Pyrolysis GC–MS Reveals Different Phthalate Isomers in Vinyl Polymers

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The Application Notebook

The Application Notebook, The Application Notebook-09-02-2018, Volume 36, Issue 9
Pages: 721

CDS 6000 Series Pyroprobe coupled to a GC–MS is beneficial in phthalate analysis of plastics. This application uncovers intriguing information about phthalates used in vinyl products.

Because pure vinyl is a rigid material, flexible finished vinyl products contain a high amount of phthalate plasticizer. During analytical pyrolysis, these plasticizers are easily thermally desorbed, producing a large peak at the end of the pyrogram, which can be identified using a library search and their unique retention times.

These phthalate plasticizers may also produce unique decomposition products. Electrical tape has a peak for dioctyl phthalate (DOP), and among other things, a decomposition product of DOP, phthalic anhydride (Figure 1).

Figure 1: Electrical tape at 300 °C.

Unique decomposition products can help with phthalate identification. In the next example (Figure 2), a clear vinyl and a green vinyl each contain typical pyrolysis products of PVC, like the aromatics benzene, toluene, and indene. Each vinyl also has large plasticizer peak. Each peak has a similar retention time and similar mass spectra. With such similar mass spectra, a library search could easily mischaracterize them.


Figure 2: Green Vinyl (top), Clear Vinyl (bottom), 700 °C. Phthalate decomposition products circled.

However, each plasticizer has a unique thermal decomposition product, circled in the figure. An ortho-substituted phthalate in the clear vinyl generates phthalic anhydride, but the para-substituted phthalate in the green vinyl generates 2-ethyl hexyl benzoate, helping to simply distinguish between the two.

It is interesting to note that the green vinyl was taken from a child's toy, in which certain phthalate plasticizers are regulated, and there are no regulation requirements for para-substituted phthalates.

The data presented here show clear advantages to identifying phthalates in vinyl materials using pyrolysis GC–MS.

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