Method for determining a scale inhibitor concentration in a sample
The invention relates to a method for determining a scale inhibitor concentration in a sample comprising at least a first scale inhibitor, which is a synthetic organic compound comprising at least one ionized group. The method comprises optionally diluting and/or purifying the sample, and allowing the sample to interact with a reagent comprising a lanthanide(III) ion. The sample is excited at a first excitation wavelength and a sample signal deriving from the lanthanide(III) ion is detected at a signal wavelength by using time-resolved luminescence measurement, and the concentration of the at least first scale inhibitor in the sample is determined by using the detected sample signal.
1. A method for determining a scale inhibitor concentration in a sample comprising at least a first scale inhibitor, which is a synthetic organic compound comprising at least one ionised group, the method comprising
optionally diluting and/or purifying the sample,
allowing the at least first scale inhibitor in the sample to interact with a reagent comprising a 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, and
determining the concentration of the at least first scale inhibitor in the sample by using the detected sample signal.
2. The method according to claim 1 , wherein the reagent comprising a lanthanide(III) ion is a lanthanide(III) salt or a luminescent lanthanide chelate.
3. The method according to claim 1 wherein the lanthanide(III) ion is selected from europium, terbium, samarium or dysprosium ions, preferably from europium or terbium ions.
4. The method according to claim 1 , wherein the concentration of the lanthanide(III) ion in the sample 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.
5. The method according to claim 1 , wherein the scale inhibitor comprises two or more ionised groups, the ionised groups being selected from phosphates, phosphonates, carboxylates, sulphonates, and/or amines, preferably from carboxylates, sulphonates and/or amines.
6. The method according to claim 5 , wherein the scale inhibitor is selected from the group consisting of polyelectrolyte compounds comprising carboxylate and/or phosphonate groups; homopolymers and copolymers of ethylenically unsaturated acid monomers; organophosphonates; and combinations thereof.
7. The method according to claim 1 , wherein the concentration of the scale inhibitor in the sample is in the range of 0.5-200 ppm, preferably 1-50 ppm, more preferably 1-10 ppm.
8. The method according to claim 1 , wherein the sample comprises two or more scale inhibitors, whereby the detected sample signal deriving from the lanthanide(III) ion at the signal wavelength by using time-resolved luminescence measurement corresponds to the total concentration of the two or more scale inhibitors in the sample.
9. The method according to claim 1 , wherein the sample comprises a second scale inhibitor, optionally a plurality of successive scale inhibitors, and the individual concentrations of each scale inhibitor in the sample are determined.
10. The method according to claim 9 , wherein the concentration of the second scale inhibitor, or any successive scale inhibitor, is determined by using luminescence, time-resolved 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, or a combination thereof.
11. The method according to claim 9 wherein the concentration of the second scale inhibitor is determined by exciting the sample at a second excitation wavelength and detecting a second sample signal deriving from the lanthanide(III) ion by using time-resolved luminescence measurement.
12. The method according to claim 11 , wherein the difference between the first excitation wavelength and second excitation wavelength is at least 10 nm, preferably at least 20 nm, more preferably at least 25 nm.
13. The method according to claim 1 , wherein the method includes adding a signal modifier comprising a metal ion, to the sample before the excitation of the sample.
14. The method according to claim 13 , wherein the signal modifier comprises a metal ion which is selected from the group consisting of copper, nickel, chromium, iron, gold, silver, cobalt, and any of their mixtures.
15. The method according to claim 1 , wherein the time-resolved luminescence measurement is time-resolved fluorescence measurement.
16. The method according to claim 1 , wherein the sample is purified by using a purification method selected from centrifugation, size exclusion chromatography, cleaning with solid-phase extraction (SPE) cartridges, dialysis techniques, extraction methods for removing hydrocarbons, filtration, microfiltration, ultrafiltration, nanofiltration, membrane centrifugation and any combinations thereof.
17. The method according to claim 1 , wherein a pH value of the sample is adjusted to a level in the range between pH 3 and pH 8, preferably in the range from pH 5 to pH 8.
18. The method according to claim 1 , wherein the sample originates from an oilfield or an oil well or from an oil production process.