Simple and fast determination of free cyanide in drinking water by liquid chromatography electrospray ionization tandem mass spectrometry following “in vial” derivatization

We have developed a highly sensitive method for the determination of free cyanide (CN−) in drinking water using derivatization and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The derivatization reaction was conducted at 25 °C for 10 min, and sample preparation consists only of the addition of N-(2-(bromomethyl)benzyl)-N,N-diethylethanaminium bromide (CAX-B) directly into an injection vial containing sample prior to LC-ESI(+)-MS/MS analysis, without any purification step. The conditions used for derivatization, including reaction temperature, time, pH, and of CAX-B concentration, and chromatography conditions were optimized. The LC cycle time was 8 min, and the CN derivative (CAX-CN) was stable for at least 48 h at ambient temperature and ESI-MS/MS fragmentation of the [M+H]+ precursor ion (m/z 231) produced stable characteristic product ions at m/z 130, 103, 100, 86 and 72. The linear dynamic range of the method was 0.1–50 ng/mL, with limits of detection (LOD), identification (LOI) and quantification (LOQ) of 20 pg/mL, 20 pg/mL and 100 pg/mL, respectively. Compared with previously described GC-MS or LC-MS-based methods, the method was simpler, faster, produced more informative MS/MS spectra and was more sensitive. The method sensitivity and dynamic range would enable its use not only to detect trace amounts of cyanide for forensic investigations in cases where water supplies are suspected to be contaminated but also for the detection of higher concentrations, e.g., for the routine monitoring of maximum permissible CN− levels in drinking water. [Display omitted] •A highly sensitive method for rapid free cyanide determination in drinking water.•Simple “in vial” derivatization reaction at ambient temperature.•Sample preparation consisted of the addition of CAX-B prior to LC-MS/MS analysis.•The MS/MS fragmentation of the CN derivative produced informative product ions.•Total method time was 18 min: derivatization (10 min) and analysis (8 min).