Using wavelength fraction absorption ratios to improve substance ID across platforms

[dobrodude]

I have been thinking about the problem of variability in the spectrum of a substance based on different setups and even within the same setup with respect to sample concentration differences.

One way to reduce the effect of variability might be to quantify the absorption of a range of wavelengths (arbitrarily 300-400nm, 401-500nm etc)  by adding a routine that automatically measures the area under the curve of each range and divide each area by the total.

This would produce a ratio or percentage of the total for each set of wavelengths that should be more consistent across concentrations and different spectrometers provided the same light source was used like halogen.
The ratios or percentages for each substance could be stored in the database along with the actual spectrum itself and searched by matching the closest percentage sets with unknowns. The search data could contain perhaps as few as five values or perhaps more depending on the wavelength ranges chosen and automated.

Hypothetical example:
A spectrum of an unknown  substance is run and the absoprtion percentages might be:
300-400nm = 12% of total absorption
401-500nm = 38%  "
501-600nm = 16%
601-700nm = 18%
701-800nm = 26%

A routine could automatically display all posted spectra of knowns with that percentage set or close to it.

Measuring the absorption ratios of various proteins in blood is a standard technique in clinical laboratories.
Let me know what you think!
GB

[Jeffrey Warren]

Bumping to spectrometry list! Sounds interesting, Gary, thanks!

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[Richard Winkel]

I'll throw in a resounding YES vote!

The question I would like to pose, to be answered by the new logic is:

"Looking at wavelength range from x nm to y nm, and with bins z nm wide, what is the percentage of absorption taking place in each bin?"

This is essentially what I would do in Excel if not available in the online software.

Regards,

Dick Winkel

[Gary Barker]

How do you measure area under the curve with the online software? I have never seen a demo of it.
GB

[Jeffrey Warren]

Sorry to keep doing this, but we really want to keep spectrometry discussion on the spectrometry list -- please try to reply all to plots-spectrometry only, thanks!

What's the best way to measure area under the curve? It would seem to be pretty easy to do with the JavaScript API: http://publiclab.org/wiki/spectral-workbench-api

I was thinking of just summing the values of all the data points, and divide by the total # of points (for the desired region) -- that'd be the average, not the area under the curve... but easier since we have binned data, not a smooth curve.

Anyhow i'm not so strong on the math... but i can help implement it in JavaScript as a macro.

Jeff

Jeff