Amperometric detection of heavy metal ions in ion pair chromatography at an array of water/nitrobenzene micro interfaces

A novel amperometric detector for heavy metal ions has been developed and successfully applied for ion pair chromatography. The detector is based on the electrochemical transfer of the metal ions across an array of water/nitrobenzene micro interfaces. The ion transfer is facilitated by the neutral ionophores methylenebis(diphenylphosphineoxide) and methylenebis(di- phenylphosphinesulfide). More than eight metals are separated in less than 15 min on an RP18 column using octyl sulfonate as ion pair reagent. For the heavy metals, the limits of decision are 19(Pb²⁺), 9(Zn²⁺), 9l (Co²⁺), 8(Cd²⁺) and 1.6(Mn²⁺) g/L. The applicability of the new method for water samples is demonstrated.     

Application of l-thiazolidine-4-carboxylic acid monolayer in electrochemical determination of copper(II)

L-Thiazolidine-4-carboxylic acid monolayer was prepared on gold electrodes through the self-assembly approach. Such novel thioether-based monolayer could efficiently preconcentrate Cu²⁺, which provided a simple, stable and reproducible method for the determination of Cu²⁺. The modified electrodes were stable enough to be continuously used for one week (more than 30 times regeneration) with lower than 10% decrease in the response. They retained their initial activity for more than one month if used once a day. The calibration curve was linear for Cu²⁺ from 0.6 to 158.8 μg L^?1 with a detection limit of 0.38 μg L^?1. The relative standard deviation was 3.2% for a series of six successive measurements. The proposed method was applied in the determination of Cu²⁺ in mineral water and human hair samples.     

Speciation analysis of mercury contaminants in water samples by RP-HPLC after solid phase extraction on modified C18 extraction disks with 1,3-bis(2-cyanobenzene)triazene

A highly sensitive and accurate method for preconcentration and determination of ultra trace amounts of inorganic mercury and organomercury compounds in different water samples is proposed. The preconcentration is achieved using octadecyl silica (C₁₈) extraction disks modified with 1,3-bis(2-cyanobenzene)triazene (CBT). The retained analytes as their triazenide complexes on the solid phase was eluted with 10 ml acetonitrile and measured by reversed-phase high-performance liquid chromatography (RP-HPLC). Type and amount of eluent, pH, amount of CBT, flow rates of sample solution and eluent have been optimized in order to obtain quantitative recovery of the analytes. The effect of interfering ions, such as Cu²⁺, Mn²⁺, Fe²⁺, Al³⁺, Zn²⁺, Cd²⁺, Ca²⁺, Mg²⁺, Ba²⁺, Pb²⁺, K⁺ and Na⁺ usually present in water samples on the recovery of the analytes has also been investigated. The enrichment factor of 100 was obtained for all mercury species and the analytical detection limits of phenylmercury, methylmercury and Hg²⁺ were found as 0.8, 1.0 and 1.3 ng l^− 1, respectively. Stability of mercury species after extraction on the modified disks was studied and the results showed that complexes collected on the disks were stable for at least 5 days. The proposed method has been applied to the quantitative determination of mercury species in natural and synthetic water samples with recoveries more than 90%.     

Formation and Dissociation Mechanism of Amide Complexes,IV. Protonation and deprotonation of the Cu2+ and Ni2+ complexes of 3,7-diazanonanediamide and 3,7-diazanonane-N,N′-diethylamide

The protonation and deprotonation rates of the coordinated amide groups in the Ni²⁺ and Cu²⁺ complexes of 3,7-diazanonanediamide (DANA) and in the Cu²⁺ complex of 3,7-diazanonane-N,N′-diethylamide (DANEA) have been studied by stopped-flow techniques. For the interconversion M(H_?2L) ? ML, two consecutive reactions are observed in the case of Cu²⁺ with DANA or DANEA, whereas there is only one reaction for Ni²⁺ with DANA. Cu(H_?2DANEA) is unusually labile, indicating a strong interaction between the N-ethyl groups. The conversion of the O- into the N-coordinated amide groups in NiDANA²⁺ is 25 times slower than in CuDANA²⁺. In the case of Ni²⁺ this excludes a step with water substitution, which is involved in one of the reaction paths observed for the Cu²⁺ complexes, since the rates of water exchange differ by a factor of 10⁵ for the two metal ions.     

Electrochemical determination of cadmium and lead based on the joint enhancement effects of SBA-16 and iodide

Mesoporous SBA-16 was synthesized using tetraethoxysilane as silicon source and a ternary system consisting of surfactant F127, water and butanol. Owing to the excellent properties of SBA-16 such as lager surface area and strong accumulation ability, the stripping peak current of Cd²⁺ and Pb²⁺ remarkably increases at the SBA-16 modified carbon paste electrode. Moreover, the peak current of Cd²⁺ and Pb²⁺ further enhances after the addition of I^?. Under the joint enhancement effects of SBA-16 and I^?, the detection sensitivity of Cd²⁺ and Pb²⁺ is greatly improved. The influences of concentration of I^?, amount of SBA-16, accumulation potential and time were investigated. As a result, a new electrochemical method with high sensitivity was developed for the simultaneous determination of Cd²⁺ and Pb²⁺. The limit of detection is 0.6 nM for Cd²⁺ and 1 nM for Pb²⁺. It was used to determine Cd²⁺ and Pb²⁺ in waste water sample, and the results consisted with the values that obtained by atomic absorption spectrometry.     

L-cysteine-regulated in situ formation of Prussian blue/Turnbull’s blue nanoparticles as the colorimetric probe for the detection of copper ion

A fast, simple, sensitive, and selective colorimetric method for the detection of Cu²⁺ was developed using Prussian blue/Turnbull’s blue nanoparticles (PBNPs/TBNPs) as the probe. The colorimetric sensor is based on the following principle. Cu²⁺ can induce the aggregation of L-cysteine (L-cys) modified-PBNPs/TBNPs (L-cys-PBNPs/TBNPs), resulting in an obvious red shift of its maximum absorption peak. Thus, the concentration of Cu²⁺ can be determined based on the peak shift in the UV–Vis spectra. The optimal pH, concentration of L-cys, reaction temperature between L-cys-PBNPs/TBNPs and Cu²⁺, the formation time of L-cys-PBNPs/TBNPs, and the reaction time between L-cys-PBNPs/TBNPs and Cu²⁺ of the method were determined to be pH 4.5, 2.0 mM, 20 °C, 5.0 min, and 2.0 min, respectively. A good linearity for the colorimetric determination of Cu²⁺ at the range of 0.25–2.5 μM (R² = 0.986) was obtained, with a limit of detection (LOD) of 0.12 μM. Moreover, the negligible response of other metal ions demonstrates good selectivity and specificity of the sensor. In addition, the method was employed in the detection of Cu²⁺ in lake water samples, and the spiked recoveries are in the range of 96.7–106.6% with a relative standard deviation less than 7.4%. Therefore, the colorimetric method is applicable for Cu²⁺ detection in real water samples of high sensitivity and selectivity.     

Application of Chitosan Functionalized with 8-Hydroxyquinoline: Determination of Lead by Flow Injection Flame Atomic Absorption Spectrometry

This work describes the application of chitosan – chemically modified with 8-hydroxyquinoline – in a simple and efficient preconcentration system using flow injection flame atomic absorption spectrometry (FI-FAAS) for the determination of Pb²⁺ ions. The efficiency of the chelating resin and the accuracy of the proposed method were evaluated by the metal ion recovery technique in samples of mineral water, potable water and lake water. The recovery of Pb²⁺ ions from spiked solutions was less than 70% due to matrix effects, which were eliminated by addition of Ba²⁺ metal ions, resulting in recoveries of approximately 100% for all water samples. Ag⁺, Cd²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Zn²⁺, Hg²⁺, Ca²⁺, Mg²⁺, Cr³⁺, Al³⁺ and Fe³⁺ metal ions were studied with respect to their interference with Pb²⁺ metal ion determination, and the chelating resin exhibited high selectivity for Pb²⁺ at pH 7. The analytical properties of merit were obtained using the parameters previously optimized. The method shows high precision with a relative standard deviation (R.S.D.) of 1.1% (n=7) for a solution containing 50µgL^–1 of Pb²⁺ and a detection limit (L.O.D.) of 1.7µgL^–1.     

Speciation of aluminium fluoride complexes and Al in soils from the vicinity of an aluminium smelter plant by hyphenated High Performance Ion Chromatography Flame Atomic Absorption Spectrometry technique

The paper presents a new tool for the determination of inorganic speciation forms of aluminium: AlF_n^{(3 − n)+}, and Al³⁺ by means of the HPIC-FAAS. The proposed method has been successfully used for speciation analysis (qualitative and quantitative) of inorganic aluminium forms AlF_n^{(3 − n)+} in soil samples. In order to isolate the most environmentally available fraction, 5 g of the sample was collected and extracted in deionised water (water soluble fraction) for 1 h using a magnetic stirrer. The determinations in a hyphenated technique system were performed for a number of prepared water extracts. Concentration determinations of particular aluminium forms were performed based on model studies and real samples. The separation of Al species with nominal charge of + 1, + 2, and + 3 required a run time of less than 4 min during a single analysis. Based on the analysis of water extracts of soil, it was obtained that aluminium forms elute in the following order: 1PA (first signal) — AlF₂⁺ and/or AlF₄⁻; 2PA (second signal) — AlF²⁺ and/or AlF₃⁰; 3PA (third signal) — Al³⁺. In order to confirm the occurrence of these forms a simulation using the Mineql program was conducted. The details of speciation analysis of aluminium fluoride forms by means of an HPIC-FAAS instrument equipped are presented. Interpretation of the speciation analysis of the water soluble fraction of soil samples is proposed, based on the separation during chromatographic run and calculated data by Mineql.     

Preconcentration and Determination of Copper(II) by Novel Solid-Phase Extraction and High-Resolution Continuum Source Flame Atomic Absorption Spectrometry

Amberlite XAD-4 modified with N-para-anisidine-3,5-di-tert-butylsalicylaldimine was investigated as a new chealting sorbent for the selective separation and preconcentration of Cu(II). The metal ion was retained by chemical sorption on the modified resin, eluted by hydrochloric acid, and determined by high-resolution continuum source flame atomic absorption spectrometry. The prepared resin was characterized for the solid-phase extraction of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ in a column. The influence of the pH, the mass of solid phase, eluent, flow rate, and sample volume was optimized. Using the optimum conditions, only Cu(II) showed quantitative sorption at the 95% confidence level, and the recoveries of the other metal ions were below 80%. A preconcentration factor 125 was obtained for Cu(II) with a limit of detection of 0.56?µg?L^?1. The method was used for the determination of Cu(II) in tap water, river water, tomato leaves, and fish. The relative standard deviation and the relative error were lower than 7%.     

Sensitive and selective colorimetric detection of cadmium(II) using gold nanoparticles modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole

We have developed a simple, sensitive and selective colorimetric method for the detection of cadmium(II) (Cd²⁺) using gold nanoparticles modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole. Organic solvents or additives are not required. It is found that Cd²⁺ induces the aggregation of the modified Au-NPs via chelation, leading to a color change from red to blue. This change can be seen with bare eyes, and monitored by UV–vis spectroscopy, transmission electron microscopy and dynamic light scattering. The detection limit is 30 nM (at a signal-to-noise ratio of 3). The new approach was successfully applied to the detection of Cd²⁺ in spiked samples of tap water and lake water, and the results agree well with those obtained by flame atomic absorption spectroscopy.

Electrochemical Quantification of Lead Adsorption on TiO2 Nanoparticles

This work describes a rapid easy-to-use electrochemical method for quantifying lead (Pb²⁺) adsorption on metal oxide nanoparticles (NPs), demonstrated here for titanium dioxide (TiO₂). The method was able to quantify Pb²⁺ adsorption for concentrations as low as 0.95 μM, and up to 200 μM in NP dispersions, and to differentiate ion uptake in the presence and absence of a natural organic material, humic acid (HA). The method was selective for Pb²⁺ against Cu²⁺, As³⁺, Zn²⁺, Cd²⁺ and Cr³⁺ ions when measured in the specific potential range from −0.4 to −0.6 V and was successfully demonstrated in water and home-collected dust.     

Preconcentration and Determination of Trace Amounts of Heavy Metals in Water Samples Using Membrane Disk and Flame Atomic Absorption Spectrometry

A fast and simple method for preconcentration of Ni^2＋, Cd^2＋, Pb^2＋, Zn^2＋, Cu^2＋ and Co^2＋ from natural water samples was developed. The metal ions were complexed with sodium diethyldithiocarbamate （Na-DDTC）, then adsorbed onto octadecyl silica membrane disk, recovered and determined by FAAS. Extraction efficiency, influence of sample volume and eluent flow rates, effects of pH, amount of Na-DDTC, nature and amount of eluent for elution of metal ions from membrane disk, break through volume and limit of detection have been evaluated. The effect of foreign ions on the percent recovery of heavy metal ions has also been studied. The limit of detection of the proposed method for Ni^2＋, Cd^2＋, Pb^2＋, Zn^2＋, Cu^2＋ and Co^2＋was found to be 2.03, 0.47, 3.13, 0.44, 1.24 and 2.05 ng·mL^-1, respectively. The proposed （DDTC） method has been successfully applied to the recovery and determination of heavy metal ions in different water samples.     

Raman spectra and O NMR study effects of CaCl2 and MgCl2 on water structure

With various concentrations of CaCl₂ and MgCl₂ aqueous solution below 1.0 mol/l, Raman spectra of water in the OH stretch region of 2500-4000 cm⁻¹ and ¹⁷O NMR chemical shift of water are measured and the Raman spectra are deconvoluted. Both Raman spectra and ¹⁷O NMR of water show that the effect of Ca²⁺ on water structure is stronger than that of Mg²⁺. CaCl₂ and MgCl₂ destroy four hydrogen bonded water structure, but promote median water cluster size.     

Selective detection of phosphaphenanthrenecontaining luminophors with aggregation-induced emission enhancement to transition metal ions

Transition metal ions (Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Hg²⁺, Ag⁺, Fe³⁺) in water are used to quench emission of 2-(6-oxido-6H-dibenz 〈c,e〉 〈1,2〉 oxaphosphorin-6-yl)-1,4-phenylene-bis(p-pentyloxylbenzoate)s (MD5) with aggregation-induced emission enhancement (AIEE) in water-acetonitrile (AN) mixture (80:20 by volume). Among all metal ions, Fe³⁺ exhibits the highest quenching efficiency on AIEE of MD5 even when the concentration of Fe³⁺ is lower than 1×10⁻⁶ mol/L. The quenching efficiency of Hg²⁺ is lower than that of Fe³⁺ at the same concentration, though MD5 is used to detect Hg²⁺ efficiently, too. To other metal ions, low quenching efficiency has few relations with a wider concentration range. The UV absorbance spectra show only red shift of absorbance wavelength in the presence of Hg²⁺ and Fe³⁺, which indicates a salt-induced Jaggregation. SEM photos reveal larger aggregation and morphological change of nanoparticles of MD5 in water containing Hg²⁺ and Fe³⁺, which reduce the surface area of MD5 emission for further aggregation. The selective quenching effect of transition metal ions to emission of MD5 has a potential application in chemical sensors of some metal ions.     

Rapid detection of trace Cu2+ using an l‐cysteine based interdigitated electrode sensor integrated with AC electrokinetic enrichment

Copper is an indispensable trace element for human health. Too much or too little intake of copper ion (Cu²⁺) can lead to its own adverse health conditions. Therefore, detection of Cu²⁺ is always of vital importance. In this work, a simple sensor was developed for rapid detection of trace Cu²⁺ in water, in which L‐cysteine (Cys) as a molecular probe was self‐assembled on a gold interdigital electrode to form a monolayer for specific capture of Cu²⁺. The interfacial capacitance of interdigital electrode was detected to indicate the target adsorption level under an AC signal working as the excitation to induce directed movement and enrichment of Cu²⁺ to the electrode surface. This sensor reached a limit of detection of 4.14 fM and a satisfactory selectivity against eight other ions (Zn²⁺, Hg²⁺, Pb²⁺, Cd²⁺, Mg²⁺, Fe²⁺, As³⁺, and As⁵⁺). Testing of spiked tap water was also performed, demonstrating the sensor's usability. This sensor as well as the detection method shows a great application potential in fields such as environmental monitoring and medical diagnosis.     

Determination of Cu2+ in Drinking Water Based on Electrochemiluminescence of Ru(phen)32+ and Cyclam

A convenient and simple electrochemiluminescence (ECL) method was employed to detect trace amounts of Cu²⁺ in drinking water. This method is based on the inhibitory effect of Cu²⁺ on the ECL of Ru(phen)₃²⁺ and 1,4,8,11‐tetraazacyclotetradecane (cyclam) system. ECL intensity of Ru(phen)₃²⁺ was considerably enhanced by the addition of cyclam because of the ECL reaction between them. The ECL intensity of Ru(phen)₃²⁺/cyclam system rapidy decreased with the addition Cu²⁺ because of the formation of chelate complex [Cu(cyclam)]²⁺. Good linear response (R ²=0.9948) was obtained at Cu²⁺ concentration of 1.0×10⁻⁹−1.0×10⁻⁵ mol ⋅ L⁻¹ at glassy carbon electrode in 0.1 mol ⋅ L⁻¹ phosphate buffer (pH 9.0). Observed detection limit of 4.8×10⁻¹⁰ mol ⋅ L⁻¹ satisfied the maximum contaminant level goal (MCLG) for Cu²⁺ set by the US Environmental Protection Agency (US EPA). Applicability of the proposed method was verified by the good reproducibility and stability of the method when applied to determine Cu²⁺ in tap water and simulated wastewater. Thus, a novel ECL detection method was developed for Cu²⁺ detection.     

Dual recognition strategy for ultra-sensitive fluorescent detection of Hg2+ at femto-molar level based on aptamer functionalized sulfur quantum dots

In the present study, a dual recognition strategy for ultrasensitive detection of Hg²⁺ was successfully developed for the first time based on aptamer functionalized sulfur quantum dots (Apt-SQDs). The developed Apt-SQDs not only retained the good fluorescence properties of quantum dots but also overcame the problem of poor selectivity of SQDs for heavy metal ions. This system used the dual recognition strategy, including the combination of S_x^2? and Hg²⁺ and T-Hg²⁺-T structures to excellently identify and capture Hg²⁺, and an ultrahigh sensitivity fluorescent aptasensor was fabricated. The fluorescent aptasensor had a good response to Hg²⁺ at concentrations ranging of 10^?15 to 10^?7 M with an ultralow limit of detection of 0.3 fM, and the response to other metal ions was far less than that to Hg²⁺. It was successfully applied to detect Hg²⁺ in nearby environmental water samples (tap water, lake water and river water) with a good recovery rate. Moreover, portable test papers that would be useful for Hg²⁺ monitoring in environmental water were designed. The dual recognition strategy not only achieves ultrasensitive fluorescent detection of Hg²⁺ but also provides a new insight into the further expansion of the application of SQDs.     

Differential determination of arsenic(III) and arsenic(V), and antimony(III) and antimony(V) by hydride generation-atomic absorption spectrophotometry,and its application to the determination of these species in sea water

A method is described for the differential determination of As(III) and As(V). and Sb(III) and Sb(V) by hydride generation-atomic absorption spectrophotometry with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of As(III) and Sb(III), most of the elements, other than Ag⁺, Cu²⁺, Sn²⁺, Se⁴⁺ and Te⁴⁺, do not interfere in an at least 30,000 fold excess with respect to As(III) or Sb(III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5–2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 μgl^?1, 0.27 μgl^?1 and 0.22 μgl^?1 for As(total), As(III) and Sb(total), respectively, but Sb(III) was not detected in the present sample. The effect of acidification on storage was also examined.     

Factorial design for optimization of experimental variables in preconcentration of copper by a chromotropic acid loaded Q-Sepharose adsorbent

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5 ml portion of a 0.02 mol l⁻¹ HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18 mol l⁻¹ sodium nitrate in the matrix. A 5 ml portion of a 0.02 mol l⁻¹ CTA was sufficient for loading of a 0.5 ml column prior to preconcentration of copper from a 150 ml sample solution. Matrix ions of Ca²⁺, Mg²⁺, Na⁺ and K⁺ and potentially interfering ions of Pb²⁺, Ni²⁺, Cd²⁺, Co²⁺, Zn²⁺ and Mn²⁺ with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0 μg l⁻¹ was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.