Rapid determination of volatile bases in fish by using an ammonia ion-selective electrode

A simple and rapid method using an ammonia ion-selective electrode (ISE) to measure volatile bases in fish is proposed. Accuracy and precision were determined with 5, 10, 20, and 30 ppm NH3 standard solutions. Ammonia values obtained with the method correlate strongly with total volatile basic nitrogen (r2 = 0.88). Recoveries of added ammonia to homogenized fish samples ranged from 83.7 to 96.0%. Responses of the probe to trimethylamine (TMA), calculated as NH3 (mg/100 mL), ranged from 74.9 to 91.7%. These findings indicate that the probe measured TMA as well as ammonia. Storage trials on 8 fish species illustrated that the results obtained with the ISE method reflected nitrogen concentrations based on total volatile base (TVB) analysis. This procedure may be used in lieu of the traditional TVB method for on-site rapid screening of fish.