A method of determining whether a water- or steam-contacted surface of a water cycle or steam cycle contains a protective amount of at least one film forming organic amine of the formula having at least one linear or branched, acyclic hydrocarbon group having 12 to 22 carbon atoms R 1 -(NR 3 R 2 ) n -NR 4 R 5 (I) wherein n is 0, 1, 2, 3 or 4, R 1 is a linear or branched, acyclic hydrocarbon group having 12 to 22 carbon atoms, R 2 is C 1 -C 4 -alkanediyl, R 3 ,R 4 ,R 5 are independently H or C 1 -C 4 alkyl or -(C m H 2m-2 O) p -H, wherein m is 1, 2, 3, or 4 and p is = 1, 2, 3 or 4, the method comprising taking a sample from the surface and analyzing the sample for the presence of the least one film forming organic amine; wherein for taking the sample an absorber material is brought into intimate contact with the surface to transfer the at least one organic amine to the absorber material; where the method comprises the following steps: i) transfer of the at least one organic amine of the formula (I) to the absorber material, which comprises a solvent a), ii) extraction of the amine of the formula (I) out of the absorber material with a second solvent b), which is the same as or different from the solvent a) to obtain an extract comprising the solvent b), the at least one organic amine of the formula (I) and optionally the solvent a), iia) optionally, filtration of the extract, iii) optionally, adjusting the pH-value of the obtained extract, iv) adding a reagent capable to form a colored complex with the at least one organic amine of the formula , v) detecting the colored complex. n is 0, 1, 2, 3 or 4, R 1 is a linear or branched, acyclic hydrocarbon group having 12 to 22 carbon atoms, R 2 is C 1 -C 4 -alkanediyl, R 3 ,R 4 ,R 5 are independently H or C 1 -C 4 alkyl or -(C m H 2m-2 O) p -H, wherein m is 1, 2, 3, or 4 and p is = 1, 2, 3 or 4, the method comprising taking a sample from the surface and analyzing the sample for the presence of the least one film forming organic amine; wherein for taking the sample an absorber material is brought into intimate contact with the surface to transfer the at least one organic amine to the absorber material; where the method comprises the following steps: i) transfer of the at least one organic amine of the formula (I) to the absorber material, which comprises a solvent a), ii) extraction of the amine of the formula (I) out of the absorber material with a second solvent b), which is the same as or different from the solvent a) to obtain an extract comprising the solvent b), the at least one organic amine of the formula (I) and optionally the solvent a), iia) optionally, filtration of the extract, iii) optionally, adjusting the pH-value of the obtained extract, iv) adding a reagent capable to form a colored complex with the at least one organic amine of the formula , v) detecting the colored complex. i) transfer of the at least one organic amine of the formula (I) to the absorber material, which comprises a solvent a), ii) extraction of the amine of the formula (I) out of the absorber material with a second solvent b), which is the same as or different from the solvent a) to obtain an extract comprising the solvent b), the at least one organic amine of the formula (I) and optionally the solvent a), iia) optionally, filtration of the extract, iii) optionally, adjusting the pH-value of the obtained extract, iv) adding a reagent capable to form a colored complex with the at least one organic amine of the formula , v) detecting the colored complex. <EOS>