Hydrogen chromate PVC matrix membrane sensor for potentiometric determination of chromium(III) and chromium(VI) ions

A novel potentiometric Cr(6+) PVC matrix membrane sensor incorporating nickel tris(1,10-bathophenanthroline) hydrogen chromate as an electroactive material and 2-nitrophenyl phenyl ether as solvent mediator is described. In a phosphate buffer solution of pH 5, the sensor displays a rapid and linear response for Cr(6-) over the concentration range 2 x 10(-2)-8 x 10(-6) M with an anionic slope of 55.5 +/- 0.2 mV decade(-1) and a detection limit of the order of 0.4 microg ml(-1). The sensor is used for sequential determination of Cr(6+) and Cr(3+) by direct monitoring of Cr(6+) followed by oxidation of Cr(3+) and measurement of the total chromium. The average recoveries of Cr(3+) and Cr(6+) at concentration levels of 0.5-50 microg ml(-1) are 98.1 +/- 0.4% and 99.1 +/- 0.4% respectively. Redox and precipitation titrations involving Cr(6+) as a titrant are monitored with the sensor. Cr(3+) and/or Cr(6+) in wastewaters of some industries (e.g., leather tanning, electroplating, aluminum painting) and the chromium contents of some alloys and refractory bricks are assessed. The results agree fairly well with data obtained using the standard diphenylcarbazide spectrophotometric method.     

利用salen型荧光探针测定Cr3+

研究了salen型席夫结构的荧光探针N,N’-二(2-羟基-1-萘甲醛)-l,2-苯二胺(NAPPDIH)对Cr3+的响应。Cr3+能够使该探针的荧光猝灭。研究表明,在pH3.5(乙酸胺-盐酸)和DMSO/H2O(V/V,8:2)的条件下,8.0×10-6 mol/L的Cr3+可以导致NAPPDIH 65%的荧光猝灭。并且,Cr3+的浓度在5.0×10-7～8.0×10-6 mol/L的范围内,与荧光强度的变化值呈良好的线性关系,检出限为3.7×10-7 mol/L。方法可用于直接检测水样中的Cr3+。     

Anodic Behavior of Nickel-Chromium Alloys in Sodium Chloride Solutions: Pitting and Transpassivity

Anodic potentiodynamic and chronoamperometric curves on nickel-chromium alloys (2–50 wt % Cr) are obtained in NaCl solutions at various concentration, pH, and temperature. The dependences of pitting and repassivation potentials on the concentration and temperature are determined for alloy with 20 wt % Cr. The effect of the Cr content and pH on the anodic behavior of the alloys, in particular, the transition from a pitting breakdown of passivity to transpassivation, is shown. Quantitative time dependences of the current in the passive range are obtained and the steady-state values of this current are determined. The corrosion potential of the alloy with 20 wt % Cr is measured. Cathodic voltamograms for passive and chloride-ion-activated surface of the alloy are obtained.     

Investigations of nitrogen diffusion in austenitic CrNi steels

Parameters of the diffusion of N (up to 0.3 wt.%) in austenitic stainless steels (12 to 19 wt.% Cr, 12 to 16 wt.% Ni, up to 2 wt.% Mo) were determined within the temperature range of 1283–1573K. The small concentration gradients of N were successfully investigated using (1) mechanical serial sectioning technique in combination with either chemical N analysis or X-ray precision lattice parameter determination, and (2) measurements on microsections by means of either electron probe microanalysis or Kossel technique.The diffusion coefficients of N were found to be independent of its concentration. The alloying elements Cr and Mo reduce the N diffusivity in austenitic stainless steels which on the other hand is increased by Ni.     

Production and characterization of oil-in-water emulsions containing droplets stabilized by multilayer membranes consisting of beta-lactoglobulin, iota-carrageenan and gelatin

The influence of environmental conditions (pH, NaCl, CaCl2, and temperature) on the properties and stability of oil-in-water (O/W) emulsions containing oil droplets surrounded by one-, two-, or three-layer interfacial membranes has been investigated. Three oil-in-water emulsions were prepared with the same droplet concentration and buffer (5 wt % corn oil, 5 mM phosphate buffer, pH 6) but with different biopolymers: (i) primary emulsion: 0.5 wt % beta-Lg; (ii) secondary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan; (iii) tertiary emulsion: 0.5 wt % beta-Lg, 0.1 wt % iota-carrageenan, 0-2 wt % gelatin. The secondary and tertiary emulsions were prepared by electrostatic deposition of the charged biopolymers onto the surfaces of the oil droplets so as to form two- and three-layer interfacial membranes, respectively. The stability of the emulsions to pH (3-8), sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) was determined. We found that multilayer emulsions had better stability to droplet aggregation than single-layer emulsions under certain environmental conditions and that one or more of the biopolymer layers could be made to desorb from the droplet surfaces in response to specific environmental changes (e.g., high salt or high temperature). These results suggest that the interfacial engineering technology used in this study could lead to the creation of food emulsions with improved stability to environmental stresses or to emulsions with triggered release characteristics.     

PVC membrane based potentiometric sensors for uranium determination

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO₂²⁺ ions over the concentration range 1×10⁻¹–2×10⁻⁵ mol l⁻¹ UO₂²⁺ with a cationic slope of 25.0±0.2 mV decade⁻¹. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,N′,N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10⁻¹–5×10⁻⁵ mol l⁻¹ UO₂²⁺ with near-Nernstian slope of 27.5±0.2 mV decade⁻¹ are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th⁴⁺, Cu²⁺, Fe³⁺) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml⁻¹ uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence.     

Determination of L- and D-fucose using amperometric electrodes based on diamond paste

Monocrystalline diamond (natural diamond, synthetic-1 and synthetic-2) based electrochemical electrodes were designed for the analysis of L- and D-fucose. Response characteristics of the electrochemical electrodes were determined using cyclic voltammetry and differential pulse voltammetry (DPV). L-fucose was determined using DPV with electrodes based on natural diamond, synthetic-1 and synthetic-2, respectively, at 240 mV using NaCl as the electrolyte (pH 3.0); at 160 mV using KNO(3) (pH 10.0) and at 80 mV using KCl as the electrolyte (pH 10.0) while D-fucose was analyzed at 120 mV using KCl as the electrolyte (pH 1.0); at 140 mV using KNO(3) as the electrolyte (pH 1.0) and at 160 mV using NaNO(3) as the electrolyte (pH 3.0). The linear concentration ranges for L-fucose were between 10(-13) and 10(-9) mol L(-1) (natural diamond), 10(-11) and 10(-8) mol L(-1) (synthetic-1) and 10(-6) and 10(-3) mol L(-1) (synthetic-2) with detection limits of 10(-14), 10(-12) and 10(-8) mol L(-1) magnitude order, respectively. For D-fucose, the linear concentration ranges were 10(-6) to 10(-3) mol L(-1) (natural diamond), 10(-5) to 10(-3) mol L(-1) (synthetic-1) and 10(-9) to 10(-3) mol L(-1) (synthetic-2) with detection limits of 10(-7), 10(-7) and 10(-10) mol L(-1) magnitude order, respectively. The sensors were used for the assay of L-fucose in serum and urine samples.     

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5+/-0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66 x 10(-6)-1.0 x10(-2) mol dm(-3)). The potential of this electrode is independent of pH in the range of 3.0-5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8 x 10(-7) M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.     

HPLC同时检测血清和尿样中肌酐、假尿苷、尿酸

用反相高效液相色谱法同时测定了３９例糖尿病患者的血清和尿样中的假尿嘧啶核苷、肌酐和尿酸,并与２４ｈ尿白蛋白排泄量进行了比较分析。发现血清假尿嘧啶核苷是糖尿病肾病早期诊断的一种新颖而敏感的指标,有助于连续监测肾脏的功能状态以了解病程的转归。     

Electrochemical determination of 8-oxoguanine in the presence of uric acid

The electrochemical oxidation of 8-oxoguanine (8-oxoG) in the presence of uric acid (UA) was studied by differential pulse voltammetry over a wide pH range (1-12). The results showed that both compounds follow a pH-dependent oxidation mechanism that involves two electrons and two protons corresponding to reversible charge transfer reactions. The difference between the peak potential for the oxidation of each analyte was found to be always less than 100 mV over the whole pH range, the separation being greater in the pH interval 4-7. In mixtures of both analytes, pH 6 was shown to be the best for 8-oxoG determination in the presence of uric acid, since the peak current is higher and a greater peak separation is achieved.     

聚苯胺修饰碳纤维针型复合微pH传感器

由电聚合法用聚苯胺修饰碳纤维电极作为ＰＨ敏感电极。把Ｋ３Ｆｅ（ＣＮ）６／Ｋ４Ｆｅ（ＣＮ）６体系填入医用注射针头内成为参比电极。把经聚苯胺修饰的碳纤维电极安置入该针型参比电极内构成复合针型微ｐＨ传感器。在ＰＨ ２～１２范围内，该传感器呈现超Ｎｅｒｎｓｔ响应，斜率为－７８ ｍＶ／ｐＨ；响应时间<１ｍｉｎ。该传感器成功地应用于在体ｐＨ测定以及水果内微区ｐＨ测定。     

A potentiometric rhodamine-B based membrane sensor for the selective determination of chromium ions in wastewater.

The construction and performance characteristics of a novel chromate ion-selective membrane sensor are described and used for determining chromium(III) and chromium(VI) ions. The sensor is based on the use of a rhodamine-B chromate ion-associate complex as an electroactive material in a poly(vinyl chloride) membrane plasticized with o-nitrophenyloctyl ether as a solvent mediator. In a phosphate buffer solution of pH 6 - 7, the sensor displays a stable, reproducible and linear potential response over the concentration range of 1 x 10(-1) - 5 x 10(-6) mol l(-1) with an anionic Nernstian slope of 30.8 +/- 0.5 mV decade(-1) and a detection limit of 1 x 10(-6) mol l(-1) Cr(VI). High selectivity for Cr(VI) is offered over many common anions (e.g., I-, Br-, Cl-, IO4-, CN-, acetate, oxalate, citrate, sulfate, phosphate, thiosulfate, selenite, nitrate) and cations (e.g., Ag+, Ca2+, Sr2+, Co2+, Ni2+, Cu2+, Mn2+, Fe2+, Zn2+, Cd2+, Al3+, Cr3+). The sensor is used for determining Cr(VI) and/or Cr(III) ions in separate or mixed solutions after the oxidation of Cr(III) into Cr(VI) with H2O2. As low as 0.2 microg ml(-1) of chromium is determined with a precision of +/-1.2%. The chromium contents of some wastewater samples were accurately assessed, and the results agreed fairly well with data obtained by atomic absorption spectrometry.     

Micellar Nanocarriers Assembled from Doxorubicin‐Conjugated Amphiphilic Macromolecules (DOX–AM)

Amphiphilic macromolecules (AMs) have unique branched hydrophobic domains attached to linear PEG chains. AMs self‐assemble in aqueous solution to form micelles that are hydrolytically stable in physiological conditions (37 °C, pH 7.4) over 4 weeks. Evidence of AM biodegradability was demonstrated by complete AM degradation after 6 d in the presence of lipase. Doxorubicin (DOX) was chemically conjugated to AMs via a hydrazone linker to form DOX–AM conjugates that self‐assembled into micelles in aqueous solution. The conjugates were compared with DOX‐loaded AM micelles (i.e., physically loaded DOX) on DOX content, micellar sizes and in vitro cytotoxicity. Physically encapsulated DOX loading was higher (12 wt.‐%) than chemically bound DOX (6 wt.‐%), and micellar sizes of DOX‐loaded AMs (≈16 nm) were smaller than DOX–AMs (≈30 nm). In vitro DOX release from DOX–AM conjugates was faster at pH 5.0 (100%) compared to pH 7.4 (78%) after 48 h, 37 °C. Compared to free DOX and physically encapsulated DOX, chemically bound DOX had significantly higher cytotoxicity at 10^?7 M DOX dose against human hepatocellular carcinoma cells after 72 h. Overall, DOX–AM micelles showed promising characteristics as stable, biodegradable DOX nanocarriers.

     

Effect of concentration of ion exchanger, plasticizer and molecular weight of cyanocopolymers on selectivity and sensitivity of Cd(II) ion selective electrode

Potential response of cadmium(II) ion selective electrode based on cyanocopolymer matrices and 8-hydroxyquinoline as ionophore has been evaluated by varying the amount of ionophore, plasticizer and the molecular weight of the cyanocopolymer. The sensitivity, working range, response time, and metal ions interference have shown a significant dependence on the concentration of ionophore, plasticizer and molecular weight of cyanocopolymers. The electrodes prepared with 2.38×10⁻² mol kg⁻¹ of ionophore, 1.23×10⁻² mol dm⁻³ of plasticizer and 2.0 g of cyanocopolymer (molecular wt., 59 365) have shown a Nernstian slope of 29.00±0.001 mV per decade activities of Cd²⁺ ions with a response time of 12±0.007 s. Electrodes have shown an appreciable selectivity for Cd²⁺ ions in the presence of alkali and alkaline earth metal ions and could be used in a pH range of 2.5–6.5. The cyano groups of the copolymers contributed significantly to enhance the selectivity of the electrode. The electrode has shown an appreciable average life of 6 months without any significant drift in the electrode potential and found to be free from leaching of membrane ingredients. Electrode response is explained considering phase boundary model based on thermodynamic considerations.     

Quantitative Bestimmung von Paraquat in Urin und Serum durch Differential-Puls-Polarographie

Zusammenfassung Es wird eine empfindliche und spezifische Differential-puls-polarographische Methode zum direkten quantitativen Nachweis von Paraquat (P) in ammoniakalischer Ammoniumchloridlösung (pH 8), Urin (pH 7) und Serum (pH 6,5–8) beschrieben. Die Peakpotentiale (E _p ) in mV, gemessen gegen eine gesättigte Kalomelelektrode, sind für die ammoniakalische Ammoniumchloridlösung –686 mV, für Urin –679 mV und für Serum –692 mV. Die Analysen von Urin und Serum wurden für Paraquat-vergiftete und auch für gesunde Personen mit Paraquatzusatz durchgeführt. Die Zeit für eine vollständige Analyse beträgt 25 min. Die Nachweisgrenze beträgt in der ammoniakalischen Ammoniumchloridlösung 0,03 g P/ml, im Urin 0,05 g P/ml und im Serum 0,03 g P/ml.

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Quantitative determination of paraquat in urine and serum by differential pulse polarography

Summary A sensitive and specific differential pulse polarographic method for the direct quantitative determination of paraquat (P) in ammoniacal ammonium chloride solution (pH 8), urine (pH 7) and serum (pH 6.5–8) is described. The peak potentials (E _p ) in mV vs. saturated calomel electrode (SCE) were –686 mV for ammoniacal ammonium chloride solution, –679 mV for urine, and –692 mV for serum. Analyses were performed in urine and serum both from persons poisoned with paraquat and from healthy persons. Urine and serum from the latter to which paraquat had been added served as control. The time needed for one complete analysis was 25 min. Detection limits were 0,03 g P/ml for ammoniacal ammonium chloride solution, 0,05 g P/ml for urine and 0,03 g P/ml for serum.

Die Verfasser danken Fräulein M. Schneider und Herrn H. Bewig für die sorgfältige Durchführung von Messungen.     

Development of pH sensor based on aromatic polyurethane matrix

The synthesized aromatic polyurethane (APU)-based all-solid-state (ASS) pH sensor was developed with the same APU-based reference site in an ASS multi sensing electrode. The best analytical performance (the linear range of pH 3.0–11.5, slopes of 57 mV pH⁻¹) was obtained with the membrane composition of 33:66:1 (wt.%) of APU/plasticizer (NPOE)/ionophore (N,N-dioctadecylmethylamine) with the addition of lipophilic additive (KTpClPB, 5 mol.%). This ASSE exhibits more advantages of increasing stability, reducing membrane resistance and reducing anion interference.     

Trennung der 8-Hydroxychinolate von V, Mo, W, Co und Cr durch HPLC

Zusammenfassung 8-Hydroxychinolin-Chelate von V, Mo, W, Co, Cr können mit der Hochdruckflüssigkeits-Chromatographie getrennt werden [polare stationäre Phase: Si 60; Eluentien: Tetrahydrofuran/Chloroform (64) bzw. Dioxan/Chloroform (64)]. Die Nachweisgrenzen sind: < 1 ng für V, Mo und Cr; 0,5 ng für Co; 1,5 ng für W.

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Separation of the 8-hydroxyquinolinates of V, Mo, W, Co and Cr by HPLC

Summary The oxinates of V, Mo, W, Co and Cr can be separated by HPLG employing Si 60 as stationary phase and either tetrahydrofuran/chloroform (64) or dioxan/chloroform (64) as eluents. Limits of detection are: < 1 ng for V, Mo and Cr; 0.5 ng for Co; 1.5 ng for W.

Ich danke der Deutschen Forschungsgemeinschaft für die Bereitstellung von Geräten und Sachbeihilfen.Mein besonderer Dank gilt Frl. Pohlmann für die Durchführung zahlreicher Meßreihen.     

Separation and preconcentration of chromium species by selective absorption on Lemna minor and determination by slurry atomisation electrothermal atomic absorption spectrometry

A novel method for the separation and preconcentration of Cr(III)/Cr(VI) with Lemna minor and determination by slurry atomization electrothermal atomic absorption spectrometry (ETAAS) was developed. A sample solution was added to a polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 1.0, stirred for 8 min for selective absorption of Cr(III) and then centrifuged. The upper layer of solution was transferred into another polyethylene beaker containing 10 mg of 160 mesh pre-treated Lemna minor, adjusted to pH 5.0, stirred for 12 min for adsorption of the residual Cr(VI) and centrifuged. The two residues in two centrifuge tubes were washed twice with water, 2 ml of agar solution added, stirred for 2 min, then two slurries were prepared and used for the determination of Cr(III) and Cr(VI) by ETAAS. Detection limits (3sigma) of 0.01 microg L(-1) for Cr(III) and 0.03 microg L(-1) for Cr(VI) were obtained. The relative standard deviation was 2.8% for Cr(III) and 3.3% for Cr(VI) at the 1 microg L(-1) level. The method was applied to the determination of Cr(III)/Cr(VI) in water samples. The analytical recoveries of Cr(III) and Cr(VI) added to samples were 97-102 and 96-103%, respectively.     

Construction of a new Ho<Superscript>3+</Superscript> PVC-membrane electrochemical sensor based on <Emphasis Type="Italic">N,N</Emphasis>′-dipyridoxyl(1,4-butanediamine)

N,N′-dipyridoxyl(1, 4-butanediamine) (PYBA) (2 wt % ), nitrobenzene (66 wt %), sodium tetra phenyl borate (2 wt ), and poly vinyl chloride (30 wt %) were applied to create a PVC membrane in Ho³⁺ selective electrode (Ho-SE). Over the concentration range of 1.0 × 10^?5 to 1.0 × 10^?2 M in holmium(III) solution a linear response with lower detection of limit equal 4.0 × 10^?6 M was exhibited by new holmium(III) sensor. Ho-SE possessed a Nernstian slope of 20.1 ± 0.8 mV decade^?1 in very short time spans (~9 s). The potential response of electrode remains without any changes over a pH range of 2.77–8.71. The selectivity coefficient data which was considered by matched potential method for variety of common cations indicated no significant interference. An acceptable recovery for Ho³⁺ in the blend of several cations has been achieved. The utility of Ho-SE in potentiometric titration as an end point indicator electrode gave successfully results.     

多壁碳纳米管修饰电极阳极溶出法测定痕量锌

报道了自制的多壁碳纳米管修饰电极测定锌离子的电分析方法。在浓度0.20mol/L的乙酸钠溶液中,以此修饰电极作为工作电极,以-1.50V为富集电位,150s为富集时间,用方波伏安溶出法(起始电位:-1.5V;终止电位:-0.8V;电位增量:0.01V;振幅:0.05V;频率:5Hz)测定-1.30V处的峰电流,用峰高定量。结果表明,该电极对锌离子吸附的灵敏度较高;当锌离子浓度为1.0×10-6～9.0×10-6mol/L时,线性关系好,相关系数为0.9992;对自来水样本进行了测定,取得了满意的结果,加标回收率在97%～105%之间。