A laser-generated spark was used to analyze liquids spectroscopically for elemental constituents. The spark was produced directly in liquids by a focused laser pulse of 15 ns duration and an energy of about 45 mJ/pulse. The size, temperature, and electron density of the spark are reported. Emissions from once-ionized and neutral atoms and simple molecules were observed. Limits of detection for Li, Na, K, Rb, Cs, Be, Mg, Ca, B, and Al in aqueous solutions were established with the use of a 10 Hz repetitive single spark (RSS). Most of these elements were only detectable at levels above 1 μg/mL, although the detection limit for Li was 0.006 μg/mL. The relative standard deviation for replicate sample analysis was 4-8%. The detectability of some species was enhanced with the use of a 10 Hz repetitive spark pair (RSP): a pair of sparks separated in time by about 18 μs. The detection limits for B/H2O with the RSP and the RSS were 80 and 1200 μg/mL, respectively. Species were also detected in organic solvents and in flowing samples. The laser spark method of liquid analysis would be useful in situations requiring noninvasive monitoring of species at high or moderate concentrations.
David A. Cremers, Leon J. Radziemski, and Thomas R. Loree, "Spectrochemical Analysis of Liquids Using the Laser Spark," Appl. Spectrosc. 38, 721-729 (1984)
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