A fluorescence flow injection method for the quantitation of cyanide: its application to the quantitation of bound cyanide in cassava using an immobilized linamarase bioreactor

A fluorimetric flow injection method is described for the quantitation of cyanide ions in aqueous media. The method is based on the isoindole fluorogenic adduct formed when o-phthalaldehyde reacts with taurine in the presence of CN− ions. Under optimized flow injection conditions (loop size, 130 μl; flow rate, 0.75 ml min−1; delay coil length, 0.4 m) linear calibration curves in the range 10−5 to 10−7 M CN− are obtained with detection limits of 1.8×10−7 M. Using naphthalene dialdehyde instead of o-phthalaldehyde the detection limit is lowered to 5.8×10−8 M. Recovery yields vary between 97–102%. Incorporation of a linamarase bioreactor into the flow injection manifold gives a rapid and sensitive method for the quantitation of the cyanogenic glucoside, linamarin, in cassava. Linamarin concentrations as low as 3.2×10−6 M can be detected. The immobilized linamarase shows excellent storage stability at 4°C retaining about 72% of its activity after 109 days.