Improved ninhydrin-based reagent for spectrophotometric determination of ppb levels of cyanide. Issue 1 (2nd January 2016) - Surleva, Andriana
ABSTRACT: Cyanide is an extremely severe poison that has been raising concerns and controversies regarding its toxic effects on humans and the environment. A short-term human exposure to elevated levels can induce coma or death. Toxic effects occur at blood cyanide concentrations of 0.05 mg/dL, while death can occur at levels of 0.3 mg/dL. Numerous law and systems regulate cyanide levels in various environments. To exemplify, the maximum contamination limit imposed by United States Environmental Protection Agency in drinking water is 200 µg/L, while the European Union presents a lower limit of 50 µg/L. Ninhydrin has proved to be an effective color reagent for the spectrophotometric determination of trace levels of cyanide. This article reports a ninhydrin-based color reagent that was employed in cyanide determination involving real samples of water, cigarette smoke, urine, and cyanogenic plants, achieving an appropriate sample pretreatment procedure for cyanide liberation and separation. The reaction between cyanide and ninhydrin is fast enough to be performed at ambient conditions, but the ninhydrin reagent must be freshly prepared in oxygen-free solvent. Beer's law is obeyed in the range between 20 and 400 ppb CN − (r = 0.992; N = 7) with molar absorptivity of 1.4 × 10 5 L mol −1 cm −1 and limit of detection of 8 ppb cyanide. Recovery at 100 ppb CN − was (100.5 ± 0.1) %, whereas precision was 1.7%. Also, absorbance at 485 nm proved to be temperature-dependent, with a maximum at ambient conditions. Throughout all measurements, the ninhydrin-based assay proved to be reliable, economical and environmentally friendly. Significance of the assay for the determination of cyanide in the field of environmental forensics, as well as its potential aid in elucidating incidents with legal consequences are highlighted.