An Eco-Friendly, Interference, and Solvent Free Surfactant-Assisted Dual-Wavelength β-CorrectionSpectrometric Method for Total Determination and Speciation of Cu2+ Ions in Water

Spectral interference through the presence of uninformative variables, excess reagents, and complications in the refinement of the analyte signal is common in the quest to identify complex species in real samples. Therefore, an economical green, facile, and sensitive strategy has been developed for Cu2+ detection using the anionic surfactant sodium dodecylsulphate- (SDS-) assisted dual-wavelength β-correction spectrophotometric strategy combined with the chromogenic reagent zincon (ZI). The low limits of detection (LOD) and quantification (LOQ) of Cu2+ using ordinary (single wavelength) spectrophotometry were 0.19 (3.02) and 0.63 (10.0) μgmL−1, and these values were improved to 0.08 (1.27) and 0.26 μgmL−1 (4.12 μM)) using β-correction (dual wavelength) spectrophotometry, respectively. The LOD and LOQ were improved from 0.08 (1.27) and 0.26 (4.12) μgmL−1 to 0.02 (0.32) and 0.08 μgmL−1 (1.27 μM) using SDS-assisted dual-β-correction spectrometry, respectively. Ringbom, s, and the corrected absorbance (Ac) versus Cu2+ concentration plots were linear over the concentration range 1.10–2.4 (17.4–38.1) and 0.50–2.40 μgmL−1 (7.94–38.1 μM), respectively. Sandell's sensitivity index of 3.0 × 10−3 μg/cm2 was achieved. The selectivity was further confirmed via monitoring the impact of common diverse ions and surfactants on the corrected absorbance. Total determination and Cu2+ speciation in water were favorably implemented and validated by ICP-OES at 95% (P=0.05). Satisfactory Cu2+ recoveries in tap (92.2–98.0%) and mineral (105–111.0%) water samples were achieved. The sensing system is simple, reliable, sensitive, and selective for Cu2+ detection.


Introduction
Copper is a crucial micronutrient for phytoplankton and in the human body, and it is an important component of human proteins and enzymes, where the lack of Cu 2+ will hinder the physiological activities of the human body and easily cause various diseases [1][2][3].Chemical speciation (labile and chelated) of copper (II) also plays a strong role in defning the bioavailability and toxicity upon exposure of copper in marine environments.In addition, Cu is a heavy metal widely discovered in the environment and excessive Cu 2+ ions in water causes severe environmental pollution and even risk of the health of organisms [4].Furthermore, Cu 2+ ions beyond the recommended levels of copper causes adverse health efects, e.g., Alzheimer's disease and numerous neurological sicknesses [5].Industrial and agricultural anthropogenic activities were responsible for a dramatically impact on the environment and human health.Maximum allowable limit (MAL) of copper contamination has been set at 1.3 mg•kg −1 (∼20 μM) by the United States-Environmental Protection Agency (US-EPA) and the World Health Organization (WHO) in drinking water and food stafs' regulations [5,6].Tus, searching for low-cost, sensitive, and precise reagent for total determination and speciation of Cu 2+ in water is of great concern [7,8].
Ordinary spectrophotometric methods for the detection of metal ions including Cu 2+ have many advantages such as simplicity, e, applicability, availability, easy to use, and low cost [41][42][43][44][45][46][47][48][49][50][51].However, the excess of the chromogenic reagent minimizes the sensitivity and precision and limits the linear range of concentration of these methods because of the substantial interfering of the extra concentration of the colored reagent with the analyte at λ max [52,53].In contrast, the dual-wave β-correction spectrophotometric technique has gained great attention and has a promising impact as an alternative approach due to its simplicity, low cost, portability, and elimination of the interference of the excess colorant chromogenic reagent [53,54].In the dual-wave β-correction spectrophotometric technique, quantifcation of the correct absorbance equivalent to the fractions of the chromogenic reagent that reacted with the analyte in the presence of excess of the chromogenic reagent is very much possible for precise analysis of the analyte [52][53][54].β-Correction approach ofers simple, rapid, costefectiveness, and selective over most of the accessible modern instrumentation and also improves the sensitivity, precision, and accuracy of the ordinary single-wavelength spectrophotometry by solving the problem arising from the interference due to the excess chromogenic reagent [54][55][56][57][58]. Tus, dual-wave β correction spectrophotometry is the most signifcant and well-defned aspect for measuring the correct (real) absorbance of the formed colored Cu 2+ -zincon complex.
Recently, speciation of copper species forms of copper is essential for analytical laboratories in the copper industry because of the technological importance of such analytical information [59,60].Kumar et al. [59] have reported that, ordinary natural organic compounds such as humic acid (HA), fulvic acid (FA), phenols, and surfactants can complex with copper, infuencing its speciation and decreasing its bioavailability.To the best of our knowledge, zincon reagent has been used for detection of Cu 2+ and other metal ions in water samples using only ordinary single-wavelength spectrophotometric methods [6,15,[40][41][42][43].Terefore, the current study was aimed to: (i) developing a low cost, and selective surfactant assisted β-correction spectrophotometric assay for total determination and copper speciation in water using zincon (ESI. 1) and (ii) assigning the stoichiometry, stability, and thermodynamic behavior of Cu 2+ -ZI chelate.A cohesive collaboration of industry and academic institutes will be desired to miniaturize and automate the developed assay, where it has the advantages of miniaturization, automation, simplicity, and sensitivity.

Experimental
2.1.Apparatus.Te electronic spectra and absorbance of the reagent and its Cu 2+ -zincon complex were recorded using UV-Vis spectrophotometer (Shimadzu UV-Vis 1800, Japan) connected to a Shimadzu TCC-ZUOA temperature controller unit.A Perkin-Elmer ICP MS (Sciex model Elan DRC II, USA) was also employed as a standard technique for copper analysis at the optimized operational parameters summarized in ESI. 2. A Perkin Mattson 5000 FTIR spectrometer was used for recording the FTIR.A Volac digital micropipette (10-100 μL) and a Jenway pH-meter (model 3510) were used for preparation of diluted solutions in deionized water and pH measurements, respectively.

Chemicals and Reagents.
Analytical reagent (A.R.) grade chemicals and reagents were used as received.All laboratory glassware's including high-density polyethylene (HDPE) bottles were soaked in hot detergent, soaked in HCl solution (50% v/v)-conc.HNO 3 (2.0M) at 1 : 1 v/v ratio rinsed with deionized water and fnally dried at 80 °C in an oven.Sodium salts of humic acid, fulvic acid, and phenol HA were purchased from Sigma-Aldrich.HDPE sample bottles were soaked overnight, washed with HNO 3 (10%, v/v) solution, and rinsed with deionized water prior to use, and fnally placed in precleaned HDPE.A stock solution of Cu 2+ (1 mg/ mL) was prepared by dissolving the appropriate mass of Cu (NO 3 ) 2 .3H where b and m are the intercept and slope of the linear calibration plot, respectively, C std is the known Cu 2+ concentration, and V x is the sample volume.Alternatively, the standard addition method was performed as follows: Te corrected absorbance was computed in the absence and in the presence of known fractions (20.0-100 μL) of the standard Cu 2+ under the optimized parameters.Te corrected absorbance (A c ) of each solution was subsequently evaluated, and the Cu 2+ content was then calculated via the extrapolated abscissa of the linear plot of the standard addition, employing the following equation: where C std is the known Cu 2+ concentration, Ac sam and Ac std are the real absorbance exhibited by the unknown and after adding known Cu 2+ concentrations, respectively.

Total Determination and Speciation of Cu 2+ in Water.
An approximate volume (0.3-0.5 L) of the tap water (TW) and mineral water (MW) samples were collected in HDPE bottles, fltered through a 0.45 μm pore size cellulose membrane flter, and stored in precleaned HDPE sample bottles (0.5 L) at 4 °C.Known volumes (5.0 mL) of the water sample adapted to pH 3 were transferred to measuring fasks (25.0 mL) containing zincon and standard Cu 2+ concentrations at the optimized conditions.Te solutions mixtures were completed to the mark with Milli-Q water, and the absorbance at λ 1 and λ 2 was recorded.Te corrected absorbance's were calculated before and after spiking of standard Cu 2+ concentrations from the standard addition linear plot.Another water sample was exposed to UV radiation at 254 nm for 4 h in the HCl (10% v/v), stored in HDPE bottles, and subjected to Cu 2+ analysis within one day of collection as follows: Transfer an accurate volume (5.0 mL) of prefltered water sample onto a series of measuring fasks containing zincon at the optimal parameters.Based on these bases, the Ac of the frst aliquot (Ac 1 ) will be a measure of labile Cu 2+ ions in the mixture, while the Ac of the second aliquot (Ac 2 ) is a measure of the sum of labile and chelated Cu 2+ with organic matter in the aliquot.Te difference of corrected absorbance (Ac 2 -Ac 1 ) is a measure of the complexed fractions of Cu 2+ in water samples.

Electronic Spectra of Zincon and Its Cu 2+ -Chelate Omitted.
Zincon reagent (ESI. 1) contains four protonating groups: two acidic, sulfonic (pKa1) and carboxylic (pKa2); and two basic, a secondary amine (pKa3) and a phenolic one (pKa4).Te most acidic group of zincon is the sulfonic group, which is usually omitted since zincon is commercially available as a monosodium salt and because of its rapid decomposition in acidic pH [16,49].Spectrophotometric measurements of zincon display signifcant change of the absorption at 565 nm around pH 4, which is characteristic for the carboxylic group rather than the sulfonic one.Te UV-visible spectrum of zincon vs. water displayed distinct peak at 465 nm (λ 1 ) and was safely assigned to n⟶π * electronic transition (Figure 1, curve A) [62,63].Te UV-visible spectrum of the reaction product of zincon with Cu 2+ at pH � 3 (Figure 1 curve B) revealed broad and ill-defned peak like shoulder in the range 563-569 nm and a strong absorption peak at 600 nm.Tese peaks were safely assigned to charge transfer (L⟶MCT) and electronic d⟶d transitions from shorter to longer wavelength in tetrahedral environment, respectively 16, [63].Te spectrum of Cu 2+ -International Journal of Analytical Chemistry zincon chelate vs. zincon (Figure 1, curve C) displayed strong peak at 625 nm (λ 2 ).Te experiential bathochromic (red) shift and the high value of the molar absorptivity (ε � 2.5 × 10 4 L M −1 cm −1 ) suggested the suitability of the produced colored Cu 2+ -zincon chelate for establishing simple, cost-efectiveness, and reliable β-correction spectrophotometry approach for Cu 2+ detection and speciation of Cu 2+ species in water.

Programing of the Analytical Parameters.
To explore the impact of pH (pH 1.0-10.0) of the aqueous solution on the developed Cu 2+ -zincon colored chelate, the electronic spectra and the actual absorbance of Cu 2+ (3.0 μgmL −1 ) solution containing zincon (1.0 × 10 −4 M) were recorded at various pH.Te absorbance of the produced colored Cu 2+ -zincon complex reached its maximum value at pH 3.0 (Figure 2(a), dotted line).Te binding sites of phenolic OH and azo (-N�N-) groups of zincon reagent at pH 3 are capable to coordinate with Cu 2+ [54] in consistence with the data published for the Cu 2+ -zincon complex [54,55].Terefore, the solution pH was adopted at pH 3 in the following study.
Te impact of the solution temperature (10-50 °C) on the absorbance of the Cu 2+ -zincon {3.0 μg mL −1 Cu 2+ } at pH 3 was examined.Te data are displayed in Figure 3. Te absorbance of the formed Cu 2+ -zincon chelate increased on growing temperature up to 25 °C, followed by a gradual decrease in the absorbance.Te degradation of the formed Cu 2+ -zincon chelate and/or the decrease in the interaction between Cu 2+ ions and ZI at a temperature higher than 25 °C are most likely accounted for the observed trend.Hence, a room temperature (25 ± 1 °C) was selected as a suitable condition for the formation of the Cu 2+ -ZI complex.
Te absorbance of Cu 2+ -ZI at known Cu 2+ (2.0 µg mL −1 ) and zincon (1.0 × 10 −4 M) concentrations after mixing was recorded immediately over a wide range of time (0.0-80 min at pH 3. Te absorbance and the corrected absorbance (A c ) of the produced Cu 2+ -ZI complex were measured at several shaking time intervals (0.0-85 min) employing single wavelength and β-correction spectrophotometry, respectively.Te colored Cu 2+ -ZI complex was established within 1-2 min of shaking, and the absorbance remained constant up to a standing time of 85 min (ESI.3).Tese data added further provision to the analytical utility of the established Cu 2+ -ZI complex for developing a solvent-free ß-correction spectrophotometry assay for Cu 2+ detection in water.Tus, in the next study, the absorbance of the Cu 2+ -Zi complex was measured within 80 min of mixing at pH 3.
Te infuence of various proportions (0.0-1000 µL) of NaCl (1.0 × 10 3 µgmL −1 ) and standing time (0.0-70 min) on the absorbance of the tested Cu 2+ -Zincon complex at pH 3 under the optimal parameters was also studied.Te plots of 4 International Journal of Analytical Chemistry the absorbance of the formed Cu 2+ -ZI complex in the presence of various volumes of the salt added and time are shown in Figure 4.In the absence of the salt added, the corrected absorbance of the Cu-ZI complex computed for the added salt concentration was about 4.2% (Figure 4).Tese results, clearly simplifes that Cu 2+ complexation with ZI was less infuenced by the salt added to the medium.Tus, in the next study, no salt was added to the reaction medium.

Termodynamic Parameters of Cu 2+ -ZI Complex.
Te thermodynamic features of the developed Cu 2+ -ZI complex in the temperature range of 293-323 K were determined.Te Cu 2+ species present as neutral species at pH 3 only one species of Cu 2+ -ZI chelate existed, and no precipitation obtained.On rising the solution temperature from 293 to 323 K, the equilibrium constant (K c ) decreased signifying that, the complex formation is exothermic process [64,65].
Growing temperature minimizes Cu 2+ interaction with ZI, resulting in decrease in the percent yield of the complex.Te ΔG value (−26.98 kJ mol −1 ) at 298 K decreased on increasing temperature, supporting the spontaneous nature of the complex., and metal ions, e.g., Na + , K + , Cd 2+ , Ni 2+, Sr 2+ , Mn 2+ , Fe 3+ , Co 2+ , Pb 2+ , Hg 2+ , and Ag + , and the oxy ions (MnO 4 − , IO 3 − , and WO 4 2− ) was studied individually in the presence of Cu 2+ -ZI complex at the optimized parameters of pH and zincon concentrations.Te absorbance of Cu 2+ -ZI complex was compared with that in the presence of the interfering species.Te tolerance limit (acceptance edge) (m/m) was distinct as the added concentration of the interfering species producing a relative standard deviation (RSD) of ±5% of the true absorbance of Cu 2+ -ZI chelate.Te results obtained are summarized in Table 1.Te ions Cl − , Br − , NO 3 − , SO 4 2− , IO 3 − , Na + , K, and Ca 2+ revealed negligible change in the corrected absorbance of Cu 2+ -ZI complex at 1 : 1000 molar excess of Cu 2+ to the diverse species.Te ions Cd 2+ , Ni 2+ , Sr 2+ , Mn 2+ , Cr 3+ , Hg 2+ , and Pb 2+ were tolerable up to 50-fold excess to Cu 2+ .Te ions Cr 3+ , Hg 2+ , and Pb 2+ at level up to 20 fold greater than Cu 2+ ions did not interfered on the absorbance of Cu 2+ -zincon chelate, whereas Fe 3+ , Co 2+ , and Ag + ions interfered extremely with the complex.Te interference of Fe 3+ and Co 2+ was masked by adding a few drops of NaF (0.1% m/v) via the formation of colorless [FeF 6 ] 3− complex, whereas Co 2+ interference was minimized by adding ethanolamine (0.01%) to form a colorless complex in the test aqueous solution.Te oxyanions MnO 4 − and WO 4 2− were tolerable by adding a few drops of sodium azide (NaN 3 ).

Efect of Surfactants.
Te impact of surface-active agents (0.1-10 ppm) on the stability and the corrected absorbance of Cu 2+ -zincon chelate in the developed procedure are critical.Tus, the impact of all kinds of surfactant such as cationic (BTAC), anionic (SDS) and nonionic (Triton X-100) on the selectivity of the established assay for Cu 2+ was studied at the optimized condition.Cationic and nonionic surfactants have nonsignifcant changes on the absorbance of the developed colored Cu 2+ -ZI chelate, whereas in the presence of SDS, a synergistic increase in the value of the absorbance was only seen (Figure 5).Te impact of SDS may be due to its ability to form versatile interactions including International Journal of Analytical Chemistry electrostatic, hydrophobic, bi-bi interaction, complex ion association, and/or H bonding with the Cu 2+ complex.Te change in the efective microenvironment by SDS micellar solution around Cu 2+ in the aqueous solution and their contribution to the physicochemical features such as rate constant and spectral characteristics may also participated in the trend observed.Te possible association between the cationic Cu 2+ -zincon complex and SDS as a bulky anion by forming ternary complex ion associate between SDS may also enhanced the molar absorptivity of the produced ternary complex ion associate.Te available hydroxy groups and water molecules may also screened by SDS at the boundary and subsequently resulting in a worthy association between ZI and Cu 2+ ions.Tus, it is worthy to note that, the use of SDS is attractive in developing surfactant assisted β-correction spectrophotometry for Cu 2+ detection owing to its low cost, toxicity, and reduced environmental impact.Tus, the efect of SDS in the absorbance was continual to improve the detection of Cu 2+ .3).Te data revealed good stability over a period up to 100 min, revealing the good stability of the produced copper (II) chelate.Assuming the existence of one complex species of Cu 2+ -ZI, Job's and mole ratio methods at pH 3 [62,63] were used to determine the stoichiometry and stability of the formed Cu 2+ -ZI chelate.Te results of Job's (ESI.4) suggested formation of 1 : 2 stoichiometry of Cu 2+ -zincon complex.Te stoichiometry of Cu 2+ : zincon was also supported from the mole ratio plot (ESI.5) [62].Refectance electronic spectrum of Cu 2+ -zincon complex also displayed broad peak cantered at 17241cm −1 interpretable in terms of square planar stereochemistry [16,66,67].Te FTIR spectra of the free zincon reagent and its copper (II) chelate are displayed in ESI. 6. Te v(C�N) band in the complex was found in the same position of the FTIR of free zincon indicating no participation of the azomethine in the complex formation with Cu 2+ ions [16,66].Te spectra added further support to the participation of the azo (-N�N-) group N and the involvement of the phenolic OH in the complex formation with Cu 2+ ions (see ESI. 6) [66].Tus, it can be concluded that, the zincon coordinated to Cu 2+ via two N and two O of the azo and phenolic OH groups, and the structure of the produced copper-zincon complex can be postulated as [CuL 2 ], where L � zincon and the most probable structure of Cu 2+ -zincon chelate, can be proposed as shown in ESI. 1. Te stability constant (K) of the Cu 2+ -ZI complex was further successfully computed from Job's plot (ESI.4), where the extrapolated absorbance (A extp.) near to the equivalence point corresponds to the absorbance of the Cu 2+ -ZI complex.Based on the Job's plot (ESI.4), the Cu 2+ -ZI complex is dissociated in the area of extrapolation, and the true absorbance of the produced Cu 2+ complex is to some extent lower than the hypothetical value.Tus, the produced Cu 2+ -ZI complex can be stated by the following chemical equilibrium [62]: Table 1: Selectivity data and tolerance limit of diverse ions in Cu 2+ determination by the developed dual-wave β-correction spectrophotometry.

Diverse ions
Tolerance limit 6 International Journal of Analytical Chemistry where L � zincon ligand (L) in the complex formation, and [CuL 2 ] refer to the formed Cu 2+ chelate, respectively.Te fraction of the true corrected absorbance (Ac) at a given value on the X-axis of Job's plot (ESI.4) to the extrapolated absorbance (A exp ) determined from the extrapolated lines corresponding to the same point in the X-axis is equivalent to the mole fraction of the formed chelate [CuL 2 ].Te K s value of the formed [CuL 2 ] complex was also computed from Job's plot (ESI 4) using the following equation ( 7) [62]: where C m is the molar analytical concentration of the metal, C x is the total molar analytical concentration of the ligand depending on the controlling reactant at the end point and n is ligand to metal ratio in the Cu 2+ -zincon chelate, respectively.Te average computed K s value (2.0 × 10 6 ) displayed acceptable stability and the suitability of the Cu 2+ -ZI complex for developing spectrophotometric method for Cu 2+ determination.
Further, the LOD and LOQ of the surfactant-(SDS-) assisted β-correction spectrophotometry were enhanced from 0.08 μg mL −1 (1.27 µM) and 0.26 μg mL −1 (4.13 µM) to 0.02 μg mL −1 (0.32 µM) and 0.078 µg/mL (1.24 µM), respectively.Te change in the efective microenvironment by micelles solution around Cu 2+ ions may also improve formation of ternary ion associate of Cu 2+ -zincon complex and SDS.Te hydroxy groups and the available free water molecules may also screened by SDS at the boundary and successively resulting in better organization between ZI and Cu 2+ ions.
Te precision and accuracy of the proposed β-correction spectrophotometry assay were further computed from the recovery of three replicate measurements of known Cu 2+ concentrations in water.Te results demonstrated in Figures 6(a) (Table inset) revealed good performance of the planned β-correction spectrophotometric assay and support the current protocol for Cu 2+ detection in water.Further, a judgment between the efcacies of the established β-correction spectrophotometry with several reported spectrometric methods is summarized in Table 2. Te LOD, LOQ, and LDR of developed surfactant assisted-correction spectrophotometry assay are favorably associated with most of the established spectrophotometric protocols (Table 2).Te LOD of the planned β-correction assay was higher than the LOD (0.018 μg L −1 ) using paper-based chip for fuorescence Cu 2+ detection (Table 2).However, the measured value by the established assay below the acceptable limit of Cu 2+ fxed by WHO and US-EPA in water.Te proposed assay frees from the interfering of various anions and cations present in water samples.Tus, the proposed assay could be suitable for Cu 2+ detection in water and it has the benefts of low cost, simple, practical, and eco-friendly.

Analytical Applications and Validation of the Established
Methodology.Due to the unavailability of certifed reference materials (CRM) for Cu 2+ to check the reliability and validity of the established assay for Cu 2+ detection, known concentrations (0.4-2.4 μgmL −1 ) of Cu 2+ were spiked into International Journal of Analytical Chemistry mineral water (MW) and tap water (TW) samples as mentioned before and analyzed using the established β-correction spectrophotometric assay.Te results of Cu 2+ determined in tap (TW) and mineral (MW) water samples are summarized in Table 3. Representative plots for measuring Cu 2+ in tap water and mineral (MW) water samples are also shown in Figure 7. Te results were further validated by determination of Cu 2+ by the ofcial ICP-OES at the optimal operation parameters.Acceptable percentage recoveries of Cu 2+ in tap (90.4-113.9%)and mineral (97.5-110.7%)water samples were attained.Te "added," "found" and recovery percentage (91-102%) of Cu 2+ concentrations were found comparable and acceptable.At 95% confdence (n � 5, P < 0.05) [66], the tabulated Student t tab and F values were greater than the experimental Student t exp (1.96-2.1)and F exp (2.3-2.8),respectively, revealing acceptable consequence between the tabulated and experimental values for the detection of Cu 2+ in water.

Conclusion, Advantages, Limitations, and Outlooks
In summary, our research demonstrates the potential for the development of signifcant surfactant simple, efective, costefectiveness, interference, and solvent free β-correction spectrophotometric approach for total determination and speciation (labile and chelated) of Cu 2+ .Te molar absorptivity of the assay reveals good sensitivity and linear 0.0 0.5   range, LOD, reliability, rapid analysis, no extra costly material necessary, and free from interference of common metal ions.Te planned methodology may also substitute the common analytical methods (AAS and ICP-OES) that sufered from time consuming, complicated instrumentation and multiple preconcentration steps.Further, the developed assay can be drawn-out for detection and speciation of Cu 2+ at ultra-trace low levels in water via online enrichment from water samples by dispersive liquidliquid microextraction [69] and/or on sorbent packed column and succeeding elution prior analysis [70].Tus, the assay can set the trend for coupling sorbent packed column that can assist as a new dimension in β-correction spectroscopy.Te accuracy and applicability of the proposed assay were proved by recovery studies for water samples and the results were close to 100%.Te absence of the interactive efects of the analytical parameters using one issue at a time represent the main drawback and might decrease the analytical utility of the current study.Accepting the positive impact of SDS in the absorbance will be studied properly in more detail to advance Cu 2+ detection and to assign the most probable mechanism.Te method could also be extended for detection of Cu 2+ ions in natural waters with high complexing capacity of organic matter, e.g., humic, fulvic acids, phenols, surfactants, etc. Design experiment is also extremely suggested for advance the present approach for attaining efective and perfect Cu 2+ detection.

Figure 7 :
Figure 7: Plot of the standard addition for Cu 2+ detection as Cu 2+ -ZI complex in mineral (MW) and in tap (TW) water samples.

Table 2 :
A comparison between the fgures of merits (μM) of the developed β-correction and some of the reported spectrophotometric methods for Cu 2+ detection * .

Table 3 :
Analytical results of Cu 2+ determination in tap and mineral water samples by the developed dual-wave β-correction spectrophotometric method * .