title: [Absolute quantification of carminic acid in cochineal extract by quantitative NMR].
abstract: A quantitative NMR (qNMR) method was applied for the determination of carminic acid. Carminic acid is the main component in cochineal dye that is widely used as a natural food colorant. Since several manufacturers only provide reagent-grade carminic acid, there is no reference material of established purity. To improve the reliability of analytical data, we are developing quantitative nuclear magnetic resonance (qNMR), based on the fact that the intensity of a given NMR resonance is directly proportional to the molar amount of that nucleus in the sample. The purities and contents of carminic acid were calculated from the ratio of the signal intensities of an aromatic proton on carminic acid to nine protons of three methyl groups on DSS-d6 used as the internal standard. The concentration of DSS-d6 itself was corrected using potassium hydrogen phthalate, which is a certified reference material (CRM). The purities of the reagents and the contents of carminic acid in cochineal dye products were determined with SI-traceability as 25.3-92.9% and 4.6-30.5% based on the crystalline formula, carminic acid potassium salt trihydrate, which has been confirmed by X-ray analysis. The qNMR method does not require a reference compound, and is rapid and simple, with an overall analysis time of only 10 min. Our approach thus represents an absolute quantitation method with SI-traceability that should be readily applicable to analysis and quality control of any natural product.
authors.affiliation: National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Sugimoto
authors.forename: Atsuko
authors.initials: A
authors.lastname: Tada
authors.forename: Takako
authors.initials: T
authors.lastname: Suematsu
authors.forename: Kazunori
authors.initials: K
authors.lastname: Arifuku
authors.forename: Takeshi
authors.initials: T
authors.lastname: Saito
authors.forename: Toshihide
authors.initials: T
authors.lastname: Ihara
authors.forename: Yuuichi
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Reiji
authors.initials: R
authors.lastname: Kubota
authors.forename: Maiko
authors.initials: M
authors.lastname: Tahara
authors.forename: Kumiko
authors.initials: K
authors.lastname: Shimizu
authors.forename: Sumio
authors.initials: S
authors.lastname: Ito
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Yoko
authors.initials: Y
authors.lastname: Kawamura
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Nishimura
mesh_terms: D002329:Carmine / Q000031:analogs & derivatives* / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D004396:Coloring Agents / Q000032:analysis*; D005505:Food Coloring Agents / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*
chemical_list: D004396:Coloring Agents; D005505:Food Coloring Agents; D002329:Carmine