Determination of the oxidation products of the reaction between α-pinene and hydroxyl radicals by high-performance liquid chromatography

In this paper a method is described for determining and quantifying the degradation products of the reaction of α-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semi-volatile products are collected on a liquid nitrogen trap (LN2 trap) coated with a 2,4-dinitrophenylhydrazine (2,4-DNPH) solution and the batch samples are subsequently analyzed by HPLC. In order to perform quantitative measurements the batch samples contained two internal standards: benzaldehyde–2,4-DNPH and tolualdehyde–2,4-DNPH. In the experiments carried out at 50 Torr and 100 Torr, HPLC measurements showed that the semi-volatile products formaldehyde, acetaldehyde, acetone, campholenealdehyde and pinonaldehyde could be quantified as oxidation products for the α-pinene/OH reaction, with pinonaldehyde being the main product. Assuming that all these five oxidation products have the same collection efficiency on the LN2 trap, one arrives at the following relative product yields (expressed in mol %) at 50 and 100 Torr, respectively: 9.7±0.7 and 6±5 for formaldehyde; 1.1±0.1 and 0.9±0.5 for acetaldehyde; 16±1 and 6±2 for acetone; 11±2 and 5.5±0.7 for campholenealdehyde; 63±3 and 82±7 for pinonaldehyde.