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Nondestructive quantitation of oxygen in different types of packaged foods was performed using disposable phosphorescent oxygen sensor inserts placed in every individual sample and a fiber-optic phosphorescent phase detector. Oxygen levels and their changes over storage time are presented for vacuum-packed raw and cooked meat, smoked fish, and MAP sliced ham and bread. Damage to vacuum-packages was simulated by slitting the package film and monitoring the sensor response at different locations from the site of damage. The performance of the optical oxygen sensor in packaged foods was evaluated, and its usefulness for food research and industrial applications discussed.

b p-Nitrobenzaldehyde reacts with cyanide specifically to give an active reductant, which is capable of effecting the reduction of various compounds to form highly colored products. The intermediate cyanohydrin reacts with o-dinitrobenzene to give a highly colored purple compound, the dianion of o-nitrophenyl hydroxyiamine, or with triphenyl tetrazoiium chloride to produce a red dye, triphenyl formazan. Because cyanide is regenerated, a catalytic reaction occurs, with corresponding increase in sensitivity. Adding isonitroso benzoyl acetone, as little as 1.3 X gram of cyanide per mt. of total solution (3 nanograms total CN-) may be detected. Only p-nitro-and p-cyanobenzaldehyde of over 3 0 aldehydes tested react at an appreciable rate to form the reductive cyanohydrin. Only cyanide of more than 3 5 anions tested is detectable by this procedure. N A PREVIOUS paper (5), we de-

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