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Denoting the wavelength of light at which two related compounds have identical extinction coefficients; for example, the wavelength at which the absorption spectra of hemoglobin and oxyhemoglobin cross is their isosbestic point. Spectrophotometry at that wavelength measures total concentration of hemoglobin, regardless of the extent to which it might be oxygenated.
[Ger. isosbestisch, fr. G. isos, equal, + sbestos, extinguished]
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References in periodicals archive ?
Two isosbestic points are detectable, at 515 nm (Figure 5(b)) and 556 nm, respectively, indicating the formation of a certain complex between [beta]-carotene and gold nanoparticles.
All the three redox pairs have isosbestic points at 230-240 nm suggesting a minimal interference with the robust signal of conjugated dienes.
The above spectral changes also demonstrate an isosbestic point which evidences that the molecule possesses two forms which transform to each other.
The state of equilibrium between various protonated and deprotonated species was examined from the spectral changes like shifting of peaks and formation of isosbestic points.
Excitation with the 360 nm filter (close to the Fura-2 isosbestic point) allowed observation of the cells' morphology and of the changes in the concentration of the dye, irrespective of the changes in [[[Ca.sup.2+]].sub.i], while the 360/380 nm ratio allowed visualization of the [[Ca.sup.2+]].sub.i] changes in the cytoplasm.
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.
We measured the absorbance at 540 nm (COHb) and 555 nm (isosbestic point) and calculated the percent COHb concentration.
Fura-2 fluorescence was alternately excited at the isosbestic point (357 nm) and at the calcium-sensitive wavelength (.380 am), and the ratio of fluorescence emission ([[F.sub.357]/[F.sub.380]) in regions of interest positioned around cell somata was calculated.
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.
An isosbestic point at 575 nm also provided an evidence for the new Tm(III)-ASA complex formation.