A modified ninhydrin micro-assay for determination of total cyanogens in plants

Indirect quantification of total cyanogenic compounds (cyanogens) in plants was studied using a novel ninhydrin-based spectrophotometric micromethod. The ninhydrin–cyanide system obeys Beer’s law in the range from 20 μg L−1 to 800 μg L−1 CN− with molar absorptivity ε = 1.4 × 105 L mol−1 cm−1. Recovery at 100 μg L−1 CN− was 100.5 ± 0.1% and LOD and LOQ were 8 and 22 μg L−1, respectively. The conditions for ninhydrin reagent preparation were discussed. The extraction and separation solutions, extraction and incubation time, and solvent volume were also investigated for maximum recovery of total cyanogens. 0.1% NaHCO3 was used as an extraction solvent for cyanide formed after enzymatic hydrolysis of cyanogens. The procedure was suitable for samples containing more than 90 mg CN−/100 g sample. When cyanogen concentrations were lower, the resulted cyanide was separated by microdiffusion in a Conway cell. Water was used as a hydrolysis medium and a donor solvent, while 2% Na2CO3 as an absorbing solution. Total cyanogen content in plum and almond kernels, as well as apple and flax seeds was determined.