Laser ablation particle beam glow discharge time of flight mass spectrometry for the analysis of halogenated polymers and inorganic solid material

摘要

A laser ablation particle beam pulsed glow discharge mass spectrometer (LA-PB-GD-TOFMS) was designed and used for fundamental studies. The instrument consists of a three stage aerodynamic lens system, a hollow cathode pulsed glow discharge and a time-of-flight mass spectrometer. The particle beam interface was constructed to provide an efficient particle transfer into the hollow cathode. Calculations showed that particles between 1 and 3000 nm in diameter are able to pass through this interface. Glass and metal (SRM N1ST610 and CRM JK37) ablated by laser ablation and introduced into a pulsed, He glow discharge showed no ionization, even for major elements such as ~(27)A1~+, ~(28)Si~+, ~(23)Na~+ or ~(56)Fe~+. This can be explained by the low gas temperature of a pulsed glow discharge which is not sufficient to vaporize particles with high melting and vaporization points. In contrast, ablated particles of soft materials such as PTFE or PVC polymers were vaporized and ionized in a pulsed glow discharge. Ion signals for elements such as carbon (~(12)C~+), hydrogen (~1H_3~+), fluorine (~(19)F~+) and chlorine (~(35/37)Cl~+) were detected when generating an aerosol by laser ablation and introduced into the hollow cathode. Furthermore, various fragments such as ~(12)C_X~1H_v~(19)F_y~+ and ~(12)C_x~1H_v~(35/37)Cl_y~+ were identified and provide a "fingerprint" of the ablated polymer. The influence of the laser fluence and glow discharge voltage was investigated with respect to the ratio of fragments to elemental ion signals. The decrease in laser energy leads to an increase of the ~(12)C~+/~(12)C~(19)F/ ratio. Lowering the glow discharge plasma power favors the appearance of fragments such as ~(12)C~(19)F_x~+ whereas higher plasma power favors the ion signals of the elements, such as ~(12)C~+ and ~(19)F~+. A set of experiments comparing different PVC polymers with increasing PVC content was evaluated with respect to the ~(12)C~+/~(35)C1~+ ratio. A correlation between the ratio and the concentration of the PVC in the sample was determined and indicates the capability for quantitative analysis of halogens in organic particulate matter by LA-PB-GD-TOFMS.