An Infrared Spectrophotometric Analysis for Natural Rubber in Guayule Shrubs

Abstract An accurate assay of rubber content in guayule plant tissues is essential to any genetic improvement or bioregulator program. The simpler, more rapid and less expensive the assay, the better. The several methods of rubber assay that have been used have various limitations. Earlier methods for assaying rubber content in guayule are described in two USDA reports. These are principally gravimetric methods which are tedious and relatively nonselective. One of the better ones consists in bromination of the guayule double bonds, precipitation from solution, collection, drying, and weighing the crystalline rubber bromide. This bromide method is more selective for rubber in the presence of resins than the gravimetric methods where rubber is weighed directly. For multiple and repetitive analyses, it is time consuming and somewhat unpleasant due to the recommended excess of bromine. A gravimetric method reported by Tysdal in 1951 was modified recently. The method consists of grinding guayule shrub in an ef...