Thiocyanate-selective electrode based on N-salicylidene-benzylamineato copper(II) complex

Highly selective poly(vinyl chloride) (PVC) membrane electrode based on N-salicylidene-benzylamineato copper(II) complexes [Cu(SBA)₂] as new carriers towards thiocyanate-selective electrode was reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The resulting electrode exhibits anti-Hofmeister selectivity sequence: SCN⁻ > ClO₄⁻ > Sal⁻ > I⁻ > Br⁻ > NO₃⁻ > NO₂⁻ > SO₃²⁻ > H₂PO₄⁻ > Cl⁻ > SO₄²⁻, and a near-Nernstian potential linear range for thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ M with a detection limit of 7.0 10⁻⁷ M and a slope of , over a wide pH range of 3.0–9.0 in phosphate buffer solution at 20°C. The proposed electrode has a fast response time of about 5–10 s and can be used for at least 3 months without any considerable divergence in potential. The electrode was successfully applied to the determination of thiocyanate in waste water and human urine and saliva samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 3, pp. 293–299. The text was submitted by the authors in English.     

Highly Selective Thiocyanate Electrode Based on Bis‐bebzion Schiff Base Binuclear Copper(II) Complex as Neutral Carrier

Abstract

A highly selective polyvinyl chloride (PVC) membrane electrode, based on N,N′‐(aminoethyl)ethylenediamide bis(2‐benzoideneimine) binuclear copper(II) complex [Cu(II)‐AEBB] as neutral carrier, was prepared for thiocyanate (SCN^?) determination, which displays an anti‐Hofmeister selectivity sequence for a series of anions in the following order: SCN^?>ClO₄ ^?>Sal^? > I^?>NO₃ ^?>Br^?> Cl^?>NO₂ ^?>SO₃ ^2?>F^?>H₂PO₄ ^?>SO₄ ^2?. The electrode exhibited near‐Nernst response for SCN^? with a slope of –59.0 mV/decade over a wide concentration range (8.5×10^?7～6.8×10^?1 mol/L) with a detection limit of –5.0×10^?7 mol/L in pH 5.0 phosphate buffer solution at 25°C. Alternating current (AC) impedance and equivalent circuits were used to investigate the thiocyanate response mechanism of the membrane doped with [Cu(II)‐AEBB].     

The photogalvanic effect of Fe(II)-β-diketonate/thionine systems in aqueous acetonitrile

Summary The photogalvanic effect of ferrousbis-(acetylacetonate) (Fe(II)(acac)₂) and ferrousbis-(trifluoroacetylacetonate) (Fe(II)(tfac)₂) complexes in aqueous acetonitrile thionine dye solutions has been studied in a photogalvanic cell of 70 cm³ capacity with identical platinum electrodes (area: 0.25 cm²) using visible light (80 mW/cm²) at 25°C. The theoretical Sunlight Engineering Efficiency (SEE) was determined for both complexes and it was found that the best SEE was obtained when Fe(II)(tfac)₂ was used at a concentration of 1.5×10^–4 mol/dm³ with a thionine concentration of 1×10^–4 mol/dm³ atpH=4 in 40% aqueous acetonitrile. Effects of incident light intensity and temperature on the photogalvanic performance and the action spectrum of the present system were also investigated. A mechanism of the photoredox reaction between the Fe(II)-complex and the dye molecule is proposed.

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Der photogalvanische Effekt von Fe(II)--Diketonat/Thionin-Systemen in wäßrigem Acetonitril

Zusammenfassung Der photogalvanische Effekt von Eisen(II)-bis-(acetonylacetonat) (Fe(II)(acac)₂) und Eisen(II)-bis-(trifluoracetylacetonat) (Fe(II)(tfac)₂ in wäßriger acetonitrilischer Thioninlösung wurde in einer photogalvanischen Zelle (70 cm³) mit identischen Platinelektroden (Fläche: 0.25 cm²) mit sichtbarem Licht (80 mW/cm²) bei 25°C untersucht. Für beide Komplexe wurde die theoretische Sunlight Engineering Efficiency (SEE) bestimmt; der beste SEE-Wert wurde für Fe(II)(tfac)₂ bei einer Konzentration von 1.5×10^–4 mol/dm³ beipH=4 in 40%igem Acetonitril gefunden (Thioninkonzentration: 1.0×10^–4 mol/dm³). Effekte, die durch Änderung der Lichtintensität und der Temperatur hervorgerufen werden, werden diskutiert. Ein Mechanismus für die Photoredoxreaktion zwischen dem Fe(II)-Komplex und dem Farbstoffmolekül wird vorgeschlagen.

     

新型双核铜金属配合物为中性载体的硫氰酸根离子高选择性电极的研究

研制了基于N,N'-亚乙基(μ-5,5-亚甲基-二水杨醛根)(乙酰丙酮根)合二铜(II) [Cu₂(II)-MDSBAE]金属配合物为中性载体的阴离子选择性电极. 试验表明, 以Cu₂(II)-MDSBAE金属配合物为中性载体的电极对SCN^－具有良好的电位响应特性, 且呈现反Hofmeister行为,其选择性序列为: SCN^－＞Sal^－＞I^－＞ClO₄^－＞NO₃^－＞Br^－＞NO₂^－＞Cl^－≈SO₃^2－＞SO₄^2－. 在pH 5.0的磷酸盐缓冲体系中, 电极电位呈现近能斯特响应, 线性响应范围为1.0×10^－6～1.0×10^－1 mol/L, 斜率为－53. 6 mV/dec (25 ℃), 检测下限为8.1×10^－7 mol/L. 用交流阻抗研究了电极的响应机理, 并用紫外可见光谱技术测定了电极载体与SCN^－, Sal^－, I^－, ClO₄^－和NO₃^－离子间的配位数及缔合常数. 将该电极用于实验室废水和工业废水中硫氰酸根的检测, 其结果令人满意.     

Electrical properties of poly(bis(β-phenoxyethoxy)phosphazene) and its complexes

Electrical and dielectrical properties of poly(bis(-phenoxyethoxy)phosphazene) (I) and its complexes with various content ratios of AgSO₃CF₃ to monomeric unit (0.25/1 (II) and 0.5/1 (III) in molar ratio) were investigated.Dc conductivity of respective samples at 18 °C were 6.1×10^–12, 4.4×10^–9, and 7.1×10^–8 S/m.Dc conduction was considered to be due to ion hopping. Charge mobility ranged from 3×10^–12 to 6× 10^–11 m²/Vs depending on the applied field in sample II. In sample I, a tan peak was found which can be ascribed to molecular relaxation of main chains. The peak vanished upon introducing AgSO₃ CF₃. Temperature dependence of total conductivity ( _T ) measured byac method in the temperature range between –150 °C and 50 °C showed several peaks at the temperatures corresponding to the peak temperatures of tan. Total conductivities of respective samples at 100 kHz were 4.9×10^–7 (69 °C), 1.7×10^–4 (45 °C), and 1.5×10^–4(40°C)S/m.     

Photoredox properties of Kojic acid and its derivatives complexed to Iron(III)

Summary Iron(III) complexes of the formcis-[Fe(SB(X - K)] in whichSB ^2– are open-chain tetradentateSchiff base N₂O₂-ligands ofacacen,benacen orsalen type, andX - K ^– are bidentate anions of kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) or other -pyranones undergo photoredox transformations when being irradiated in methanol into intraligand orLMCT bands. The quantum yields of the photoredox reactions depend on the peripheral constitution of the N₂O₂ ligands, the substituentsA andB of the ligandsX - K ^–, and the wavelength of irradiation _irr. The proposed mechanism involves the population of photoredox reactiveLMCT states by photophysical deactivation steps, primary photoredox formation ofX - K radicals and Fe(II), and subsequent dark redox processes giving back the anionsX - K ^– and the final products Fe(II) and formaldehyde formed in the molar ratio 2:1.

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Photoredoxeigenschaften von Fe(III)-Komplexen von Kojic Acid und ihren Derivaten

Zusammenfassung Eisen(III)-Komplexe der Formcis-[Fe(SB)(X - K)] mitSB ^2–=offenkettige tetradentateSchiff-Basen-N₂O₂-Liganden undX - K ^–=bidentate Anionen von 5-Hydroxy 2-hydroxymethyl-4H-pyran-4-on oder andere -Pyranone unterliegen bei Bestrahlung in Methanol Photoredoxumwandlungen, was durch Intraligand- oderLMCT-Banden belegt wird. Die Quantenausbeuten der Reaktionen hängen von der Konstitution der N₂O₂-Liganden, den SubstituentenA undB und dem LigandenX - K ^– sowie der Anregungswellenlänge _irr ab. Der vorgeschlagene Mechanismus beinhaltet die Population photoredoxreaktiverLMCT-Zustände durch photophysikalische Deaktivierungsschritte, die Bildung vonX - K*-Radikalen und Fe(II) und-Über Dunkelprozesse — die Rückbildung der AnionenX - K ^– sowie die Reaktion zu den Endprodukten Fe(II) und Formaldehyd im molaren Verhältnis 2:1.

     

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO₃)₄], has a Nernstian potentiometric response from 2.0×10^–8 to 2.0×10^–2 mol L^–1 with a detection limit of 8.0×10^–9 mol L^–1 and a slope of –59.0±0.5 mV/decade in 0.01 mol L^–1 phosphate buffer solution (pH 3.0, 20°C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV–Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.     

Complexes of dioxouranium(VI) with zwitter-ionic forms of Bi- and tetra-dentateSchiff bases

Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO₂H₂ LX ₂, UO₂H₂ LX ₂ and UO₂(HL)₂ X ₂ [H₂ L=N,N-propane-1,3-diylbis(salicylideneimine), H₂ L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^–, and NCS^–]. Because of marked spectral similrities with the structurally known Ca(H₂ L) (NO₃)₂, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.

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Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen

Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO₂H₂ LX ₂, UO₂H₂ LX ₂ und UO₂(HL)₂ X ₂ [H₂ L=N,N-Propan-1,3-diylbis(salicylidenimin), H₂ L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^– und NCS^–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H₂ L) (NO₃)₂ wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX ^– sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.

     

Perchlorate-selective membrane electrode based on a new complex of uranil

A potentiometric ion-selective electrode based on new compound, as a carrier, has been successfully developed for detection of perchlorate anion in aqueous solution. Within the perchlorate ion concentration range 1.0×10^–6 to 1.0 mol L^–1 the electrode had a linear response with a Nernstian slope of 60.6±1.0 mV per decade . The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot was 8.0×10^–7 mol L^–1. The proposed electrode has fairly a good discriminating ability towards ClO₄^– ion in comparison to other anions. The sensor has a response time of 10 s and can be used for at least 2 months without substantial divergence in potential. It was successfully applied to direct determination of perchlorate in urine and water.     

Highly selective thiocyanate electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) complex as neutral carrier

A novel selective thiocyanate PVC membrane electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) [Cu(II)₂–BBSTA] as neutral carrier is reported, which displays an anti-Hofmeister selectivity sequence in following order: SCN⁻ > ClO₄⁻ > I⁻ >Sal⁻ >SO₃²⁻ >NO₃⁻ > H₂PO₄⁻ > Cl⁻ >NO₂⁻ > SO₄²⁻. The electrode exhibits Nernstian potential linear range to thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ mol/l with a detection limit 7.0 × 10⁻⁷ mol/l and a slope of −57.0 mV/decade in pH 5.0 of phosphorate buffer solution at 25 °C. The response mechanism is discussed in view of the AC impedance technique and the UV spectroscopy technique. From comparison of potentiometric response characteristics between the binuclear metallic complex copper(II) [Cu(II)₂–BBSTA] and mononuclear copper(II) metallic complex [Cu(II)–BBSDA], an enhanced response towards thiocyanate from the electrode based on binuclear metallic complex copper (II) [Cu(II)₂–BBSTA] was observed. The electrode based on binuclear copper(II) compound was used to determine the thiocyanate content in waste water with satisfactory results.     

Crystal structure and spectra of the Ni(II) complex of pyridine-2,6-dithio-carbomethylamide

The crystal structure of the paramagnetic bis(pyridine-2,6-dithiocarbomethylamide) nickel(II) nitrate (NiPDTA) is described: C₁₈H₂₂N₆S₄·(NO₃)₂·(H₂O)_1,5, monoclinic, C2/c,Z=4,a=14.705 (3) Å,b=23.254 (8) Å,c=8.383 (3) A, =98.18 (2)°,d _x=1.55 gcm^–3,d _m=1.53 gcm^–3. The structure was solved withPatterson and differenceFourier techniques and refined to a residual ofR=0.053. The nickel is surrounded by a square bipyramidal coordination of four thioamide sulfur atoms and two pyridine nitrogen atoms. Vibrational and electronic band positions for this compound are discussed.

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Kristallstruktur und Spektren des Pyridin-2,6-dithiocarbomethylamid Nickel(II)-Komplexes

Zusammenfassung Die Kristallstruktur des paramagnetischen bis(Pyridin-2,6-dithiocarbomethylamid) Nickel(II)-nitrats (NiPDTA) wurde bestimmt. C₁₈H₂₂N₆S₄Ni·(NO₃)₂·(H₂O)_1,5, monoklin, C2/c,Z=4,a=14,705 (3) Å,b=23,254 (8) Å,c=8,383 (3) A, =98,18 (2)°,d _x=1,55gcm^–3,d _m=1,53gcm^–3. Das Phasenproblem wurde mittelsPatterson-und Differenz-Fourier-Synthese bestimmt und die Struktur bis zu einem kristallographischenR-Faktor vonR=0.053 verfeinert. Das Nickel-Atom ist von vier Thioamid-Schwefelatomen und zwei Pyridin-Stickstoffatomen in quadratisch-bipyramidaler Anordnung umgeben. Schwingungsspektren und Anregungsspektren des Komplexes werden diskutiert.

     

Adsorptive stripping voltammetric determination of 1-(4′-bromophenyl)-3,3-dimethyltriazene

The optimum conditions were established for the determination of the genotoxic substance 1-(4-bromophenyl)-3,3-dimethyltriazene by differential-pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 × 10^–4 to 1 × 10^–7 mol dm^–3. The sensitivity of the determination can be improved through adsorptive accumulation of the investigated substance on the surface of the hanging mercury drop electrode: differential pulse adsorptive stripping voltammetry can be used in the concentration range 1 × 10^–7 to 2 × 10^–10 mol dm^–3. The relative standard deviation (for ten determinations at 2 × 10^–10 mol dm^–3) was 7.5%.     

Fabrication of a novel Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MoO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> film modified electrode and its application as an electrochemical sensor of iodate

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10^–7 to 1×10^–4 mol L^–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10^–7 mol L^–1.     

Disposition of copper(II) inβ-cyclodextrin

Distances of glucose protons in-cyclodextrin (BCD) from copper(II) in copper(II)--cyclodextrin have been determined from¹H NMR spin-lattice relaxation time (T ₁) measurements for the first time. Very lowT _1p /T _2p values indicated the dipolar mechanism to be the most dominant one in determining the paramagnetic contribution to relaxation. The distances of copper(II) from BCD glucose protons indicated copper(II) to be present almost in the centre, inside the cavity in the same plane as H-1 and H-4. An average distance of about 5.0–5.9 Å was obtained for copper(II) from the H-2, H-3, H-1, H-4 and H-6 a and b protons in BCD.     

Spectrophotometric determination of molybdenum(V) by extraction of its 2-(2′-furyl)-3-hydroxychromone complex

A simple method is described for the rapid spectrophotometric determination of molybedenum in synthetic and industrial samples containing 0.1-5% Mo. Molybdenum is reduced with ascorbic acid at room temperature in 1 mol dm^–3 H₂SO₄ and extracted with chloroform after adding 2-(2-furyl)-3-hydroxychromone (FHC). The yellow colour of the 1 2 Mo-FHC complex is measured at 414 nm against a reagent blank. Beer's law is obeyed over the range 0-2.7 g Mo cm^–3 of solvent phase. The molar absorptivity and Sandell's sensitivity are 5.18 × 10⁴ dm³ mol^–1 cm^–1 and 0.0018 g Mo cm^–2, respectively. Relative standard deviations are 0.2% for solutions and 0.5–1.5% for solid samples. Interference from tungsten and tin is removed by adding citrate and EDTA, respectively, while niobium and tantalum are masked by fluoride. Many elements such as V, Fe, Ti, U, Mn, Cr, Co, Ni, Re, Ru, Pt, Rh, Se, Au, Bi, Zr, Th, Ce, As and Al do not interfere even in large amounts, but antimony always interferes. Among the anions and complexing agents, only thiocyanate interferes seriously.     

Thiocyanate: selective membrane electrode based on macrotricyclic binuclear Cu(II)–Schiff base complex

A highly selective PVC membrane electrode was prepared for thiocyanate (SCN^?) determination, based on macrotricyclic binuclear Cu(II)–Schiff base complex as an ionophore. The novel macrotricyclic compound (cryptand) was synthesized by condensation of 4,4′-diamino-dibenzo-18-crown-6 with bis(4-formyl phenyl)terephthalate under high-dilution condition and the structure was confirmed by FT-IR, ¹H NMR,¹³C NMR and MS studies. The Cu(II) complex of the compound was prepared and was examined for use as anion-selective electrode as a carrier which displays an anti-Hofmeister selectivity sequence in following order: SCN^? > ClO₄ ^? > NO₃ ^? > CN^? > I^? > CO₃ ^2? > NO₂ ^? > Br^? > Cl^? > SO₄ ^2? with a preference for thiocyanate ion over many common anions. The electrode has a linear dynamic range between 1.0 × 10^?7 and 1.0 × 10^?1 M, with a Nernstian slope of ?58.9 mV decade^?1 and detection limit of 3.1 × 10^?8 M. The working pH range of the sensor was found be in the range of 3.0–8.0. It exhibits a fast response time of 20 s and has a lifetime of about 2 months. Application of the electrode for determination of thiocyanate in waste water samples and in human urine samples have also been demonstrated.     

Organomineral sorbents based on clinoptilolite-containing tuffs

The anion-exchange properties of a new organomineral sorbent obtained by modification of clinoptilolite-containing tuffs by polyhexamethyleneguanidine have been studied after different periods of storage (time after synthesis) and numbers of sorption-regeneration cycles. The sorbent can be used as a cation- and an anion-exchanger simultaneously. Selectivity coefficients (exchange constants) for F^–, SO₄ ^2–, and HPO₄ ^2– ionsvs. Cl^– ions on modified clinoptilolite-containing tuffs have been determined. The modification improves the mechanical properties of clinoptilolite tuffs.For part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1554–1556, September, 1994.     

A novel salicylate-selective electrode based on a Sn(IV) complex of salicylal-imino acid Schiff base

A novel poly(vinyl chloride) membrane electrode with high selectivity toward salicylate (Sal^–), based on the use of the salicylal-imino acid Schiff base dibenyl complex of Sn(IV) [Sn(IV)-SIADBen] as ionophore is described. The influence of lipophilic charged additives on the performance of the electrode was studied. The results suggested that Sn(IV)-SIADBen according to a positively-charged carrier mechanism. The influence of several other variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The electrode based on Sn(IV)-SIADBen, with 30.44 wt% PVC, 64.55 wt% plasticizer [dioctyl phthalate (DOP)], 3.81 wt% ionophore, and 1.2 wt% anionic additive exhibited a linear response for the Sal^– ion over the concentration range 1.0×10^–1 to 2.5×10^–6 mol l^–1, and displayed an anti-Hofmeister selectivity sequence as follows: salicylate perchlorate > thiocyanate > benzoate > iodide > nitrate > chloride > nitrite acetate > citrate > sulfate. UV-Visible absorption spectra were used to examine the specific interaction of salicylate with the ionophore. The electrode was applied to clinical medical analysis, and the results obtained were consistent with those obtained by conventional methods.     

Solid-Phase Extraction and Spectrophotometric Determination of Trace Amounts of Mercury in Natural Samples

A sensitive and selective solid phase spectrophotometric method for the determination of trace amounts of inorganic mercury is described. Hg²⁺ was sorbed on a silica gel-packed column as an Hg²⁺–N,N-bis(2-mercaptophenyl)ethanediamide (H₂L) complex. The Hg²⁺ complex was eluted from the column using 7mL of acetone. Various parameters including pH, column flow rate, and ligand concentration were optimized. The complex was found to obey Beers law from 2.3 to 73.7µgmL^–1 within the optimum range when the preconcentration factor was two. The effective molar absorption coefficient at 523nm was 1.17×10³Lmol^–1cm^–1 at 523nm. The concentration limits in Beers law dropped from 0.09 to 2.95µgmL^–1 within the optimum range when the preconcentration factor was 50. The relative standard deviation at a concentration level of 5µgmL^–1 Hg²⁺ (9 repetitive determinations) was 1.6%. The detection limits are 0.34µgmL^–1 and 0.015µgmL^–1 when the preconcentration factors are 2 and 50, respectively. The method has been used for routine determination of trace levels of Hg²⁺ in natural waters. The potential application of this method for the removal of Hg²⁺ from natural samples (sea water and lake water) spiked with 100ngmL^–1 of Hg²⁺ was studied. In order to validate the proposed method, LGC 6156 (harbour sediment – extractable metals) was analysed by this method. The results proved that excellent extraction of Hg²⁺ from both natural water samples was obtained by solid phase extraction using N,N-bis(2-mercaptophenyl) ethanediamide.     

Effects of ionization on the phase behavior of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-acrylic acid) and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacrylamide-co-acrylic acid) in water

Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (T_p) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pK_a for the AA units, determined from the pH dependencies of T_p, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between T_p for PiPA-AA and T_p for PiPA homopolymer (T_p) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of T_p for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between T_p and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at T_p of the copolymer. Heating the solution above T_p leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm^–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm^–1) suggest that a partial protonation of the carboxylate groups (COO^–+H⁺COOH) takes place upon the phase transition.