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EXTRACTION OF PHENOLIC COMPOUNDS FROM A SPODOSOL PROFILE: AN EVALUATON OF THREE EXTRACTANTS

We extracted phenolic compounds from each horizon of a Spodosol profile using three extractants: 0.1 M sodium pyrophosphate at pH 7.0 and 10.2, and 0.5 N sodium hydroxide at pH 13.4. Of 28 standard compounds evaluated seven phenolic compounds were identified: three carboxylic acids—protocatechuic, p-hydroxybenzoic, and vanillic acids; two aldehydes—vanillin and p-hydroxybenzaldehyde; and two cinnamic acids—trans p-coumaric and ferulic acids. The three most abundant compounds evaluated were protocatechuic acid, p-hydroxybenzoic acid, and vanillic acid. The amounts of each phenolic compound extracted increased with increasing pH of the extractant except for protocatechuic acid. Protocatechuic acid was extracted in the highest amounts by sodium pyrophosphate pH 10. The pyrophosphate (pH 10) extracts revealed that protocatechuic acid tended to accumulate in the B horizons, suggesting that it may play a role in the translocation of metal ions during podzolization. The two cinnamic acids, trans p-coumaric and ferulic, were extracted primarily by NaOH. The identification of these cinnamic derivatives in an NaOH extraction of roots separated from the Bh horizon suggested that their presence may be due to degradation of plant residues by NaOH. Pyrophosphate (pH 7) extracted only small amounts of phenolic compounds. The specificity of pyrophosphate (pH 10) in removing organic complexes of a possible pedogenic nature suggests that it was the better extractant. Sodium pyrophosphate (pH 10) is recommended for use in future pedological studies of phenolic substances.