High resolution ¹⁹F{¹H} nuclear magnetic resonance spectroscopy and liquid chromatography-solid phase extraction-offline ¹H nuclear magnetic resonance spectroscopy for conclusive detection and identification of cyanide in water samples.

We report herein a new, sensitive and efficient method for detection, identification and quantification of cyanide in water samples. Cyanide was converted (>95% yield) to its versatile and stable derivative, 1-cyano-2,2,2-trifluoro-1-phenylethyl acetate (CTPA).The crude reaction mixture was directly subjected to high resolution fluorine-19 nuclear magnetic resonance ((19)F{(1)H} NMR) spectroscopy. In order to do away with signal overlap and dynamic range problems associated with (1)H NMR spectroscopy, liquid chromatography with UV detection hyphenated to online solid phase extraction (LC-UV-SPE) was performed. The trapped and enriched CTPA was thereafter subjected to offline (1)H NMR spectroscopy. In this way the δ(1)H, δ(19)F spectral signatures and LC-UV retention time were used for specific detection and identification and quantification of cyanide. The three techniques (viz. LC-UV and LC-UV-SPE followed by offline (1)H NMR and (19)F{(1)H} NMR spectroscopy) demonstrated good linearity (r(2)>0.99), reproducibility (inter-day RSD: 1.43-1.89%, 2.60-2.80%, 1.42-1.60; intra-day: RSD 1.20-1.38%, 3.21-3.25%, 1.00-1.19%), accuracy (recoveries: 95.1-97.2%, 77.5-82.8%, 96.8-98.9%) and LODs (1.31 μg/mL, 4.24 μg/mL, and 2.14 μg/mL) respectively. Total time required for the analysis was ∼3 h. Utility of the method was demonstrated by the detection and identification of spiked water samples. Since the derivative CTPA was volatile, could also be analyzed by GC-MS and GC-FTIR instruments.