Assessment of stable carbon isotope ¹³С/¹²С ratio in phthalates from surface waters using HPLC-HRMS-TOF approach

A method for estimating the ratio of stable carbon isotopes ¹³С/¹²С in the composition of phthalates from surface water at a trace concentration level is proposed. It is based on the concentration of hydrophobic components of water using an analytical reversed phase HPLC column followed by their gradient separation and detection of eluted phthalates using a high-resolution time-of-flight mass spectrometer (ESI-HRMS-TOF) in the form of molecular ions. The ratio of stable carbon isotopes ¹³С/¹²C in phthalates is calculated as a ratio of integrals under the monoisotopic [M+1+H]⁺ and [M+H]⁺ peaks. The Δ¹³C value is calculated relatively to the ¹³C/¹²C ratio in commercial DnBP and DEHP phthalates used as standards. The minimal concentration of DnBP and DEHP in water required for a reliable determination of Δ¹³C value is estimated by the level of ca. 0.2 μg L^-1. The technique has been verified during the monitoring of priority phthalates in the waters of Lake Baikal.