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wavelengths as concentrations change, creating the impression that the isosbestic point is 'out of focus', or that it will shift as conditions change. The reason for this is that it would be very unlikely for three compounds to have extinction coefficients linked in a linear relationship by chance
589:
The requirement for an isosbestic point to occur is that the two species involved are related linearly by stoichiometry, such that the absorbance is invariant at a certain wavelength. Thus, ratios other than 1-to-1 are possible. The presence of an isosbestic point typically indicates that only
145:
is a specific wavelength, wavenumber or frequency at which the total absorbance of a sample does not change during a chemical reaction or a physical change of the sample. The word derives from two Greek words: "iso", meaning "equal", and "sbestos", meaning "extinguishable".
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species that vary in concentration contribute to the absorption around the isosbestic point. If a third one is partaking in the process, the spectra typically intersect at
879:
200:) involves a pair of substances with an isosbestic point, the absorbance of the reaction mixture at this wavelength remains invariant, regardless of the
817:
307:
89:
863:
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61:
576:{\displaystyle A=l\cdot (\epsilon _{X}c_{X}+\epsilon _{Y}c_{Y})=l\cdot \epsilon \cdot (c_{X}+c_{Y})=l\cdot \epsilon \cdot c}
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940:: Total synthesis of vitamin B12 provided a framework for exploration in several areas of organic chemistry".
57:
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787:. The isosbestic points provide proof for a direct conversion of the seco-corrin complex to the metal-free
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does not depend on the extent of reaction (i.e., on the particular concentrations of X and Y)
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750:(541 nm). The wavelength of the isosbestic point determined does not depend on the
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204:(or the position of the chemical equilibrium). This occurs because the two substances
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spectrum. The spectra of basic, acid and intermediate pH solutions are shown. The
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The absorbance of the reaction mixture (assuming it depends only on X and Y) is:
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A pair of substances can have several isosbestic points in their spectra.
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Isosbestic points are used in medicine in a laboratory technique called
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the analytical concentration is the same at any point in the reaction:
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without intermediary or side products (within the detection limits of
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But at the isosbestic point, both molar absorptivities are the same:
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corresponds to a wavelength at which these spectra cross each other.
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of the substance used, and so it becomes a very reliable reference.
24:
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When an isosbestic plot is constructed by the superposition of the
850:
and Arthur
Atwater Frost (3rd Edition, John Wiley and Sons, 1981)
936:; Wintner, C. E. (1977). "Natural Product Synthesis and Vitamin B
662:, isosbestic points are used as reference points in the study of
375:{\displaystyle A=l\cdot (\epsilon _{X}c_{X}+\epsilon _{Y}c_{Y})}
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and keeping the same molar concentration for both species), the
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light of that specific wavelength to the same extent, and the
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429:{\displaystyle \epsilon _{X}=\epsilon _{Y}=\epsilon \,}
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of an A/D-seco-corrin to the corresponding metal-free
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ring closure reaction, which was the key step in the
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have (not exclusively) isosbestic points at 586
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page 49 of
Kinetics and Mechanism By John W. Moore,
49:. Unsourced material may be challenged and removed.
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670:remains constant throughout the whole reaction.
757:One example of the use of isosbestic points in
738:of the substance). The standards used include
681:concentration, regardless of its saturation.
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16:Spectroscopic property in chemical reactions
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109:Learn how and when to remove this message
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133:of the dye is the same in all solutions.
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162:for the representation, or by using
47:adding citations to reliable sources
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696:Isosbestic points are also used in
13:
823:Compendium of Chemical Terminology
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14:
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158:of two species (whether by using
728:conditions (above and below the
716:. This is done by measuring the
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601:for one particular wavelength.
290:{\displaystyle c_{X}+c_{Y}=c\,}
34:needs additional citations for
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237:{\displaystyle X\rightarrow Y}
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904:(Promotionsarbeit Nr. 5158).
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666:, as the absorbance at those
890:Total Synthesis of Vitamin B
7:
881:Totalsynthese von Vitamin B
10:
1008:
746:(325 and 498 nm) and
894:: The Photochemical Route
621:system, measured through
911:10.3929/ethz-a-000086601
885:: Der photochemische Weg
210:analytical concentration
131:analytical concentration
125:Isosbestic point in the
878:Fuhrer, Walter (1973).
836:10.1351/goldbook.I03310
440:Hence, the absorbance
964:10.1126/science.867037
704:method, to verify the
693:and near 808 nm.
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740:potassium dichromate
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43:improve this article
956:1977Sci...196.1410E
950:(4297): 1410–1420.
920:20.500.11850/131362
900:(PhD) (in German).
796:UV/VIS spectroscopy
653:UV/VIS spectroscopy
176:When a 1-to-1 (one
770:cycloisomerization
698:clinical chemistry
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638:cycloisomerization
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215:For the reaction:
212:remains constant.
202:extent of reaction
160:molar absorptivity
156:absorption spectra
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58:"Isosbestic point"
864:978-0-471-03558-9
759:organic synthesis
724:at two different
722:standard solution
714:spectrophotometer
702:quality assurance
660:chemical kinetics
194:chemical reaction
127:bromocresol green
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687:deoxyhaemoglobin
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683:Oxyhaemoglobin
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633:Following the
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60: –
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54:Find sources:
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32:This article
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992:Spectroscopy
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605:Applications
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139:spectroscopy
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41:Please help
36:verification
33:
774:Eschenmoser
668:wavelengths
615:haemoglobin
196:(including
902:ETH ZĂĽrich
802:References
778:ETH ZĂĽrich
710:wavelength
679:hemoglobin
198:equilibria
184:gives one
164:absorbance
99:March 2022
69:newspapers
781:vitamin B
748:congo red
568:⋅
565:ϵ
562:⋅
524:⋅
521:ϵ
518:⋅
490:ϵ
467:ϵ
460:⋅
423:ϵ
411:ϵ
398:ϵ
351:ϵ
328:ϵ
321:⋅
229:→
986:Category
706:accuracy
675:oximetry
640:of a Cd
182:reactant
952:Bibcode
943:Science
718:spectra
708:in the
700:, as a
642:complex
598:varying
190:product
83:scholar
972:867037
970:
896:]
862:
854:
792:ligand
789:corrin
767:corrin
649:ligand
646:corrin
206:absorb
85:
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898:(PDF)
888:[
818:IUPAC
720:of a
712:of a
141:, an
90:JSTOR
76:books
968:PMID
860:ISBN
852:ISBN
798:).
765:A/D-
685:and
613:The
186:mole
178:mole
62:news
960:doi
948:196
916:hdl
906:doi
832:doi
830:".
658:In
651:by
593:two
188:of
180:of
137:In
45:by
988::
966:.
958:.
946:.
938:12
914:.
892:12
883:12
870:^
858:,
820:,
810:^
783:12
776:/
726:pH
691:nm
617:/
192:)
974:.
962::
954::
922:.
918::
908::
834::
735:a
732:K
730:p
571:c
559:l
556:=
553:)
548:Y
544:c
540:+
535:X
531:c
527:(
515:l
512:=
509:)
504:Y
500:c
494:Y
486:+
481:X
477:c
471:X
463:(
457:l
454:=
451:A
436:.
420:=
415:Y
407:=
402:X
382:.
370:)
365:Y
361:c
355:Y
347:+
342:X
338:c
332:X
324:(
318:l
315:=
312:A
297:.
284:c
281:=
276:Y
272:c
268:+
263:X
259:c
232:Y
226:X
112:)
106:(
101:)
97:(
87:·
80:·
73:·
66:·
39:.
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