributed directly into the medium by gaining magnetic properties. Different magnetic particles as the potential adsorbents have been used by researchers for the separation and enrichment of heavy metal ions such as surfactants [23], metal oxides [24], polymeric materials [25], ionic liquid [26], etc. [27, 28, 29]. Among the nanomaterials, magnetite Fe₃O₄ has been widely used as an adsorbent due to having a high surface‐to‐volume ratio, which increases its capacity for adsorbing target analytes [30, 31]. Also, it is low‐cost, has a small size, the lowest toxicity, and a strong magnetic property. However, pure Fe₃O₄ can be oxidized to form maghemite (Fe₂O₃), resulting in the formation of different chemical and magnetic properties [32]. To overcome this problem, it is usually coated with more stable materials such as nanometal oxides and silica [33]. In this field, among nanometal oxides, zinc oxide (ZnO) is the most commonly used in catalysis and adsorption due to its high catalytic activity, high thermal stability, wide bandgap, economic value, abundance, and environmentally friendly. ZnO facilitates hydrogen bonding with ligands and water molecules due to its unique structural characteristics, ensuring improved bonding outcomes [34, 35, 36]. The usefulness of ZnO can be increased by combining it with magnetic nanoparticles (Fe₃O₄) to utilize in different applications in MSPE. The surface area and porosity of the adsorbent can be enhanced due to the mixed Fe₃O₄ and ZnO. Therefore, metal ion adsorption can be facilitated by having many active sites of –OH groups on their surface. These properties make them suitable adsorbents for the separation and adsorption of heavy metals.

This study developed a new separation‐enrichment method based on magnetic ZnO@Fe₃O₄ nanoparticles to remove Pb (II) and Cd (II) ions. According to our literature survey, ZnO@Fe₃O₄ nanoparticles are first used in the MSPE for the elimination of Pb (II) and Cd (II) in water samples in the presented study. The magnetic ZnO@Fe₃O₄ nanoparticles were obtained using the hydrothermal synthesis method suggested by Hasanoğlu Özkan and coworkers [37]. Hydrothermal synthesis is one of the most common methods in synthesizing hybrid nanoparticles. In this method, high temperatures and pressures are used to recrystallize a nanostructure via convection in a supersaturated formation. Also, the method provides good nanostructure size and shape control. The structures of nanoparticles were characterized using various techniques such as scanning electron microscopy (SEM), x‐ray diffraction (XRD), and energy‐dispersive x‐ray spectroscopy (EDX). The synthesized ZnO@Fe₃O₄ nanoparticles have high adsorption capacity due to the synergistic effect between them. Analytical parameters were also evaluated based on the analysis result of metal ions obtained from flame atomic absorption spectroscopy (FAAS). When the literature data was examined, few studies were found on using magnetic nanoparticles to remove heavy metal ions. This study will contribute significantly to the literature with detailed characterization analyses, the synthesis of nanoparticles with a large adsorption capacity by hydrothermal method, and their use for the enrichment of heavy metal ions (see Scheme 1). The method was subsequently applied to analyze Pb (II) and Cd (II) ions in seawater, mineral water, tap water, and bottled water samples. The advantages of this method include the synthesis of the adsorbent without the use of hazardous organic solvents or costly reagents, a simple and rapid detection procedure, and the obtaining of sensitive analytical results.

SCHEME 1.

Schematic summarizing the experimental workflow of the study.

2. Materials and Method

2.1. Synthesis of ZnO@Fe₃O₄ Magnetic Nanoparticles

For the synthesis of ZnO@Fe₃O₄ magnetic nanoparticles, firstly ZnO nanoparticles were synthesized. Then, magnetic ZnO@Fe₃O₄ was obtained by doping Fe₃O₄ onto the ZnO nanoparticles. ZnO nanoparticles were synthesized using the hydrothermal production method under laboratory conditions. To a mixture of ethylene glycol:ethanol:water (7:7:10; v/v/v), 0.52 g Zn(NO₃)₂⋅6H₂O was added and dissolved in a magnetic stirrer. 0.8 g NaOH was slowly added and stirred for 1 h. The mixture was transferred to a 100 mL capacity Teflon‐lined stainless steel autoclave. It was kept in the oven at 120°C for 12 h. After cooling to room temperature, the precipitate obtained was separated by centrifugation. The solid phase was washed several times with deionized water and ethanol and dried in an oven at 80°C for 24 h. The dried ZnO was annealed at 450°C for 3 h [38].

For the synthesis of magnetic ZnO@Fe₃O₄ nanoparticles, 0.656 g of iron(II) sulfate heptahydrate (FeSO₄⋅7H₂O) and 3.2 g of NaOH were dissolved in deionized water (40 mL) by stirring for 15 min. In a separate beaker, 0.4 g of ZnO nanoparticles synthesized in the previous step were dissolved in deionized water (25 mL) by stirring vigorously for 10 min. Fe solution was slowly added to the ZnO mixture and stirred for 5 min. This solution was transferred to a Teflon autoclave, sealed, and kept at 150°C for 6 h. After cooling to room temperature, the precipitate was centrifuged. The solid phase was washed several times with deionized water and ethanol and dried in an oven at 80°C for 24 h [39].

2.2. Solid Phase Extraction Procedure

In the adsorption studies, 50 mg ZnO@Fe₃O₄, 10 mL ultra‐pure water, 0.25 mL solution containing 50 mg/mL of selected metal ion (Pb(II)/Cd(II)), and 1 mL buffer solution (pH:6) were added into a 50 mL falcon tube, respectively. The pH of this prepared solution was adjusted to 6 by adding NaOH (0.01 M) or HCl (0.01 M). The solution volume was adjusted to 25 with ultra‐pure water. The solution was kept in an ultrasonic bath for 10 min and then centrifuged at 9000 rpm for 10 min. The solid and liquid phases were separated, and the liquid phase was stored for analysis. The appropriate acid solution (5 mL HNO₃ or HCl) was added to the solid phase as the elution solution, and this mixture was sonicated for 10 min. Then, the liquid part was separated with a magnet and analyzed in AAS for Pb(II) and Cd(II).

Parameters such as pH, eluent type and concentration, adsorbent (magnetic nanoparticles) amount, solution volume, and extraction time were determined for optimum conditions. 0.1, 1.0, 2.0, and 3.0 M HNO₃ and 0.5, 1.0, and 2.0 M HCl were used for elution solutions. The optimum pH was determined using phosphate buffer at different pH values (4, 5, 6, 6.5, 7, 7.5, and 8). The adsorbent amount experiments were studied at 50, 100, 150, 200, and 250 mg, while the eluent volume was studied at 2.5, 5, 10, 20, and 30 mL ultra‐pure water. The effect of extraction time study was performed at 2.5, 5, 10, 20, 30, and 60 min. The optimization studies were conducted using a synthetic solution that contains possible coexisting ions in the real waters that can have an interfering effect. The content of the synthetic solution is Na(I), K(I), Ca(II), Cu(II), Fe(II), Ni(II), Zn(II), and Mn(II). These studies were made of three independent extractions with three repetitions.

2.3. Preparation of Real Samples for Analysis

The accuracy of the method was tested using four different water samples (seawater, tap water, bottled water, and mineral water) for Pb(II) and Cd(II) in the optimum conditions. Seawater and a tap water sample were collected from Kırklareli/Turkey and used without any further pretreatment. Bottled water and mineral water were purchased from the local market.

3. Results and Discussion

3.1. Characterization of Magnetic Nanoparticles

XRD, SEM‐EDX, and VSM measurement of ZnO@Fe₃O₄ magnetic nanoparticles were given in the Supporting Information [39, 40].

3.2. Optimization Studies With Nanoparticles

pH, eluent type and concentration, adsorbent amount, sample volume, and extraction time were tested in optimization studies carried out with ZnO@Fe₃O₄ nanoparticles for heavy metal ions Pb(II) and Cd(II).

3.2.1. Effect of pH on the Recovery of Lead(II) and Cadmium(II)

pH is an important factor in the adsorption performance because it changes some functional groups or charges on the adsorbent surface. Thus, heavy metal ions can be easily removed. The effect of pH on the removal performance of ZnO@Fe₃O₄ nanoparticles on Pb(II) and Cd(II) was investigated by changing the initial pH values from 4 to 8.

The best pH and recovery percentage for Pb(II) and Cd(II) metal ions using ZnO@Fe₃O₄ nanoparticles were found to be 88.2% at pH 6.0 and 87.0% at pH 6.0, respectively. The recovery‐pH graphs are shown in Figure 1. The decrease in the recovery values at higher pH can be explained by the formation and precipitation of hydroxide species of target metal ions on the adsorbent surface. At pH values lower than 6, the decrease in recovery can be attributed to the protonation of the adsorbent surface and the occupation of active sites by protons rather than target metal ions. In addition, the observation of maximum adsorption efficiency at pH 6.0 means that the ZnO@Fe₃O₄ surface is negatively charged and creates a strong electrostatic attraction with metal ions.

FIGURE 1.

pH effect on the recovery of Pb(II) and Cd(II) (ZnO@Fe₃O₄ amount: 150 mg for Pb(II) and 200 mg for Cd(II); eluent volume: 5 mL for both Pb(II) and Cd(II); extraction time: 5 min for Pb(II) and 10 min for Cd(II), N = 3).

3.2.2. Effect of Eluent Type and Concentration

Both the type of eluent and its concentration used in MSPE have a crucial effect on the recovery of targeted ions from the solid phase. In this study, HNO₃ and HCl were chosen as the eluent types. Also, various concentrations of HNO₃ and HCl were optimized to determine the elution of Pb(II) and Cd(II) ions using the ZnO@Fe₃O₄ nanoparticles. 1.0 M of HNO₃ were sufficient for the complete elution of Pb(II) (82.4%) and 1.0 M of HCl for Cd(II) (86.8%) as depicted in Figure 2.

FIGURE 2.

Determining the most suitable eluent type and concentration (ZnO@Fe₃O₄ amount: 150 mg for Pb(II) and 200 mg for Cd(II); eluent volume: 5 mL and pH: 6 for both Pb(II) and Cd(II); extraction time: 5 min for Pb(II) and 10 min for Cd(II), N = 3).

3.2.3. Effect of Amount of Magnetic Nanoparticles

The amount of adsorbent may directly influence the extraction performance [40]. Optimization studies of the amount of ZnO@Fe₃O₄ nanoparticles as adsorbent were made for 50, 100, 150, 200, and 250 mg for Pb(II) and Cd(II) metal ions. As seen in Figure 3, the best recovery percentage for Pb(II) was found to be 93.5% at 150 mg, and for Cd(II), it was found to be 96.9% at 200 mg.

FIGURE 3.

The optimum ZnO@Fe₃O₄ nanoparticles amount (eluent volume: 5 mL and pH: 6 for both Pb(II) and Cd(II); extraction time: 5 min for Pb(II) and 10 min for Cd(II), N = 3).

ANOVA, namely the F test, was applied to test the variance difference in our Pb and Cd data to determine whether there was a significant difference between the two groups. As a result of the calculations, the F value was found to be 0.79, and the p value was found to be 0.216. Since p > 0.05, it was concluded that there was no significant difference between Pb and Cd in the enrichment study. In other words, the use of nanoparticles was quite effective for both Pb and Cd. Although the results from our data calculated from the absorbance values read as a result of reading with FAAS were close to each other, the milligram value that provided the highest efficiency in % recovery was selected.

3.2.4. Effect of Sample Volume

Optimization of sample quantity is critical to reaching the maximum preconcentration factor in the extraction method [41]. The effect of sample volume was studied at 2.5, 5, 10, 20, and 30 mL, keeping the other parameters constant using ZnO@Fe₃O₄ nanoparticles for Pb(II) and Cd(II), which is shown in Figure 4. Maximum interaction between the analyte and the adsorbent was obtained through a better dispersion of the adsorbent in the 5 mL sample volume, while this insufficient homogeneous dispersion in large‐volume samples [14]. So, 5 mL was chosen as the optimum sample volume for both Pb(II) and Cd(II), with recoveries of 97.8% and 98.8%, respectively.

FIGURE 4.

The optimum value of sample volume (ZnO@Fe₃O₄ amount: 150 mg for Pb(II) and 200 mg for Cd(II); pH: 6 both Pb(II) and Cd(II); extraction time: 5 min for Pb(II) and 10 min for Cd(II), N = 3).

3.2.5. Effect of Extraction Time

Extraction time is also one of the critical parameters in adsorption studies. The effect of extraction time was studied between 5 and 60 min, and the recovery rates are shown in Figure 5. The best recovery percentages for Pb(II) and Cd(II) were found to be 98.9% at 5 min and 99.2% at 10 min, respectively. The recovery decreased in high sonication times. Inadequate adsorption can be observed when extraction time is insufficient, while too long extraction time might bring about some losses due to interaction with species in the sample environment that may interfere [42].

FIGURE 5.

Effect of extraction time on the recovery (ZnO@Fe₃O₄ amount: 150 mg for Pb(II) and 200 mg for Cd(II); eluent volume: 5 mL and pH: 6 both Pb(II) and Cd(II), N = 3).

The optimum conditions obtained in enrichment with magnetic nanoparticles are given in Table 1.

TABLE 1.

Optimum conditions for enrichment with ZnO@Fe₃O₄ nanoparticles.

Metal ion	Eluent type and its concentration	Buffer pH value	ZnO@Fe3O4 nanoparticles amount (mg)	Eluent volume (mL)	Time (min)
Pb(II)	1.0 M HNO3	6	150	5	5
Cd(II)	1.0 M HCl	6	200	5	10

3.2.6. The Effect of Matrix Ions

In this SPE study using ZnO@Fe₃O₄ magnetic nanoparticles, the effect of possible interfering ions on recovery was examined, which are found in the real water samples due to competing with the target ions for adsorption sites and affecting the extraction performance. The real water samples were simulated by adding Na(I), K(I), Ca(II), Cu(II), Fe(II), Ni(II), Zn(II), and Mn(II) ions to examine the effect of them on the target ions. The results given in Table 2 showed that the primary matrix ions in natural waters do not significantly interfere with the preconcentration of Pb(II) and Cd(II) ions. Therefore, the presented procedure can recover heavy metal ions from aqueous media and can be used in enrichment applications.

TABLE 2.

Effects of possible interfering metal ions on the recovery of Pb(II) and Cd(II) (Sample volume: 25 mL, amount of Pb(II) and Cd(II): 10 µL from 50 mg/L, N = 3, 95% confidence level).

Ions	Added	Added (mg/L)	Pb(II)	Cd(II)
Na(I)	NaCl	250	99.6 ± 1.2	99.7 ± 0.2
K(I)	KCl	100	98.8 ± 1.1	98.7 ± 0.9
Ca(II)	CaSO4⋅2H2O	100	104 ± 3	98.4 ± 0.8
Cu(II)	Cu(NO3)2	0.25	96.6 ± 1.2	97.2 ± 0.8
Fe(II)	Fe(NO3)2⋅6H2O	0.5	98.2 ± 0.3	98.9 ± 0.2
Ni(II)	Ni(NO3)2⋅6H2O	0.25	98.6 ± 1.5	97.6 ± 0.3
Zn(II)	ZnSO4⋅7H2O	2.50	99.6 ± 0.3	99.2 ± 0.3
Mn(II)	Mn(NO3)2⋅4H2O	0.1	97.8 ± 0.9	98.5 ± 0.2

3.2.7. Analytical Parameters of the System

Analytical performance was evaluated under the optimum experimental conditions summarized in Table 3 for Pb(II) and Cd(II). The parameters used to validate the developed method were the limit of detection (LOD), the limit of quantification (LOQ), the linear regression, the correlation of coefficient (R ²), and the percent relative standard deviation (RSD%). Using the slope (m) of the calibration plot and the standard deviation (SD) calculated for the blank signal, the LOD and LOQ values were calculated with the expressions given below:

$$\mathrm{LOD}:3\times \mathrm{SD}/m$$ (1)

$$\mathrm{LOQ}:10\times \mathrm{SD}/m$$ (2)

TABLE 3.

Analytical performance of the developed ZnO@Fe₃O₄ nanoparticles MSPE‐FAAS procedure for the blank signal (N = 3).

Ions	LOD (µg/L)	LOQ (µg/L)	Linear regression (y = ax + b)	Correlation of coefficient, R 2	Linear concentration range (µg/L)	RSD%
Pb(II)	2.36	5.08	0.045x + 0.0038	0.9998	50–5000	0.3–9.5
Cd(II)	7.86	16.9	0.0179x + 0.0009	0.9978		0.5–9.8

3.3. Reliability of the Method and Enrichment Application of Nanoparticles on Real Samples

ZnO@Fe₃O₄ magnetic nanoparticles were applied to real samples in the optimum conditions. A recovery study was carried out in tap water by adding appropriate volume from 50 mg/L stock solution prepared from the 1000 ppm NIST standard in a 1.0 M HNO₃ environment. The results obtained using the standard addition method to the tap water samples to check the reliability of the method are presented in Table 4 based on the average of three replicates. The water samples without the addition of NIST did not show any signals, probably due to Pb(II) and Cd(II) not being present in tap water samples or being lower than the detection limit. So, the specified concentrations of Pb(II) and Cd(II) contained in NIST were added to water samples.

TABLE 4.

Additional recovery tests for ZnO@Fe₃O₄ nanoparticles MSPE‐FAAS of Pb(II) and Cd(II) from tap water samples (N = 3).

	Added (mg/L)	Found (mg/L)	Recovery (%)	RSD%
Pb(II)	0	—	—	—
	0.25	0.248 ± 0.02 a	99.2 ± 0.9	3.2
	0.50	0.50 ± 0.01	100 ± 1	0.8
	1.00	1.01 ± 0.01	101 ± 2	0.3
Cd(II)	0	—	—	—
	0.25	0.251 ± 0.002	100 ± 2	3.8
	0.50	0.498 ± 0.002	99.6 ± 0.1	1.2
	1.00	0.998 ± 0.05	99.8 ± 0.1	0.5

^a Mean ± standard deviation.

Also, the enrichment application of nanoparticles was studied in the optimum conditions for Pb(II) and Cd(II) on four different sample types (tap water, seawater, mineral water, and bottled water). The results are given in Table 5, and the quantitative values found show that the procedure can be applied to enriching heavy metal ions in real samples.

TABLE 5.

Pb(II) and Cd(II) levels in various samples in the developed method (solution pH: 6.0; extraction time: 5 and 10 min; amount of ZnO@Fe₃O₄: 150 and 200 mg; eluent volume: 5 mL; for Pb(II) and Cd(II), respectively) (N = 3).

Sample	Pb(II) (mg/L)	Cd(II) (mg/L)
Seawater	0.42 ± 0.01a	4.43 ± 0.01
Bottled water	0.21 ± 0.02	4.32 ± 0.01
Tap water	0.25 ± 0.01	4.32 ± 0.02
Mineral water	0.23 ± 0.01	4.35 ± 0.01

^aMean ± standard deviation.

3.4. Comparison with Reported Procedures

The developed method based on ZnO@Fe₃O₄ nanoparticles MSPE‐FAAS was compared with other relevant methods for determining Pb(II) and Cd(II). As seen from the results in Table 6, the present method provided either similar or superior sensitivity to that in the reports.

TABLE 6.

Comparison of the separation and enrichment performance between relevant methods and the developed method.

Method	Material	Ion	pH	LOD (µg/L)	Ref.
d‐µSPE a FAAS	Ag modified ZnO nanoflower	Pb(II)	4	8.52	[2]
Vortex assisted SPE FAAS	NCp b ‐ZnO	Cd(II)	4	1.0	[43]
		Pb (II)		6.5
DSPE c ‐FAAS	MnO2 NF d	Pb (II)	3	6.09	[14]
MSPE e FAAS	HA‐Fe3O4 MNPs f	Pb (II)	6	4.9	[44]
Magnetic‐dSPµE FAAS	Fe3O4@C, MMC g	Pb (II)	6	2.8	[45]
ICP‐OES h	MNPs/SiO2‐EDTA i	Cd(II)	5.5	0.06	[46]
		Pb (II)		0.76
MSPE‐FAAS	ZnO@Fe3O4 nanoparticles	Cd(II)	6	7.86	This study
		Pb (II)	6	2.36

^a d‐µSPE: dispersive micro‐solid phase extraction.

^b NCp: nano‐clinoptilolite.

^c DSPE‐FAAS: dispersive solid phase extraction‐.

^d MnO₂ NF: manganese dioxide nanoflower.

^e MSPE: magnetic solid phase extraction.

^f HA‐Fe₃O₄ MNPs: humic acid modified magnetic nanoparticles.

^g MMC: magnetic mesoporous carbon.

^h ICP‐OES: inductively coupled plasma–optical emission spectrometry.

ⁱ MNPs/SiO₂‐EDTA: core–shell superparamagnetic nanoparticles with the immobilized derivative of ethylenediaminetriacetic acid.

4. Conclusions

This study aimed to prove that ZnO@Fe₃O₄ nanoparticles can be used as sensitive, environmentally friendly, and cost‐effective adsorbent for the removal of trace amounts of Pb (II) and Cd (II) from water samples using the FAAS method. The hydrothermally synthesized adsorbent was characterized different techniques, including SEM, XRD, and EDX. Many benefits, such as high recovery, fast separation, low detection limit, and satisfactory extraction, were carried out by the developed method as compared to other methods.

Recovery rates for Pb (II) and Cd (II) heavy metal ions were calculated after SPE using the concentration difference between the samples before and after the extraction process. In our investigations, optimum eluent type, pH, adsorbent type, amount of adsorbent, and solution volume were assessed to achieve maximum Pb (II) and Cd (II) heavy metal ion recovery. Under the optimization conditions, LODs of 2.36 and 7.86 µg/L for Pb (II) and Cd (II) were obtained with a wide concentration range from 50 to 5000 µg/L, respectively. The presented method was successfully applied to real water samples with spiked recoveries in the range of 99.2%–101% for Pb (II) and 99.6%–100% for Cd (II).

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supplementary information

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.