Method for analysing a sample comprising at least a first and a second scale inhibitor

1. Method for analysing a sample comprising at least a first and a second scale inhibitor, which scale inhibitors are synthetic organic compounds comprising at least one ionised group, and determining concentrations of the scale inhibitors in an industrial water system,

the method comprising

optionally diluting and/or purifying the sample,

allowing the sample interact with a reagent comprising lanthanide(III) ion,

exciting the sample at a first excitation wavelength and detecting a sample signal deriving from the lanthanide(III) ion at a signal wavelength by using time-resolved luminescence measurement,

determining the total concentration of the first and the second scale inhibitor by using the detected sample signal,

determining the concentration of the first scale inhibitor in the sample,

determining the concentration of the second scale inhibitor mathematically by using the obtained results for the total concentration and for the first scale inhibitor concentration.

2. Method according to claim 1 , wherein the concentration of the first scale inhibitor is determined by exciting the sample at a second excitation wavelength and detecting a first scale inhibitor signal by using time-resolved luminescence measurement.

3. Method according to claim 2 , wherein the first scale inhibitor signal is detected at the signal wavelength or a first signal wavelength, which is different from the signal wavelength wherein the difference between the first excitation wavelength and second excitation wavelength, and any successive excitation wavelength, is preferably at least 10 nm, more preferably at least 20 nm, even more preferably at least 25 nm.

4. Method according to claim 1 , wherein the time-resolved luminescence measurement is time-resolved fluorescence measurement.

5. Method according to claim 1 , wherein the concentration of the first, second and/or any successive scale inhibitor is determined by using luminescence, direct fluorescence, absorbance, spectrophotometry, optical rotation measurement, photon counting, inductively coupled plasma (IPC), high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), size exclusion chromatography, colorimetric methods, NMR, time-resolved luminescence, or a combination thereof.

6. Method according to claim 1 , wherein the reagent comprising lanthanide(III) ion is a lanthanide(III) salt or a luminescent lanthanide chelate.

7. Method according to claim 1 wherein the lanthanide(III) ion is selected from reagents comprising europium, terbium, samarium or dysprosium ions, preferably from europium or terbium ions.

8. Method according to claim 1 , wherein the concentration of the lanthanide(III) ion is in the range of 0.01-10 mM, preferably 0.01-1 mM, more preferably 0.01 mM -0.1 mM, even more preferably about 0.01 mM.

9. Method according to claim 1 , wherein the first and/or second scale inhibitors comprise two or more ionised groups, which are selected from phosphates, phosphonates, carboxylates, sulphonates, and/or amines, preferably from carboxylates, sulphonates and/or amines.

10. Method according to claim 9 , wherein the scale inhibitors are selected from group comprising polyelectrolyte compounds comprising carboxylate and/or phosphonate groups; homopolymers and copolymers of ethylenically unsaturated acid monomers; organophosphonates, and combinations thereof.

11. Method according to claim 1 , wherein the industrial water system is selected from a group consisting of

cooling tower water systems;

boilers and boiler water systems;

mineral process waters;

paper mill digesters, washers, bleach plants and white water systems;

black liquor evaporators in the pulp industry;

gas scrubbers and air washers;

continuous casting processes in the metallurgical industry;

air conditioning and refrigeration systems;

indirect contact cooling and heating water;

water reclamation and purification systems;

membrane filtration water systems;

food processing streams; and

waste treatment systems.

12. Method according to claim 1 , wherein the method is performed as on-line measurement.

13. Method according to claim 1 , wherein the scale inhibitor is anionic.

14. Method according to claim 1 , wherein the first and/or second scale inhibitor is a polycarboxylic acid selected from polyacrylic acid, polymethacrylic acid, polymaleic acid or any of their salts with monovalent cations.

15. Method according to claim 1 , wherein the scale inhibitor has a molecular weight of from 500 to 100 000 Daltons, more preferably 500-30 000 Daltons, even more preferably 500-12 000 Daltons.