Use of an ion-pairing reagent for high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry determination of anionic anticoagulant rodenticides in body fluids.

The on-line combination of high-performance liquid chromatography with mass spectrometry (HPLC-MS) has become a powerful tool for trace analysis thanks to the developments in interface techniques. However, non-volatile salts such as ion-pairing reagents are considered to be incompatible with HPLC-MS systems; they cause drops in analyte signals because of contamination of mass analyzers and also because of blocking of the capillary transferring ions from atmospheric pressure to the vacuum manifold. In this work, a new type of ion-pairing reagent, di-n-butylammonium acetate (DBA), was evaluated for use in HPLC-MS. DBA did not cause these problems to HPLC-MS systems; a possible explanation might be that DBA decomposed to volatile compounds under APCI conditions. In addition, DBA was very useful for obtaining sharp peaks, which resulted in high sensitivity. With this ion-pairing reagent, we developed a procedure for the measurement of five (including internal standard) anticoagulant rodenticides in whole blood and urine samples by SIM detection of [M-H]- ions. Calibration range, recoveries and precision of the method were examined; detection limits as low as 1-5 ng/ml blood sample or 0.5-2.5 ng/ml urine sample were achieved.