I forwarded this 1992 article, "Fingerprinting petroleum contamination using synchronous scanning fluorescence spectroscopy," around a while ago (and posted on the wiki) but it's open access and there's a particular section that's really great and related to our Oil Testing Kit.
Synchronous Scanning Fluorescence Spectroscopy
(jargon warning) In the paper, they're discussing Synchronous Scanning Fluorescence (SSF) spectroscopy, which is where you shine a light into the sample that's 5 nanometers shorter wavelength than where you measure, and you scan up the wavelength scale. It lists some advantages (here I quote):
- simplification of the spectral profile
- sharper peaks resulting from spectral bandwidth reduction
- less background because of a reduction of scattered light
It's not clear to me if the bandwidth referred to for sharper peaks is exitation or emission bandwidth.
I want to find an article on non-scanning fluorescence, because that's what we're doing -- one line in particular worries me in this report:
In normal fluorescence of complex samples like gasoline, the sample is excited at 254 nm, with the resulting fluorescence emission spectrum consisting of a rather large and indistinct peak. This makes it impossible to identify one gasoline sample from any other grade or brand of gasoline (see Figure 1). However, SSF spectroscopy may be used to simplify the spectrum by reducing the spectral bandwidth as seen in Figure 2.
I think "impossible" is an overstatement here, and we're looking at much heavier petroleum products, like crude and motor or fuel oil. Surfrider has used normal fluorescence curves to distinguish crude from dispersant. But we'll have to demonstrate that there's enough differentiation that we can tell our samples apart.
Some plots in the article show down to <300nm, but several also show good data in the 400-700 nanometer range, which is what our device can do. Tetracene, for example, is cited as being entirely between 460 and 600nm.
This is the best section, especially the one with the graph shown here:
Here, we see used motor oil, fuel oil and an unknown. Again, SSF, but in the right wavelength range.
Aging of samples
The paper also discusses old vs. new samples, and says that after 3 months there was no noticeable difference -- hard to say if this is true for all types of samples, but it's encouraging.
Pharr, Daniel Y., J. Keith McKenzie, and Aaron B. Hickman. "Fingerprinting petroleum contamination using synchronous scanning fluorescence spectroscopy." Groundwater 30.4 (1992): 484-489.