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RESEARCH PRODUCT
Spectrophotometric Determination of Cystine with O-Phthalaldehyde in the Absence of Thiol
M.j.medina HernándezR. M. Villanueva CamañasM.c.garcía Alvarez-coqueC.mongay Fernándezsubject
chemistry.chemical_classificationChromatographyBiochemistry (medical)Clinical BiochemistryCystineProtonationBiochemistryAnalytical ChemistryAmino acidchemistry.chemical_compoundO-PhthalaldehydechemistryElectrochemistryThiolAbsorption (chemistry)SpectroscopyDerivative (chemistry)StoichiometryNuclear chemistrydescription
Abstract A spectrophotometric method for the determination of cystine with o-phthalaldehyde (OPA) in the absence of thiol is described. When cystine is heated at 60[ddot]C for 30 min in a low excess of OPA (pH 9.5), a very stable derivative with 1:2 stoichiometry (cystine:OPA) and an absorption maximum at 335 nm (E = 4600) is formed. At pH < 1 the derivative is protonated (protonation constants: log K1 = 5.88 and log K2 = 3.70 at I = 0.1 and 20[ddot]C) and another absorption band at 440 nm (E = 3800) appears, which allows the determination of cystine in the presence of other amino acids.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 1988-09-01 | Analytical Letters |