Frequently Asked Questions (FAQ)
How many hours/days of EPMA do I need? How many samples can I analyze?
It depends on the number of samples you want to analyze, the number of samples/holders we can fit into the machine, as well as on what you want from your samples (quantitative analyses, WDS element maps, etc). Think that you can usually analyze not more than 4 thin sections in 24 hours (e.g. 1-morning session, 1-afternoon session and 1 overnight session). This means a very long evening for you to set automate ca 150-200 analyses for the night, to take relevant BSE images for every site of interest, etc. We can fit no more than 4 thin sections in the EPMA holder at the time. If using 1-inch (25 mm) diameter round blocks we can fit 6 to 9 blocks at a time. If you have blocks of 30 mm diameter, we can fit 2, only. No matter how many samples fit in, you will be limited to a max of 200-300 analyses for major elements per day and overnight (depending on the number of different phases and number of elements to be analyzed). In budgeting your EPMA time also keep in mind that you might want to run element maps, which, depending on size and resolution, the number of maps, etc can take 2 to 10 hours or more.
How should I prepare my thin sections for the EPMA session? Analysis planning – Sample navigation
For a better estimation of the EPMA use, the following information is needed:
- The number of samples to be analyzed
- The type of samples (thin sections, round blocks of 1’, 5 mm brass/aluminum pins etc)
- The type of material (e.g. rock sample, mounted mineral aggregate, mounted experimental products, bone, fossil, etc)
- The type of material/mineral/phases you want to analyze (e.g. unknown glass, unknown mineral, known silicates, oxides, sulfides, etc)
- The elements you want to be analyzed in each phase (e.g. Si, Al, Ti, Cr, Mg, Fe, Mn, Ca, Na, K in all silicates and glasses; Ni in olivine, F and Cl in biotite, Sr in plagioclase, etc); Cu, Fe, Ni, Co, S in pentlandite, Zn, Fe, Cd, S, in sphalerite, etc. This information is essential for standard calibration.
Do your Petrography, in order to understand your mineral assemblages. Before coming to the microprobe you have to know: i) what mineral phases you want to analyze (and why) and ii) what elements you want to analyze in each of your phases;
Polish your samples as well as possible. The quality of the images and quantitative EPMA data is drastically dependent on the quality of the polishing and flatness of your samples. Check the polishing quality before taking any further step in analyzing your samples;
- Scan your sample at high resolution, so that, when enlarging the image, you can recognize the sites of interest you want to image or analyze at the EPMA. Change brightness/contrast so that to allow recognition of different types of phases present in your sample. Print on Letter or A4 size paper your scanned image (have with you the printed images when at the EPMA);
- Clean the surface of your samples before coming to your EPMA session. Use ethanol and/or ultrasound;
- Mark the sites of interest on the Printed Scanned Image (not on the sample). You need to know exactly what grain you want to analyze and you should be able to identify the grain under the Back Scattered Electrons (BSE) image. It is useful (time-saving) to know what mineral phase you expect to be from your microscopic examination. A full scan/picture of the sample will help tremendously in navigating and identifying the locations of analytical interest. See the example of marking the scanned image in Figure 1.
- Have with you photomicrographs of the sites of interest for each sample. Use 40x magnification (or higher) for your micrographs. Do not acquire pictures in XPL mode, but in PPL mode, using transmitted and/or reflected light. These photomicrographs will help you to identify the grains you want to analyze;
- Bring the polished sections for carbon coating to the EPMA lab (preferably one day before your EPMA session)
Scanned_thin section_marked_on_picture_example_Rice_University
Figure 1. Example of a marked image of a thin section (do not use a marker to draw on the thin section itself but mark the picture of it). If you do not have a good scanner, you can even use a smartphone to take a good resolution picture of the sample/thin section, as long as grains are still visible.
Carbon coating
Our carbon coater (JE-420 can coat 9 thin sections or 12 1-inch round blocks at the time). The time for one coating is ~ 30-40 minutes. We recommend (for Rice users, at least) to do the carbon coating one day before your EPMA session. However, if you have a few samples only (one single episode of carbon coating) we can do the coating starting at 8.30 am on the day when your EPMA session starts. This is valid for external users and visitors, as well.
Calibration (standard calibration)
If you plan to do quantitative analysis, the elements to be analyzed need to be previously calibrated. We can do the calibrations for you or you can do it yourself, after proper training. The choice is up to you. However, if you want to do your own calibrations, you have to consider that calibration is not trivial and usually requires some experience before doing it, therefore, proper training is needed. We recommend that new users and beginners have the calibration made by us. Frequent (experienced) users, by request, can be trained to do standard calibrations for their routine work.
How do I get my EPMA reports/data?
The EPMA reports will be sent via e-mail. If a very big data file, a zip archive will be sent to you using the free-share wetranfer.com link, where up to 2 Gb of data can be sent. For additional questions relating to the file transfer, contact the lab manager.
When can I have my samples back?
You can come to the lab to collect your samples any time after your EMA session. However, we are not responsible for the samples left in the lab for more than 30 days.
If agreed with the Lab Manager, the samples can also be mailed (FedEx-ed) to your address and the charge for FedEx will be billed into your invoice.
Can I use my cell phone in the EPMA Lab?
Yes. However, we advise you to keep your phone away from the EPMA console.
Can I bring food and drinks to the lab?
No.
About the lab: EPMA configuration and capabilities
Contact
Dr. Gelu (Gabi) Costin
EPMA Lab Manager
Department of Earth Science
Rice University
6100 Main Street, Keith-Wiess Geological Laboratory, MS-126
Houston, TX, 77005
e-mail: g.costin@rice.edu Phone: Office: 713 348 2054