Separation and ldentiiicationof Cinnamic Acids by TLC Cinnamic acids are among the most frequently found organic acids in plant extracts' and are the acids generally esterified a t C4 of the sugar moiety of antho~yanins.~ Paper chromatography has been used2 to separate several cinnamic acids. while TLC has heen less suecessful.3 We wish to report the separation and identification of cinnamicacids from their mixtures by TLC
Experlmedal Dilute EtnOsolutmn Of several cinnamic acids (see table) were spatted on silica gel plates4 previously activated for 4 h at 90-95 OC. The partially or totally air-dried, developed plates were sprayed with a 2% solution of FeC13acidified with 2 N HC1.3 The colors produced were visually stable for several hours. Dlscusslon and Results 'l'hr Rr's reported in the tahle are the mean values of at least firedifferent rhrumawgrams run at 20-25 Y!. The Rtvalues ohtnined w t h literature reporred solvents rfoutnoter o, (I, c, and d in the table) are very similar and considrrnhl~ overlapping occurs in mixtures of acids. Chromatographic Charaderlstlcs of Clnnamlc Add and Its Derlvatlves
Acid
BAWa
cinnamic phydroxy (coumaric) 3.4dihydroxy (caffeic . 3-methoxy-4-hydmxy (ferulic) 3.5di-methow-4hydroxy (sinapic)
.BAW. n-butanol-acstic acid-water, 6:1:2. dCMF: chlaoform-methand-brmic acid. 85:10:5. RN: Rpropanol-ammaniumhydroxide. 7 9 . 6TAW: m l ~ ~ n e - a ~ acid-water. eti~ 4:1:5 (upper layer).
CMFa
RNr
TAWa
TAEo
TAE'
TAEg
Color TAE~withFeCI~I
0.74 0.61 0.49 0.60 0.55 0.65 0.62 0.69
0.68 0.48 0.29 0.33 0.47 0.61 0.57 0.64
0.76 0.56 0.37 0.60 0.51 0.71 0.84 0.68
brightyellow orange dark green light brown bright pink dull yellow orange reddish oranae
.TAE: mlusne-acetic acid-ethanol. 4:l:l. ITAE: taluene-aceticacid-ethanol. 5:1:1. ITAE: mluene-acetic acibethanol. 10:2:1.
V A E : mbene-acetic acid-ethanol. 153:l.
While paper generally required several hours for a satisfactory migration of the solvent front, by using the TAE solvents the developing time was shortened to less than 30 min. Very little overlapping occurred, resulting in a clear identification of the colors in the sprayed chromatogram. The use of FeC13 as an inexpensive ehromogenie agent, instead of more complex methods,' is recommended for the distinct and stable colors produced with various cinnamic acids.
Acknowledgment One of us (S. C. de S.') gratefully acknowledges s scholarship granted hy FundaqBo de Amparo Pesquisa do Estado de SBo Paulo.
a
Rib6rau-Oayon, P. Les m p o s & ph@noliqoesdes veg8taux;Dunod: Paris, 1968: 89. Francis. F. J. In Anfhocyanins as F w d Colors: Msrkakis. P.. Ed.; Academic: New York. 1982; Chap 7 Pitferi. P. G. Vitis, 1965, 5. 24. Silica Gel G, hom Merck, West Germany.
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Florlnda 0. Bobblo, Paulo A. Bobblo, and Sandra C. d e SOUZa DBpartamentO de Ciencia de Alimentos, Faculdade de Engenharia de Alimentas. universidade Estadual de Campinas, 13081 Campinas. SP., Brazil
182
Journal of Chemical Education
