Advancing Phthalates and Mixed Alkyl Phthalates Analysis in Plastics Using GC-MS with Cold EI

Oneg Elkabets , School of Chemistry, Tel Aviv University , Tel-Aviv , Israel (Onegelkabets@mail.tau.ac.il)
Aviv Amirav, School Of Chemistry, Tel Aviv University , Tel-aviv , Israel
Benny Neumark, School Of Chemistry, Tel Aviv University , Tel-aviv , Israel

Phthalates are widely employed as plasticizers to enhance flexibility and durability in numerous consumer products, yet their widespread use raises health concerns, including endocrine disruption, reproductive toxicity and developmental effects. Consequently, regulatory agencies have restricted the use of several phthalates, particularly in products intended for children. Heavy phthalates such as diisononyl-phthalate (DINP) and diisodecyl-phthalate (DIDP) are investigated as safer alternatives to dioctyl-phthalate – the benchmark PVC plasticizer, yet their analysis is complicated due to structural complexity, multiple isomers and the absence of molecular ions under standard electron ionization (EI). The most critical limitation, however, arises with mixed-alkyl phthalates, such as nonyl-decyl and decyl-undecyl species. In these compounds, standard EI fails to generate molecular ions, forcing reliance on fragment ions that lack selectivity. This non-selectivity occurs because many phthalates share the same dominant fragment ions, making it impossible to distinguish mixed-alkyl phthalates from non-mixed analogs. As a result, analyses based solely on fragment ions often misidentify mixed-alkyl phthalates, leading to qualitative errors and inaccurate quantification. Gas chromatography-mass spectrometry (GC-MS) with Cold Electron Ionization (Cold EI) uniquely addresses this problem by interfacing GC with supersonic molecular beams, producing vibrationally cold molecules that are ionized in a fly-through ion source. This process greatly enhances molecular ions, providing the selectivity and structural information essential for correct identification. Consequently, we developed a method coupling a Thermal Separation Probe (ChromatoProbe) with GC-MS Cold EI, enabling direct thermal desorption of small plastic pieces and eliminating the need for extensive sample preparation. The method revealed complex isomeric profiles in both commercial standards and consumer products, unambiguous detection of mixed-alkyl phthalates, and evidence of a shift toward heavier, less regulated plasticizers such as trioctyl-trimellitate. These findings demonstrate that only Cold EI enables reliable identification and quantification of phthalates, particularly mixed-alkyl phthalates.