Challenging identifications of polymer coatings by radiofrequency pulsed glow discharge-time of flight mass spectrometry

Abstract

Radiofrequency pulsed glow discharge (RF-PGD) coupled to time of flight mass spectrometry (TOFMS) has become a powerful tool for obtaining both elemental and molecular information directly from solid samples. Two GD Grimm-type based designs coupled to TOFMS are compared for the analysis of polymers. One of the chambers is an in-house design (“UNIOVI GD”), while the other (named “GD.1”) corresponds to the source included in the initial GD-TOFMS prototype. Operating conditions were similar for both GD designs (15 W of applied power with both chambers, 200 Pa of pressure for GD.1 and 150 Pa for the UNIOVI GD), with argon being the plasma gas used. Experimental results showed that the GD.1 design provides richer molecular information and also better detection limits for polyatomic ions (in the low μg g⁻¹ range); this fact could be attributed to higher distance between the sample and the mass spectrometric interface in GD.1 design. Furthermore, this GD source contains a flow tube inside the anode favouring the formation of polyatomic ions and, thus, providing higher molecular information. Moreover, the use of an argon pre-chamber to minimize the entry of external air, which could interfere in the sought polymer identification, has been successfully evaluated as well. Finally, four conductive polymers (polyaniline, polyphenylene sulfide, polypyrrole and polythiophene) containing carbon, hydrogen and either sulphur or nitrogen have been characterized using RF-PGD-TOFMS (using the GD.1 chamber and the Ar pre-chamber). Results showed that some of the polyatomic ions can be eventually considered as fragments coming from the structures of the corresponding monomers constituting each polymer. Thus, the molecular information provided by RF-PGD-TOFMS under appropriate experimental conditions enables a fast and reliable identification of the studied polymers.