Method and kit for dosing iron ions in lubricating compositions

1. Method for determining iron ions in a lubricating composition, comprising the following steps:

a) Taking a sample of the lubricating composition to be analysed in a first container;

b) Placing said first container containing the sample to be analysed on a magnet;

c) Adding to a second container:

a first aqueous reactive composition (CR 1 ) comprising at least one extracting agent for extracting ferric and ferrous ions from an oil phase of the lubricating composition towards an aqueous phase of the lubricating composition formed by water in the first aqueous reactive composition (CR 1 ) when the aqueous reactive composition (CR 1 ) is added to the lubricating composition, wherein the ferric and ferrous ions are moved from the oil phase of the lubricating composition to the aqueous phase of the lubricating composition;

a second aqueous reactive composition (CR 2 ) comprising at least one reducing agent of ferric ions (Fe 3+ ) to ferrous ions (Fe 2+ );

a third reactive composition (CR 3 ) comprising at least one emulsion destabilising agent; and

a fourth reactive composition (CR 4 ) in an aqueous solution comprising at least one complexing agent of ferrous ions, characterized in that this agent changes colour when complexing with ferrous ions;

 and mixing thereof in order to form a mixture;

d) optionally, photochemical measurement of an absorbance of the mixture obtained at step c);

e) Taking drops of the lubricating composition contained in the first container, held in position on the magnet, and adding these drops to the second container comprising the mixture of the first, second, third and fourth reactive compositions obtained at step c);

f) Agitating the mixture obtained at step e);

g) Conducting photochemical measurement of an absorbance of the mixture obtained at step f); and

h) determining a quantity of ferrous ions in the lubricating composition from the measurement obtained at step g) or if step d) is present, by subtraction of the measurement of step d) from the measurement of step g).

2. The method according to claim 1 , wherein the at least one extracting agent is selected from among agents solubilising ferric and ferrous ions and being immiscible in the lubricating composition.

3. The method according to claim 2 , wherein the at least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

4. The method according to claim 1 , wherein the at least one extracting agent is selected from among sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid, alone or in a mixture.

5. The method according to claim 4 , wherein the at least one extracting agent is sulfuric acid.

6. The method according to claim 5 , wherein the a least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

7. The method according to claim 4 , wherein the at least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

8. The method according to claim 1 , wherein the at least one reducing agent of ferric ions to ferrous ions is selected from among hydroquinone, hydroxylamine hydrochloride, hydrazine and dithionite, alone or in a mixture.

9. The method according to claim 8 , wherein the at least one reducing agent of ferric ions to ferrous ions is hydroxylamine hydrochloride.

10. The method according to claim 9 , wherein the at least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

11. The method according to claim 8 , wherein the at least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

12. The method according to claim 1 , wherein the at least one destabilising agent is selected from among primary or secondary alcohols having from 4 to 10 carbon atoms non-miscible in water, alone or in a mixture.

13. The method according to claim 12 , wherein the at least one destabilising agent is isoamyl alcohol, octan-1-ol, octan-2-ol, 1-heptanol, 2-ethyl-hexanol or 2-ethyl-butanol.

14. The method according to claim 13 , wherein the at least one complexing agent is selected from among ferrous ion complexing agents and for which complexing is a cause of a change of colour able to be detected by spectrophotometric measurement of an absorbance of a mixture obtained at step e).

15. The method according to claim 14 , wherein the at least one complexing agent is nitroso-R salt.

16. The method according to claim 1 , wherein the at least one complexing agent is selected from among ferrozine, ferene, phenantroline and derivatives thereof, bipyridine, thioglycolic acid, nitroso-R salt (sodium salt of 3-hydroxy-4-nitroso-2,7-naphthalenedisulfonic acid), potassium ferricyanide, and 2,4,6-tripirydyl-s-triazine (TPTZ).

17. The method according to claim 1 , wherein the first and second reactive compositions are included in an aqueous reactive composition CR 1 ′.

18. Kit to implement the method according to claim 1 , comprising:

a first aqueous reactive composition (CR 1 ) comprising at least one extracting agent for extracting ferric and ferrous ions from an oil phase of the lubricating composition towards an aqueous phase of the lubricating composition formed by water in the first aqueous reactive composition (CR 1 ) when the aqueous reactive composition (CR 1 ) is added to the lubricating composition, wherein the ferric and ferrous ions are moved from the oil phase of the lubricating composition to the aqueous phase of the lubricating composition;

a second aqueous reactive composition (CR 2 ) comprising at least one reducing agent of ferric ions (Fe3+) to ferrous ions (Fe2+);

a third reactive composition (CR 3 ) comprising at least one emulsion destabilising agent;

a fourth reactive composition (CR 4 ) in an aqueous solution comprising a ferrous ion complexing agent, wherein this agent changes colour when complexing with ferrous ions;

a spectrophotometer;

at least one second container;

a device (D 2 ) to take up each of the first, second, third and fourth reactive compositions;

a magnetised support;

a first container; and

at least one device (D 3 ) to take up drops of the lubricating composition located in the first container.

19. The kit of claim 18 , further comprising at least one device (D 1 ) to take a sample of lubricating composition to be analysed.