isosbestic point

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isosbestic point

[‚ī·səs‚bes·tik ′point]
(physical chemistry)
During a chemical reaction, a point in the absorption spectrum (that is, a wavelength) where at least two chemical species (for example, reactant and product) have identical molar absorption coefficients, which remain constant as the reaction proceeds. A stable isosbestic point is evidence that a reaction is proceeding without forming an intermediate or multiple products.
References in periodicals archive ?
They either measure the absorbance of whole blood photometrically at the isosbestic point--the wavelength in which the absorbance the two main hemoglobin derivatives, oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb), is the same--or, more recently, use broad spectrum photometry with multiple wavelength to get an overall picture of the absorbance spectrum, while scattered light is prevented from arriving at the sensor.
Antioxidants themselves also absorbed in the UV range; however their difference "oxidized minus reduced" spectra had isosbestic points close to 234 nm (Figure 4) and therefore could not notably contribute to the absorbance changes as monitored at 234 nm.
2+]-induced quenching of fura-2 fluorescence was estimated at 360 nm excitation wavelength (F360), which represents the isosbestic wavelength and is not sensitive to the changes in the [[Ca.
Furthermore, spectroscopic titration studies for the interaction of these food additives with DNA showed that these dyes bind to calf thymus DNA and distinct isosbestic points are observed clearly suggesting binding of the dyes to DNA.
Fura-2 fluorescence was alternately excited at the isosbestic point (357 nm) and at the calcium-sensitive wavelength (.
A separate measurement at an isosbestic point (815 nm for hemoglobin), a wavelength at which the absorption coefficients of the two species are equal, provides the total amount of reduced and oxidized forms, which is proportional to blood volume.
Overlapping the absorbance spectra for mixtures of ITX and MA having differing irradiation times between 0 and 60 min showed that a single isosbestic point was produced at approximately 350 nm (Fig.
While in the presence of increasing concentration of CTAB in a fixed concentration of 5-FU, the signal at 206 nm showed increase in absorbance (hyperchromic effect) accompanied with red shift (bathochromic effect), generation of another signal at 296 nm and an isosbestic point.