Improving the reliability of phthalate esters analysis in water samples by gas chromatography-tube plasma ionization-high-resolution mass spectrometry (GC-TPI-HRMS)

The monitoring of phthalate esters (PAEs) is challenging due to background contamination as well as the low selectivity observed when analyzing them by gas chromatography coupled to mass spectrometry (GC-MS) using electron ionization (EI). In this sense, alternative and soft ionization techniques could help to enhance the performance of the analytical determinations of PAEs in food samples. In this work, the use of a novel and soft ionization technique tube plasma ionization (TPI) has been explored to enhance the selectivity and sensitivity in the determination of PAEs in drinking water samples with GC-MS. First, the ionization behavior of PAEs by TPI is evaluated showing the generation of an abundant protonated molecule. Source and plasma related parameters were carefully optimized to increase the ionization efficiency and ion transmission, showing that the fragmentor voltage is a key parameter to avoid in-source fragmentation. Moreover, the use of additives and different electrode materials is also tested to enhance the ionization efficiency and to better understand TPI mechanisms. Tungsten-made electrode with no additives showed the highest performance and better robustness for long-term operation. The proposed methodology using GC-TPI-MS was instrumentally compared with other atmospheric pressure ionization sources showing significantly lower limits of detection for the TPI source compared to atmospheric pressure ionization techniques (up to 700 times). Moreover, TPI also demonstrates comparable figures of merit in regard to the gold-standard ionization technique (EI). The combination of the GC-TPI-HRMS method together with a headspace-solid phase microextraction (HS-SPME) allows the detection of PAEs in drinking water up to 1 ng L−1 with precision (RSD