Rocío Muñiz

Capabilities of radiofrequency pulsed glow discharge-time of flight mass spectrometry for molecular screening in polymeric materials: positive versus negative ion mode

Negative ionization mode in the recent commercialized “PP-TOFMS, Plasma Profiling Spectrometer” instrument from Horiba has been examined in detail for the analysis of different polymeric materials and the results were compared with those of positive ion mode. Three compounds (tetrabromobisphenol A, tris-2-chloroethyl-phosphate and polytetrafluoroethylene) embedded in a polyurethane matrix were employed for such a purpose. Both, elemental information from the heteroatoms (F, Cl, Br and P) and/or molecular information provided, using either Ar or Ar + 4% O2 as discharge gases, were investigated. Also, the analytical potential of the negative ionization mode for integral speciation of polymers was explored, both in Ar and Ar + 4% O2. The screening of polymeric materials with similar elemental composition, in particular, four brominated flame retardants (BFRs), was performed to investigate this point. The results showed that elemental sensitivity for halogens in the negative mode of the instrument was higher as compared to positive detection. Sensitivity was observed to be directly dependent on the electron affinity of the analyte. Polyatomic information measured in negative mode using Ar as the discharge gas has demonstrated to be promising for a successful identification of the four different BFRs investigated. The adverse effects of reactions occurring in the plasma in the presence of oxygen have proved to be a serious drawback to be tackled for polymer characterization using this novel PP-TOFMS glow discharge-based technology.

Depth profile analysis of rare earth elements in corroded steels by pulsed glow discharge – time of flight mass spectrometry

Depth profiling of 304L stainless steel surfaces exposed to rare earth nitrate solutions over varying time lengths has been undertaken using the recently commercialized “PP-TOFMS Plasma Profiling Spectrometer” by Horiba. This combines a pulsed glow discharge source with a time-of-flight mass spectrometer (TOFMS) which allows elemental depth profiling with nanometric resolution of almost all elements of the periodic table. In this work special attention is paid first to the optimization of the new PP-TOFMS for depth profile analysis of low concentrations of rare earth elements (REE) in the samples. Sensitivity given in [(cps X × sputtering rate in μg s−1)/(μgX g−1)], being the concentration of the element X (μgX g−1) corrected by the abundance of the measured isotope, was in the order of 20 for all REEs under investigation. Moreover, a quantification strategy for these samples resembling the relative sensitive factors concept has been developed. Validation was done using a homogeneous reference material containing certified concentration values for La (6 ± 1 μg g−1), Ce (14 ± 1 μg g−1) and Nd (6 ± 1 μg g−1). Concentrations of 4 ± 1 μg g−1, 13 ± 1 μg g−1 and 5 ± 1 μg g−1 were calculated for La, Ce and Nd respectively with the proposed strategy. Quantitative depth profiles of the investigated samples have shown that the contaminants did not penetrate the substrate deeper than 80 nm even after a month of exposure to 12 M HNO3.

Technical note: Characterization of gold coated ceramics by radiofrequency pulsed glow discharge – time of flight mass spectrometry

Although it is well known that glow discharge (GD) spectrometry can be used for characterization of both conductive and non-conductive materials, its application to insulators is limited and can be challenging when aiming at the analysis of thick samples. Voltage drop across the material can lead to low power deposition and so to non-efficient sputtering. In this article successful depth profile characterization studies on 6 mm thick ceramic samples coated with a thin (in the nm range) gold layer by means of a commercially available radiofrequency pulsed GD (RF-PGD) coupled time of flight mass spectrometry (RF-PGD-TOFMS) instrument are presented. Careful optimization of the operating conditions was required to achieve proper sputtering of the insulator substrate. 30 W applied rf power, 95 Pa pressure in the GD chamber and a pulse width of 500 μs with a period of 1.49 ms were selected. Characterization of a set of industrially prepared ceramic samples under different conditions was carried out. To overcome problems related to the roughness of the samples, estimation of sample thickness was achieved with an alternative approach based on the use of flat glasses with known Au layer thicknesses. Results of the investigated ceramic samples have shown Au layer thicknesses ranging between 20 and 120 nm. Moreover, screening of other metallic elements within the Au thin coating was carried out, and the presence of Rh, Bi, Pt, Ir and Pd in the Au layer was observed.