Simultaneous determination of copper, nickel, cobalt and zinc using zincon as a metallochromic indicator with partial least squares

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.

Physico-analytical studies on some heterocyclic azo dyes and their metal complexes with some transition metals

In this investigation, the azo dyes; 2-(3′-phenyl-5′-pyrazolyl azo) schaffer acid (la) and 2-(3′-phenyl-5′-pyrazolyl azo) resorcinol (Ib); were prepared through diazotizing 3-phenyl-5-aminopyrazole (PAP) and coupling the resulting diazonium salt with Schäffer acid and resorcinol respectively. The prepared azo dyes are characterized using both IR spectra and the elemental analysis (C, H, N and S). The prepared azo dyes are used as chromogenic reagents for the spectrophotometric determination of copper (II), nickel (II), cobalt (II) and zinc (II) ions. The conditional acid dissociation constants of these azo dyes (la and Ib) and the stability constants of its metal ion complexes have been determined by spectro-analytical methods. The effect of pH, time, organic solvent and the foreign ions on the spectrophotometric determination of these ions and their complexes with the azo dyes under study were studied. The stoichiometric ratio (M:L) of the formed complexes was also determined. The molar absorptivity, the Sandell's sensitivity values, the obeyance of Beers law and the stability constants of the formed complexes have been also determined and discussed.

Remediation of zinc-contaminated groundwater by iron oxide in situ adsorption barriers - From lab to the field

Heavy metals such as zinc cannot be degraded by microorganisms and form long contaminant plumes in groundwater. Conventional methods for remediating heavy metal-contaminated sites are for example excavation and pump-and-treat, which is expensive and requires very long operation times. This induced interest in new technologies such as in situ adsorption barriers for immobilization of heavy metal contamination. In this study, we present steps and criteria from laboratory tests to field studies, which are necessary for a successful implementation of an in situ adsorption barrier for immobilizing zinc. Groundwater and sediment samples from a contaminated site were brought to the lab, where the adsorption of zinc to Goethite nanoparticles was studied in batch and in flow-through systems mimicking field conditions. The Goethite nanoparticles revealed an in situ adsorption capacity of approximately 23 mg Zn per g Goethite. Transport experiments in sediment columns indicated an expected radius of influence of at least 2.8 m for the injection of Goethite nanoparticles. These findings were validated in a pilot-scale field study, where an in situ adsorption barrier of ca. 11 m × 6 m × 4 m was implemented in a zinc-contaminated aquifer. The injected nanoparticles were irreversibly deposited at the desired location within <24 h, and were not dislocated with the groundwater flow. Despite a constantly increasing inflow of zinc to the barrier and the short contact time between Goethite and zinc in the barrier, the dissolved zinc was effectively immobilized for ca. 90 days. Then, the zinc concentrations increased slowly downstream of the barrier, but the barrier still retained most of the zinc from the inflowing groundwater. The study demonstrated the applicability of Goethite nanoparticles to immobilize heavy metals in situ and highlights the criteria for upscaling laboratory-based determinants to field-scale.

Simultaneous measurement of Cr(III) and Cu(II) based on indicator-displacement assay using a colorimetric nanoprobe

High-performance analysis of heavy metal ions is great importance in both environment and food safety. In this work, a facile and reliable colorimetric sensor was presented for simultaneous detection of Cu²⁺ and Cr³⁺ based on indicator-displacement assay (IDA). As a typical silicate nanomaterials, ZnSiO₃ hollow nanosphere (ZSHS) exhibited an outstanding ion exchange capacity. Zincon was incorporated with the ZSHS to form a zincon/ZSHS hybrid ionophore with a blue color. Upon the addition of Cr³⁺, IDA reaction and selective ion exchange occurred with the color change of zincon/ZSHS ionophore from blue to yellow. With such a design, colorimetric measurement of Cr³⁺ was realized. The linear concentration for Cr³⁺ detection ranged from 0.5 μM to 75 μM with the LOD of 83.2 nM. Furthermore, we also screened different kinds of complexing agents that may respond with zincon/ZSHS ionophore and various metal ions. It was found that tartaric acid (TA) showed the chelation capability of Zn²⁺-TA is stronger than that of Zn²⁺-zincon. Thus zincon/ZSHS/TA presented a yellow color due to the chelation reaction of Zn²⁺-TA, releasing the zincon as a free state. After addition of Cu²⁺, a stronger chelation reaction of Cu²⁺-zincon occurred. This process involved in the color change from yellow to blue and realized colorimetric measurement of Cu²⁺. The detection limit of Cu²⁺ was calculated to be 43.7 nM with linear range from 0.1 to 20 μM. In addition, the zincon/ZSHS nanoprobe was successfully applied for simultaneous measurement of Cu²⁺ and Cr³⁺ in sorghum and river water, indicating that the zincon/ZSHS nanoprobe provided a promising sensing platform in environment and food safety.

Determination of prostate cancer marker Zn2+ with a highly selective surface-enhanced Raman scattering probe on liquid-liquid self-assembled Au nanoarrays

As the concentration of Zn²⁺ in patients with prostate cancer is much less than that in healthy persons, Zn²⁺ concentration can be used as a marker to expediently screen prostate cancer. In this study, a sensitive and highly selective surface-enhanced Raman scattering (SERS) method to detect Zn²⁺ concentration in human prostatic fluids by utilizing water-insoluble 2-carboxyl-2'-hydroxyl-5'-sulfoformazylbenze (Zincon) as a SERS probe based on self-assembled Au nanoarrays at a liquid-liquid interface between n-hexane and Au colloids was proposed. Zincon showed remarkably different SERS bands before and after coordinating Zn²⁺ in the controlled conditions (70 μL of ethanol, 500 μL of n-hexane, pH value of 7.1 and 10 s of vortex mixing time), which can be used in quantifying Zn²⁺ with characteristic peaks. The proposed SERS method presented a good linear relationship ranging from 0.5 to 10 μmol/L and a satisfactory detection limit of 0.1 μmol/L as well as low interference with other metal ions. Moreover, the detection results are close to those of the conventional standard atomic absorption spectroscopy (AAS) method.

Simultaneous magnetic dispersive micro solid phase extraction of valsartan and atorvastatin using a CMC-coated Fe3O4 nanocomposite prior to HPLC-UV detection: multivariate optimization

In this study, a sensitive, rapid, accurate and practical procedure is established for determination of atorvastatin and valsartan from human biological fluids by dispersive micro solid phase extraction (D-μ-SPE) combined with HPLC-UV detector.

Nanoporous Carbon Derived from MOF-5: A Superadsorbent for Copper Ions

In this work, nanoporous carbon (NPC) was synthesized by direct carbonization of MOF-5 (a famous metal-organic framework). The structure and morphology of the prepared MOF-derived nanoporous carbon (MOF-NPC) were investigated by X-ray diffraction, N₂ adsorption/desorption isotherm, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy methods. The MOF-NPC was then used to adsorb copper ions from aqueous solutions. To evaluate the performance of the prepared MOF-NPC to remove copper ions, both adsorption kinetics and adsorption equilibrium experiments were carried out and then the obtained data were modeled with various models. Also, the efficacy of temperature and the pH of the solution on the removal efficiency were checked. The results show that the prepared MOF-NPC is a superadsorbent for the removal of copper ions from aqueous solutions. Finally, the removal percentage of copper ions by the prepared MOF-NPC was compared with other activated carbon adsorbents to show its incredible efficiency.

Quantitative colorimetric paper analytical devices based on radial distance measurements for aqueous metal determination

The On-Target test cards are a rapid testing method for untrained users to quantitatively assess contaminants in aqueous samples.

Leukemia cells detection based on electroporation assisted surface-enhanced Raman scattering

In this study, an electroporation-based surface-enhanced Raman scattering (SERS) technique was employed to differentiate the human myeloid leukemia cells from the normal human bone marrow mononuclear cells with the aim to develop a fast and label-free method for leukemia cell screening. The Ag nanoparticles were delivered into living cells by electroporation, and then high quality SERS spectra were successfully obtained from 60 acute promyelocytic leukemia cells (HL60 cell line), 60 chronic myelogenous leukemia cells (K562 cell line) and 60 normal human bone marrow mononuclear cells (BMC). Principal component analysis (PCA) combined with linear discriminant analysis (LDA) differentiated the leukemia cell SERS spectra (HL60 plus K562) from normal cell SERS spectra (BMC) with high sensitivity (98.3%) and specificity (98.3%). Furthermore, partial least squares (PLS) approach was employed to develop a diagnostic model. The model successfully predicted the unidentified subjects with a diagnostic accuracy of 96.7%. This exploratory work demonstrates that the electroporation-based SERS technique combined with PCA-LDA and PLS diagnostic algorithms possesses great promise for cancer cell screening.

Simultaneous detection of trace metal ions in water by solid phase extraction spectroscopy combined with multivariate calibration

Solid Phase Extraction Spectroscopy (SPES) developed in this paper is a technique to measure spectrum directly on the solid phase material where the analytes are concentrated in SPE process. Membrane enrichment and UV-Visible spectroscopy were utilized to fulfill SPES, and multivariate calibration method of partial least squares (PLS) was used to simultaneously detect the concentrations of trace cobalt (II) and zinc (II) in water samples. The proposed method is simple, sensitive and selective. The complexes of analyte ions were collected on the cellulose acetate membranes via membrane filtration after the complexation reaction with 1-2-pyridylazo 2-naphthol (PAN). The spectra of the membranes which contained the complexes of metal ions and PAN were measured directly without eluting. The analytical conditions including pH, reaction time, sample volume, the amount of PAN, and flow rates were optimized. Nonionic surfactant Brij-30 was absorbed on the membranes prior to SPES to modify the membranes for improving the enrichment and spectrum measurement. The interference from other ions to the determination was investigated. Under the optimal condition, the absorbance was linearly related to the concentration at the range of 0.1-3.0 μg/L and 0.1-2.0 μg/L, with the correlation coefficients (R(2)) of 0.9977 and 0.9951 for Co (II) and Zn (II), respectively. The limits of detection were 0.066 μg/L for cobalt (II) and 0.104 μg/L for zinc (II). PLS regression with leave-one-out cross-validation was utilized to build models to detect cobalt (II) and zinc (II) in drinking water samples simultaneously. The correlation coefficient between ion concentration and spectrum of calibration set and independent prediction set were 1.0000 and 0.9974 for cobalt (II) and 1.0000 and 0.9956 for zinc (II). For cobalt (II) and zinc (II), the errors of the prediction set were in the range 0.0406-0.1353 μg/L and 0.0025-0.1884 μg/L.

Simultaneous spectrophotometric determination of copper, cobalt, nickel and iron in foodstuffs and vegetables with a new bis thiosemicarbazone ligand using chemometric approaches

A newly synthesized bis thiosemicarbazone ligand, (2Z,2'Z)-2,2'-((4S,5R)-4,5,6-trihydroxyhexane-1,2-diylidene)bis(N-phenylhydrazinecarbothioamide), was used to make a complex with Cu(2+), Ni(2+), Co(2+) and Fe(3+) for their simultaneous spectrophotometric determination using chemometric methods. By Job's method, the ratio of metal to ligand in Ni(2+) was found to be 1:2, whereas it was 1:4 for the others. The effect of pH on the sensitivity and selectivity of the formed complexes was studied according to the net analyte signal (NAS). Under optimum conditions, the calibration graphs were linear in the ranges of 0.10-3.83, 0.20-3.83, 0.23-5.23 and 0.32-8.12 mg L(-1) with the detection limits of 2, 3, 4 and 10 μg L(-1) for Cu(2+), Co(2+), Ni(2+) and Fe(3+) respectively. The OSC-PLS1 for Cu(2+) and Ni(2+), the PLS1 for Co(2+) and the PC-FFANN for Fe(3+) were selected as the best models. The selected models were successfully applied for the simultaneous determination of elements in some foodstuffs and vegetables.

Label-free detection of serum proteins using surface-enhanced Raman spectroscopy for colorectal cancer screening

Surface-enhanced Raman scattering (SERS) spectra of serum proteins purified from human serum samples were employed to detect colorectal cancer. Acetic acid as a new aggregating agent was introduced to increase the magnitude of the SERS enhancement. High-quality SERS spectra of serum proteins were acquired from 103 cancer patients and 103 healthy volunteers. Tentative assignments of SERS bands reflect that some specific biomolecular contents and protein secondary structures change with colorectal cancer progression. Principal component analysis combined with linear discriminant analysis was used to assess the capability of this approach for identifying colorectal cancer, yielding diagnostic accuracies of 100% (sensitivity: 100%; specificity: 100%) based on albumin SERS spectroscopy and 99.5% (sensitivity: 100%; specificity: 99%) based on globulin SERS spectroscopy, respectively. A partial least squares (PLS) approach was introduced to develop diagnostic models. An albumin PLS model successfully predicted the unidentified subjects with a diagnostic accuracy of 93.5% (sensitivity: 95.6%; specificity: 91.3%) and the globulin PLS model gave a diagnostic accuracy of 93.5% (sensitivity: 91.3%; specificity: 95.6%). These results suggest that serum protein SERS spectroscopy can be a sensitive and clinically powerful means for colorectal cancer detection.

Simultaneous monitoring of photocatalysis of three pharmaceuticals by immobilized TiO2 nanoparticles: chemometric assessment, intermediates identification and ecotoxicological evaluation

In this study, the photocatalytic degradation of a mixture of three pharmaceuticals, Metronidazole (MET), Atenolol (ATL) and Chlorpromazine (CPR), was quantified simultaneously during the UV/TiO2 process. The investigated TiO2 was Millennium PC-500 immobilized on ceramic plates by sol-gel based method. The partial least squares modeling was successfully applied for the multivariate calibration of the spectrophotometric data. The central composite design was applied to model and optimize the UV/TiO2 process. Predicted values of removal efficiency were found to be in good agreement with experimental values for MET, ATL and CPR (R(2)=0.947 and Adj-R(2)=0.906, R(2)=0.977 and Adj-R(2)=0.960 and R(2)=0.982 and Adj-R(2)=0.969, respectively). The optimum initial concentration of pharmaceuticals, reaction time and UV light intensity was found to be 10 mg L(-1), 150 min and 38.45 W m(-2), respectively. The main degradation intermediates of pharmaceuticals produced in this process were identified by GC-MS technique. The chronic ecotoxicity of pharmaceuticals was evaluated using aquatic species Spirodela polyrrhiza prior to and after photocatalysis. The TOC results (90% removal after 16 h) and ecotoxicological experiments revealed that the photocatalysis process could effectively mineralize and reduce the ecotoxicity of the pharmaceuticals from their aqueous solutions.

Sensitive metal ions (II) determination with resonance Raman method

In this paper, a new proposal for the quantitative evaluation of divalent metal ions (M(2+)) is developed by the use of the competitive resonance Raman (RR)-based method. Upon excitation with light of the appropriate wavelength (532 nm), a strong electric field is generated that couples with the resonance of the complex (zincon-M(2+)), increasing the character signals of these complexes, resulting in sensitive detection. Herein, the RR probe, zincon-M(2+) complex that the RR intensity gets lower with the decreasing of the M(2+) concentration, which leads to the transformation of the Raman information. As a result, by using the proposed RR-based method, we could find the liner calibration curves of Cu(2+) and Ni(2+), which show the potential in quantitative evaluation of an unknown sample. In addition, the abundant fingerprint information shows that RR leads to the successful analysis of a blended solution, which contains two ions: Cu(2+) and Ni(2+).

Simultaneous spectrophotometric determination of trace amount of malachite green and crystal violet in water after cloud point extraction using partial least squares regression

In this work, a new method has been proposed to simultaneously determine the trace amount of malachite green and crystal violet from aqueous solution by spectrophotometry after cloud point extraction (CPE) using partial least squares regression. The optimal extraction and operating conditions, such as pH, reagents concentration and effect of time and temperature, and so on, have been investigated using the non-ionic surfactant Triton X-114. The maximum absorption wavelength for malachite green and crystal violet is 624 and 579 nm, respectively; linearity is obeyed in the range of 9.9-800 and 16-1000 ng mL(-1) with detection limit of 2.9 and 4.8 ng mL(-1), and the root mean square error of prediction (RMSEP) are 0.0197 and 0.0343, respectively. The proposed method has been applied successfully to simultaneously determine the trace amount of malachite green and crystal violet in real matrix samples with the recoveries of 92.45-102.5%.

A spectrophotometric method for the determination of zinc, copper, and cobalt ions in metalloproteins using Zincon

Zincon (2-carboxy-2'-hydroxy-5'-sulfoformazylbenzene) has long been known as an excellent colorimetric reagent for the detection of zinc and copper ions in aqueous solution. To extend the chelator's versatility to the quantification of metal ions in metalloproteins, the spectral properties of Zincon and its complexes with Zn(2+), Cu(2+), and Co(2+) were investigated in the presence of guanidine hydrochloride and urea, two common denaturants used to labilize metal ions in proteins. These studies revealed the detection of metals to be generally more sensitive with urea. In addition, pH profiles recorded for these metals indicated the optimal pH for complex formation and stability to be 9.0. As a consequence, an optimized method that allows the facile determination of Zn(2+), Cu(2+), and Co(2+) with detection limits in the high nanomolar range is presented. Furthermore, a simple two-step procedure for the quantification of both Zn(2+) and Cu(2+) within the same sample is described. Using the prototypical Cu(2+)/Zn(2+)-protein superoxide dismutase as an example, the effectiveness of this method of dual metal quantification in metalloproteins is demonstrated. Thus, the spectrophotometric determination of metal ions with Zincon can be exploited as a rapid and inexpensive means of assessing the metal contents of zinc-, copper-, cobalt-, and zinc/copper-containing proteins.

Simultaneous square wave voltammetric determination of 2-mercaptobenzothiazole and 2-mercaptobenzoxazole by partial least squares method in water samples

A rapid sensitive and versatile method for simultaneous determination of 2-mercaptobenzothiazole (MBT) and 2-mercaptobezoxazole (MBO) based on the square wave voltammetric (SWV) using mercury drop electrode (SMDE) has been presented. A three-electrode system containing SMDE working electrode, Pt auxiliary electrode and Ag/AgCl reference electrode was used throughout. The linear calibration graphs are in the concentration range of 7-40 microg mL(-1) and the equations are: (Deltai)=1.372CMBT-9.112 (r=0.9982) and (Deltai)=0.246CMBO-1.736 (r=0.9985) for MBT and MBO, respectively. Partial least squares regression (PLS) was applied to resolve the seriously overlapped voltammograms without any pre-separation step. The five level partial factorial design was used as calibration design method and the cross-validation method was used to select the number of significant factor for PLS model building. Five significant PLS components are used for MBT and MBO. A set of synthetic sample mixtures were used to validate the propose method. The root-mean-square errors of predictions (RMSEPs) and percent of relative prediction errors (RPEs) are 0.841 and 0.777 microg mL(-1) and +/-3.58 and +/-3.74% for MBT and MBO, respectively. The developed method was then applied to the analysis of these two compounds in different water samples with satisfactory results.

Resolution of Biparametric Mixtures Using Bead Injection Spectroscopic Flow-through Renewable Surface Sensors

A new, sensitive and simple bead injection spectroscopy-flow injection analysis (BIS-FIA) sensor with spectrophotometric detection, using a commercially available flow-cell, is described to the determination of biparametric mixtures. As an analytical model, the metallic mixture Cu(II) and Zn(II) has been chosen. The flow-cell (Hellma 138-OS) is filled by injecting in the flow system 300 microl of a homogeneous bead suspension of an anion exchanger gel (Sephadex QAE A-25) previously loaded with the chromogenic reagent 2-carboxyl-2-hydroxy-5-sulfoformazylbenzene (Zincon). A sequential reaction of Cu(II) and Zn(II) with Zincon to form two complexes is performed on the bead sensing support and the absorbance is monitored at 627 nm, after two successive injections from the mixture solution. The sample containing these metal ions is injected into the first carrier (deionized water, pH 5.9), and Cu(II) selectively reacts with Zincon on the beads, developing the analytical signal. Then, 600 microl of 2 M HCl is injected to decompose the complex, and the carrier solution is changed. At pH 11 (second carrier) both Cu(II) and Zn(II) react with the chromogenic reagent, the absorbance now corresponding to both analytes. The eluent is again injected to descompose both complexes. After three analyses the sensing bead surface is not regenerated. Then, beads are automatically discarded from the flow cell by reversal of the flow, and instantaneously transported out of the system. So the procedure exploits the combination of the concepts of flow-through renewable sensors with bead injection spectroscopy. Using a sample volume of 1000 microl, the calibration graph for Cu(II) is linear over the range 0.05 to 1 microg ml(-1) and for Zn(II) from 0.1 to 1.8 microg ml(-1) in the presence of each other. RSDs (%) lower than 5% are obtained for both analytes. The sensor is satisfactorily applied to individual determination or mixture resolution in waters, pharmaceuticals, soils and human hair samples.

H-Point Standard Addition Method for the Selective Simultaneous Determination of Nickel and Copper Using 1-(2-Pyridylazo)-2-naphthol in Tween 80 Micellar Media

The H-point standard addition method (HPSAM) has been applied for the simultaneous determination of nickel and copper in trace levels, using 1-(2-pyridylazo)-2-naphthol (PAN) as a chromogenic reagent in aqueous Tween 80 micellar media. Under the optimum condition, the simultaneous determinations of nickel and copper by HPSAM were performed. The absorbances at one pair of wavelengths, 548 and 579 nm, were monitored with the addition of standard solutions of copper. The method is able to accurately determine copper-to-nickel ratios of 15:1 to 1:10 (Wt/Wt). The effects of diverse ions on the determination of nickel and copper to investigate the selectivity of the method were also studied. The recommended procedure was successfully applied to some water and alloy samples.