Organic solvent extraction and spectrophotometric quantification of total phenolic content of soil

Abstract

Phenolic compounds are regarded as the most abundant plant metabolites that are known to decompose progressively into soils, likened to other soil organic materials. Once assimilated into soils, they can control soil processes, including organic matter decomposition and nutrient cycling. Established that phenolic compounds can influence nutrients availability and soil quality, it becomes crucial to investigate into soil phenolics through the application of appropriate extraction technique and quantification of ​total phenolic content ​in soils. This study therefore aimed at utilizing ethanol, hexane and diethyl ether organic solvents to extract and quantify total phenolic content of soil, sampled from a vegetable growing area. Conventional organic solvent extraction method was employed to extract phenolics, while spectrophotometric technique was utilized to quantify total phenolic content. The highest extraction yield of 34.52% was achieved with ethanol followed by diethyl ether (28.23%) and hexane (25.47%). Interestingly, hexane, which had the least extraction yield, rather recorded the highest phenolics concentration of 5.50 ± 0.02 mgGAE/g, with ethanol producing a concentration of 2.04 ± 0.05 mgGAE/g and 3.82 ± 0.01 mgGAE/g for diethyl ether. The percent recovery, limit of detection (LOD) and limit of quantification (LOQ) of phenolic compounds were found to be 102%, 0.8 mg/g and 1.5 mg/g for ethanol; 96%, 0.6 mg/g and 1.2 mg/g for diethyl ether and 94%, 0.4 mg/g and 1.0 mg/g for hexane respectively. These results indicate that for an extraction efficiency and greater yield, the use of ethanol as solvent is preferred whereas extraction using hexane is suitable for total phenolics quantification. The findings of this study have provided a vital insight regarding the influence of organic solvents on the extractability and quantification of total phenolic content of soil.

Keywords: Organic solvents; Soil; Spectrophotometry; Total phenolic content.

Figure 1

A bar chat representation of the influence of organic solvents on the extraction yield and total phenolic content of soil from vegetable growing area. TPC = Total Phenolic Content. Different letters (a, b and c) indicate statistically significant difference (P < 0.05) among solvents. Thus, extraction yield: P = 0.0326 and TPC: P = 0.0214.

Figure 2

UV-visible spectra of total phenolic content of organic solvent soil extracts.