Wednesday, September 30, 2009

Abrasive Sampling: Spectra of Intractable Samples


There is a sampling technique used on powders and solids called Diffuse Reflectance Infrared Fourier Transform Spectroscopy, or DRIFTS for short. I think some graduate student spent several months thinking up that acronym. At any rate, the technique involves using a special sampling accessory that fits into your FTIR sample compartment to bounce the light off the sample. The light is then collected and sent to the IR detector (more on DRIFTS in a later blog post). Abrasive sampling is an interesting application of DRIFTS. Some FTIR accessory manufacturers make flat metal posts that fit into their DRIFTS accessories and SiC disks with an adhesive backing. The SiC disk is adhered to the metal post, and then the disk is rubbed against the sample to abrade off sample particles. The SiC disk with particles is then placed at the focal point of a DRIFTS accessory, the light is reflected off of the sample particles, and is collected and sent to the detector to obtain the sample spectrum. The background spectrum is run on a clean SiC disk.

The attached spectrum is of the white paint on a light fixture obtained by abrasive sampling using an Alpha spectrometer from Bruker Optics (http://www.brukeroptics.com/). This spectrum would have been difficult to obtain any other way. The light fixture was firmly attached to the ceiling and so could not be taken down. In theory, one could scrape a lot of the paint off and make a KBr pellet or cast a film of the paint. However, this would damage the light fixture, involve time consuming trial and error, and may still not work. With abrasive sampling, only a small hidden part of the light fixture was scratched, and the entire measurement process took about 2 minutes. Abrasive sampling is useful for spectra of large, intractable objects such as furniture, large pieces of plastic, or anything that is simply too big to be analyzed by normal FTIR sampling techniques. The beauty of abrasive sampling is that it is fast and easy. However, the SiC scatters the IR beam a lot, so abrasive sampling spectra can be noisy. This can sometimes be dealt with by increasing the number of scans, perhaps to as many as 256.

A note on the SiC disks. I have seen labs try to save a little money by going to the hardware store, buying SiC paper, and then using a cork borer to punch out SiC disks of the proper size. As long as these disks fit into the sample cup that came with your DRIFTS accessory this should at least in theory allow you to obtain abrasive sampling spectra.

Use your imagination…what type of applications might abrasive sampling have at your company?

1 comment:

  1. Hello Brian,
    I am searching for a technique to examine surface reaction of activated carbon under combustion environments and when I looked at your blog, the message about DRIFTS is very attractive to me. Could you give me some more information about DRIFTS whether the abrasive technique can be used with activated carbon in DRIFTS under oxidizing condition at 900 C?

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