Plasma profiling-time of flight mass spectrometry: considerations to exploit its analytical performance for materials characterization

Abstract

The combination of pulsed glow discharge (PGD) with time-of-flight mass spectrometry (TOFMS) provides quasi-simultaneous mass spectra of fast transient signals directly from solid materials. Moreover, pulse profiles of the analytes can be useful for understanding ionization and transport processes to the mass analyser. In this work, studies have been carried out for a better understanding and analytical exploitation of the capabilities of PP (Plasma Profiling)-TOFMS, the first PGD-TOFMS commercial instrument. The PGD operating conditions of the “PP-TOFMS” have been optimized and evaluated in terms of temporal signal distribution and sensitivity for a large variety of elements present in the standard reference material NIST 1262b (hot-rolled and cold-drawn steel with a certified composition of 24 elements). Short pulses and duty cycles have been proved to be crucial for high sensitivity of heavy elements. In addition, the PP-TOFMS has a blanking interface stage that allows filtering (or blanking) of up to four of the most intense ions to achieve higher sensitivities for trace and minor elements. Here, a thorough investigation is presented to understand the blanking behaviour and its benefits. Results have shown that sensitivity increases for high m/z isotopes when attenuating the major ion coming from the discharge gas (⁴⁰Ar) and from the major matrix isotope (⁵⁶Fe): e.g. sensitivity increases up to a factor of 100 in the case of W compared to no blanking experiments.