This part of ISO 7270 specifes a pyrolytic gas-chromatographic method for the determination of the styrene/butadiene/isoprene ratio in copolymers, or blends of homopolymers and/or copolymers, in raw rubbers or in unvulcanized or vulcanized compounds. It is applicable to copolymers/terpolymers consisting of styrene, butadiene and isoprene, and blends of these polymers.NOTE 1 The use of this part of ISO 7270 pre-supposes suffcient working knowledge of the principles and techniques of gas chromatography for the analyst to perform the operations described and interpret the results correctly.NOTE 2 The styrene/butadiene/isoprene ratio determined by this test method is affected by the presence of resin and by a high level of sulfur.