Translate this page into:
Application Of Voltammetry In The Assessment Of Some Metal Ions In Drinking Water Samples In Al-Baha City, Saudi Arabia
* Corresponding author: Dr. Anas Alfarsi Department of Chemistry, Al-Baha University, Al-Baha University, Al-Baha, Al-Baha 65779, Saudi Arabia. alfarsi@bu.edu.sa
-
Received: ,
Accepted: ,
How to cite this article: Alfarsi A. Application Of Voltammetry In The Assesment Of Some Metal Ions In Drinking Water Samples In Al-baha City, Saudi Arabia. J Qassim Univ Sci. doi: 10.25259/JQUS_42_2025
Abstract
Objectives
Metal ions such as, Cd (II), Pb (II), Cu (II), and Zn (II) in drinking water samples were investigated by employing differential pulse anodic stripping voltammetry (DPASV) at carbon paste electrode (CPE).
Materials and methods
The investigated samples were collected from Al-Baha city, KSA. The samples were taken from eight sampling regions. The effects of various factors were examined. The lower limits of the investigated metal ions at 150s deposition time (n= 5) are 0.314 µg/L (r = 0.9899) for zinc(II), 0.368 µg/L (r = 0.8992) for cadmium(II), 1.28 µg/L (r = 0.9899) for lead(II) and 0.118 µg/L (r = 0.9998) for copper(II), respectively.
Results
The assessments of the investigated metal ions in drinking water were in the range for Zn (II) (0.42–68.5 µg/L with SD= 0.13–0.96, n= 5), Cd(II) (0.29–0.87 µg/L with SD = 0.03–1.02, n= 5), Pb(II) (1.5–22.35 µg/L with SD = 0.08–0.73, n = 5), and for Cu(II) (0.58–2.58 µg/L with SD = 0.02–0.85, n= 5), respectively. The resulting data were compared with those estimated by the atomic absorption spectrophotometric technique. The interfering and the storage conditions of the samples were examined.
Conclusion
The determined concentrations were within internationally accepted drinking water standards, indicating the suitability and the instantaneous estimation of the proposed method for trace metal analysis in water samples.
Keywords
Anodic stripping voltammetry
Atomic absorption spectroscopy
Drinking water samples of Al–Baha city
Real-time analysis
INTRODUCTION
Water pollution by heavy metal ions increased rapidly in the latter century. Human activities have increased the amount of heavy metal ions in the atmosphere.[1,2] Heavy metal ions are environmental concerns as they are non-biodegradable, toxic, and persistent.[3] Heavy metal ions, as well as some trace metal ions, can be biologically toxic, impacting human life due to their presence in the nutrition series. It is well known that humans are in contact with about 35 elements, either through occupational or domestic exposure; 23 of these are heavy metal ions. Certain heavy metal ions are essential for good health, but excessive amounts of some can be harmful. Heavy metal ions may enter the human body through water, food, and the atmosphere. These metal ions become toxic when they aren’t consumed by the body & are deposited in soft tissues.[4] These metal ions are among the most dangerous contaminants, unlike many others.[5]
The aquatic chemistry of heavy metal ions is quite complex; it represents a challenging field of study with a wide range of properties that must be investigated for each specific aquatic system. From a practical standpoint, such studies constantly require advanced procedures and highly sensitive methodologies typical of modern trace element chemistry. While metal ions are essential to human life at low concentrations, they are regarded as contaminants and, in some cases, even carcinogenic at high concentrations. Various metal ions occur in the environment in different chemical forms, which differ not only in their physicochemical properties but also in their varying degrees of toxicity toward living organisms.[6] A review of water quality assessment for energy, drinking, and irrigation purposes in the Jouf region of Saudi Arabia has been presented.[7] According to recent studies on heavy metal ions, Cd(II) and Pb(II) are generally toxic even at trace levels, whereas Cu(II) and Zn(II) are considered potentially toxic only at higher concentrations.[4,8] Moreover, Pb(II) is an extremely poisonous element commonly present in diesel fuels; it can cause serious health impairment, particularly severe damage to the nervous system. Since heavy metal ions may be present in drinking water at ultra-trace concentrations, highly sensitive analytical techniques are essential for their reliable detection. Atomic absorption spectrometry (AAS) is a widely used quantitative technique for metal analysis, suitable for the determination of more than seventy elements. AAS measures the concentration of elements by detecting the absorption of characteristic wavelengths of light emitted by a radiation source specific to each metal (e.g., mercury, arsenic, lead, etc.).[9] Numerous methods have been employed for the determination of heavy metal ions in various water samples, including electrothermal AAS (ET-AAS),[10,11] flame AAS (FAAS),[12,13] and cold vapor AAS (CV-AAS).[14]
The detection of metal ions in environmental samples using capillary electrophoresis is an important area of research in environmental chemistry. Several studies have reviewed the separation of metal ions by capillary electrophoresis under different conditions.[15-17] The separation of eight essential transition metal ions has been investigated using pure and modified silica gel films.[18] An improved Amberlite XAD-4 resin has also been utilized for the determination of some heavy metals through selective solid-phase extraction.[19]
However, most of these methods are relatively sophisticated and require expensive instrumentation. Therefore, simpler, accurate, precise, and selective techniques, such as electrochemical methods, are particularly useful for the simultaneous determination of metal ions in drinking water samples.
Electrochemical procedures may be easier and more appropriate methods for estimating trace levels of heavy metal ions in solution. The most common one for environmental samples is anodic stripping voltammetry. This method is appropriate and sensitive for several metal ions, cost–effective for multi–element investigation, and well-suited for automation. Specifically, it shows promise for detecting Cd(II), Pb(II), Cu(II), and Zn(II).[20]
Over the past 20 years, voltammetric techniques have been widely applied to trace metal chemistry in all types of water, including drinking water. For several metal ions (e.g., Cd(II), Pb(II), Cu(II), and Zn(II)), differential pulse anodic stripping voltammetry (DPASV) at a carbon paste electrode (CPE) has been extensively used. In this method, the pre-concentration step involves reducing the metal ions.[20]
Furthermore, over the last 30 years, electrochemical methods have been widely applied to trace metal analysis of various types of water, including drinking water.[3,20-23] In particular, DPASV using a CPE is an excellent tool for the determination of numerous metal ions such as Cd(II), Pb(II), Cu(II), and Zn(II). In this technique, the accumulation step involves reducing the metal ions, followed by amalgamation with the mercury surface.[20,21,24,25] Moreover, the CPE has also been successfully applied for the determination of various cationic and anionic metal ions as well as organic compounds.[26-31]
The primary objective of the present study was to determine the concentrations of Cd(II), Pb(II), Cu(II), and Zn(II) in drinking tap water samples collected from Al-Baha city, Saudi Arabia, between January and March 2025, using DPASV. Interferences among these metal ions were also investigated. A secondary objective was to evaluate the possibility of long-term storage of the samples at pH 2 and –4 °C.
The study was extended to using DPASV for the detection of ultratrace metal ions in 8 drinking water samples (Al Aqiq, Al Hawey, Al Zarga, Bany Sar, Al Dapheer, Al Soug region, Al Swad region, and Bin Farwa) located in Al-Baha city, KSA (period from January to March, 2025). The obtained data (for all metal ions’ convenience) are similar to those obtained via the AAS procedure.
MATERIAL & METHODS
Instruments
All voltammetric experiments were performed on an EG&G PAR Modeling 273A potentiostat, produced by Princeton Applied Research, NJ. USA. The potentiostat is connected to a three-electrode system comprising an unpolarized reference electrode (Ag/AgCl), an auxiliary electrode (Pt wire), and the handmade working electrode, a carbon paste electrode (CPE), prepared as previously mentioned.[20,21,32] A magnetic stirrer (KIKA Labortechinik, Germany) at approximately 400 rpm with a teflon–coated bar was employed to stir the solution. A Teflon cell was used to prevent contamination of the water at a pH ≈ 2. All AAS and pH measurements were done employing the Lowest Scientific instrument (Modelling 220–GF, USA) and the Orion model 601 digital, USA, respectively.
Reagents and solutions
Standard solutions of 1.0 M HNO₃ (BDH, UK) were prepared by diluting an appropriate volume of concentrated HNO₃ (BDH, UK) with bidistilled water. After preparation, the solutions were standardized by neutralization with a carbonate-free NaOH stock solution (BDH, UK).[33] Solutions of 0.010 M NaNO₃, KClO₄, and sodium citrate (all BDH, UK) were prepared by dissolving the appropriate amounts of each salt in bidistilled water and making up to the required volume. Similarly, 1 × 10⁻2 M stock solutions of Cd(II), Pb(II), Cu(II), and Zn(II) (as their nitrate salts, BDH, UK) were prepared by dissolving the required quantities of each salt in bidistilled water. All glassware and polyethylene bottles were soaked in 2 M HNO₃ for at least one week, rinsed repeatedly with bidistilled water, and finally soaked in 0.1 M HCl until use.
Methods
For all stripping voltammetry procedures (for Cd(II), Pb(II), Cu(II), and Zn(II) ions) with 0.01 M HNO3 as the supporting electrolyte, the solutions were transferred to a 10 mL electrochemical cell and purged with clean N2. The voltammogram was recorded after a 5-second equilibrium time at a scan rate of 10 mV s–1, with a pulse amplitude of 25 mV and a pulse width of 0.5 V. These conditions were suitable for removing electrode memory and assessing repeatability in the duplicate measurements. The same process was repeated after adding a 5 mL drinking water sample, instead of bidistilled water. All the data were acquired at 25°C.
Real water random sample
The drinking water samples were collected from 8 regions (Al Aqiq, Al Hawey, Al Zarga, Bany Sar, Al Dapheer, Al Soug region, Al Swad region, and Bin Farwa), at Al–Baha city, Saudi Arabia (period from January to March 2025), in polyethylene flasks with a volume of 1.0–1.5 L. Previous to the real sample, the sampling flasks were full with the taping water and emptied numerous times. Then, it was left full for about half an hour before being emptied and refilled with a fresh sample. The air was never in connection with the inside of flasks; they were open and closed below tap water. A water sample was collected from 8 areas distributed throughout Al–Baha city, Saudi Arabia, 15 minutes after the taps were opened.
Water sample preparations
Suspended materials were removed from the water sample through filtration[34] utilizing Whatman No. 1 filter paper. The filtrate was then acidified to pH 2 by adding ultra–pure HNO3,[35] which prevents adsorption of solute ions onto the vessel walls,[36] thereby facilitating the separation of the metal ions from some interactions, allowing these metal ions to be obtained for examination. The acidified sample could be kept at -4°C. The digestion step is not required because tap water samples generally don’t contain specific substances or significant organic content. In the AAS method, water samples were concentrated by vaporization, then placed in polyethylene flasks and stored at -4°C in a refrigerator until needed.[20]
RESULTS AND DISCUSSION
The optimal conditions
The optimal conditions for the proposed DPASV technique were investigated through a series of preliminary experiments. The anodic peak signals were optimized with respect to the following parameters: pH, supporting electrolyte, accumulation potential, deposition time, scan rate, pulse height, and pulse width. These parameters were systematically adjusted to establish the best conditions for the simultaneous or individual determination of Cd(II), Pb(II), Cu(II), and Zn(II) ions using the developed DPASV procedure.
The influence of the supporting electrolyte and pH
Various supporting electrolytes, including NaClO4, KNO3, sodium citrate, and HNO3, were examined by DPASV to determine the optimal electrolyte. In this study, HNO3 was used as a supporting electrolyte to analyze the total concentration of the studied heavy metal ions.[37] Nitric acid (HNO₃) was selected as the supporting electrolyte because it effectively releases metal ions from any complexes and prevents the accumulation of metal ions or organic substances on the electrode surface. It also minimizes the formation of inert complexes with the metal ions under investigation (i.e., the medium itself has negligible complexing ability). Consequently, HNO₃ adjusted to pH ≈ 2 was used as the supporting medium for the determination of the studied metal ions, as reported previously.[20]
The effect of ionic strength
The effect of ionic strength was calculated using different concentrations of HNO3 (0.01–0.1 M) for 3 x 10-4 M of each metal ion under examination. It was observed that the peak height is not significant for copper(II) and lead(II), but it is reduced as the concentration of HNO3 increases to 0.08 M for Zn(II) and Cd(II) ions. Therefore, the optimum ionic strength chosen for the investigation of the examined metal ions was 0.01 M HNO3.
The effect of initial potential
The influence of initial potential on the peak height for all studied metal ions (metal concentrations: 6.0 µg L-1, 0.05 µg L-1, 0.7 µg L-1, and 4.0 µg L-1 of Cd (II), Pb (II), Cu (II), and Zn (II), respectively) was examined. It has been found that the maximum signal of individual metal ions depends significantly on the initial potential. However, the initial potential, which showed little intermetallic interference, was specific to individual metal ions. In this case, –1.2 V is not the optimal initial potential, but it is suitable for the simultaneous determination of the studied metal ions in real water samples.[38] As we can see in Figure 1, the obtained data reveals that the best signal height and shape for the simultanous investigation of studied metal ions concentrations; Cu(II) 4 µg L-1; lead (II) 0.7 µg L-1; Cadmium(II) 0.05 µg L-1 and Zn(II) 6 µg L-1; at 0.01 M nitric acid, pH = 2, 150 s accumulation time, scan rate 10 mV S-1, pulse highit 0.06 V, pulse width 0.5 S and initial potential −1.2 V.
- DPAS voltammetry of trace metal ions in drinking tap water samples via CPE of studied metal ions concentrations; Cu(II) 4 µg L-1; lead (II) 0.7 µg L-1; Cadmium(II) 0.05 µg L-1 and Zn(II) 6 µg L-1 at 0.01 M nitric acid, pH = 2, 150 s accumulation time, scan rate 10 mV S-1, pulse height 0.06 V and pulse width 0.5 S.
The effect of scan rate, pulse height, and pulse width
Effect of scan rate The effect of scan rate on the anodic peak current was investigated for 3 × 10⁻⁴ M solutions of each metal ion (Cd(II), Pb(II), Cu(II), and Zn(II)) in the range of 2 to 14 mV s⁻1, using a pulse width of 0.5 s, pulse height of 25 mV, and accumulation time of 60 s. The peak current increased with increasing scan rate up to 14 mV s⁻1 for all metal ions. However, at scan rates above 14 mV s⁻1, significant distortion of the peak shape was observed. In general, slower scan rates are preferred in DPASV because they allow the potential to remain relatively constant during the pulse lifetime, resulting in better-defined peaks. Nevertheless, a scan rate of 10 mV s⁻1 was selected for all subsequent experiments as it provided a good compromise between sensitivity and peak shape.
Effect of pulse height The influence of pulse height on the anodic peak current was examined for 3 × 10⁻⁴ M of each metal ion in the range of 0.03-0.15 V. The peak current increased with increasing pulse height from 0.03-0.06 V. Beyond 0.06 V, no significant further increase in peak current was observed up to 0.15 V. Therefore, a pulse height of 0.06 V was chosen as the optimal value for all subsequent measurements.
Effect of pulse width The effect of pulse width on the peak current was studied for 3 × 10⁻⁴ M solutions of Cd(II), Pb(II), Cu(II), and Zn(II) over the range of 0.05 to 1.0 s. The peak current decreased with increasing pulse width. Although narrower pulse widths produced higher peak currents, pulse widths below 0.5 s resulted in poorly defined or erratic peak currents, particularly at low concentrations of the metal ions in real water samples. Consequently, a pulse width of 0.5 s was selected for all further experiments.
The effect of scan rate on the anodic peak current of 3×10−4 M of each metal ion under examination was studied, ranging from 2-14 mV s-1 with 0.5 s pulse width, 25 mV pulse height, and 60 s accumulation time. The peak current increased with increasing scan rate, reaching 14 mV s-1 for each metal ion, but at scan rates above 14 mV s-1, the peak shape was distorted. In general, a slow scan rate was preferable in the DPASV method. So, the potential is not influenced during the pulse life cycle. However, a 10 mV s-1 scan rate was employed in all studies.
Effect of a pulse height of 3×10−4 M of each metal ion under examination in the range of 0.03–0.06 V were considered. It was observed that the peak height increased from 0.03-0.06 V (pulse height), with no effect on the peak current from 0.06-0.15 V. So, 0.06V was chosen as pulse height in all experiments. Moreover, the effect of pulse width for 3×10−4 M Cd (II), Pb (II), Cu (II), Zn (II) ions as particular runs were done in the range 0.05-1.0 s. It was observed that the peak current decreased with increasing pulse width, even at small pulse widths, indicating a growing peak current. In water samples containing low concentrations of the studied metal ions, pulse widths less than 0.5 s yielded indefinite peak currents. Therefore, a 0.5 s pulse width was chosen in the consecutive analysis steps.
The influence of deposition time
The influence of the accumulation time of Cd (II), Pb (II), Cu (II), and Zn (II) metal ions at different accumulation times (30 and 150 s) was studied. It is found that, with increasing deposition time, the peak current increases linearly. The lower detection limits (computed as 3 times the noise at a specific concentration for each metal ion, based on a signal-to-noise ratio of 3) are for individual metal ions.
However, Table 1 lists all the optimal conditions required to estimate the metal ions under study.
| Metal ion | Supporting electrolyte | Ionic strength (M) | pH | Initial potential (V) | Deposition potential (s) |
Scan rate (mV s-1) |
Pulse height (V) | Width height (s) |
|---|---|---|---|---|---|---|---|---|
| Zn (II) | HNO3 | 0.01 | 2 | -1.2 | 150 | 10 | 0.06 | 0.5 |
| Cd (II) | HNO3 | 0.01 | 2 | -1.2 | 150 | 10 | 0.06 | 0.5 |
| Pb(II) | HNO3 | 0.01 | 2 | -1.2 | 150 | 10 | 0.06 | 0.5 |
| Cu (II) | HNO3 | 0.01 | 2 | -1.2 | 150 | 10 | 0.06 | 0.5 |
DPASV: differential pulse anodic stripping voltammetry
The influence of interferences
Intermetallic interference is equally significant in the detection of metal ions using CPE. When metal ions like Zn(II) and Cu(II) exist in great concentration, there is an affinity for a zinc–copper intermetallic to be designed. In contrast, these metal ions are accumulated on CPE. Though this kind of interference can be mitigated by adjusting the accumulation period to reduce the concentration of metal ions, only the types of interest are deposited and determined. Conversely, DPASV is useful because deposition times can be reduced, thereby minimizing the accumulation of metal ions on the CPE. Also, the interference is not detected at the CPE. When 3×10–4 M for each metal ion in the presence of different concentrations of the remaining 3 metal ions, ranging from 3×10–4-3×10–3 M (i.e., fraction of individual metallic ion/other 3 metal ions is from 1:1 up to 1: 10), were added in separate runs. Then, DPASV was verified after an accumulation time of 30 s in 1×10–2 M HNO3 as the supporting electrolyte. The data show that:
-
The increase in peak current of Copper (II) at –1.2 volt, as originally observed, indicates that the formation of a copper–zinc intermetallic combination occurs at the same initial potential as Cu(II), and this is in good agreement with the stated data.[20]
-
At an initial potential of –0.5 V, we observed that the diminution in peak current of copper (II) was recorded, which means that the formation of Cu–Zn intermetallic was not affected by the peak potential of Copper(II), so that the copper–zinc intermetallic was altered by the ratios of copper/zinc.
-
In the occurrence of 2 x 10-4 M and 3 x 10-4 Molar Copper (II) ions at an initial potential of –1.2 V and at the same conditions mentioned earlier, the recorded current of Pb(II) ions becomes more intense by about 22% and 24%, respectively. In comparison, there is no change in the peak current of Pb(II) on the addition of 3×10–5 M to 9×10–5 M copper (II).
-
In the presence of 1:1 up to 1:10 (zinc or cadmium ions/metal (II) ions), there is no influence on the peak current of zinc or cadmium, respectively.
In addition, the effect of different foreign metal ions such as Mn(II), iron(II), and Co(II) ions (250 µg L-1 individually) in the occurrence of each investigated metal ion via: 60 µg L-1 zinc (II), 2 µg L-1 Cadmium (II), 3 µg L-1 lead (II) and 5 µg L-1 Copper (II) ions, were discussed. So, lead (II) and Cadmium (II) currents were not affected by the existence of these ions. But a rise in the zinc peak and a known reduction in the Cu signal were observed. However, previous analysis,[20] shows that in the case of a mixture of interfering ions, a small enhancement or reduction in the current in the presence of intrusive ions, as a mixed, doesn’t indicate the examination breakdown. However, the standard addition method can effectively address such interferences.[34,35]
The influence of storage
Before determining dissolved metal under optimal conditions, water samples must be filtered and acidified by adding a small amount of concentrated HNO3 (2 ml L-1) to adjust the pH to 2 and finally stored at -4°C. The rise in the heavy metal ions is absolute by the addition of such small amounts of ultrapure acid. Purification must be performed previously by acidifying the sample, since otherwise heavy metal ions could be filtered from the suspended substance and shifted into solution on acidification. However, the acid media also have significant effects on reducing pollution by biological action in the remainder and by adsorption onto the container wall. So, such acidulated samples can be kept unchanged in their heavy metal ion contents for around time, especially if they are kept at -20°C and in the darkness.[34,36,39]
The influence of storing drinking tap water samples from Al–Baha city, Saudi Arabia (January to March, 2025), on Cadmium (II), Zinc (II), Copper (II), and lead(II) ions was assessed using the DPASV method. The variations in metal ion concentrations of the water samples were considered. The data showed that:
-
The concentration of Zinc(II) ions has little effect, especially during the first month.
-
The concentration of Cd(II) ions was not affected.
-
During storage of lead(II) ions, they were adsorbed onto the container walls; thus, their concentration decreased.
-
The concentration of copper (II) ions was changed via (4.4-14.5%) during the storage over the three months.
Real sample analysis
Drinking water samples from eight locations (Al Aqiq, Al Hawey, Al Zarga, Bany Sar, Al Dapheer, Al Soug region, Al Swad region, and Bin Farwa) located in Al–Baha city, Saudi Arabia, were collected on three different dates of the year (period from January to March, 2025). By means of the standard addition technique, the analysis of the 4 metal ions Cd(II), Pb(II), Cu(II), and Zn (II) was performed via DPASV in HNO3 medium at pH ≈ 2, after deposition on CPE, with an initial potential of –1.2 V. Greatly split peaks of the 4 metal ions were documented, which facilitate their simultanous estimation from one sample.[40] The analysis was performed by adding a reagent solution of the individual metal ions to the sample and extrapolating the linear relationship between the peak intensity and the concentration of the additional metallic ion (illustrative curves are shown in Figure 2).
- Plot of current against concentration in the study of Cd (II) ions in eight of the drinking water samples at Al–Baha city, Saudi Arabia (period from January to March 2025) at 0.01 M HNO3 and pH = 2.2: (1) and all other optimal conditions are as represented in Table 1. Al Aqiq; (2) Al Hawey; (3) Al Zarga; (4) Bany Sar; (5) Al Dapheer; (6) Al Soug region; (7) Al Swad region; (8) Bin Farwa.
Results for the assessments of Cd(II), Pb(II), Cu(II), and Zn (II) in drinking water samples are presented in Table 2. However, the lower limits of the investigated metal ions at 150 s deposition time (n= 5) are 0.31 µg L-1 (r = 0.9899) for zinc(II), 0.37 µg L-1 (r = 0.8992) for cadmium(II), 1.28 µg L-1 (r = 0.9899) for lead(II) and 0.12 µg L-1 (r = 0.9998) for copper(II), respectively.
| Metal ions | Deposition times (s) | Linearity ranges (ppb) | Detection limit (ppb) at (150 s) | Corr. Coeff.(r) |
|---|---|---|---|---|
| Zn(II) | 30 | 1.21–70.00 | 0.31 | 0.9899 |
| 150 | 0.61–67.50 | 0.9892 | ||
| Cd(II) | 30 | 1.10–10.92 | 0.37 | 0.9887 |
| 150 | 0.02–1.09 | 0.9885 | ||
| Pb(II) | 30 | 20.27–280.50 | 1.28 | 0.9899 |
| 150 | 2.020–28.75 | 0.9888 | ||
| Cu(II) | 30 | 6.25–75.50 | 0.12 | 0.9897 |
| 150 | 0.62–7.50 | 0.9998 |
DPASV: differential pulse anodic stripping voltammetry; CPE: carbon paste electrode
Comparison among the DPASV and AAS methods
The results obtained with both methods (DPASV and AAS) are in good agreement with the maximum value of the tap water sample and also demonstrate that they are appropriate for estimating metal ions at the µg L-1 level in the tap water sample. The variance in the data for some water samples between the two methods is mostly due to the chief source of contamination in the AAS technique. The workers in the laboratory did not follow the standard techniques accepted by the United States Environmental Protection Agency (EPA) or the American Public Health Association (APHA). In those procedures, the trace metal ion must be preconcentrated via chelation with ammonium pyrrolidine dithiocarbamate (APDC) and extraction with methyl isobutyl ketone (MIBK) to achieve a concentration within the linearity range of the apparatus. The statistical parameters for Pb(II), Cu(II), Zn(II), and Cd(II) were estimated via AAS and DPASV in different tap water samples and are presented in Table 3. The assessment of Cu (II), Cd (II), Pb (II) and Zn(II) in all drinking water samples under investigation were in the range, for Zn(II) (0.42–68.5 µg L-1), Cadmium (II) (0.29–0.87 µg L-1), lead (II) (1.5–22.35 µg L-1) and Copper (II) (0.58–2.58 µg L-1). The data results were summarized in Table 3. The obtained data are within the acceptance limits of the local and global standards.
| Metals | Period | Concentration* (µg L-1) | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Al Aqiq | Al Hawey | Al Zarga | Bany Sar | Al Dapheer | Al Soug region | Al Swad region | Bin Farwa | ||
| Zn(II) |
Jan. Feb. Mar. |
0.44 (045) 0.42 (0.43) 0.42 (0.41) |
10.51 (10.85) 10.51 (10.70) 10.32 (10.72) |
68.50 (67.00) 67.30 (68.00) 68.15 (67.00) |
14.11 (14.00) 14.25 (13.50) 14.12 (14.00) |
10.12 (10.15) 10.33 (10.14) 10.65 (10.16) |
10.32 (10.79) 10.12 (10.82) 10.41 (10.86) |
9.12 (9.72) 9.13 (9.70) 9.11 (9.78) |
10.35 (10.30) 10.41 (10.20) 10.55 (10.29) |
| Cd(II) |
Jan. Feb. Mar. |
0.52 (0.55) 0.41 (0.53) 0.50 (0.52) |
0.31 (0.35) 0.29 (0.32) 0.32 (0.32) |
0.81 (0.88) 0.83 (0.82) 0.79 (0.87) |
0.75 (0.74) 0.74 (0.80) 0.77 (0.80) |
0.63 (0.64) 0.63 (0.62) 0.62 (0.63) |
0.43 (0.40) 0.45 (0.42) 0.46 (0.45) |
0.51 (0.50) 0.55 (0.50) 0.53 (0.53) |
0.32 (0.33) 0.33 (0.34) 0.31 (0.34) |
| Pb(II) |
Jan. Feb. Mar. |
3.51 (1.56) 3.49 (1.55) 3.39 (1.50) |
2.91 (3.00) 2.85 (3.23) 2.78 (3.30) |
15.10 (14.70) 14.9 (14.56) 14.1 (14.2) |
20.00 (18.60) 21.10 (18.90) 20.00 (19.00) |
22.10 (22.34) 21.20 (22.34) 22.00 (22.35) |
2.92 (2.58) 2.91 (2.58) 3.03 (2.50) |
10.05 (9.90) 10.10 (9.70) 10.10 (9.80) |
2.11 (2.51) 2.16 (2.55) 2.23 (2.53) |
| Cu(II) |
Jan. Feb. Mar. |
1.52 (1.53) 1.42 (1.42) 1.55 (1.56) |
1.46 (1.50) 1.45 (1.46) 1.50 (1.52) |
2.50 (2.50) 2.52 (2.50) 2.53 (2.58) |
0.58 (0.58) 0.63 (0.62) 0.58 (0.57) |
1.45 (1.48) 1.43 (1.47) 1.47 (1.49) |
1.53 (1.56) 1.52 (1.58) 1.55 (1.54) |
1.51 (1.50) 1.52 (1.51) 1.52 (1.52) |
2.42 (2.35) 2.41 (2.35) 2.35 (2.36) |
*Average of 5 replicates.
Data between brackets is from the AAS method
DPASV: differential pulse anodic stripping voltammetry; CPE: carbon paste electrode; AAS: Atomic absorption spectrometry
In all cases, the confidence (at 95% confidence for (n = 5)), and correlation coefficient were computed, which tells the applicability of the recommended procedures [Table 4]. Negative or minor values of the correlation coefficient in a small sample might be due to changes in results over the months, resulting from seasonal effects, phytoplankton influence, and contamination.
| Metals |
Type of Statistics (n = 5) |
Site of Samples | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Al Aqiq | Al Hawey | Al Zarga | Bany Sar | Al Dapheer | Al Soug region | Al Swad region | Bin Farwa | ||
| Zn(II) |
SD Corr. Coef. Confide.* |
0.22–0.83 0.8980 0.25–1.08 |
0.41–0.91 – 0.6654 0.47–1.05 |
0.33–0.96 0.12100 0.22–1.01 |
0.33–0.81 0.12120 0.45–1.05 |
0.13–0.62 0.9894 0.115–0.539 |
0.25–0.63 0.3563 0.39–0.82 |
0.24–0.65 – 0.8871 0.38–0.82 |
0.52–0.88 0.9989 0.69–1.09 |
| Cd(II) |
SD Corr. Coef. Confide.* |
0.33–0.95 0.12 0.35–1.18 |
0.25–0.35 0.8790 0.15–0.28 |
0.28–1.02 0.1200 0.28–1.16 |
0.33–0.99 0.8750 0.25–1.09 |
0.15–0.31 0.8880 0.171–0.342 |
0.03–0.06 – 0.8870 0.03–0.06 |
0.03–0.07 0.9919 0.02–0.07 |
0.03–0.14 – 0.8780 0.03–0.15 |
| Pb(II) |
SD Corr. Coef. Confide.* |
0.13–0.42 – 0.7860 0.13–0.38 |
0.08–0.13 – 0.750 0.08–0.16 |
0.132–0.35 – 0.866 0.15–0.38 |
0.13–0.41 0.1230 0.16–0.35 |
0.15–0.28 0.510 0.135–0.278 |
0.14–0.73 0.796 0.14–0.70 |
0.15–0.72 0.7980 0.16–0.69 |
0.09–0.42 0.9989 0.04–0.12 |
| Cu(II) |
SD Corr. Coef. Confide.* |
0.04–0.11 0.5409 0.05–0.15 |
0.03–0.06 0.4327 0.03–0.07 |
0.025–0.05 0.0125 0.03–0.08 |
0.02–0.06 0.124 0.02–0.06 |
0.021–0.039 – 0.5865 0.13–0.35 |
0.03–0.075 0.758 0.03–0.08 |
0.03–0.08 0.786 0.02–0.08 |
0.04–0.09 – 0.798 0.32–0.12 |
*Confidence interval for SD
DPASV: differential pulse anodic stripping voltammetry; AAS: Atomic absorption spectrometry; SD: standard deviation
The generated Results demonstrate that the concentration of metal ions under investigation in drinking water at Al–Baha city, Saudi Arabia, is within the allowed limits of American,[38] European,[41] World[42] standards, and Saudi Ministry of Environment, Water & Agriculture.[43,44] This research shows that the projected technique (DPASV) can be used for the quantitative simultaneous analysis of the four metal ions in drinking water samples.
CONCLUSION
Simple, accurate, precise, and selective methods (DPASV and AAS) were effective and valuable for the instantaneous estimation of four metal ions in drinking water samples. The data obtained for a similar tap water sample, compared with AAS data, were in good agreement. The assessment of Cu (II), Cd (II), Pb (II) and Zn(II) in all drinking water samples under investigation were in the range, for Zn(II) (0.42–68.5 µg L-1), Cadmium (II) (0.29–0.87 µg L-1), lead (II) (1.5–22.35 µg L-1) and Copper (II) (0.58–2.58 µg L-1). The obtained data are within the acceptance limits of the local and global standards.
Based on the results of the storage influence on the metal ion concentration, the generated data indicates that the concentration of cadmium ions was not achieved. The concentration of zinc (II) ions has a small effect, especially during the first month. The concentration of copper (II) ions was affected by (4.4–14.5%) during the three-month storage time.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
References
- An assessment study of heavy metal distribution within soil in upper course of Zarqa River basin/Jordan. Environ Geol. 2006;49:1116-24.
- [CrossRef] [Google Scholar]
- Assessment of groundwater quality in a typical rural settlement in southwest Nigeria. Int J Environ Res Public Health. 2007;4:307-18.
- [CrossRef] [PubMed] [PubMed Central] [Google Scholar]
- Determination of cadmium and lead in perch fish samples by differential pulse anodic stripping voltammetry and furnace atomic absorption spectrometry. Arab J Chem. 2017;10:347-54.
- [CrossRef] [Google Scholar]
- Toxicity, mechanism and health effects of some heavy metals. Interdiscip Toxicol. 2014;7:60-72.
- [CrossRef] [PubMed] [PubMed Central] [Google Scholar]
- Prevention of contamination and other accuracy risks in voltammetric trace metal analysis of natural waters. Z Anal Chem. 1979;299:97-102.
- [CrossRef] [Google Scholar]
- Water treatment: Low-cost alternatives to carbon adsorbents. Encyclopedia of Surface and Colloid Science. 2015;1:7618-7652.
- [CrossRef] [Google Scholar]
- Physical and chemical evaluation of groundwater quality in Jouf region in Saudi Arabia for energy, agriculture and drinking purposes. Desal Water Treat. 2023;294:51-9.
- [CrossRef] [Google Scholar]
- Toxic metal ions contamination in the groundwater, Kingdom of Saudi Arabia. J Taibah Univ Sci. 2020;14:1571-9.
- [CrossRef] [Google Scholar]
- A review: Analytical methods for heavy metals determination in environment and human samples. Anal Method Environ Chem J. 2019;2:97-126.
- [CrossRef] [Google Scholar]
- Green approaches to determine metals in lubricating oils by electrothermal atomic absorption spectrometry (ET–AAS) Microchem J. 2013;108:74-80.
- [Google Scholar]
- Morzan E, Tudino M, Etcheniqu, R. Determination of cadmium in commercial tobacco by ET–AAS. J. Anal At Spectrom. 2018;33:1970-73.
- [PubMed] [Google Scholar]
- Application of constrained mixture design and Doehlert matrix in the optimization of dispersive liquid–liquid microextraction assisted by ultrasound for pre-concentration and determination of cadmium in sediment and water samples by FAAS. Microchem J. 2017;130:56-63.
- [Google Scholar]
- Sensitive and accurate determination of cobalt at trace levels by slotted quartz tube-flame atomic absorption spectrometry following pre-concentration with dispersive liquid–liquid microextraction. Anal Lett. 2019;52:745-53.
- [Google Scholar]
- Optimization of instrument conditions for the analysis for mercury, arsenic, antimony and selenium by atomic absorption spectroscopy. Methods X. 2018;5:824-33.
- [CrossRef] [Google Scholar]
- Metal ion speciation and capillary electrophoresis: Application in the new millennium. Electrophoresis. 2005;26:3988-4002.
- [CrossRef] [PubMed] [Google Scholar]
- Determination of metal ions in water, soil, and sediment by capillary electrophoresis. Anal Lett. 2002;35:2053-76.
- [Google Scholar]
- Speciation of metal ions by capillary electrophoresis. Crit Rev Anal Chem. 2002;32:337-50.
- [Google Scholar]
- TLC separation of transition metal ions and their quantitative estimation by atomic absorption spectroscopy. J Liq Chromatogr. 1995;18:1671-8.
- [CrossRef] [Google Scholar]
- Determination of some heavy metals from aqueous solutions using modified Amberlite XAD–4 resin by selective solid–phase extraction. J Anal Sci Technol. 2022;13:15.
- [Google Scholar]
- Direct and simultaneous voltametric analysis of heavy metals in tap water samples at Assiut city: An approach to improve the analysis time for nickel and cobalt determination at mercury film electrode. Microchem J. 2003;75:119-31.
- [Google Scholar]
- Determination of zinc, cadmium, lead and copper ions in the underground water by differential pulse anodic stripping voltammetry. Egypt J Anal Chem. 1999;8:70-83.
- [Google Scholar]
- Farghaly application of electro analytical in trace metals determinations: Environmental and industrial samples. Determinations Nanomed. Nanotechnol. 2021;2:5.
- [Google Scholar]
- Cathodic stripping voltametric determination of uranium with potassium hydrogen phthalate. Talanta. 1199;49:31-40.
- [Google Scholar]
- Direct determination of trace concentrations of lead in freshwater samples by adsorptive cathodic stripping voltammetry of a lead–Calcein Blue complex. Anal Chim Acta. 1993;316:363-69.
- [Google Scholar]
- The voltametric approach in trace metal chemistry of natural waters and atmospheric precipitation. Analytica Chimica Acta. 1984;164:1-21.
- [Google Scholar]
- Voltametric methods for the determination of heavy metals in domestic waste and compost produced from it. Fresenius J Anal Chem. 1994;349:620-4.
- [Google Scholar]
- Prevention of contamination and other accuracy risks in voltametric trace metal analysis of natural waters. 3. Voltametric ultratrace analysis with a multicell system designed for clean bench working. Z Anal Chem. 1980;300:350-62.
- [Google Scholar]
- Simultaneous stripping detection of Pb(II), Cd(II) and Zn(II) using a bimetallic Hg–Bi/single–walled carbon nanotubes composite electrode. J Electroanal Chem. 2011;656:78-84.
- [Google Scholar]
- Applications of adsorptive stripping voltammetry in the determination of trace and ultratrace metals. Electroanalysis. 1993;5:355-73.
- [CrossRef] [Google Scholar]
- Cathodic stripping voltammetric determination of lisinopril in dosage forms and biological fluids. Egypt J Chem. 2022;65:421-8.
- [Google Scholar]
- Voltametric determination of quercetin in urine at carbon paste electrode. Anal Lett. 2005;38:2247-58.
- [Google Scholar]
- Voltametric determination of azithromycin at the carbon paste electrode. Talanta. 2004;62:531-8.
- [CrossRef] [PubMed] [Google Scholar]
- Text book of quantitative inorganic analysis (4th ed). London: Longmann; 1978.
- Evaluation of metal fractions in river sediments and waters: application of chelation chromatography–differential pulse anodic stripping voltammetry. Talanta. 1995;42:1395-1409.
- [CrossRef] [PubMed] [Google Scholar]
- Square–wave stripping voltammetry for direct determination of eight heavy metals in soil and indoor–airborne particulate matter. Environ Res. 2005;97:229-35.
- [CrossRef] [PubMed] [Google Scholar]
- Method validation for determination of metals in soils by ICP–MS. Rom Rep Phys. 2012;64:221-31.
- [Google Scholar]
- Potentials and potentialities of cathodic stripping voltammetry of trace elements in natural waters. Analytica Chimica Acta. 1991;250:265-76.
- [CrossRef] [Google Scholar]
- Standard methods for the examination of water and wastewater (20th ed). Washington (DC): American Public Health Association; 1999. p. :344-427.
- Applications of polarography and voltammetry to marine and aquatic chemistry. Fresenius Z Anal Chem. 1976;282:357-6.
- [Google Scholar]
- Voltametric method for the determination of Zn, Cd, Pb, Cu and Ni in interstitial water. Anal Bioanal Chem. 1996;354:735-7.
- [CrossRef] [PubMed] [Google Scholar]
- Guidelines for drinking-water quality. 4th ed., incorporating the 1st addendum [Internet]. Geneva: WHO; 2017. Available from: https://www.who.int/publications/i/item/9789241549950 [Last accessed on 2025 Dec 13]
- Guidelines for drinking-water quality. 4th ed., incorporating the 1st and 2nd addenda [Internet]. Geneva: WHO; 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK579461/ [Last accessed on 2025 Dec 13]
- Drinking water quality in the Kingdom of Saudi Arabia. Water.. 2024;16(13):1-26. Available from: https://doi.org/10.3390/w16131810 [Last accessed on 2025 Dec 13]
- [CrossRef] [Google Scholar]
- Unbottled drinking water quality standards in the Kingdom of Saudi Arabia [Internet]. Riyadh (Saudi Arabia): Saudi Water Authority; 2024. Available from: https://hse.kaust.edu.sa/wp-content/uploads/2024/11/Unbottled-Drinking-Water-Standard-KSA-2024.pdf [Last accessed on 2025 Dec 13]