Oil in river water is generally measured by weight method as n-hexane extracts. But it needs much river water for determination in the case of low concentration and the determination procedure is complicated.On the other hand, nondispersive infrared method has high sensitivity and the determination procedure is simple. Therefore, the availability of the infrared method to the screening of oil content in river water was investigated.
The mean recovery of oils was 79% by the infrared method, and more than 90% by the weight method.As to the coefficient of variation of the recovery for camellia oil, it was 3.2% by the infrared method, but 26% by the weight method
Oil content of the actual samples at 37 points in river was determined by both method and the relation between the measured values by nondispersive infrared method (Y) and the weight method (X) was described as Y= 1.1X + 0.07, r=0.93; and the limits of 95% confidence of 0.5ppm by the nondispersive infrared method were shown to be in 0.3-0.5ppm by the weight method. Oil content of all samples (at 16 points), which showed more than 0.5ppm by the weight method, exceeded 0.5ppm by the nondispersive infrared method.
From these results, the nondispersive infrared method was found to be very useful as the screening of oil content in river water.
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