BIOMONITORING OF METALS IN SPANISH MOSS USING LASER-INDUCED BREAKDOWN SPECTROSCOPY
Description
A LIBS analysis of Spanish moss samples in Tallahassee FL. The samples correlate to locations of High motor traffic and Low motor traffic. Since Spanish moss is an Epiphyte it should accumulate more atmospheric metal in areas of high traffic than in areas of low traffic. We found emissions of Cu, Cr, Al and Ca. It should be noted that the spectrophotometer used was high resolution able to accurately display lines at a width of ~6nm. The system was calibrated using chips of pure metal and metal oxides. The data for each sample was gathered from ten, 20-shot accumulations. The experimental setup used in this investigation was as follows: Plasma was generated by a Q-switched Nd:YAG laser (Quantel Brilliant B, 532 nm, 5 ns pulse width), which was focused to a 1 mm spot on the sample surface after passing through a 150 mm focal length lens and a periscopic assembly. Photodiodes connected to an oscilloscope were employed to monitor both the laser pulses and the plasma formation. The laser trigger pulses, and the photodiode output were simultaneously displayed on the oscilloscope. The photodiodes measured the integrated plasma intensity at approximately 25 to 50 mm from the target. By observing these signals in parallel, the optimal timing for coupling the laser sources to the plasma could be determined. A timing generator (SRS DG-535) was used to control the timing of the pulses and data acquisition. In these experiments, the rising edge of the voltage signal from a fast photodiode was used to define the onset of plasma formation. This signal was delayed by the timing generator and used to trigger a gate-open pulse to an Andor iStar 740 (iCCD), mounted on an Acton SpectroPro 750i spectrometer (3600 gr/mm, 240 nm blazed grating), enabling the capture of plasma emission intensities. During data acquisition, the iCCD integrated 50 transients at each location on the target prior to data transfer to a computer using Andor Solis Software.
Files
Institutions
- Florida Agricultural and Mechanical University