Spectrophotometric investigations on immobilized acid-base indicators

Bacci, Mauro; Baldini, Francesco; Scheggi, A. M.

doi:10.1016/s0003-2670(00)80812-0

Cited by 36 publications

(16 citation statements)

References 12 publications

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“…Normalized absorption spectra of the R form (1,3) and HR + form (2,4) of neutral red in aqueous solutions at pH 10.0 and 4.0, respectively (1,2) and in the gelatin film at pH 10.5 and 6.0, respectively (3,4). Figure S2.…”

Section: Protolytic Properties Of Dyes Embedded In Gelatin Filmsmentioning

confidence: 99%

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Protolytic properties of dyes embedded in gelatin films

Никитина¹,

Reshetnyak²,

Svetlova³

et al. 2011

J. Braz. Chem. Soc.

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O filme de gelatina endurecida fixo em uma base transparente de triacetilcelulose pode ser utilizado como um suporte conveniente para indicadores ácido-base. Azul de bromofenol, verde de bromocresol, eosina, etil-eosina, n-decil-eosina, n-decil-fluoresceína, vermelho neutro e verde de malaquita foram incorporados nos filmes de gelatina por extração em meio aquoso sob condições apropriadas. A absorção de luz dos filmes dopados com corante exibe uma resposta ao pH de soluções tampão aquosas nas quais foram imersos. Valores reprodutíveis das constantes aparentes de dissociação dos indicadores, pK a app , foram calculados pelo tratamento convencional dos valores de pH do tampão aquoso e também para a água absorvida nos filmes de gelatina. Os experimentos com pH abaixo e acima do ponto isoelétrico da gelatina (em torno de pH 5) resultaram em valores de pK a app semelhantes àqueles em meios micelares de tensoativos catiônicos e aniônicos, respectivamente. Os filmes de gelatina modificados por corantes podem ser recomendados para uso em sensores óticos e dispositivos similares.The hardened gelatin film fixed on the transparent triacetylcellulose support can be utilized as a convenient carrier for acid-base indicator dyes. Bromophenol blue, bromocresol green, eosin, ethyleosin, n-decyleosin, n-decylfluorescein, neutral red, and malachite green were embedded into the gelatin films by extracting from aqueous media under appropriate conditions. The light absorption of dye-doped films exhibits a response to the pH values of aqueous buffer solutions, where they were soaked in. The well-reproducible indices of the apparent ionization constants, pK a app , of the indicators were calculated by conventional equating the pH values of the bulk aqueous buffer and those of the 'internal' water into the gelatin films. The experiments with pH below and above the isoelectric point of gelatin (around pH 5) result in pK a app values, which resemble those in micellar media of cationic and anionic surfactants, respectively. The dye-modified gelatin films can be recommended for use in optical sensors and related devices. Keywords: dye-modified gelatin film, indicators, apparent ionization constants, medium effects IntroductionThis paper is devoted to the influence of hardened gelatin media on the spectral and acid-base properties of immobilized xanthene, sulfonephthalein, and some other dyes.The immobilization of reagents in solid matrix (cellulose, ion-exchangers, polymers, silica, xerogels, etc.) 1-7 or using organized solutions, e.g., surfactant-based ones, [8][9][10][11][12] modifies the properties of guest molecules owing to the change of the microenvironment.Such modifications, or medium effects, are most studied and well documented for acid-base indicators. 8,9 In this case, the influence of the microenvironment results in the shift of the indicator equilibrium as compared to that in aqueous media. The main reasons are the local polarity and the local electrical charge. The latter often (but not always) manifests itself in the decre...

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Section: Protolytic Properties Of Dyes Embedded In Gelatin Filmsmentioning

confidence: 99%

“…[1][2][3][4][5][6][7] or using organized solutions, e.g., surfactant-based ones, [8][9][10][11][12] modifies the properties of guest molecules owing to the change of the microenvironment.…”

Section: Introductionmentioning

confidence: 99%

Protolytic properties of dyes embedded in gelatin films

Никитина¹,

Reshetnyak²,

Svetlova³

et al. 2011

J. Braz. Chem. Soc.

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“…Indicators immobilized on (and in) hydrophobic matrices have been found to exhibit acid–base properties that are quite different from those in aqueous solution. 19 , 22 , 102 …”

Section: Introduction Definition Of the Ph Value And General Considmentioning

confidence: 99%

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

2020

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This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and p K a values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

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“…A =1og-clc (7) where I, and I are the light intensities transmitted in the absence and in the presence of the absorbing sample, respectively; c is the absorption coefficient, 1 is the optical path, and c is the concentration ofthe absorbing substance. Clearly, this is true if the substance under investigation is the only one absorbing at the considered wavelength; otherwise, the absorption of other substances present in the solution must be considered.…”

Section: Working Principlesmentioning

confidence: 99%

<title>Critical review of pH sensing with optical fibers</title>

Baldini¹

1999

Chemical, Biochemical, and Environmental Fiber Sensors X

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The chemical parameter most investigated with optical fibres is doubtless pH. The first pH optical fibre sensor was described in 1980. Since then, more than one hundred and twenty original papers describing different pH sensors have been published, based on absorption-based indicators or fluorophores. Such interest is perfectly justified, since pH detection is essential in many fields of application, ranging from the environment and medicine to industry and process control. Moreover, pH transduction can be used for measuring different chemical species, such as carbon dioxide, ammonia and pesticides. Notwithstanding the great number ofprototypes realized in different laboratories all over the world, only a few products are available on the market. A critical analysis of the state of art in pH sensing using optical fibres is described, outlining the advantages and disadvantages of an optical approach.

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Spectrophotometric investigations on immobilized acid-base indicators

Cited by 36 publications

References 12 publications

Protolytic properties of dyes embedded in gelatin films

Protolytic properties of dyes embedded in gelatin films

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

<title>Critical review of pH sensing with optical fibers</title>

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