Chemical & Isotopic Mass Spectrometry Elemental and Isotopic Analysis in Environmental Samples

Elemental and Isotopic Analysis in Environmental Samples

Researchers
Lee Riciputi (PI)
Debra Bostick (PI)
Eddie McBay

Introduction

This group supplies analytical support to numerous ORNL, national, and international programs with emphasis on developing high precision, high sensitivity analysis for elemental and isotopic composition. In addition, activities support numerous interactions and joint research projects with university, commercial, national and international governments. A number of ionization techniques can be utilized to introduce the samples into a mass spectrometer, including thermal ionization, secondary ionization, glow discharge, inductively coupled plasma (ICP), and laser ablation. Instrumental configurations include time of flight, single and multi-sector analyzers. Detector types are ion counting, Faraday cups, and electron multipliers. MS components are selected to optimize for reduced sample size, minimal preparation time, maximum precision and accuracy for isotopic characterization.

Analytical Instrumentation

The dusty plasma features an rf powered glow discharge source operating with the following parameters:

13.56 Mhz generator frequency
Ar gas pressures from 0.085 to 1.20 Torr
Air gas pressures from 0.085 to 1.20 Torr
Forward power of 1 to 20 Watts
Suspended particles include 0.3 mm alumina particles, 1 mm glassy carbon particles and other particles used for optical interrogation

Discussion

Shown below is a variety of data obtained using our dusty plasma device. Our initial goal was to non-selectively remove particles from the plasma as well as optically detect them. As can be seen in the pictures and movies below, not only can the particle cloud be moved up and down through the electrode orifices, but particles can also be individually removed from the plasma at will. Further, a diverse array of particle cloud geometries can be obtained under varying experimental conditions. These include different cloud geometries such as tear drop, sphere, sheet or disk.

Here is what it actually looks like with alumina particles suspended in the plasma. Click on the images to go to a large, high resolution version.

Future Directions

Currently this project is nearing completion. Goals were to be able to non-selectively introduce and remove particles in the plasma. This is clearly shown in some of the above videos. Further, we have been able to optically detect particles suspended in the plasma. Ongoing work will include atmospheric pressure particle introduction as well as developing techniques to selectively interrogate and sample individual particles.

Chemical & Isotopic Mass Spectrometry Group

Provided by Oak Ridge National Laboratory's Chemical Sciences Division
Rev: November 2005