The main goal of the Murray Group is to build better instruments for chemical analysis centered around laser ablation and mass spectrometry. The best way to build better instruments is to understand the chemical and physical processes behind them. We are investigating the fundamental processes of laser ablation and ionization. These include the effect of wavelength and energy on desorption, ablation and the production of ions from biological samples.
Laser Ablated Particles
What kinds of particles are created when you shoot a sample with a laser for mass spectrometry? We use a combination of particle sizing instruments to find out. We especially like infrared lasers because they are more efficient at removing material. The trick is to make them remove material that is the most efficient for the mass spectrometry analysis that you want to do.
Musapelo & Murray, Particle Formation by Infrared Laser Ablation of MALDI Matrix Compounds. J. Mass Spectrom. 2014, 49, 543–549.
Musapelo & Murray, Particle Production in Reflection and Transmission Mode Laser Ablation: Implications for Laserspray Ionization. J. Am. Soc. Mass Spectrom. 2013, 24, 1108–1115.
Musapelo & Murray, Size Distributions of Ambient Shock-Generated Particles: Implications for Inlet Ionization. Rapid Commun. Mass Spectrom. 2013, 27, 1283–1286.
Musapelo & Murray, Particle Formation in Ambient MALDI Plumes. Anal. Chem. 2011, 83, 6601–6608.
In our particle sizing experiments, we are using a scanning mobility particle sizers can detect particles with diameters smaller than 500 nm and a light scattering aerodynamic particle sizers that can detect particles efficiently with diameters greater than 500 nm. The two instruments allow us to study laser ablated particles with sizes between 10 nm and 20 µm.
In these experiments, glycerol ablation was studied using fast photography. An infrared laser was used to irradiate a droplet of glycerol and after an adjustable delay, a dye laser strobed the expanding plume. The scattered light was imaged with a high-speed CMOS camera. The time delay between the IR and UV lasers was varied from tens of nanoseconds up to a millisecond.
Fan & Murray, “Wavelength and Time-Resolved Imaging of Material Ejection in Infrared Matrix-Assisted Laser Desorption.” J. Phys. Chem. A 2010, 114, 1492–1497.
Finite Element Modeling
Laser ablation is widely used in conjunction with ambient ionization techniques and a fundamental understanding of the mechanism of material removal is important to its optimal use in mass spectrometry. Here, a two-dimensional finite element model was developed to simulate infrared laser irradiation of glycerol using a wavelength-tunable infrared (IR) laser.
Huang & Murray, “Finite Element Simulation of Infrared Laser Ablation for Mass Spectrometry.” Rapid Commun. Mass Spectrom. 2012, 26, 2145–2150.