Rapid determination of diphenylamine residues in apples and pears with a single multicommuted fluorometric optosensor.

In this work, a single flow injection multicommuted system using solid-surface fluorescence spectroscopy has been explored for the determination of diphenylamine in apples and pears. The native fluorescence signal of diphenylamine retained on the solid support (C18 silica gel) was used for its determination (lambda(exc)/lambda(em) 291/372 nm). The sample treatment consists of a liquid-liquid extraction with acetonitrile followed by a cleanup step using primary-secondary amines. The use of a continuous flow assembly implementing multicommutation, based on a set of three-way solenoid valves controlled by appropriate software, provides the automatic control of sample, carrier, and eluting solution with remarkable advantages in relation to conventional flow injection approaches. Using an optimized sampling time, the proposed method was linear in the range 0.25-5 mg kg(-1) with a detection limit of 0.06 mg kg(-1) and RSD (percent) values better than 3%. The proposed method was successfully applied to the analysis of diphenylamine in different apple and pear samples fortified at different concentrations, and recoveries between 78 and 104% were found. The results obtained illustrate the usefulness of the proposed method for the screening and evaluation of postharvest treatment of crops possibly containing diphenylamine.