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 ?
This technique utilizes reflected polarized light at the wavelength of the isosbestic point of oxy- and deoxyhemoglobin (548 nm).
The absorption intensity of the complexes was affected resulting in the tendency of hyperchromism (in the range of 224-270 nm) and no red shift (small shift ~2nm for [C.sub.2]) and no sharp isosbestic points on the concomitant addition of DNA to the fixed concentration of complexes were observed.
One clear isosbestic point that is observed at 685 nm (Figure 3(b)) proves that the phenomenon is due to some equilibrium processes leading to the formation of chemical intermediates between [beta]-carotene and the MnTTPCl/n-Au hybrid.
The performance of the measuring system can be probably further improved by (i) increasing the signal to noise ratio of the block PD/front-end electronic/ADC (see Figure 9) by redesigning the electronic and/or exploiting best performing components, (ii) tuning the bandwidth of the source, and (iii) exploiting the isosbestic point of the CENTA spectra, thus measuring the absorption of the sample also at 370 nm (see Figure 5).
Retinal images of the same area are captured at a wavelength sensitive (nonisosbestic) and insensitive (isosbestic) to changes in absorptivity between oxygenated and deoxygenated hemoglobin.
The average isosbestic point was 363 nm, and we found an almost linear relation between [[Ca.sup.2+]] and the fluorescence intensity (excitation ratio 360/380) from 17 nM to 1.35 [micro]M of [[Ca.sup.2+]].
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.
The [Mn.sup.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.sup.2+].sub.i] and emission at 510 nm.
From fluence- compensated PA measurements at the isosbestic wavelengths of hemoglobin (498 nm, 568 nm, and 794 nm), the PA signal amplitude reflects the CHb distribution, regardless of the oxygenation level [5].
Moreover, the isosbestic point about 308 nm gives support to the DNA/Au@tiopronin complex formation.
An isosbestic point at 472 nm (Figure 1) supports this conclusion, since it indicates that only two molecular forms are present in the solution.