A new iodometric microwave-assisted method for peroxide determination in Secondary Organic Aerosols

Peroxides (H2O2, ROOR, ROOH) play an important atmospheric role in both the gas and particle phases. Several techniques are available in the literature for their quantification, although current techniques are very expensive or time-consuming. In the present work, a new fast and sensitive iodometric-spectrophotometric method, based on the traditional one, has been developed for the trace SOA (Secondary Organic Aerosols)-bound peroxides of laboratory-generated samples. The proposed method is based on the acceleration by microwave radiation of the reaction of peroxides with potassium iodide in acid medium. Iodine is liberated and in the presence of excess of iodide forms I 3 that could be monitored at three different wavelengths (288, 351 and 420 nm). The linear range of concentrations of the method is at least 1-35 & mu;M. The limit of detection of the method was 1 & mu;M without degasification and decreased to 0.25 & mu;M with degasification, respectively. The optimum conditions and other analytical parameters were evaluated for H2O2, tert-butyl hydroperoxide and cumene hydroperoxide. The main advantages of the new method in comparison with the traditional method are: it is less time consuming, it is applicable even in the presence of oxygen, it has a lower limit of detection (for 1 cm pathlength cell) and there are no sensitivity differences between different peroxides types.The proposed method has been successfully applied and compared with the traditional method for the determination of peroxides in SOA generated in laboratory by the gas phase ozonolysis of & alpha;-pinene.