Linear Dependence Of Absorbance Research Articles

Kinetic-spectrophotometric approach to the modified Berthelot procedure for serum urea determination

The results of developed kinetic-spectrophotometric method for serum urea determination by modified colorimetric Berthelot procedure were presented in this paper. To obtain high sensitivity, all reaction rates were monitored spectrophotometrically by measuring the change of absorbance with time at 700 nm. A differential variant of the tangent method was used for the processing of the kinetic data based on linear dependence of absorbance on time. The method is valid over the 0.25–2.50 µg cm−3 urea concentration interval with RSD range 8.33–2.02%. The limit of detection was calculated as 0.09 µg cm−3. The interference effects of some metal ions, anions, antibiotics, and other molecules were investigated to access the method selectivity. The method was successfully applied for the determination of urea in human quality control blood serum.

Interactions between surfactants and {1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}

The interaction between the water-soluble anionic conjugated copolymer poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) and various surfactants has been studied in aqueous solution by UV–vis absorption spectra, fluorescence and electrical conductivity. It is suggested from the linear dependence of absorbance, fluorescence and electrical conductivity on concentration that in the absence of surfactant, moderately stable dispersions are formed. These are affected in different ways on adding cationic, anionic or neutral surfactants. With the cationic cetyltrimethylammonium bromide, quenching of fluorescence intensity and lifetime, and formation of a new emission occurs at concentrations well below the critical micelle concentration (cmc). Electrical conductivity measurements indicate a discontinuity at surfactant/polymer ratio corresponding to electroneutrality, due to complexation. With the anionic sodium dodecyl sulfate, fluorescence quenching is also observed, but is attributed to formation of some mixed polymer/surfactant aggregate. The most striking changes are observed with the non-ionic pentaethyleneglycol monododecyl ether (C 12E 5), where a blue shift in fluorescence emission, dramatic increases in lifetime and quantum yield, and changes in electrical around the cmc are interpreted in terms of incorporation of single polymer chains in elongated cylindrical micelles. This is supported by 1H NMR spectroscopic measurements.

Novel Method for Spectrophotometric Determination of L-Tryptophan in the Enzymatic Resolution of DL-N-Acetyl-Tryptophan

A novel spectrophotometric method for the determination of tryptophan (Trp) has been proposed. The sensitive and simple method was based upon the finding that NaNO2 and Trp formed a diazotized product in nitric acid medium, and that a bright magenta color developed for the product on coupling to N-(1-naphthyl) ethylenediamine dihydrochloride (NEDA) which was stable for at least 40 min. The absorption maximum was observed at 550 nm, and the apparent molar absorptivity was 8.48×103 L·mol−1·cm−1. A linear dependence of absorbance on Trp concentration allowed sensitive quantification of Trp over the range of 1–20 µg mL−1, and the detection limit was 0.5 µg mL−1. The method has been successfully applied to the determination of L-Trp in the DL-N-acetyltryptophan enzymatic resolution system. The relative standard deviations (n=6) and recoveries were found to be 0.97–2.21% and 97.5–101.3%, respectively. The accuracy of the new method was confirmed by the results from capillary electrophoresis. Furthermore, the interference study showed that DL-N-acetyltryptophan (substrate), CoCl2 (activator), and other common amino acids did not exhibit any detectable interference with Trp determination.

Polyelectrolyte self-assembled thin films containing cyclo-tetrachromotropylene for chemical and bio-sensing

Thin composite films containing cyclo-tetrachromotropylene (Chromo1) were deposited onto glass slides by means of polyelectrolyte self-assembly technique. The films obtained were characterised by UV–visible spectral measurements, and a linear dependence of absorbance on the number of deposited layers has been found. It was also found that the shape of UV–visible spectra depends on the presence of ammonia in both gaseous and liquid phases. Other amines, such as n-butylamine, can also affect the spectra. An attempt of urease immobilisation has been done using polyelectrolyte self-assembly. Composite films containing both Chromo1 and urease demonstrated the possibility of optical registration of enzyme reactions, in particular, decomposition of urea which releases ammonia. After immersion into urea solution, the samples show spectral transformations similar to those observed in the presence of ammonia.

Nonlinearity of absorbance with sample concentration and path length in evanescent wave spectroscopy using optical fiber sensors

The dependence of absorbance on sample concentration and sample length in evanescent wave spectroscopy, carried out by means of weakly guiding step index optical fiber sensors, is investigated theoretically. The absorbance is found to depend on the product of the sample bulk attenuation coefficient (α), the length of the fiber in contact with the sample ( L ), and the inverse of the normalized frequency ( V ) of the sensing section of the waveguide. When the mode volume of the fiber sensor is filled, the absorbance is predicted to vary nonlinearly with concentration (or sample length) at low values of α L/V and to increase as the cube root of α L/V at high values. However, if the mode volume of the sensing section of the fiber is only partially filled, a linear dependence of absorbance on α L/V is indicated. The results of the model are compared with experimental data already published by various groups.

Preparation of uranium(III) by mercury cathode electrolysis and its absorption spectra in hydrochloric acid solution

The reduction of hexavalent to trivalent uranium by mercury cathode electrolysis in hydrochloric acid solution was investigated. The dependence of the reducton ratio on the different media, the acid and uranium concentrations, and on the time of electrolysis was determined. It was found that hexavalent uranium can be reduced quantitatively to trivalent state by mercury cathode electrolysis. The absorption spectra of U(III) and U(IV) in 1M and 9M hydrochloric acid solutions were examined. The molar extinction coefficient of U(III) at 521 nm was 16.7 m2·mol−1 within the HCl concentration range of 0.5–4.5M. U(IV) practically does not interfere in the photometric determination of U(III) at this wavelength. A good linear dependence of absorbance on the concentration of U(III) was found.