Determination of elements in polymers by laser ablation inductively coupled plasma atomic emission spectrometry: effect of the laser beam wavelength, energy and masking on the ablation threshold and efficiency

Abstract

The application of laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) to the direct determination of solid inorganic additives in polymeric materials has been studied. The use of a Nd:YAG laser, operating at both infrared (IR) (1064 nm) and ultraviolet (UV) (355 and 266 nm) wavelengths, has been investigated for poly(vinylidene fluoride) (PVDF), poly(vinyl chloride) (PVC) and poly(ethylene) (PE) materials. In order to obtain reliable ablation conditions, emphasis was placed on the control of the experimental parameters and the understanding of the laser-surface interaction characteristics. It has been shown that, at low energies, a threshold process characterized by the swelling of the surface takes place, accounting for the rims surrounding the craters. This threshold was dependent not only on the energy, but also on the laser wavelength. In order to eliminate the formation of the swelling and to find the most reproducible conditions, it has been shown that the use of UV laser radiation and beam masking offer a better control of the laser ablation process, leading to a satisfactory relative standard deviation on both the estimated ablated mass (6.4%) and the emission signal obtained by ICP-AES (in the 2%–5% range). It has also been established that the optimum laser energy is in the frame of 6 mJ (10 J cm −2) to 10 mJ (14 J cm −2) at 266 nm. Erosion rate, linearity of the ablated mass against time for PVDF, PVC and PE, and a titanium calibration graph obtained for a PVC matrix are then briefly discussed and illustrate the technique's analytical potential.