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Gregory Korshin – One of the best experts on this subject based on the ideXlab platform.

  • Spectroscopic in situ examination of interactions of rare earth ions with humic substances
    Water Research, 2014
    Co-Authors: Yao Chen, Marc Benedetti, Massimiliano Fabbricino, Gregory Korshin
    Abstract:

    This study utilized the methods of fluorescence quenching and differential Absorbance to probe in situ the extent and the nature of the interactions between rare earth ions (REIs) and humic substances. Experiments were conducted with the standard Suwannee river humic acid (SRHA) in the presence of varying amount of lanthanum, europium and terbium. The data of differential Absorbance showed that the mechanism of SRHA-metal complexation was largely the same for all the examined REIs. In all cases several discrete bands whose properties were discerned via numerical decomposition of the differential spectra Absorbance were observed. Their nature was examined based on the comparison of the experimental data and those of NICA-Donnan modeling carried out for Eu3+. The observed effects suggested that the changes of SAHA Absorbance induced by REIs binding are likely to be caused by a bathochromic shift of the Absorbance bands associated with such chromophores. The intensity of the Gaussian band with a maximum at 387 nm was observed to be proportional to the total concentration of SRHA-bound REIs. The data obtained in this study demonstrate the existence of complex yet quantifiable changes of the spectroscopic properties of humic species in the presence of REIs and their utility to quantify modes of interactions in such systems.

  • Study of iron and aluminum binding to Suwannee River fulvic acid using Absorbance and fluorescence spectroscopy: Comparison of data interpretation based on NICA-Donnan and Stockholm humic models
    Water Research, 2013
    Co-Authors: Mingquan Yan, Marc Benedetti, Gregory Korshin
    Abstract:

    This study examined the evolution of Absorbance and fluorescence spectra of standard Suwannee River fulvic acid (SRFA) induced by its interactions with iron and aluminum. The results show that changes of SRFA Absorbance are associated with a consistent response of the carboxylic and phenolic functional groups to iron and aluminum forming bonds with these groups, and their deprotonation induced by such binding. The observed changes of SRFA Absorbance were quantified via the use of DSlope(325-375) parameter that determines the behavior of the slope of logarithms of SRFA Absorbance in the range of wavelengths 325 -375 nm in the presence of varying concentrations of iron or aluminum. DSlope(325-375) values were correlated linearly with the concentration of SRFA-bound iron and aluminum determined using either NICA-Donnan or Stockholm Humic Model (SHM) but the correlation was stronger for the former model (R-2 > 0.98). The slopes of these correlations were similar for both iron and aluminum concentrations

  • In situ study of binding of copper by fulvic acid: Comparison of differential Absorbance data and model predictions
    Water Research, 2012
    Co-Authors: Mingquan Yan, Deborah Dryer, Gregory Korshin, Marc Benedetti
    Abstract:

    This study examined the binding of copper(II) by Suwannee River fulvic acid (SRFA) using the method of differential Absorbance that was used at environmentally-relevant concentrations of copper and SRFA. The pH- and metal-differential spectra were processed via numeric deconvolution to establish commonalities seen in the changes of Absorbance caused by deprotonation of SRFA and its interactions with copper(II) ions. Six Gaussian bands were determined to be present in both the pH- and Cu-differential spectra. Their maxima were located, in the order of increasing wavelengths at 208 nm, 242 nm, 276 nm, 314 nm, 378 nm and 551 nm. The bands with these maxima were denoted as A0, A1, A2, A3, A4 and A5, respectively. Properties of these bands were compared with those existing in the spectra of model compounds such as sulfosalicylic acid (SSA), tannic acid (TA), and polystyrenesulfonic acid-co-maleic acid (PSMA). While none of the features observed in differential spectra of the model compound were identical to those present in the case of SRFA, Gaussian bands A1, A3 and possibly A2 were concluded to be largely attributable to a combination of responses of salicylic- and polyhydroxyphenolic groups. In contrast, bands A4 and A5 were detected in the differential spectra of SRFA only. Their nature remains to be elucidated. To examine correlations between the amount of copper(II) bound by SRFA and changes of its Absorbance, differential Absorbances measured at indicative wavelengths 250 nm and 400 nm were compared with the total amount of SRFA-bound copper estimated based on Visual MINTEQ calculations. This examination showed that the differential Absorbances of SRFA in a wide range of pH values and copper concentrations were strongly correlated with the concentration of SRFA-bound copper. The approach presented in this study can be used to generate in situ information concerning the nature of functional groups in humic substances engaged in interactions with metals ions. This information can be useful for further elaboration and development of detailed theoretic models that describe the complexation of metals in the environment

Renu Chauhan – One of the best experts on this subject based on the ideXlab platform.

  • Spectrophotometric Methods for Simultaneous Estimation of Meclizine Hydrochloride and Caffeine in Their Combined Tablet Dosage Form
    Asian Journal of Research in Chemistry, 2011
    Co-Authors: M.b. Ravalji, Shailesh A. Shah, D.r. Shah, K.l. Daxina, Renu Chauhan
    Abstract:

    Two simple spectrophotometric methods have been developed for simultaneous estimation of meclizine hydrochloride and caffeine from tablet dosage form. Method I is an Absorbance correction method in which Absorbance is measured at two wavelengths, 288 nm at which meclizine hydrochloride has no Absorbance and 236 nm at which both the drugs have considerable Absorbance. Method II is simultaneous equation method which involves two wavelengths, 236nm (for measurement of meclizine hydrochloride) and 273nm (for measurement of caffeine). Both the methods were found linear between the range of 4–20 μg/ml for caffeine and 5–25 μg/ml for meclizine hydrochloride. The accuracy and precision were determined and found to comply with ICH guidelines. Both the methods showed good reproducibility and recovery with % RSD in the desired range. The methods were found to be rapid, specific, precise and accurate and can be successfully applied for the routine analysis of meclizine hydrochloride and caffeine in their combined tablet dosage form.

R. S. Deshmukh – One of the best experts on this subject based on the ideXlab platform.

  • Simultaneous Estimation of Aspirin and Atorvastatin Calcium in Capsule Dosage Form by Spectrophotometric Method
    Asian Journal of Research in Chemistry, 2010
    Co-Authors: R.k. Nanda, Sachin E. Potawale, V.v. Bhagwat, S.c. Hamane, R. S. Deshmukh
    Abstract:

    A simple, precise and economical procedure for the simultaneous estimation of Aspirin and Atorvastatin Calcium in capsule formulation has been developed. The first method employs simultaneous equations (Method I) which involve Absorbance measurement at 225.5 nm (λ max of Aspirin) and 246.0 (λ max of Atorvastatin Calcium). Second method involves Absorbance ratio (Method II), which uses the ratio of Absorbances measured at two selected wavelengths, one at isoabsorptive point (232.5 nm) and other being the max of one of the two compounds. Third method involves measurement of area under curve (AUC). For this method wavelength ranges were chosen between 223.5-227.5 nm and 244-248 nm for Aspirin and Atorvastatin Calcium respectively. Results of analysis for methods were tested and validated for various parameters according to ICH guidelines, hence can be adopted for the routine analysis of Aspirin and Atorvastatin Calcium in tablet dosage form.

M.b. Ravalji – One of the best experts on this subject based on the ideXlab platform.

  • Spectrophotometric Methods for Simultaneous Estimation of Meclizine Hydrochloride and Caffeine in Their Combined Tablet Dosage Form
    Asian Journal of Research in Chemistry, 2011
    Co-Authors: M.b. Ravalji, Shailesh A. Shah, D.r. Shah, K.l. Daxina, Renu Chauhan
    Abstract:

    Two simple spectrophotometric methods have been developed for simultaneous estimation of meclizine hydrochloride and caffeine from tablet dosage form. Method I is an Absorbance correction method in which Absorbance is measured at two wavelengths, 288 nm at which meclizine hydrochloride has no Absorbance and 236 nm at which both the drugs have considerable Absorbance. Method II is simultaneous equation method which involves two wavelengths, 236nm (for measurement of meclizine hydrochloride) and 273nm (for measurement of caffeine). Both the methods were found linear between the range of 4–20 μg/ml for caffeine and 5–25 μg/ml for meclizine hydrochloride. The accuracy and precision were determined and found to comply with ICH guidelines. Both the methods showed good reproducibility and recovery with % RSD in the desired range. The methods were found to be rapid, specific, precise and accurate and can be successfully applied for the routine analysis of meclizine hydrochloride and caffeine in their combined tablet dosage form.

Marc Benedetti – One of the best experts on this subject based on the ideXlab platform.

  • Spectroscopic in situ examination of interactions of rare earth ions with humic substances
    Water Research, 2014
    Co-Authors: Yao Chen, Marc Benedetti, Massimiliano Fabbricino, Gregory Korshin
    Abstract:

    This study utilized the methods of fluorescence quenching and differential Absorbance to probe in situ the extent and the nature of the interactions between rare earth ions (REIs) and humic substances. Experiments were conducted with the standard Suwannee river humic acid (SRHA) in the presence of varying amount of lanthanum, europium and terbium. The data of differential Absorbance showed that the mechanism of SRHA-metal complexation was largely the same for all the examined REIs. In all cases several discrete bands whose properties were discerned via numerical decomposition of the differential spectra Absorbance were observed. Their nature was examined based on the comparison of the experimental data and those of NICA-Donnan modeling carried out for Eu3+. The observed effects suggested that the changes of SAHA Absorbance induced by REIs binding are likely to be caused by a bathochromic shift of the Absorbance bands associated with such chromophores. The intensity of the Gaussian band with a maximum at 387 nm was observed to be proportional to the total concentration of SRHA-bound REIs. The data obtained in this study demonstrate the existence of complex yet quantifiable changes of the spectroscopic properties of humic species in the presence of REIs and their utility to quantify modes of interactions in such systems.

  • Study of iron and aluminum binding to Suwannee River fulvic acid using Absorbance and fluorescence spectroscopy: Comparison of data interpretation based on NICA-Donnan and Stockholm humic models
    Water Research, 2013
    Co-Authors: Mingquan Yan, Marc Benedetti, Gregory Korshin
    Abstract:

    This study examined the evolution of Absorbance and fluorescence spectra of standard Suwannee River fulvic acid (SRFA) induced by its interactions with iron and aluminum. The results show that changes of SRFA Absorbance are associated with a consistent response of the carboxylic and phenolic functional groups to iron and aluminum forming bonds with these groups, and their deprotonation induced by such binding. The observed changes of SRFA Absorbance were quantified via the use of DSlope(325-375) parameter that determines the behavior of the slope of logarithms of SRFA Absorbance in the range of wavelengths 325 -375 nm in the presence of varying concentrations of iron or aluminum. DSlope(325-375) values were correlated linearly with the concentration of SRFA-bound iron and aluminum determined using either NICA-Donnan or Stockholm Humic Model (SHM) but the correlation was stronger for the former model (R-2 > 0.98). The slopes of these correlations were similar for both iron and aluminum concentrations

  • In situ study of binding of copper by fulvic acid: Comparison of differential Absorbance data and model predictions
    Water Research, 2012
    Co-Authors: Mingquan Yan, Deborah Dryer, Gregory Korshin, Marc Benedetti
    Abstract:

    This study examined the binding of copper(II) by Suwannee River fulvic acid (SRFA) using the method of differential Absorbance that was used at environmentally-relevant concentrations of copper and SRFA. The pH- and metal-differential spectra were processed via numeric deconvolution to establish commonalities seen in the changes of Absorbance caused by deprotonation of SRFA and its interactions with copper(II) ions. Six Gaussian bands were determined to be present in both the pH- and Cu-differential spectra. Their maxima were located, in the order of increasing wavelengths at 208 nm, 242 nm, 276 nm, 314 nm, 378 nm and 551 nm. The bands with these maxima were denoted as A0, A1, A2, A3, A4 and A5, respectively. Properties of these bands were compared with those existing in the spectra of model compounds such as sulfosalicylic acid (SSA), tannic acid (TA), and polystyrenesulfonic acid-co-maleic acid (PSMA). While none of the features observed in differential spectra of the model compound were identical to those present in the case of SRFA, Gaussian bands A1, A3 and possibly A2 were concluded to be largely attributable to a combination of responses of salicylic- and polyhydroxyphenolic groups. In contrast, bands A4 and A5 were detected in the differential spectra of SRFA only. Their nature remains to be elucidated. To examine correlations between the amount of copper(II) bound by SRFA and changes of its Absorbance, differential Absorbances measured at indicative wavelengths 250 nm and 400 nm were compared with the total amount of SRFA-bound copper estimated based on Visual MINTEQ calculations. This examination showed that the differential Absorbances of SRFA in a wide range of pH values and copper concentrations were strongly correlated with the concentration of SRFA-bound copper. The approach presented in this study can be used to generate in situ information concerning the nature of functional groups in humic substances engaged in interactions with metals ions. This information can be useful for further elaboration and development of detailed theoretic models that describe the complexation of metals in the environment