A study on lowering the detection limit with solid-state lead-selective electrodes

The detection limit of a Pb²⁺ ion-selective electrode with a solid state (PbS/Ag₂S) membrane was successfully lowered to the nanomolar range. The electrode was applied in direct potentiometric determination of Pb²⁺ in aqueous solutions. Hydrodynamics, redox reaction at the solid-state surface as well as time dependency were investigated and found as key factors affecting the low detection limit. By optimizing these parameters improving detection limit by ca. three orders of magnitude was achieved.     

Interpretation of the selectivity and detection limit of liquid ion-exchanger electrodes

An equation has been derived which describes the e.m.f. of a liquid ion-exchanger membrane electrode in conditions of low concentration levels of the primary and interfering ions. The equation is based on the assumption that if the external solution contains no excess of ions which may exchange with the organic phase, then the concentration of the exchanger at the interface decreases, and this is responsible for formation of a diffusion layer inside the membrane. Therefore the potential response depends on the initial concentration of the ion-exchanger in the membrane phase, on the thicknesses of the diffusion layer on both sides of the interface, and on the diffusion coefficients of the species in both phases. This equation explains the non-Nernstian behaviour of the electrode in the presence of interferents, as well as the variation of the conditional selectivity coefficients. The parameters mentioned also influence the detection limit of an electrode. The electrode behaviour has been tested in unstirred solutions and in solutions stirred at different rates. Through its influence on the diffusion layer thickness, the stirring also influences the electrode potential and the characteristics of the electrode.     

Subnanomolar detection limit application of ion-selective electrodes with three-dimensionally ordered macroporous (3DOM) carbon solid contacts

Solid-contact ion-selective electrodes (SC-ISEs) can exhibit very low detection limits and, in contrast to conventional ISEs, do not require an optimization of the inner filling solution. This work shows that subnanomolar detection limits can also be achieved with SC-ISEs with three-dimensionally ordered macroporous (3DOM) carbon contacts, which have been shown recently to exhibit excellent long-term stabilities and good resistance to the interferences from oxygen and light. The detection limit of 3DOM carbon-contacted electrodes with plasticized poly-(vinyl chloride) as membrane matrix can be improved with a high polymer content of the sensing membrane, a large ratio of ionophore and ionic sites, and conditioning with a low concentration of analyte ions. This permits detection limits as low as 1.6 × 10⁻⁷ M for K⁺ and 4.0 × 10⁻¹¹ M for Ag⁺.     

Studies on the application of salts of complex cations to microscopic detection of anions

Summary Crystalline reaction products have been obtained when triethylene-diaminocobaltic chloride is allowed to react with solutions containing cobaltinitrite, ferricyanide, ferrocyanide, orthovanadate and xanthate ions. Of these, the reaction product obtained with the ferricyanide ion is recommended as the most sensitive and characteristic, while those with the orthovanadate and xanthate ions, while not so sensitive, are equally characteristic. The reagent is most sensitive with the ferrocyanide ion but the reaction product is not quite as characteristic as in the case of the ferricyanide.

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Zusammenfassung Bei der Reaktion von Triäthylendiamin-kobalt(III)-chlorid mit Lösungen, die Kobalt(III)-nitrit, Eisen(III)-cyanid-, Eisen(II)-cyanid-, Orthovanadat-und Xanthat-Ion enthalten, wurden kristalline Reaktionsprodukte erzielt. Von diesen ist das mit Eisen(III)-cyanid entstandene Reaktionsprodukt das empfindlichste und charakteristischeste, während die Reaktionsprodukte mit Orthovanadat- und Xanthat-Ion zwar nicht so empfindlich, jedoch gleichermaßen charakteristisch sind. Das Reagens reagiert am empfindlichsten mit Eisen(II)-cyanid-Ion, doch ist dieses Reaktionsprodukt nicht ganz so charakteristisch wie das mit Eisen(III)-cyanid erhaltene.

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Résumé (W) On obtient des produits de réaction cristallisés en faisant agir le chlorure de triéthylènediaminocobalt sur des solutions contenant des ions cobaltinitrites, ferrocyanures, ferricyanures, orthovanadates et xanthates. Parmi ceux-ci, le produit do la réaction de l'ion ferricyanhydrique permet l'identification la plus sensible et la plus caractéristique tandis que les produits de réaction des ions orthovanadique et xanthique, bien que moins sensibles sont également caractéristiques. Le réactif est très sensible vis-à-vis de l'ion ferrocyanhydrique; mais le produit de réaction n'est pas tout à fait aussi caractéristique que celui du ferricyanure.

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Acknowledgement is made to the Works Progress Administration for the City of New York for assistance rendered under Project No. 465-97-3-120.

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With 6 figures     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Crystalline reaction products were obtained when 1,6-carbonatotetramminocobaltic nitrate reacts with bifluoride and bromate ions.

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Zusammenfassung Bei der Reaktion von 1,6-Carbonatotetramminokobaltinitrat mit Bifluorid-und Bromat-Ion wurden kristalline Reaktionsprodukte erhalten.

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Résumé On a obtenu des produits de réaction cristallisés, en faisant réagir le nitrate de 1,6-carbonatotetramminocobalte avec des ions de bifluorure et de bromate.

     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Table II sums up the products obtained from the various test substances on interaction with the individual complex cations. The substances are arranged according to the periodic table, and, when several anions derived from the same element have been studied, these anions are listed alphabetically. In cases of polybasic acids, the acid salt precedes the neutral salt. Characteristically shaped crystalline products are represented by +, turbidities byT, and non-characteristic precipitates byNC. It will be noted that in some cases no reaction products were obtainable. This is especially true with many of the organic acids as well as their salts. With some of the organic acids, this is probably due to the extreme dilution of their saturated aqueous solutions.For ease of application and rapidity of detection, taking the ions in the order in which they appear in the table, we make the following recommendations: The luteo chloride is applicable for differentiation of ferri- and ferrocyanides, the reactions of ferricyanide ion also being very characteristic with the purpureo and roseo chlorides. Hence, these two latter reagents may also be used for detection of this anion.Of the free organic acids tried, only sulfosalicylic and tartaric reacted at all. These may be readily distinguished from each other by the luteo chloride, the long needles being very characteristic of most sulfur containing compounds. The reaction products obtained from sulfosalicylic acid and either purpureo or roseo chlorides are also very characteristic, and may well be used to differentiate this substance from the other organic anions mentioned. The crystals formed by alkali metal oxalates with the croceo, xantho and roseo complex reagents are characteristic enough to serve as a means of differentiating the oxalate ion from other organic anions, particularly citrates and tartrates.Fluosilicates and silicotungstates may be readily differentiated by the flavo nitrate, both because of size and aggregation pattern of the needles obtained. The clumps of needles formed by silicotungstic acid are especially characteristic of this substance.The roseo and xantho salts give almost the same type of precipitate with salts of phosphomolybdic acid. These will serve to distinguish salts of this acid from corresponding salts of phosphotungstic acid. In the latter case, only turbidities of spherular masses were obtainable. The chloroaquo complex may be recommended particularly for the detection of secondary phosphate. The luteo salt has already been recommended for microscopic detection of pyrophosphates, but care must be taken not to mistake the hexagonal platelets formed by this anion for those obtainable with tellurites. The size and degree of transparency will serve to differentiate these substances.Microscopically no distinction can be made between arsenates and arsenites by the complexes thus far studied. By means of color reactions on heating in alkaline medium, however, it is possible to distinguish between these two anions by using the luteo chloride. The reaction product formed by pyroantimonate with the isoxantho complex may be recommended for microscopic detection of this anion. The reaction with the croceo chloride will serve to distinguish ortho- from metavanadate.Nearly all sulfur containing anions react with the luteo chloride, and, in most cases, needles or flat rods are formed as a result of the reaction. However, in terms of the reaction products formed, bisulfites are readily distinguishable from bisulfates after treating with the flavo nitrate, and sulfates and sulfites are distinguished by the reaction with the luteo chloride. For purposes of detection of other sulfur acids, the following reactions may be recommended: for dithionates reaction with the luteo, flavo, xantho and roseo complexes, and for thiosulfates the reaction with the luteo chloride. The reaction of the selenate with flavo nitrate may be used to differentiate this substance from selenites. In like manner the tellurite may be distinguished from the tellurate by the reaction product obtained with the luteo chloride. As differential reagents between chromates and dichromates, both the luteo and flavo complexes may be employed. In addition, the reaction products with the croceo, xantho and purpureo complexes can also be recommended for detection of the chromate, and that with the croceo for detection of the dichromate ion.The carbonato complex may be used to differentiate between fluorides and bifluorides, and also between bromates and bromides (sodium salts only). As characteristic reagents for bifluorides we also recommend the croceo and xantho salts. The luteo chloride may be utilized to differentiate between iodates and iodides, the bushy needles formed with iodates being especially characteristic. The isoxantho complex can be recommended for detection of perchlorates and the luteo salt for detection of permanganates.

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Zusammenfassung Die Ergebnisse einer Reihe von Untersuchungen über die Eignung von Kobaltkomplexen für den Nachweis von Anionen werden zusammengefaßt. Tabelle II gibt die mit 9 Komplexen erhaltenen Resultate in gedrängter Form. Die Bildung kristallisierter Niederschläge ist durch das Zeichen + angezeigt,T weist auf das Auftreten einer Trübung hin; Niederschläge, die nicht charakteristisch sind, sind mitNC gekennzeichnet. Leere Stellen bedeuten das Ausbleiben einer sichtbaren Reaktion. Besonders mit organischen Säuren und ihren Salzen wurden oft keine Niederschläge erhalten, bei ersteren wohl wegen der großen Verdünnung ihrer gesättigten wäßrigen Lösungen.Bezüglich der analytischen Verwendung werden die folgenden Vorschläge gemacht: Das Luteochlorid eignet sich für die Unterscheidung von Ferrocyanid und Ferricyanid. Das letztere Anion gibt außerdem charakteristische Kristallisationen mit Purpureochlorid und Roseochlorid. Von den freien organischen Säuren wurden nur mit Weinsäure und Sulfosalicylsäure Niederschläge erhalten, und diese beiden können mittels des Luteochlorides unterschieden werden. Auch Purpureochlorid und Roseochlorid können zur Unterscheidung der Sulfosalicylsäure von anderen organischen Säuren benutzt werden. Oxalat gibt charakteristische Kristalle mit Croceo-, Xantho-und Roseosalzen und kann derart von anderen organischen Anionen, darunter besonders Citrat und Tartrat, unterschieden werden. Flavonitrat gestattet die Unterscheidung von Fluosilikat und Silicowolframat. Die Nadeln des Fluosilikates unterscheiden sich von denen des Silicowolframates in Größe und Anordnung. Roseo- und Xanthosalze geben Kristallisationen von nahezu gleicher Form mit Phosphomolybdänsäure. Da diese beiden Reagenzien mit Phosphowolframaten jedoch nur Trübungen liefern, eignen sie sich für die Differenzierung von Phosphowolframat und Phosphomolybdat. Der Chloroaquokomplex gestattet die Erkennung des sekundären Phosphat-Ions. Das Luteosalz dient bekanntlich zum Nachweis von Pyrophosphat, doch können die hexagonalen Plättchen leicht mit jenen des entsprechenden Telluritniederschlages verwechselt werden. Das Luteotellurit unterscheidet sich aber hinsichtlich der Größe und der Transparenz der Kristalle.Arsenit und Arsenat geben mit den bisher untersuchten Kobaltkomplexen Kristallisationen von so ähnlichem Aussehen, daß eine Unterscheidung durch das mikroskopische Bild unmöglich ist. Wird jedoch die mit Luteochlorid versetzte Lösung alkalisch gemacht und erhitzt, so werden für Arsenat und Arsenit charakteristische Färbungen erhalten. Pyroantimonat kann durch die Kristallfällung mit Isoxanthosalz erkannt werden. Ortho- und Metavanadat sind mit Hilfe des Croceochlorides zu unterscheiden.Fast alle Schwefel enthaltenden Anionen reagieren mit Luteochlorid, und die meisten dieser Niederschläge kristallisieren als Nadeln oder Stäbchen. Das Reagens gestattet die Unterscheidung von Sulfat und Sulfit. Für die Differenzierung von Bisulfat und Bisulfit eignet sich Flavonitrat. Luteochlorid ermöglicht ferner die Auffindung von Thiosulfat; Dithionat kann mit Hilfe der Luteo-, Flavo-, Xantho- und Roseosalze entdeckt werden. Flavonitrat empfiehlt sich für die Unterscheidung von Selenat und Selenit, Luteochlorid zur Differenzierung von Tellurat und Tellurit. Zur Unterscheidung von Chromat und Bichromat können Luteo- oder Flavosalze benutzt werden. Die Fällungen mit Croceo-, Xantho- und Purpureosalzen eignen sich zur Erkennung von Chromat und die Kristallisation mit Croceosalz kann zur Auffindung von Bichromat herangezogen werden.Der Carbonatokomplex kann einerseits zur Unterscheidung von Fluorid und Bifluorid, anderseits von Bromid und Bromat verwendet werden, vorausgesetzt, daß diese Anionen in Form ihrer Natriumsalze vorliegen. Auch Croceo- und Xanthosalze geben charakteristische Reaktionen mit Bifluorid. Luteochlorid eignet sich für die Unterscheidung von Jodid und Jodat, wobei die mit dem letzteren gebildeten Nadeln besonders charakteristisch sind. Der Isoxanthokomplex wird für die Auffindung von Perchlorat vorgeschlagen und das Luteochlorid eignet sich für den Nachweis von Permanganat.

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Résumé (W) Les auteurs résument une série des recherches sur l'utilisation de complexes de cobalt pour l'identification d'anions. La tabelle II indique d'une façon abrégée les résultats obtenus avec neuf complexes. La formation de précipités cristallins est indiquée par le signe +; leT correspond à un trouble et les précipitations qui ne sont pas caractéristiques, sont marquésNC. Les places blanches indiquent l'absence de réaction visible. Particulièrement, lors de l'emploi de certains acides organiques et de leurs sels, il ne se produit pas de précipité. Ceci provient, dans le cas de quelques uns de ces acides organiques, de la trop grande dilution de leur solution aqueuse saturée.En ce qui concerne l'emploi analytique on fait les propositions suivantes: Pour différencier le ferrocyanure du ferricyanure on prend de préférence le lutéochlorure. Le ferricyanure produit en outre des cristallisations caractéristiques avec le purpuréochlorure et le roséochlorure. Parmi les acides organiques libres on n'a obtenu des précipités qu'avec les acides tartrique et sulfosalicylique. Ceux-ci peuvent être distingués avec le lutéochlorure. Le purpuréochlorure et le roséochlorure peuvent être utilisés pour la différenciation de l'acide sulfosalicylique d'autres acides organiques. L'oxalate donne des cristaux caractéristiques avec les crocéo-, xantho- et roséosels. Il peut alors être discerné d'autres anions organiques, spécialement du citrate et du tartrate. Le flavo-nitrate permet la discrimination du fluosilicate et du silicotungstate. Les aiguilles du fluosilicate se distinguent de celles du silicotungstate par la grandeur et l'arrangement. Les roséo- et xanthosels donnent des cristallisations presque identiques avec l'acide phosphomolybdique. Comme ces deux réactifs ne produisent que des troubles avec les phosphotungstates, ils seront indiqués pour différencier le phosphotungstate du phosphomolybdate. L'aquochlorocomplexe permet l'identification de l'ion phosphorique secondaire. On sait que le lutéosel sert à l'identification des pyrophosphates; mentionnons cependant que les tablettes hexagonales peuvent facilement être prises pour celles du précipité correspondant de l'ion tellureux. Le lutéotellurite diffère cependant par la grandeur et la transparence des cristaux.L'arsenite et l'arséniate donnent avec les complexes de cobalt examinés jusqu'à maintenant, des cristallisations d'aspect tellement voisin qu'il est impossible de les discerner au microscope. Si par contre, on alcalinise la solution du lutéochlorure et qu'on la chauffe, on obtient des colorations caractéristiques pour les arséniates et les arsénites. On pourra reconnaître le pyroantimoniate par le précipité cristallin obtenu avec l'isoxanthosel. L'ortho- et le métavanadate peuvent être distingués avec l'aide du crocéochlorure.Presque tous les anions contenant du soufre réagissent avec le lutéochlorure et la plupart de ces précipités cristallisent sous forme d'aiguilles ou de bâtonnets. Le réactif permet de discerner le sulfate du sulfite. Pour différencier le bisulfate du bisulfite on emploie de préférence le flavonitrate. Le lutéochlorure permet de rechercher le thiosulfate. Le dithionate peut être identifié à l'aide de lutéo-, flavo-, xantho- et roséosels. On recommande l'emploi de flavonitrate pour discerner le séléniate du sélénite, tandis que le lutéochlorure peut être employé pour différencier le tellurate du tellurite. On peut se servir des lutéo- et flavosels pour discerner les chromates des bichromates. Les précipitations de crocéo-, xantho- et purpuréosels peuvent être notées pour l'identification du chromate; la cristallisation avec le crocéosel peut être utilisée à la recherche du bichromate. Le carbonate complexe peut être employé pour discerner le fluorure du bifluorure d'une part, et le bromure et le bromate d'autre part, à condition que ces anions soient sous forme de sels de sodium. Les crocéo- et xanthosels donnent aussi des réactions caractéristiques avec le bifluorure. Le lutéochlorure sert à distinguer l'iodure de l'iodate; il forme avec ce dernier des aiguilles particulièrement caractéristiques. Pour identifier le perchlorate, on propose l'isoxanthocomplexe; et le lutéochlorure enfin, sert à l'identification du permanganate.

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Reported at the 97th Meeting of the American Chemical Society, Baltimore, Md., April 1939.

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Acknowledgement is made to the Works Progress Administration for the City of New York for assistance rendered under project No. 465-97-3-120 in preparing certain of the compounds listed here.

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With 83 figures     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Characteristic crystalline reaction products are obtained when 1,6-dichlorotetrapyridinocobaltic chloride reacts either with the free acid or the sodium salt of the following radicals: azide, bitartrate, chromate, metavanadate, orthovanadate, permanganate, salicylate, and sulfosalicylate anions. Of the reaction products formed, we recommend those with chromate, orthovanadate, permanganate, salicylate, and sulfosalicylate for the detection of these anions.

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Zusammenfassung Charakteristische kristalline Reaktionsprodukte entstehen bei der Einwirkung von 1,6-Dichlortetrapyridincobaltichlorid auf die folgenden Anionen (freie Säure oder Natriumsalz): Azid Bitartrat, Chromat, Metavanadat, Orthovanadat, Permanganat, Salicylat und Sulfosalicylat. Von den entstandenen Reaktionsprodukten eignen sich die mit Chromat, Orthovanadat, Permanganat, Salicylat und Sulfosalicylat für den Nachweis der betreffenden Anionen.

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Résumé (W) Des produits de réaction cristallins caractéristiques se forment par l'action du 1,6-dichlortétrapyridinecobaltichlorure sur les anions suivants (acides libres ou sels de sodium): azides, bitartrates, chromates, metavanadates, orthovanadates, permanganates, salicylates, ainsi que l'anion sulfosalicylique. Les produits de réaction des chromates, des orthovanadates, des permanganates, des salicylates et des sulfosalicylates se prêtent à l'identification de ces anions.

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Acknowledgment is made to the Works Progress Administration for the City of New York, for assistance rendered under Project No. 465-97-3-120 in preparing the reagent listed here.

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With 10 figures     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Roseocobaltic chloride was found to furnish characteristic crystalline reaction products with oxalates, sulfosalicylic acid, dithionates, ferriand ferrocyanides, silicofluorides and phosphomolybdates. Of these, only the first four reaction products are recommended for identification of the corresponding anions.

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Zusammenfassung Aquo-pentammino-cobaltichlorid gibt mit Dithionat, Ferricyanid, Oxalat und Sulfosalicylat kristallisierte Reaktionsprodukte, die für den Nachweis dieser Ionen geeignet sind.

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Résumé (L) L'aquo-pentammino-cobaltichlorure, forme des dithionates, ferri-cyanures, oxalates et sulfosalicylates cristallins qui conviennent pour la recherche de ces ions.

     

Studies on the application of salts of complex cations to the microscopic detection of anions

Summary Characteristic crystalline reaction products were obtained when 1,6-dibromotetramminocobaltic bromide is allowed to react as a solid with solutions of salicylates, sulfosalicylates and silicotungstates. The two former reactions are recommended only for use by experienced microscopists, while the reaction with the silicotungstate is easily obtainable by anyone.

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Zusammenfassung Bei der Reaktion von festem 1,6-Dibromtetrammin-kobalt(III)-bromid mit Lösungen von Salicylaten, Sulfosalicylaten und Silicowolframaten wurden charakteristische kristalline Reaktionsprodukte erhalten. Dio beiden erstgenannten Reaktionen können nur in der Mikroskopie Erfahrenen empfohlen werden, während die Reaktion mit Silicowolframaten sich in jedermanns Hand als brauchbar erweist.

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Résumé (W) On obtient des produits de réaction cristallisés et caractéristiques en faisant réagir le bromure de dibromo-1,6-tétrammine-cobalt à l'état solide sur des solutions de salicylates, de sulfosalicylates ou de silicotungstates. Les deux premières réactions ne peuvent être recommandées qu'à des chimistes connaissant la technique microscopique, tandis que la réaction des silicotungstates est réalisable pour chacun.

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Acknowledgement is made to the Works Progress Administration for the City of New York, for assistance rendered under Project No. 465-97-3-120 in preparing the reagent listed here.

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With 3 figures     

Ferrocene-containing polyelectrolyte multilayer film-covered electrodes: electrocatalytic determination of ascorbic acid and use of inner blocking layers to improve the upper detection limit of the electrodes

A multilayer film composed of ferrocene(Fc)-appended poly(allylamine hydrochloride) (Fc-PAH) and poly(potassium vinylsulfate) (PVS) has been prepared on the surface of a gold(Au) electrode by using a layer-by-layer self-assembly technique. Fc-containing polyelectrolyte multilayer (PEM) film-modified electrodes can electrochemically catalyze the oxidation of ascorbic acid successfully. For a 2 (Fc-PAH/PVS) bilayer-covered electrode the catalytic current increased linearly with increasing concentration of ascorbic acid over the concentration range 6 mol L^–1–3 mmol L^–1. To extend the dynamic range for ascorbic acid, the surface of the Au electrode was first covered with a (PAH/PVS)₂ film on which an additional (Fc-PAH/PVS)₅ film was coated. This strategy successfully extended the dynamic range of the electrode up to 25 mmol L^–1 ascorbic acid, because the (PAH/PVS)₂ layer blocked access of ascorbic acid to the electrode surface. The upper detection limit of the (PAH/PVS)₂ (Fc-PAH/PVS)₅ film-modified electrode is much higher than those of Fc-based ascorbic acid sensors reported so far. Electron transfer is diffusion-controlled within the (PAH/PVS)₂(Fc-PAH/PVS)₅ film.     

Transport of metal salts by zwitterionic ligands; simple but highly efficient salicylaldoxime extractants

Attaching dialkylaminomethyl arms to commercial phenolic oxime copper extractants yields reagents which transport base metal salts very efficiently by forming neutral 1 ratio 1 or 1 ratio 2 complexes with zwitterionic forms of the ligands.     

Sulfonyl: a new application of electron-withdrawing substituent in highly efficient photovoltaic polymer

A strong electron-withdrawing group, sulfonyl, was firstly introduced to a semiconducting polymer, PBDTTT-S. The PCE of the PBDTTT-S device reached 6.22% with a high open-circuit voltage of 0.76 V. The sulfonyl group is thus a promising candidate as a strong electron-withdrawing group applied to high-efficiency PSCs.     

Diazonium salts: Stable monolayers on gold electrodes for sensing applications

The modification of gold electrodes with 4-carboxyphenyl diazonium salts to form stable layers for sensing applications is reported. Electrochemical reduction of 4-carboxyphenyl diazonium salts on gold electrodes yielded more stable layers than alkanethiol self-assembled monolayers in terms of extremes of electrode potential, sonication and with time. The application of the 4-carboxyphenyl modified electrodes for electrochemical sensing, which typically requires short chain alkanethiols on gold electrodes, is demonstrated via the covalent attachment of oligopeptides for the selective detection of Cu²⁺, Cd²⁺ and Pb²⁺. The diazonium salt/peptide modified gold electrodes not only had greater stability but also performed with lowest detected concentration to alkanethiol/peptide modified electrodes and with far greater sensitivity than the metal ion sensors when diazonium salt/peptide modified similar glassy carbon electrodes were employed.     

Use of tetrahydropyrimidinium salts for highly efficient palladium-catalyzed cross-coupling reactions of aryl bromides and chlorides

New, sterically demanding 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (2) as NHC precursors have been synthesized and characterized. These salts, in combination with palladium acetate, provided active catalysts for the cross-coupling of aryl chlorides and bromides under mild conditions. The catalytic system was applied to the Heck, Suzuki and benzaldehyde (Kumada) coupling reactions. Catalyst activity was found to be influenced by the presence of a methoxy group on the ring of the p-position of benzyl substituent of the ligand precursor.     

Assembly-controlled biocompatible interface on a microchip: strategy to highly efficient proteolysis

A biocompatible interface was constructed on a microchip by using the layer-by-layer (LBL) assembly of charged polysaccharides incorporating proteases for highly efficient proteolysis. The controlled assembly of natural polyelectrolytes and the enzyme-adsorption step were monitored by using a quartz-crystal microbalance and atomic force microscopy (AFM). Such a multilayer-assembled membrane provides a biocompatible interconnected network with high enzyme-loading capacity. The maximum digestion rate of the adsorbed trypsin in a microchannel was significantly accelerated to 1600 mM min(-1) microg(-1), compared with the tryptic digestion in solution. Based on the Langmuir isotherm model, the thermodynamic constant of adsorption K was calculated to be 1.6 x 10(5) M(-1) and the maximum adsorption loading Gammamax was 3.6 x 10(-6) mol m(-2), 30 times more than a monolayer of trypsin on the native surface. The tunable interface containing trypsin was employed to construct a microchip reactor for digestion of femtomoles of proteins and the produced peptides were analyzed by MALDI-TOF mass spectroscopy. The efficient on-chip proteolysis was obtained within a few seconds, and the identification of biological samples was feasible.     

Asymmetric organocatalysis: from proline to highly efficient immobilized organocatalysts

The recent results of the authors’ research group on the application of chiral ionic liquids and related compounds as recoverable organocatalysts of asymmetric reactions are reviewed.     

The electrochemical oxidation of homocysteine at boron-doped diamond electrodes with application to HPLC amperometric detection

The electrochemical oxidation of homocysteine was studied at as-deposited and anodized (oxidized) boron-doped diamond (BDD) thin film electrodes with cyclic voltammetry, flow injection analysis and high-pressure liquid chromatography with amperometric detection. At anodized boron-doped diamond electrodes, highly reproducible, well-defined cyclic voltammograms for homocysteine oxidation were obtained in acidic media, while as-deposited diamond did not provide a detectable signal. In alkaline media, however, the oxidation response was obtained both at as-deposited and anodized diamond electrodes. The potential sweep rate dependence of homocysteine oxidation (peak currents for 1 mM homocysteine linearly proportional to v(1/2), within the range of 0.01 to 0.3 V s(-1)) indicates that the oxidation involves a diffusing species, with negligible adsorption on the BDD surface at this concentration. In the flow system, BDD exhibited a highly reproducible amperometric response, with a peak variation less than 2%. An extremely low detection limit (1 nM) was obtained at 1.6 V vs. Ag/AgCl. In addition, the determination of homocysteine in a standard mixture with aminothiols and disulfide compounds by means of isocratic reverse-phase HPLC with amperometric detection at diamond electrodes has been investigated. The results showed excellent separation, with a detection limit of 1 pmol and a linear range of three orders of magnitude.     

Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode

Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C-N)(3), where (C-N) is a monoanionic cyclometalating ligand: 2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows: quantum yields of phosphorescence Phi(p) = 0.08-0.29, emission peaks lambda(max) = 558-652 nm, and emission lifetimes tau = 0.74-4.7 micros. Bathochromic shifts of the Ir(thpy)(3) family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Phi(p) of the red emissive complexes (lambda(max) > 600 nm) becomes small, caused by a significant decrease of the radiative rate constant, k(r). In contrast, the complexes with the 1-arylisoquinoline ligands are found to have marked red shifts of lambda(max) and very high Phi(p) (0.19-0.26). These complexes are found to possess dominantly (3)MLCT (metal-to-ligand charge transfer) excited states and have k(r) values approximately 1 order of magnitude larger than those of the Ir(thpy)(3) family. An organic light-emitting diode (OLED) device that uses Ir(1-phenylisoquinolinato)(3) as a phosphorescent dopant produces very high efficiency (external quantum efficiency eta(ex) = 10.3% and power efficiency 8.0 lm/W at 100 cd/m(2)) and pure-red emission with 1931 CIE (Commission Internationale de L'Eclairage) chromaticity coordinates (x = 0.68, y = 0.32).