Method for treating a liquid sample in order to remove interference by iron
The invention relates to a method for treating a liquid sample, which comprises disturbing iron and at least one organic compound of interest. The, the method comprises addition of a reagent comprising an ammonium salt, alkali metal salt or earth alkali metal salt of hexacyanoferrate to the sample. Iron in the sample is allowed to interact with the reagent and to form a reaction product, the reaction product of iron is separated from the sample, and the amount of the at least one compound of interest is determined from the sample. The invention relates also to use of salt of hexacyanoferrate.
1. A method for treating a liquid sample, the sample comprising iron in the form of iron (II) and/or iron (III) and at least one organic compound of interest, the method comprising
(i) adding ascorbic acid to the sample in order to reduce any iron (III) in the sample to iron (II);
(ii) after or simultaneous to the addition of ascorbic acid further adding a reagent comprising an ammonium salt, alkali metal salt or earth alkali metal salt of hexacyanoferrate to the sample;
(iii) allowing the iron in the sample to interact with the reagent and to form an insoluble iron containing reaction product;
(iv) separating the resultant insoluble reaction product comprising iron from the sample; and
(v) determining the amount of the at least one organic compound of interest in the sample;
wherein the method does not include the addition of any other reactants which promote the formation of another insoluble iron containing reaction product and/or the method does not include the removal of another insoluble iron containing reaction product from the sample.
2. The method according to claim 1 , wherein the organic compound of interest is a synthetic organic compound, a natural polymer or a biopolymer.
3. The method according to claim 1 , wherein the organic compound of interest is an organic compound selected from the group consisting of scale inhibitors, corrosion inhibitors, friction reducers, and polymers used in oil field applications or oil recovery processes.
4. The method according to claim 1 , wherein the method comprises a step of adjusting pH of the sample to a pH value≤7, before addition of the reagent.
5. The method according to claim 1 wherein the reagent comprises hexacyanoferrate(II).
6. The method according to claim 1 , wherein the reagent comprises ammonium or potassium hexacyanoferrate.
7. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 1:2 to 20:1.
8. The method according to claim 1 , wherein the total concentration of iron is >0.5 ppm.
9. The method according to claim 1 , wherein the method comprises separating the reaction product by filtering, centrifuging or sedimentation.
10. The method according to claim 1 , wherein the method comprises adding a flocculation agent to the sample after addition of the reagent and separating the reaction product by flocculation.
11. The method according to claim 1 , wherein the method comprises determining the amount of iron in the sample and adjusting the amount of reagent on basis of said determination.
12. The method according to claim 8 , wherein the total concentration of iron is >75 ppm.
13. The method according to claim 12 , wherein the total concentration of iron is >100 ppm.
14. The method according to claim 4 , wherein the pH ranges from 3 to 5.
15. The method according to claim 4 , wherein the pH ranges from 1 to 3.
16. The method according to claim 8 , wherein the total concentration of iron ranges from 10 ppm to ≥50 ppm.
17. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 4:5 to 15:1.
18. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 1:1 to 10:1.
19. The method according to claim 1 , wherein the insoluble reaction product is removed by filtration.