Determination of Total Petroleum Hydrocarbons in Fertilizer by Infrared Spectroscopy

A method for the determination of total petroleum hydrocarbons by infrared spectroscopy was established. The fertilizer sample of 5 g was extracted for 18 min with 15 mL of a mixture of dichloromethane and acetone at volume ratio of 1∶1 under 80% ultrasonic power (maximum power 800 W). The extraction was carried out twice, and the combined supernatant was concentrated to nearly dry at 35 ℃. The residue was dissolved with 20 mL of carbon tetracloride. The solution was transferred to solid phase extraction column and eluted with 5 mL of carbon tetracloride. The eluent was collected and determined by infrared spectroscopy. As shown by the results, linear relationship between mass concentration of total petroleum hydrocarbons and its peak area was kept in the range of 5.0-500.0 mg·L^-1, with detection limit (3s) of 5.0 mg·kg^-1. Recovery test was made on the 3 fertilizer samples by standard addition method, giving results of the amount of total petroleum hydrocarbons in the range of 123-1 515 mg·kg^-1, and recovery were in the range of 84.0%-93.2%, with RSDs (n=6) of the determined values ranged from 0.92% to 4.3%.