Determining the Quantity of a Taggant in a Liquid Sample

1 . A method for determining whether a liquid sample comprises a particular fluorescent tagging compound at a preset concentration, wherein the method comprises:

(a) obtaining a measured emission spectrum from the liquid sample, wherein the liquid sample is exposed to a light source that causes the particular fluorescent tagging compound to fluoresce over a spectral range;

(b) generating a predicted concentration of the particular fluorescent tagging compound in the liquid sample, wherein the generating comprises a process selected from the group consisting of

(i) a multivariate process comprising:

(1) selecting a library that comprises a plurality of known emission spectra, wherein each of the plurality of known emission spectra is correlated to a known concentration of the particular fluorescent tagging compound, and

(2) utilizing the library and the measured emission spectrum to generate the predicted concentration of the particular fluorescent tagging compound in the liquid sample,

(ii) a background subtraction process comprising:

(1) determining a background emission spectrum from the measured emission spectrum,

(2) eliminating the background emission spectrum from the measured emission spectrum to obtain a predicted emission spectrum, and

(3) evaluating the predicted emission spectrum to generate the predicted concentration of the particular fluorescent tagging compound in the liquid sample, and

(iii) a combination of (i) and (ii); and

(c) comparing the predicted concentration of the particular fluorescent tagging compound in the liquid sample with the preset concentration of the particular fluorescent tagging compound in the liquid sample.

2 . The method of claim 1 , wherein

(a) the liquid sample is determined to comprise the particular fluorescent tagging compound at the preset concentration when the predicted concentration is within a present range of the particular fluorescent tagging compound in the liquid sample, and

(b) the liquid sample is determined not to comprise the particular fluorescent tagging compound at the preset concentration when the predicted concentration is outside the present range of the particular fluorescent tagging compound in the liquid sample.

3 . The method of claim 1 further comprising authenticating the liquid sample, wherein

(i) the liquid sample is determined to be authentic when the predicted concentration is within a preset percentage of the preset concentration of the particular fluorescent tagging compound in the liquid sample; and

(ii) the liquid sample is determined to not be authentic when the predicted concentration is outside the preset percentage of the preset concentration of the particular fluorescent tagging compound in the liquid sample.

4 - 7 . (canceled)

8 . The method of claim 1 , wherein the particular fluorescent tagging compound is a first particular fluorescent tagging agent.

9 . The method of claim 1 , wherein

(a) the particular fluorescent tagging compound is a combination of (i) a first particular fluorescent tagging agent, and (ii) a second particular tagging agent;

(b) the preset concentration is (i) a first preset concentration of the first particular fluorescent tagging agent, and (ii) a second preset concentration of the second particular fluorescent tagging agent;

(c) the predicted concentration of the particular fluorescent tagging compound in the liquid sample comprises (i) a first predicted concentration of the first particular fluorescent tagging agent, and (ii) a second predicted concentration of the second particular fluorescent agent; and

(d) the present range of the particular fluorescent tagging compound in the liquid sample comprises (i) a first present range of the first particular fluorescent tagging agent, and (ii) a second present range of the first particular fluorescent tagging agent.

10 . The method of claim 1 , wherein

(a) the particular fluorescent tagging compound is a combination of three or more particular fluorescent tagging agents;

(b) the preset concentration is a preset concentration for each of the three or more particular fluorescent tagging agents;

(c) the predicted concentration of the particular fluorescent tagging compound in the liquid sample comprises a predicted concentration for each of the three or more particular fluorescent tagging agents; and

(d) the present range of the particular fluorescent tagging compound in the liquid sample comprises a present range for each of the three or more particular fluorescent tagging agents.

11 - 12 . (canceled)

13 . The method of claim 1 , wherein the particular fluorescent tagging compound comprises a first particular fluorescent tagging agent having an emission fluorescence in a range of from about 500 nm to about 900 nm.

14 . The method of claim 13 , wherein

(a) the particular fluorescent tagging compound comprises a second particular fluorescent tagging agent;

(b) the second particular fluorescent tagging agent has an emission fluorescence in a range of from about 500 nm to about 900 nm; and

(c) the first particular fluorescent tagging agent and the second particular fluorescent tagging agent have different emission fluorescence in a range of from about 500 nm to about 900 nm.

15 . The method of claim 14 , wherein

(a) the particular fluorescent tagging compound comprises a third particular fluorescent tagging agent;

(b) the third particular fluorescent tagging agent has an emission fluorescence in a range of from about 500 nm to about 900 nm;

(c) the first particular fluorescent tagging agent, the second particular fluorescent tagging agent, and the third particular fluorescent tagging agent have different emission fluorescence in a range of from about 500 nm to about 900 nm.

16 . (canceled)

17 . The method of claim 1 , wherein the spectral range comprises a range of from 500 nm to 900 nm.

18 . The method of claim 1 , wherein the liquid is selected from the group consisting of liquid petroleum hydrocarbon-based fuels, biologically-derived fuels (biofuels), and common industrial solvents.

19 . The method of claim 1 , wherein

(a) the liquid sample comprises a known type of liquid; and

(b) the utilizing the library comprises utilizing only the measured emission spectrum measured from the known type of liquid in the library.

20 . The method of claim 1 , wherein

(a) the liquid sample is from a known geographical region; and

(b) the utilizing the library comprises utilizing only the measured emission spectrum measured from that known geographical region.

21 . The method of claim 1 , wherein utilizing the library and the measured emission spectrum to generate the predicted concentration of the particular fluorescent tagging compound in the liquid sample comprises performing a multivariate analysis utilizing the library and the measured emission spectrum.

22 . (canceled)

23 . The method of claim 21 , wherein the multivariate analysis comprises a partial least squares analysis.

24 . The method of claim 23 , wherein the multivariate analysis comprises a principal components regression analysis.

25 . The method of claim 24 , wherein the multivariate analysis yields a calibration model that comprises a plurality of spectral vectors correlation scores relating to concentration of the particular fluorescent tagging compound.

26 . The method of claim 25 , wherein the utilizing the library and the measured emission spectrum to generate the predicted concentration of the particular fluorescent tagging compound in the liquid sample further comprises using the calibration model to calculate the predicted concentration of the particular fluorescent tagging compound in the liquid sample.

27 . The method of claim 1 , wherein the determining the background emission spectrum comprises obtaining at least three data points from the measured emission spectrum and using these three data points to calculate the background emission spectrum.

28 . The method of claim 27 , wherein the calculating the background emission spectrum comprises fitting the three data points into a quadratic curve.

29 . The method of claim 27 , wherein the calculating the background emission spectrum comprises fitting the three data points into an exponential curve.

30 . The method of claim 29 , wherein the calculating the background emission spectrum comprises fitting the three data points into a linear combination of an exponential curve and a quadratic curve.

31 . The method of claim 1 , wherein the eliminating the background spectrum from the measured emission spectrum comprises subtracting the background spectrum from the measured emission spectrum.

32 . The method of claim 1 , wherein the evaluating the predicted emission spectrum to determine a predicted concentration of the particular fluorescent tagging compound in the liquid sample comprises calculating the area under the predicted emission spectrum.

33 . The method of claim 1 , wherein the evaluating the predicted emission spectrum to determine a predicted concentration of the particular fluorescent tagging compound in the liquid sample comprises evaluating at least one peak of the predicted emission spectrum.

34 - 63 . (canceled)