HIGH REPETITION RATE FEMTOSECOND LASER ABLATION - ICPMS FOR DIRECT ANALYSIS OF TRACE ELEMENTS IN SOLID SAMPLES: APPLICATION TO SELENOPROTEINS
Fanny Claverie1, Christophe Pecheyran2, Guillaume Ballihaut3, Sandra Mounicou2, Beatriz Fernandez2, Olivier FX Donard2, Gregory Turk1.
1- NIST, Analytical Chemistry Division, Gaithersburg, Maryland - USA
2- IPREM UMR 5254, Laboratoire de Chimie Analytique Bio Inorganique et Environnement, Université de Pau et des Pays de L’Adour, Pau – France
3- NIST, Analytical Division, Charleston, South Carolina - USA
Femtosecond laser ablation coupled to an inductively coupled plasma mass spectrometry (fsLA-ICPMS) is now considered as a versatile and powerful technique for the direct analysis of trace elements in solid samples. However, this technique can be limited by the low quantity of material ablated and then sent to the ICPMS.
Thanks to the use of a high repetition rate laser source (up to 10 kHz) combined to a scanning beam device which permits to rapidly move the laser beam, we developed new ablation strategies in two dimensions. These strategies allow to increase drastically the ablation rate (quantity of material ablated per unit of time) and then lowered detection limit of the LA-ICPMS coupling. Additionally, femtosecond pulses are known to produce thinner aerosols easier to atomize and ionize into the ICP. In order to demonstrate the capabilities of these 2D femtosecond ablation strategies, the detection of selenoproteins in gel electrophoresis is presented.
The concern over the detection of heteroatoms in proteins is of growing importance in biochemical, toxicological and pharmacological sciences. However, the detection of heteroatoms still remains an important challenge due to the low concentration levels that they exhibit in proteins, particularly in biological samples. Using the fast scanning beam device combined with a high repetition rate fsLA-ICPMS, we developed a sensitive method for the detection of selenoproteins in gel electrophoresis. This association permits to improve the signal sensitivity by ablating quasi-instantaneously 2mm wide lanes of electrophoretic gels. In these conditions the mass of gel sampled was 27 times higher compared to the mass sampled with a conventional 266 ns laser ablating 120 µm wide lanes. However, the signal sensitivity was found to exceed a factor 40 which cannot be exclusively explained by the amount of gel ablated. Our hypothesis was to assign this enhanced sensitivity to the nature of the aerosol produced by femtosecond pulses. The aerosols have then been characterized in terms of particle size distribution and morphology. It appears that this femtosecond laser ablation strategy combines the advantage of the short pulse width with the advantage of the large quantity of material ablated.