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Determination of cyanuric acid in soil extracts by liquid chromatography with UV and mass spectrometric detection

Cyanuric acid is a highly polar and hydrophilic degradation product of symmetric triazine herbicides, such as widely used atrazine and simazine. It is formed by microbial degradation, chemical oxidation or photooxidation of parent compounds. Analytical methods for determination of cyanuric acid mostly employ reversed-phase high performance liquid chromatography (HPLC) with UV detection. A direct coupling of the HPLC system with a mass spectrometric detector (LC-MS) is problematic because the eluents used for HPLC-UV analysis conventionally contain non-volatile components which are not compatible with MS systems. This work was focused on optimisation of HPLC-UV and LC-MS conditions for determination of cyanuric acid in extracts of soil samples collected in the area of an industrial plant producing triazine herbicides. The mass fractions of atrazine, simazine, propazine and terbuthylazine in these samples ranged from 0.04 to 1165.93 mg/kg. Cyanuric acid was ultrasonically extracted from soil with a 2:1 acetone:n-hexane mixture and analysed by HPLC coupled to UV diode-array detector (DAD) and to quadrupole – time of flight mass spectrometer (Q-TOF MS) using the electrospray ionisation in negative mode. The soil extract was evaporated and the dry residue was redissolved in 0.01 mol/L phosphate buffer, pH 7.0, for HPLC-UV(DAD) analysis or in water for LC-MS analysis. The chromatographic column in the HPLC-UV(DAD) system was Hypersyl ODS, 250 x 4.6 mm i.d., particle size 5 &micro ; m. The elution was carried out under gradient conditions with phosphate buffer (pH 7.0) and acetonitrile as the mobile phase. The chromatographic column in the LC-MS system was a 250 x 4.6 mm i.d. LiChrospher 100 CN, particle size 5 &micro ; m. The mobile phase was modified in order to meet the conditions required for LC-MS by substitution of non-volatile phosphate buffer with water. The elution was carried out under isocratic conditions. Cyanuric acid was determined by selective monitoring of deprotonated molecule (m/z 128) extracted from the total ion current chromatogram. The identity of the analyte was additionally confirmed by accurate mass measurements of deprotonated molecule using the Q-TOF MS equipped with lock-spray option. The recovery of cyanuric acid from a soil spiked at 500 mg/kg level was 64 %. HPLC-UV(DAD) and LC-MS analyses demonstrated comparable detection sensitivity of cyanuric acid in soil: 0.2 mg/kg. However, the advantage of MS detection was the high ion selectivity of Q-TOF MS and the ability to eliminate the interferences of coeluting species that could bias the results of cyanuric acid analysis. The mass fractions of cyanuric acid in analysed soil samples ranged from 4.67 to 380 mg/kg.

Cyanuric acid; triazine herbicides; soil; LC-MS; HPLC

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