Biomedical subjects

Tom Lindfors

Publications and source records attributed to Tom Lindfors.

3 recordsLinked to original sources

PubMed2007

Application of raman spectroscopy and sequential injection analysis for pH measurements with water dispersion of polyaniline nanoparticles.

A novel method for pH measurements between pH 7.5 and 10.4 is reported in this paper. The method combines Raman spectroscopy and the automated sequential injection analysis system (SIA) and makes use of the acid-base properties of a commercially available water dispersion of polyaniline (PANI) nanoparticles with a mean particle size of 46 nm. The useful pH range of the PANI nanoparticles is broader than for conventional acid-base indicators, due to the 1:2 reaction stoichiometry of the proton-ligand complex of the nanoparticles. The pH measurements were conducted with the 633-nm laser excitation wavelength by calculating the difference between the Raman intensities of the primary and reference wavenumbers. In this study, the pH-sensitive CH=CH stretching band at 1422 cm-1 and C-H in-plane bending band of the quinoid form at 1163 cm-1 were chosen as the primary wavenumbers. The presented method is fast and allows pH to be measured with a precision of 0.2 pH unit. The advantage of the proposed method is that the hysteresis effect, which is usually observed for PANI films, can be overcome with the PANI nanoparticles, because a fresh nanoparticle solution is used in each measurement. It should be pointed out, that this work is a fundamental study showing the applicability of Raman spectroscopy in combination with the SIA technique for pH measurements in specific applications, where the conventional glass pH electrode cannot be used.

Journal Article↗

PubMed2006

Optical pH measurements with water dispersion of polyaniline nanoparticles and their redox sensitivity.

A new method for optical pH and redox measurements with a commercially available water dispersion of polyaniline (PANI) nanoparticles (mean particle size, 46 nm) is presented. The pH measurements are based on the acid-base equilibrium of PANI and were carried out either by combining both the automated sequential injection analysis (SIA) and UV-visible spectrophotometric techniques or with a fiber-optic light guide. In the former case, the detection was done in continuous mode at lambda = 800 nm by using the SIA technique for transporting the sample to a flow-through cell, which was placed in the light path of the photometer. With the fiber-optic light guide, the detection was done in batch mode at lambda = 400 and 580 nm. In both methods, fresh pH reagent (PANI) solution was used in each measurement, thus overcoming the problem with hysteresis (memory effect), which is usually observed with PANI films. The PANI nanoparticles were characterized with UV-visible spectroscopy in pH buffer solutions between pH 2-12 and a protonation constant of logK(0.5H,L)(H(0.5)L) = 4.4 was calculated from these data. Fast pH measurements can be done between pH 6 and 10.5 depending on the measuring technique. It is possible to determine pH with an accuracy of 0.1 pH unit between pH 8 and 10.5 (RSD, 0.5-2%). Redox transitions typical for PANI films were also observed for water solutions of PANI nanoparticles in the presence of the hexacyanoferrate(II/III) and the iron(II/III) oxalate redox couples. The absorbance at lambda = 875 nm is linearly dependent on the logarithm of the concentration ratio (0.1-10) of the iron oxalate redox couple.

Aniline Compounds↗

PubMed2004

Stability of the inner polyaniline solid contact layer in all-solid-state K+-selective electrodes based on plasticized poly(vinyl chloride).

A simple and powerful method based on UV-visible spectroscopy is presented for studying the stability of the inner electrically conducting polyaniline (PANI) solid contact (SC) layer in all-solid-state ion-selective electrodes (ISE). The influence of the plasticized poly(vinyl chloride) (PVC) membrane (ISM) composition and the pH of the sample solution on the stability of the solid contact is reported. PANI is used as a model compound in this study, but the method presented is universal and can be applied to different types and combinations of SCs and ISMs. It provides a tool for finding the best combination of conducting polymer and ISM for solid contact ISEs. PANI is deposited electrochemically either on glassy carbon or quartz glass covered with a thin layer of tin oxide, and a K+-selective ISM is deposited on top of the PANI layer. The short-term stability of the inner PANI layer is good for all membrane types in buffer solutions with pH 2, 6, and 9, indicating that the outer plasticized PVC membrane hinders the emeraldine salt-emeraldine base transition of the highly pH sensitive PANI layer. The solid contact K+-selective electrodes studied showed a Nernstian response of 58.2 +/- 0.1 mV/log aK. Significant differences are observed in the long-term stability of the inner PANI layer between the different membrane types. This indicates that water uptake of the PVC membrane and its permeability to OH- ions are critical parameters affecting the stability of the PANI layer. The solid contact electrodes based on PANI may require a composition of the PVC membrane different from those typically used in conventional ISEs with an inner solution.

Journal Article↗