Method of identifying a material
The invention concerns a method of measuring the amount of a particular SERS-active taggant compound in a sample of a material which includes the steps of adding an internal standard containing an isotopically-altered version of said SERS-active taggant compound to the sample, contacting the sample/internal standard mixture with a SERS substrate then subjecting the mixture and SERS substrate to Raman spectroscopy. The concentration of SERS-active taggant compound in the sample is then calculated from the ratio of (i) the Raman spectroscopy detector response to the SERS-active taggant compound to (ii) the Raman spectroscopy detector response to the internal standard.
1. A method of measuring the amount of a particular SERS-active taggant compound in a sample of liquid comprising the steps of:—
a) adding to said sample an internal standard comprising an isotopically-altered version of said SERS-active taggant compound;
b) contacting said sample containing said internal standard with a SERS substrate;
c) subjecting said sample and SERS substrate to Raman spectroscopy; and
d) calculating the ratio of (i) the Raman spectroscopy detector response to the SERS-active taggant compound to (ii) the Raman spectroscopy detector response to the internal standard.
2. A method according to claim 1 , wherein said sample is dissolved or dispersed in a liquid prior to step (b).
3. A method according to claim 1 , wherein the SERS substrate comprises silver, gold, or copper.
4. A method according to claim 1 , wherein the SERS substrate is in the form of a colloidal solution.
5. A method according to claim 1 , wherein the SERS substrate is in the form of a planar material having a metallic surface comprising microstructure.
6. A method according to claim 5 , wherein the SERS substrate is an immobilised metal colloid or a patterned surface made from or coated with a metal.
7. A method according to claim 1 , wherein a solvent is added to the sample before step (b).
8. A method according to claim 7 , wherein the solvent is a non-polar solvent.
9. A method according to claim 1 , wherein the concentration of said SERS-active taggant compound in said sample is calculated from the ratio calculated in step (d).
10. A method according to claim 1 , wherein the ratio calculated in step (d) is compared with a reference value representing the ratio of (iii) the Raman spectroscopy detector response to the SERS-active taggant compound to (iv) the Raman spectroscopy detector response to the internal standard from a reference sample containing a known concentration of SERS-active taggant compound.
11. A method of comparing a liquid material to a reference liquid material comprising the steps of:—
a. obtaining a sample of said liquid material;
b. optionally, dissolving or dispersing said sample in a liquid;
c. carrying out the method of claim 1 ;
d. comparing the ratio of (i) the Raman spectroscopy detector response to the SERS-active taggant compound to (ii) the Raman spectroscopy detector response to the internal standard with a reference value representing the ratio of (iii) the Raman spectroscopy detector response to the SERS-active taggant compound to (iv) the Raman spectroscopy detector response to the internal standard measured in a sample of said reference liquid material containing a known concentration of SERS-active taggant compound.
12. A method of marking a first liquid material and subsequently identifying whether a sample of a second liquid material is a sample of said marked first liquid material comprising the steps of adding to said first liquid material a SERS-active taggant compound and later carrying out the method of claim 11 on said second liquid material.
13. A method according to claim 12 , wherein the concentration of the SERS-active taggant compound in the reference liquid material is the same as the concentration of SERS-active taggant compound in the marked first liquid material.
14. A method according to claim 12 , wherein more than one taggant compound is added to the first liquid material.
15. A method according to claim 12 , wherein said first liquid material is an organic liquid.
16. A method according to claim 11 , wherein said liquid material is an organic liquid.
17. A method according to claim 1 , wherein the sample of liquid is an organic liquid.
18. A method according to claim 1 , wherein said sample of liquid comprises an organic liquid, water, an aqueous solution, a powdered solid, a particulate solid, a solid object, or a plurality of objects.
19. A method according to claim 18 , wherein said sample of liquid comprises a hydrocarbon, fuel, mineral oil, vegetable oil, organic solvent, alcohol, pharmaceutical, agrochemical, cosmetic, or perfume.
20. A method for determining the amount of a SERS-active taggant compound in a sample of a liquid hydrocarbon, comprising the steps of:
mixing the sample with a quantity of a non-polar solvent; adding an internal standard comprising an isotopically-altered version of said SERS-active taggant compound to the mixture;
contacting said mixture containing said internal standard with a SERS substrate;
subjecting the mixture and SERS substrate to Raman spectroscopy; and
calculating the concentration of said SERS-active taggant compound in said sample from the ratio of (i) the Raman spectroscopy detector response to the SERS-active taggant compound to (ii) the Raman spectroscopy detector response to the internal standard.