An apparatus and method for testing and analyzing the molecular structure of a sample material in an NMR device are described. A sample is held in a pre-determined stretched state in an apparatus that includes the sample arranged between two body components that are secured together with one or more retaining members that fit around the bodies or portions thereof. The apparatus is inserted into an NMR device to obtain NMR spectrums for analyzing the molecular structure of the samples, for instance, identifying strain-induced crystallinity and quantifying the same at pre-determined stretch ratios of a sample material.