Trace determination of thiosulphate and thioglycolic acid using novel inhibitory kinetic spectrophotometric method

Sulphur containing compounds such as sodium thiosulphate (STS) and thioglycolic acid (TGA) inhibit the rate of cyanide substitution by nitroso-R-salt (NRS) in hexacyanoruthenate(II) catalysed by Hg(II) ions due to their strong binding tendencies with Hg(II) catalyst. This inhibitory effect of sodium thiosulphate and thioglycolic acid is used as the basis for their determination at micro levels. The reaction was followed spectrophotometrically at 525 nm (λ_max of [Ru(CN)₅NRS]³⁻ complex) under optimised reaction conditions at 8.75 × 10^− 5 M [Ru(CN)₆⁴⁻], 3.50 × 10^− 4 M [NRS], pH 7.00 ± 0.02, ionic strength (µ) 0.1 M (KCl) and temp 45.0 ±0.1 °C. The modified mechanistic scheme is proposed to understand the inhibition caused by sulphur containing compounds (STS and TGA) on Hg(II) catalysed substitution of cyanide by NRS in [Ru(CN)₆]⁴⁻. The range of analytical concentration of inhibitor depends upon two factors; the amount of Hg(II) catalyst present in the indicator reaction and the stability of the Hg(II)-inhibitor complex under consideration. Under optimum conditions STS and TGA have been determined in the range of 0.98-7.0 × 10^− 6 M and 0.30-7.0 × 10^− 6 M. The detection limits for STS and TGA were found to be 3.0 × 10^− 7 M and 1.0 × 10^− 7 M respectively.     

环境样品中痕量甲醛的催化荧光动力学分析

基于在硫酸介质中, 痕量甲醛能促进溴酸钾氧化吡咯红并使其荧光强度减弱的反应, 建立了动力学荧光法分析测定痕量甲醛的新方法. 研究了温度、时间, 各种试剂浓度等条件对测定的影响. 在最佳实验条件下, 方法的线性范围是8～200 ng/mL, 检出限为6.1 ng/mL. 该方法用于环境水样、室内空气、食品中痕量甲醛的测定, 并与乙酰丙酮分光光度法进行了对照, 结果无显著性差异.     

Selective separation of silver(I) and mercury(II) ions in natural water samples using alumina modified thiouracil derivatives as new solid phase extractors

A simple and reliable solid-phase extraction (SPE) method has been developed to synthesise two new sorbents: 6-propyl-2-thiouracil and 5,6-diamino-2-thiouracil physically loaded onto alumina surface, phases I and II, respectively. The synthesis of these new phases has been confirmed by IR-spectroscopy. The surface concentrations of the organic moieties were determined to be 0.182 and 0.562 mmol g^?1 for phases I and II, respectively. The evaluation of the selectivity and metal uptake properties incorporated in these two alumina phases were also studied and discussed for 10 different metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Pb(II) and Ag(I) under different controlling factors. The data obtained clearly indicated that the new SP-extractors have the highest affinity for retention of Hg(II) ions. Selective separation of Hg(II) from Ag(I) as one of the most interfering ion, in addition to the other eight coexisting metal ions under investigation, was achieved successfully using the new sorbents at pH = 9.0 under static conditions. Therefore, Hg(II) exhibits major retention percentage (100.0%) using phase I or II. However, Ag(I) exhibits minor retention percentage equal to 1.33% using phase I and 0.67% using phase II. On the other hand, the retention percentage of the other eight metal ions ranged (0.0–3.08%) using phase I and (0.0–1.54%) using phase II at the same pH. The new phases were applied for separation and determination of trace amounts of Hg(II) and Ag(I) spiked natural water samples using cold vapour atomic absorption spectroscopy and atomic absorption spectroscopy with no matrix interference. The high recovery values of Hg(II) and Ag(I) obtained using phases I and II were ranged 98.9 ± 0.1–99.2 ± 0.05% along with a good precision (RSD% 0.01–0.502%, N = 3) demonstrate the accuracy and validity of the new sorbents for separation and determination of Hg(II) and Ag(I).     

Rapid and sensitive spectrofluorimetric determination of trace amounts of Hg(II) with o-vanillin-8-aminoquinoline

The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ (λ_ex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The method was successfully applied to the determination of Hg(II) in sludge. The text was submitted by the authors in English.     

Study on Separation/Enrichment and Determination of Mercury(II) using Microcrystalline Thymolphthalein Loaded with Ternary Association Complex

The paper presents a novel method for the separation/enrichment of Hg²⁺ using microcrystalline thymolphthalein loaded with ternary association complex prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of KI and dodecyl trimethyl ammonium bromide (DTAB) and thymolphthalein, various salts and acidity etc. on the enrichment yield of Hg²⁺ have been investigated to select the experimental conditions. The results showed that in the presence of 1.0 g NaCl, when the dosage of 0.1 M KI solution was 1.50 mL and 5.0 × 10⁻³ M dodecyl trimethyl ammonium bromide (DTAB) solution was 1.50 mL respectively, the water‐insoluble ternary association complex of (DTAB)₂(HgI₄) which produced by Hg²⁺ and I⁻, DTAB cation (DTAB⁺) was quantificationally absorbed on the surface of microcrystalline thymolphthalein Therefore, Hg²⁺ was separated completely from Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺, Fe³⁺, Al³⁺, Pb²⁺, Bi³⁺ and Cr³⁺ etc. by contolling acidity. The possible enrichment mechanism of Hg²⁺ was deduced. The proposed method has been successfully applied to the determination of Hg²⁺ in the sample of industrial waster water, and the results agreed well with the dithizone method. The recoveries were 94.5%∼106.5%, and the RSD was 2.0%∼2.8%.     

Development of a multi-component chemically reactive detection conjugate for the determination of Hg(II) in water samples

Mercury ions (Hg(II)) are considered highly toxic and hazardous element even at low levels. The contamination of Hg(II) is a global problem. To develop selective and sensitive technique for the detection of Hg(II) has attracted considerable attention. In this study, a multi-component chemically reactive detection conjugate for determination of Hg(II) has been synthesized and a competitive format assay was proposed. In the technique, the chemically reactive capture conjugate was coated on the plate. The reactive detection conjugate was then captured by the capture conjugate. TMB solution was added and catalyzed by HRP molecules immobilized on AuNPs. Finally, the developed enzymatic signal was measured at 450 nm. The linear range of the assay was 0.35–350 ppb with a detection limit of 0.1 ppb. The average recoveries of Hg(II) from mineral water, tap water and lake water were 100.03%, 103.13% and 102.03%, respectively. All coefficients of variation (CVs) were less than 10%. The results are closely correlated with those from inductively coupled plasma mass spectrometry (ICP-MS), which indicated that the developed technique is a reliable method for and sensitive detection of Hg(II) in water samples.     

Equilibrium and spectroscopic studies of ternary cadmium(II) and mercury(II) complexes with CMP and triamines

Formation of ternary Cd(II) and Hg(II) complexes with cytidine 5′-monophosphate (CMP) and triamines has been studied. Complexes M(CMP)(H _x PA) and M(CMP)(PA) (M?=?Cd, Hg; PA?=?polyamine) were detected and overall stability constants and equilibrium constants for their formation determined. The mode of coordination in the complexes has been proposed on the basis of the equilibrium and ¹³C, ³¹P NMR and IR studies. In the Hg(II) systems, metalation involves the donor endocyclic N(3) atom, the CMP phosphate group and nitrogen donor atoms of PA. Relative to the Hg/CMP binary systems, the presence of a polyamine in ternary systems does not change the metal–nucleotide mode of coordination. In ternary systems including Hg(II) ions, the occurrence of noncovalent interactions has not been detected. Cd(II) ions form molecular complexes as well as protonated species. Introduction of a polyamine to the Cd/CMP system changes the coordination mode of the nucleotide. The phosphate group of CMP is inactive in binary complexes (metalation by the N(3) atom) but is involved in coordination in heteroligand species. In contrast to other polyamines studied, in the system including 1,7-diamino-4-azaheptane (3,3-tri), the phosphate group of CMP in Cd(CMP)(H3,3-tri) does not participate in metalation but is engaged in intramolecular noncovalent interactions that stabilize the complex.     

Determination of mercury in ambient water samples by anodic stripping voltammetry on screen-printed gold electrodes

The applicability of commercial screen-printed gold electrodes (SPGEs) for the determination of Hg(II) in ambient water samples by square wave anodic stripping voltammetry has been demonstrated. Electrode conditioning procedures, chemical and instrumental variables have been optimized to develop a reliable method capable of measuring dissolved mercury in the low ng mL⁻¹ range (detection limit 1.1 ng mL⁻¹), useful for pollution monitoring or screening purposes. The proposed method was tested with the NIST 1641d Mercury in Water Standard Reference Material (recoveries 90.0–110%) and the NCS ZC 76303 Mercury in Water Certified Reference Material (recoveries 82.5–90.6%). Waste water samples from industrial origin and fortified rain water samples were assayed for mercury by the proposed method and by a reference ICP-MS method, with good agreement. Screen printing technology thus opens a useful way for the construction of reliable electrochemical sensors for decentralized or even field Hg(II) testing.     

Kinetic determination of cysteine and thiosulphate by inhibition of Hg(II) catalyzed ligand substitution reaction

The sulphur containing inhibitors (I), cysteine (Cys) and sodium thiosulphate (THS), have been found to inhibit Hg(II) catalyzed exchange of cyanide in hexacyanoferrate(II) by nitroso-R-salt (NRS). The inhibitory effect of both the ligands are attributed to their binding tendencies with Hg(II) leading to the formation of catalyst-inhibitor (C-I) complex. The reactions have been followed spectrophotometrically in aqueous medium at 720 nm by noting the increase in absorbance of the green colour product, [Fe(CN)₅NRS]³⁻ at pH 6.50 ± 0.02, temp 25.0 ± 0.1 °C and ionic strength (μ) 0.1 M (KNO₃). A most plausible mechanistic scheme involving the role of analytes (inhibitors) has been proposed. The values of equilibrium constants for complex formation between catalyst-inhibitor (K_CI), catalyst-substrate (K_S) and Mechaelis-Menton constant (K_m) have been computed from the kinetic data. The linear calibration curves have been established between absorbance and inhibitor concentrations under specified conditions. Cys and THS have been determined in the range 1-5 × 10^− 7 M and 4.9-16.9 × 10^− 7 M respectively. The detection limits have been computed to be 1 × 10^− 7 M and 4.9 × 10^− 7 M for Cys and THS, respectively.     

茜素红S催化动力学光度法测定痕量铜(Ⅱ)及机理探究

研究了在pH 5.0的柠檬酸-NaOH缓冲介质中,以邻菲口罗啉(phen)作活化剂,痕量Cu(Ⅱ)对H2O2氧化茜素红S(ARS)的褪色反应存在明显的催化作用,由此建立了测定痕量Cu(Ⅱ)的催化动力学光度法。应用了正交试验法确定最佳条件,测定了有关动力学参数。该方法的检出限为6.3×10-9g/mL,线性范围为0~0.8μg/mL,应用于茶叶、自来水等水样中痕量铜的测定。同时,对反应机理进行了探究。     

Selective solid phase extraction of trace cadmium(II) and lead(II) from biological and natural water samples by ofloxacin-modified-silica gel

Ofloxacin was successfully used as a chemical modifier to improve the reactivity of silica gel in terms of selective binding and extraction of heavy metal ions. This new functionalised silica gel (SG-ofloxacin) was as an effective sorbent for the solid-phase extraction (SPE) of Cd(II) and Pb(II) in biological and natural water samples and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of Cd(II) and Pb(II) were optimised with respect to different experimental parameters using the batch and column procedures. The time for 70% sorption for Cd(II) and Pb(II) was less than 2 min. Complete elution of the adsorbed metal ions from the SG-ofloxacin was carried out using 2.0 mL of 0.5 mol L^?1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.17 and 48.69 mg g^?1 for Cd(II) and Pb(II), respectively. The detection limits of the method were found to be 0.29 and 0.13 ng mL^?1 for Cd(II) and Pb(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower than 3.0% (n = 5). The method was applied to the recovery of Cd(II) and Pb(II) from the certified reference material (GBW 08301, river sediment) and to the simultaneous determination of these cations in different water and biological samples with satisfactory results and yielding 100-folds enrichment factor.     

Kinetic method for determination of nanogram amounts of copper(II) by its catalytic effect on hexacynoferrate(III)-citric acid indicator reaction

This paper describes a highly sensitive, selective catalytic-kinetic-spectrophotometric method for the determination of copper(II) concentration as low as 6 ng ml⁻¹. The method is based on the catalytic effect of copper(II) on the oxidation of citric acid by alkaline hexacyanoferrate(III). The reaction was followed by measuring the decrease in absorbance of hexacyanoferrate(III) at 420 nm (λ_max of [Fe(CN)₆]³⁻, ∈ = 1020 dm³ mol⁻¹ cm⁻¹). The dependence of rate of the indicator reaction on the reaction variables has been studied and discussed to propose a suitable mechanism to get a relation between the reaction rate and [Cu²⁺]. A fixed time procedure has been used to obtain a linear calibration curve between the initial rate and lower [Cu²⁺] or log[Cu²⁺] in the range 1 × 10⁻⁷ to 4 × 10⁻⁴ mol l⁻¹ (6.35-25,400 ng ml⁻¹). The detection limit has been calculated to be 4 ng ml⁻¹. The maximum average error is 3.5%. The effect of the presence of various cations, commonly associated with copper(II) and some anions has also been investigated and discussed. The proposed method is sensitive, accurate, rapid and inexpensive compared to other techniques available for determination of copper(II) in such a large range of concentration. The new method has been successfully applied for the determination of copper(II) in various samples.     

A novel dimeric zinc(II) complex with a tripodal peptide ligand: a structure stabilized by ligand sharing

The crystal structure of a novel dimeric zinc(II) complex, [ZnL(H₂O)]₂(ClO₄)₂·4H₂O (L?=?N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide), has been determined by X-ray diffraction. In this complex each planar N_py–N_amido–N_py moiety of the ligand coordinates to one zinc ion and the pendant pyridine of one [ZnL] unit completes the coordination sphere of a [ZnL] neighbor. Units of the complex are connected in a two-dimensional network by intermolecular hydrogen bonds. The thermodynamic properties of the ligand with bivalent metal ions Co(II), Ni(II), Cu(II) and Zn(II) were studied by potentiometric titration and the order of the stability constants is in agreement with the Irving–Williams series. The dimeric complex is stabilized through ligand sharing, as confirmed by the crystal structure and thermodynamic properties.     

Determination of trace osmium by supramolecular catalytic kinetic spectrofluorimetry of beta-CD-osmium-KBrO(3)-o-vanillin furfuralhydrazone

A supramolecular catalytic kinetic spectrofluorimetric method was developed for the determination of osmium(IV) and the possible mechanism of catalytic reaction was discussed. The method is based on the fluorescence enhancing reaction of o-vanillin furfuralhydrazone (OVFH) with potassium bromate, which was catalysed by osmium(IV) in water medium. Beta-cyclodextrin (beta-CD) obviously sensibilized the determination at pH 6.10 and 55 °C. Under optimum conditions, beta-CD-osmium(IV)-KBrO₃-OVFH supramolecular kinetic catalytic reaction system had excitation and emission maxima at 337 and 490 nm, respectively. The linear range of this method was 0-120 ng ml⁻¹ with a R.S.D. of 1.1%, and the detection limit was 0.38 ng ml⁻¹. The effect of interferences was studied. Distillation was used to separate osmium from interfering elements in the samples. The proposed method was applied successfully to determine osmium(IV) in synthetic mixture and mineral samples, the results were well consistent with the reference standard values.     

Simultaneous determination of Fe(II) and Fe(III) by kinetic spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) for simultaneous determination of Fe(II) and Fe(III) is described. The method is based on the difference in the rate of complex formation of iron in two different oxidation states with Gallic acid (GA) at pH 5. Fe(II) and Fe(III) can be determined in the range of 0.02–4.50 μg ml⁻¹ and 0.05–5.00 μg ml⁻¹, respectively, with satisfactory accuracy and precision in the presence of other metal ions, which rapidly form complexes with GA under working conditions. The proposed method was successfully applied for simultaneous determination of Fe(II) and Fe(III) in several environmental and synthetic samples with different concentration ratios of Fe(II) and Fe(III).     

Ultra trace level square wave anodic stripping voltammetric sensing of mercury(II) ions in environmental samples using a Schiff base-modified carbon paste electrode

ABSTRACT

In this approach, a new carbon paste electrode modified with N,N′-bis(5-bromo-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine Schiff base ligand (L) was synthesised for selective and effective determination of Hg²⁺ ions in aqueous environmental samples using cyclic and square wave anodic stripping voltammetric methods. First, the selective detection of mercury ion was confirmed by evaluating the stability constants of metal complexes formed between the Schiff base ligand (L) and some desired cations by conductometric measurements. Afterwards, by preparing an effective carbon paste electrode modified with L, the experimental and instrumental parameters affecting the performance of modified electrode were investigated. Square wave anodic stripping voltammograms were obtained after applying an accumulation potential ?0.5 V and accumulation time 150 s in Britton–Robinson buffer solution at pH 2.0. The optimal square wave parameters found are pulse amplitude 75 mV, frequency 50 Hz and step potential 6 mV. The procedure exhibited linear range from 0.4 to 120 μg L^?1 Hg²⁺ with a limit of detection of 0.042 μg L^?1. The proposed electrode was proved to be highly selective in the presence of various cations and anions and was successfully used for determination of mercury in tobacco and several water samples.     

Equilibrium and Kinetic Aspects of Hg(II) Extraction from Natural Waters with Diphenylthiocarbazone

A diphenylthiocarbazone (dithizone) based liquid-liquid extraction method of general utility is proposed for small-scale Hg(II) extraction from natural waters. The quantitative aspects related to the extraction are studied in terms of distribution of mercury dithizonate in carbon tetrachloride-water system at 293 K (20±1°C). Various distribution constants related to the reagent and the complex formed are evaluated. The equilibrium and kinetic studies of extraction and complex formation are analytically based on atomic absorption and colorimetric methods. Local natural waters were subjected to the proposed method for Hg(II) removal. The method is found to be capable of removing above 98% mercury in a single-step extraction under the conditions evaluated in terms of matrix pH, equilibration time and amount of reagent.     

Simultaneous kinetic spectrophotometric determination of Cu(II), Co(II) and Ni(II) using partial least squares (PLS) regression

A partial least squares (PLS-1) calibration model based on kinetic—spectrophotometric measurement, for the simultaneous determination of Cu(II), Ni(II) and Co(II) ions is described. The method was based on the difference in the rate of the reaction between Co(II), Ni(II) and Cu(II) ions with 1-(2-pyridylazo)2-naphthol in a pH 5.8 buffer solution and in micellar media at 25°C. The absorption kinetic profiles of the solutions were monitored by measuring the absorbance at 570 nm at 2 s intervals during the time range of 0–10 min after initiation of the reaction. The experimental calibration matrix for the partial least squares (PLS-1) model was designed with 30 samples. The cross-validation method was used for selecting the number of factors. The results showed that simultaneous determination could be performed in the range 0.1-2 μg mL⁻¹ for each cation. The proposed method was successfully applied to the simultaneous determination of Cu(II), Ni(II) and Co(II) ions in water and in synthetic alloy samples.      

Determination of potassium ions in biodiesel using a nickel(II) hexacyanoferrate-modified electrode

In this work, nickel hexacyanoferrate-modified electrode was developed to determine potassium ions in biodiesel by potentiometry. The modified electrodes exhibit a linear response to potassium ions in the concentration range of 4.0 × 10⁻⁵ to 1.0 × 10⁻² mol L⁻¹, with a detection limit of 1.9 × 10⁻⁵ mol L⁻¹, and a near-Nernstian slope (53–55 mV per decade) at 25 °C. The method developed in this work was compared with flame photometry and the potassium concentration found in biodiesel showed that the modified electrode method gives results similar to those obtained by flame photometry.     

Fluorescence detection of mercury(II) and lead(II) ions using aptamer/reporter conjugates

We have developed a fluorescence technique for the detection of Hg²⁺ and Pb²⁺ ions using polythymine (T₃₃)/benzothiazolium-4-quinolinium dimer derivative (TOTO-3) and polyguanine (G₃₃)/terbium ions (Tb³⁺) conjugates, respectively. Hg²⁺ ions induce T₃₃ to form folded structures, leading to increased fluorescence of the T₃₃/TOTO-3 conjugates. Because Pb²⁺ ions compete with Tb³⁺ ions to form complexes with G₃₃, the extent of formation of the G₃₃-Tb³⁺ complexes decreases upon increasing the Pb²⁺ concentration, leading to decreased fluorescence at 545 nm when excited at 290 nm. To minimize interference from Hg²⁺ ions during the detection of Pb²⁺ ions, we conducted two-step fluorescence measurements; prior to addition of the G₃₃/Tb³⁺ probe, we recorded the fluorescence of a mixture of the T₃₃/TOTO-3 conjugates and Hg²⁺ ions. The fluorescence signal obtained was linear with respect to the Hg²⁺ concentration over the range 25.0-500 nM (R² = 0.99); for Pb²⁺ ions, it was linear over the range 3.0-50 nM (R² = 0.98). The limits of detection (at a signal-to-noise ratio of 3) for Hg²⁺ and Pb²⁺ ions were 10.0 and 1.0 nM, respectively. Relative to other techniques for the detection of Hg²⁺ and Pb²⁺ ions in soil and water samples, our present approach is simpler, faster, and more cost-effective.