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Accelerated solvent extraction is a relatively rapid automated method for extracting compounds of interest from plant materials. We have developed a sequential solvent extraction method that can be used to accurately quantify the rubber and resin in samples of guayule ( Parthenium argentatum Gray), a new industrial crop now in commercial production in Arizona, USA. The method assumes that the sample has been dried under suitable drying conditions. The ASE method requires the resin extraction protocol (three 20-min cycles) to be performed first, in gaseous N 2 and at 40 °C. Higher temperatures degrade the thermolabile rubber made by guayule to acetone soluble fragments. Thus, acetone temperatures above 40 °C overestimate the resin fraction and underestimate the rubber fraction in the samples being analyzed. Following removal of the resin fraction, samples are then extracted with either cyclohexane or hexane at 140 °C. Cooler temperatures do not fully solubilize the high molecular weight guayule rubber in the three 20-min cycles. Quantification of the two extracted analytes can be performed gravimetrically, as we did in this paper, or using spectrophotometric methods. Although this high rubber extraction temperature results in good rubber quantification, the partial degradation that occurs prevents accurate molecular weight determination. |
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