Abstract
Qualitative analysis of organic acids has never been reported for sugar maple sap, but only for its products, "sugar sand" and maple syrup. A gas chromatographic (GC) method is described for the simultaneous determination of up to 13 nonvolatile organic acids in sugar maple sap. Sap is filtered through Celite, and acids are isolated via cation- and anion-exchange chromatography. Reaction of dried acids with BSA [N,O-bis(trimethylsilyl)acetamide] in the presence of pyridine and methoxyamine hydrochloride yields the more volatile TMS (trimethylsilyl) esters. Oxalic, succinic, fumaric, L-malic, tartaric, cis-aconitic, citric, and/or shikimic acids were found in maple sap at concentrations ranging from less than 50 ppb to more than 45 ppm, depending on the particular acid and the date of sap flow. Percent recoveries and coefficients of variation for the acids at the 500 ppm level were 46.0 (3.2), 92.0 (2.9), 73.0 (0.77), 94.0 (2.0), 95.0 (−), 72.0 (−), and 97.0 (0.38), respectively. Various amounts of nonvolatile organic acids are reported in the sap of one sugar maple tree throughout a sap season, and of 3 individual maples during an early sap flow. Quantitation limits were as low as 15 ppb for individual acids in the analysis of a 100 mL sap sample. Esters were separated on a mixed liquid phase column of 4% SE-52/2% SE-30 on Chromosorb W-HP. They were identified by relative retention time, using a dual flame ionization detector. Naphthalene was used as the internal standard. Concurrent identification of pyruvic, malonic, glutaric, α-ketoglutaric, cis-aconitic, and isocitric acids with those previously mentioned is also possible.
Effects of Climatic Conditions on Sap Flow in Sugar Maple