Paper No. 88
Presentation Time: 6:45 AM
MINOR AND TRACE ELEMENT ANALYSIS USING ANALYTICAL TRANSMISSION ELECTRON MICROSCOPE (TEM)
Modern TEMs are ideal for examining colloidal and nano-paticulates that are ubiquitous in low temperature environmental samples of water, soil and air. A wide variety of elements of special health concern are commonly found in these particulates but quantitative or semi quantitative chemical analysis using the TEM are rare in the literature. To determine sensitivity and reproducibility, major, minor and trace elements were analyzed. Fifteen well characterized standard reference materials (SRM) from the USGS, Smithsonian and NIST including silicate minerals (n=10); and both natural and synthetic glasses ( n=5) were analyzed using a JEOL 2010 TEM (200KV) with the analytical pole piece, beryllium sample holder and Noran ultra-thin window SiLi detector. To minimize beam damage, low emission currents, the lowest EDS counting time constant (yielding the best peak resolution) and long counting times (300 sec) were used. For each SRM twenty or more individual grains (~ 50nm in diameter) were analyzed and one grain was analyzed ten to twenty times to determine the difference between instrumental and systematic errors including sensitivity to long-term beam damage and sample heterogeneity. Soda-lime glasses and high-silica natural glasses proved to be both heterogeneous at the nanometer scale and beam sensitive losing significant alkali metals during time trials. Silicates and basaltic glass were far more homogenous and resistant to beam damage and several make ideal nano-probe(TEM) reference materials. First row t-metals,P,S, and Cl are quantifiable in silicate matrices down to ~100ppm and sometimes even well below 100ppm. Heavier elements (Ba, Sr, and Pb were only quantifiable when exceeding 500-1000ppm and have significant peak overlaps with major elements. Select average TEM minor (<1wt %) and trace-element (< 1000ppm; n>20 grains) analyses are shown below with 2σ variance and compared to SRM recommended values.
Ti(ppm) |
Mn (ppm) |
Ca(ppm) |
K(ppm) |
Cr(ppm) |
P(ppm) |
|
TEM (2σ) |
430(60) |
5400(900) |
3100(1000) |
1870(90) |
5200(1000) |
350(170) |
SRM |
450 |
5400 |
3600 |
1800 |
5100 |
500 |
TEM (2σ) |
8500(190) |
1300(100) |
4200(700) |
900(150) |
270(130) |
800(270) |
SRM |
8200 |
1100 |
6200 |
750 |
200 |
980 |
TEM (2σ) |
4500(600) |
3800(600) |
9650(1650) |
2750(300) |
1400(400) |
|
SRM |
4800 |
3800 |
10900 |
2740 |
1500 |