Method and apparatus for online analysis by laser-induced spectroscopy

A presentation module (21) is provided for presenting a fluid sample to a Laser-induced breakdown spectroscopy (LIBS)analysis. The presentation module (21) comprises an inlet (22, 27) for admitting a fluid sample flow (25) from a process flow, a measurement opening for co-operating with measurement optics (31, 32, 33, 34), and a stabilizer surface (26) facing towards the measurement opening. The stabilizer surface (26) is adapted to form a stabilized sample flow along the stabilizer surface such that the depth and the outer surface of the sample flow 25 are stabilized, and the surface fluctuation and depth variation of the stabilized sample slurry flow are reduced. As laser pulses (29) are focused on the outer surface of the planar sample flow (25) to transform at least a part of the sample into a state of a plasma, the accuracy and repeatability of the LIBS measurement are significantly improved due to the stabilized sample flow.