[Densitometric method for parallel measurement of rosmarinic and caffeic acids in plant samples].
In the last few years, the role of free radicals in the promotion of cell aging and tumour growth has focused attention on phenolic compounds. Rosmarinic acid (RA) and caffeic acid (CA), as major components of tannins, commonly occur together in many species of the Lamiaceae. A TLC-densitometric method was introduced for the parallel determination of RA and CA. Experiments were performed to establish the optimal measurement parameters related to the excitation wavelength, colour stability, linearity of the calibration curves, sensitivity and reproducibility. In the wavelength range 290-330 nm, it was found that the emission peak areas exhibit a maximum at 325 nm. Therefore, the densitometric evaluations of these tannins were made at 325 nm. The two compounds behaved very similarly as regards colour stability. The changes during the 3 hours of observation were not strong, as reflected by coefficients of variation of 8.20% for RA and 5.40% for CA. The calibration plots demonstrating the relation between the spotted amount and the measured peak area were found to include 2 intersecting linear sections, in the intervals 0-0.40 microgram and 0.40-1.20 micrograms for RA and 0-0.08 microgram and 0.08-0.30 microgram for CA. The correlation coefficients ranging between 0.991 and 0.998. The lower limits of detection were 1 ng for RA and 0.1 ng for CA. The reproducibility proved to be very good: the 10 times repeated densitometric estimation of the same spot yielded a coefficient of variation of 0.34% for RA and 0.36 for CA. The application of TLC permits utilization of the fluorescence of both phenols, often without the need for prior purification. This fluorescence measurement makes the detection extremely sensitive. The densitometric quantification allows the routine analysis of many samples in a short time with reasonable accuracy. The practical application of the elaborated method will be demonstrated on the leaves of 5 Salvia species. The results are shown in table I.
Janicsák
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MTA Okológiai és Botanikai Kutató Intézet, Szeged.
Máthé
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D000975:Antioxidants / Q000032:analysis*; D002109:Caffeic Acids / Q000032:analysis*; D002138:Calibration; D002855:Chromatography, Thin Layer / Q000379:methods; D002934:Cinnamates / Q000032:analysis*; D003720:Densitometry / Q000379:methods; D053630:Depsides; D019686:Lamiaceae / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D000097123:Rosmarinic Acid
D000975:Antioxidants; D002109:Caffeic Acids; D002934:Cinnamates; D053630:Depsides; D000097123:Rosmarinic Acid; C040048:caffeic acid