Decomposition Kinetics of Omethoate in Blood

Abstract

Objectives: To study the decomposition kinetics of omethoate in blood.

Methods: The acetonitrile precipitated protein was added into the blood, with the chromatographic column of a Waters BEH C₁₈ column （2.1 mm×50 mm, 1.7 μm）, the mobile phase of 5 mmol/L ammonium acetate aqueous solution-methanol, and the gradient elution with a flow rate of 0.3 mL/min and injection volume of 2 μL. With electrospray ionization （ESI） source and positive ion detection, qualitative and quantitative analyses were taken using multi-reaction monitoring mode. Omethoate standard was added into blank human blood to the mass concentrations of 0.78, 1.40, 2.30, 4.50, and 7.20 μg/mL, and each mass concentration was preserved at 3 temperatures of -20 ℃, 4 ℃, and 20 ℃, respectively. The content of omethoate was detected at different time points （0, 1, 3, 4, 7, 11, 15, 24, 32, 40, 48, 64, 80, 96, and 120 d）.

Results: Different concentrations of omethoate all showed a descended trend in human blood under different temperature conditions. The decomposition in storage environment of -20 ℃, 4 ℃, and 20 ℃ was fit to a one-compartment open model with a first-order kinetic process, which could be expressed as C_t=C_oe^-αt, with the calculated theoretical values of omethoate concentration close to the measured values.

Conclusions: All concentrations of omethoate are decomposed in the blood, which vary a lot in different preservation conditions. It is suggested that blood samples should be frozen and detected timely in suspected omethoate poisoning cases.

Keywords: forensic toxicology; liquid chromatography-mass spectrometry; omethoate; blood.