Abstract
Nowadays, one of the methods of choice for minimal invasive sampling of solid matter is laser ablation (LA). Routine LA sampling is performed commonly in the laboratory and the amount of ablated mass can directly be monitored and analysed. By contrast laser-based sampling in the field, using a portable laser ablation system (pLA), still remains challenging concerning low-absorbing or NIR-transparent samples. The current hardware is limited in regards to photon energy and density resulting in unsteady ablation. But as the actual amount of collected mass is the major crux of on-site sampling, with this performance it is often unknown and estimates can only be made based on the experience from prior method development and the experience of the user. In the following work an easy-to-use method to monitor the amount of ablated material collected during laser-based sampling by measuring the acoustic response is presented. The pLA-system was coupled to inductively coupled plasma mass spectrometry (ICPMS) via a diffusion driven gas exchange device (GED) which allowed to monitor mass removal and acoustic response quasi-simultaneously. For the current instrumentation only actual mass removal leads to the formation of shockwaves (SW) and, thus, acoustic signals. These events can be used as indicator for executed LA events and counted on an individual basis. The intensity of acoustic signals has been shown to correlate with the LA mass, i.e., the amount of ablated material. This allows to perform re-adjustment of the laser focus during sampling for optimal ablation based on the intensity of the acoustic signal. Likewise, acoustic intensity together with counting allows the operator to make estimates about total mass sampled. Therefore, unsuccessful laser aerosol collection in the field shall become a thing of the past.
Highlights
Laser-based sampling of solid materials for analytical purposes is almost as old as the invention of the laser itself.[1,2,3] The removal of substance through exposure to laser pulses is called laser ablation (LA), whereby the laser irradiance exceeds the material- and the wavelength-specific threshold value and the solid sample undergoes decomposition.This decomposition is accompanied by the following processes: solid-to-liquid-to-vapour ‘forward’ phase transitions of sample material and the formation of aerosols through nucleation, condensation and agglomeration,[4] including emergence and expansion of a laser induced plasma (LIP).[5]
These are various including direct mass spectrometry (LAMA/LAMS),[7,8] LIP spectroscopy as laser induced breakdown spectroscopy LIBS,[5] the operation with secondary ionization sources such as
This can be explained by surface effects and different absorption behaviour resulting in a different response regarding mass removal and intensity of the acoustic pressure wave
Summary
Laser-based sampling of solid materials for analytical purposes is almost as old as the invention of the laser itself.[1,2,3] The removal of substance through exposure to laser pulses is called laser ablation (LA), whereby the laser irradiance exceeds the material- and the wavelength-specific threshold value and the solid sample undergoes decomposition. LA as a microprobe sampling tool originates from high-resolution material processing.[6] Over time, the wish of scientists and, in particular, (analytical) chemists for multi-element- and isotope-selective analyses of the ablated material led to the development of various LA-based ‘hyphenated’ techniques. These are various including direct mass spectrometry (LAMA/LAMS),[7,8] LIP spectroscopy as laser induced breakdown spectroscopy LIBS,[5] the operation with secondary ionization sources such as. In recent years the concept has been revived,[26] especially in the field of laser induced breakdown spectroscopy (LIBS).[26,27,28]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
