Determination of Tributyltin Oxide in Marine Anticorrosive Coatings by Liquid Chromatography-Tandem Triple Quadrupole Mass Spectrometry

The uniformly mixed sample (1.00 g) was taken and placed in a colorimetric tube. 15 mL of extractant (methanol for water based coatings, and ethyl acetate for solvent based coatings) was added, and the solution was extracted by ultrasound at 35 ℃ for 15 min. The extraction solution was centrifuged for 5 min, and 10 mL of the upper clear liquid was taken and blown to near dryness by nitrogen. The residue was redissolved and made its volume up to 2 mL by methanol, and passed through 0.45 μm filter membrane(nylon filter membrane for water based coatings, and organic filter membrane for solvent based coatings). Tributyltin oxide in the filtrate was determined by liquid chromatography-tandem triple quadrupole mass spectrometry, with EC-C₁₈ chromatographic column as the stationary phase, and a mixed solution of 0.1% (volume fraction) formic acid solution and methanol at different volume ratios as the mobile phase for gradient elution. The electrospray positive ion source and multiple reaction monitoring mode were adopted into mass spectrometry analysis, and external standard method was used for quantification. As shown by the results, linear relationship between the corresponding peak areas and mass concentrations of tributyltin oxide was found in the range of 0.1-2.0 mg·L^-1, with detection limit of 0.031 mg·kg^-1. Test for recovery was made by the standard addition method, giving results in the range of 86.9%-92.9%, with RSDs (n=6) of the determined values less than 4.0%. This method was used to analyze 10 samples of solvent based coatings and 10 samples of water based coatings. Among them, tributyltin oxide was detected in 2 samples of solvent based coatings with detection amounts of 1.18 and 0.82 mg·kg^-1, and in one sample of water based coating with detection amount of 0.48 mg·kg^-1.