Forensic examinations involving the comparison of soft plastics, such as cling film and resealable bags, often conclude at the identification of the polymers, with few cases leading to further discrimination using traditional instrumentation. Isotope ratio mass spectrometry (IRMS) can strengthen comparison evidence by using the stable isotopic compositions of the polymer. To define the variability of the material, to inform forensic comparisons and interpretation of evidence, we have examined the homogeneity of rolls of cling film; ten rolls from eight different brands were measured. All films studied were shown to be isotopically homogeneous, with δ¹³C standard deviations being less than 0.08 and δ²H standard deviations being less than 1.1. A second experiment examined variability within manufactured batches; IRMS results were obtained for seven brands of seven rolls with common batch numbers. The results showed six of these batches to be isotopically homogeneous whilst the seventh batch, a WOW Select brand, showed two different clusters in the results.

涉及对软塑料（例如保鲜膜和可重新密封的袋子）进行比较的法医检查通常会在鉴定聚合物时得出结论，很少有情况会导致使用传统仪器进行进一步的区分。同位素比质谱法（IRMS）可通过使用聚合物的稳定同位素组成来加强比较证据。为了确定材料的可变性，以供法医比较和证据解释，我们检查了保鲜膜卷的均质性。测量了来自八个不同品牌的十卷。所有的膜研究了被证明是同位素均匀的，与δ ¹³ C标准偏差小于0.08和δ ²H标准偏差小于1.1。第二个实验检查了制造批次内的变异性；共有七个批次的七个品牌的七个品牌具有相同的批号，获得了IRMS结果。结果显示这些批次中的六个批次在同位素上是同质的，而第七个批次（WOW Select品牌）在结果中显示两个不同的簇。