New silicon phthalocyanine-containing polysiloxanes as stationary phases for high-temperature gas chromatography analysis

Abstract

In this work a series of thermoresistant polysiloxanes containing silarylene units and macrocyclic silicon phthalocyanine (Pc) units (PS-1 – PS-6) were synthesized. The Pc is linked to the polymer chain through a siloxane central group, which has two covalent bonds with two nitrogen atoms of the macrocycle and two covalent bonds with the polymer chain. The sol‒gel method led to the formation of polymeric chains with a random arrangement of monomers and OH-terminated chains. Thermogravimetric analyses revealed that the polymers are stable at high temperatures exhibiting, with a weight loss of 10 % between 384 and 442 °C during heating.

Coated as stationary phases for gas chromatography, polymers PS-1, PS-2 and PS-5 showed good film-forming ability. The columns prepared with PS-1 and PS-5 had 3300 and 3800 plates m⁻¹, respectively, as determined using pentadecane at 130 °C for fused silica capillary columns with an internal diameter of 250 µm, a film thickness of 0.25 µm and a length of 10 m. Polarity was estimated as moderate polarity (Rohrschneider–McReynolds constants were between 841 and 916) and stationary phases can achieve very good separation of Grob’s mixture, polycyclic aromatic hydrocarbons and essential oils. In addition, the columns provided excellent high temperature stability with very low bleeding (17.0 pA at 420 °C). Repeated injections of high boiling analytes revealed that PS-1 is the most stable stationary phase at very high temperatures, as the smallest decrease of retention times (9.2 s) were observed after 50 successive injections (temperature program from 40 °C (hold 3 min) at 7 °C/min to 420 °C (hold 2 min). Moreover, it has been demonstrated that PS-1 is more stable than commercial high-temperature columns such as ZB-XLB-HT and ZB-35HT (35 % phenyl/65 % dimethylpolysiloxane) from Phenomenex®.