The UV-Vis Hydrocarbon Analysis detects the alteration product of the fulvic acid fraction of the soil organic matter. Fulvic acid is the low moleculer weight component of soil humins. The main chemical constituents are carbonxyl acids and phenols. The compositional structure of fulvic acids vary considerably due to attached aliphatic side chains. The interesting thing is that they can incorporate available organic material into large voids present in the molecules structure. Condensation and addition reactions hold seepage related hydrocarbons that measurably alter available soil organic material.
Altered humic acids are soluble at high pH and are therefore present in the high pH halo position of a seepage anomaly. These are larger molecules containing more carbon and less oxygen than fulvic acid. Due to structural similarities to fulvic acid, humic acid will follow many of the same physical and chemical models. The Extracted Hydrocarbon Analysis exhibits low to moderate correlation with other geochemical methods which may be related to the limited pH range.
The monosaccharide portion of soil organic matter is water soluble and easily put into solution. The open aldehydes and ketones are subsequently converted to carboxyls with reduction of copper. The resulting colored solution is measured spectrophotometrically and an absorbance value is obtained. A high absorbance value is analogous to a high concentration. The Reducing Hydrocarbon Analysis hydrocarbons exhibit low to moderate correlations related to the solubility differences between monosaccharides, disaccharides, and water insoluble polysaccharides.