A sample being analyzed by laser ablation-inductively coupled plasma-mass spectr

Question

A sample being analyzed by laser ablation-inductively coupled plasma-mass spectrometry has a density of 4.61 g/mL. After a 12.0-ns laser pulse, a crater with a diameter of 34.7 ?m and a depth of 1.009 ?m was created. If the energy of the laser pulse was 2.68 mJ, determine the laser power density in watts per square centimeter.

A sample being analyzed by laser ablation-inductively coupled plasma-mass spectrometry has a density of 4.61 g/ml. After a 12.0-ns laser pulse, a crater with a diameter of 34.7 pm and a depth of 1.009 um was created. If the energy of the laser pulse was 2.68 mj, determine the laser power density in watts per square centimeter. How much sample mass was removed by the laser pulse? Assume the crater has a cylindrical shape.

Explanation / Answer

Before answering this question, I would like to give brief definition of Inductively coupled plasma mass spectrometry (ICP-MS). From Wikipedia," ICP-MS is a type of mass spectrometry which is capable of detecting metals and several non-metals at concentrations as low as one part in 1012 (part per trillion). This is achieved by ionizing the sample with inductively coupled plasma and then using a mass spectrometer to separate and quantify those ions"

Now Power density is defined as energy per unit area per unit time.

So here Energy of laser pulse (E) = 2.68 mJ, Total time of exposure (t) =12.0 ns, crater diameter (d) = 34.7 micrometer ; Area = pi* (0.5d)^2 = 3.78*10^-5 meter^2

Laser Power density = E/A*t = 2.68*10^-3/ (3.78*10^-5* 12*10^-9) = 5.90 *10^9 Watt/cm^2

Total sample removed = volume*density
Volume = 3.78*10^-5 *1.009*10^-3 cm^3 (ml)
density = 4.61 gm/ml

mass removed = 1.758 *10^-7 gm


Cheers




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