Measurement of methylene chloride.

I read with great interest the paper ‘Characteristics of peaks of inhalation exposure to organic solvents’ (Preller et al., 2004). I noticed that the authors used the MiniRAE Plus Professional Photoionization Detector (PID) (RAE Systems USA) to measure the total organic solvents exposure. My company, Shawcity Ltd, has represented RAE Systems in the UK for 10 years, and we are therefore very familiar with the MiniRAE Plus. Because this is a broadband measuring instrument, RAE publishes correction factors for compounds other than the calibration gas, isobutylene. The paper refers to these correction factors. I note from the paper that the MiniRAE Plus used was fitted with a 10.6 eV lamp. I also note that it was assumed that the correction factor for methylene chloride was 1 and the instrument was set accordingly. However, the MiniRAE Plus with a 10.6 eV lamp will not measure methylene chloride. Methylene chloride can be ionized at a voltage of 11.32 eV. Therefore, in order to measure it we would recommend an 11.7 eV lamp.