| 释义 |
isosbestic, a. Physical Chem.|aɪsəʊsˈbɛstɪk|
Also erron. isobestic.
[ad. G. isosbestisch (A. Thiel et al. 1924, in Fortschr. d. Chem. XVIII. 116), f. Gr. ἴσος equal + σβεστ-ός extinguished (f. σβεννύναι to quench, extinguish): see -ic.]
isosbestic point: a wave-length at which the absorption of light by a liquid remains constant as the acidity varies or, more generally, as the state of equilibrium between two interconvertible substances or states shifts.
1925Chem. Abstr. XIX. 2180 Photometric measurements of the absorption spectra were plotted for equal degrees of acidity and these curves intersected in general in the ‘isobetic’ point [sic: rendering G. isosbestischer Punkt.]. 1943W. R. Brode Chem. Spectroscopy (ed. 2) ix. 249 (caption) Spectrophotometric determination of hydrogen-ion concentration; mixed indicator (methyl red + bromothymol blue). (Note isosbestic points at 467 and 500 mµ.) 1954Trans. Faraday Soc. L. 802 The ionized form exhibits absorption at a longer wave-length (251 mµ) than the non-ionized (239 mµ) and there is an isobestic point at 245 mµ. 1958Meites & Thomas Adv. Analytical Chem. viii. 277 The spectra of a number of solutions having equal formal concentrations of bromthymol blue but different pH values will all intersect at 501 mµ. Such a point is known as an isosbestic point, and the appearance of such a point on a family of spectra is a necessary (but not quite sufficient) criterion of the presence of two and only two forms of the absorbing substance in equilibrium with each other. 1960Jrnl. Biol. Chem. CCXXXV. 1026/2 Each of the absorption maxima and isosbestic points is essentially the same for normal as well as for sickle cells and homozygous C hemoglobins. 1962R. E. Dodd Chem. Spectroscopy v. 299 The absence of an isobestic point indicates a more complex system. 1971F. A. Bettelheim Exper. Physical Chem. xiii. 144 The absence of an isobestic point is definite proof of the presence of more than two absorbing species. 1972Nature 24 Mar. 140/2 Control measurements are made at an isosbestic point for the rhodopsin and the product.
¶ Other anomalous forms (with quot. 1939 cf. quot. 1943 above).
1939W. R. Brode Chem. Spectroscopy ix. 206 There will be a point..where the extinction curves should have a common value at any pH concentration. Such a point is known as an isobastique point. 1949A. C. Candler Pract. Spectroscopy iv. 90 As one absorption curve fades, another develops, while the absorption at an intermediate wavelength, called by Brode the isobastic point, remains unaltered. Ibid. 91 The indicator should be of standard strength, but slight variations may be corrected if the absorption at both the centre of the absorption band and at the isobastic point are measured. |