Abstract
Use of dual-pulse laser-induced breakdown spectroscopy with an orthogonal spark orientation is presented as a technique for trace metal analysis in bulk aqueous solutions. Two separate Q-switched Nd:YAG lasers operating at their fundamental wavelengths are used to form a subsurface, laser-induced plasma in a bulk aqueous solution that is spectroscopically analyzed for the in situ detection of Ca, Cr, and Zn. Optimizing the key experimental parameters of proper spark alignment, gate delay (t d), gate width (t b), and interpulse timing (ΔT) allowed experimentally determined detection limits of the order of micrograms per milliliter and submicrograms per milliliter. We present supporting evidence of a sampling mechanism that involves the formation of a cavitation bubble with the first pulse (E 1) followed by analysis of that bubble with a second pulse (E 2). The plasma created by E 2 contains the analytically relevant information from the aqueous sample and often represents >250-fold enhancement over a single laser pulse with energy equal to E 1 alone.
© 2003 Optical Society of America
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