Determination of residual chlorine in greywater using o-tolidine

The determination of chlorine with o-tolidine in greywater has been studied, and a batch method and a sequential injection method have been proposed. It was found that the reaction of o-tolidine with chlorine was slower in a greywater matrix. Grey water samples must be filtered before analysis, or alternatively, a blank of sample must be measured. The samples are very unstable, and after 2 h of storage in dark conditions at 4 °C the chlorine concentration can diminish. The standard addition method, in some samples gave unsatisfactory results as a consequence of matrix effects. It was concluded that samples with a total organic carbon (TOC) higher than 60 mgC l−1 can not be accurately analysed using these methods. However, samples with a TOC lower than 60 mgC l−1 gave 100±3% recoveries. The linear range of the methods was 0–3.0 and 0–5.0 mgCl2 l−1, and the limit of quantification 0.2 and 0.5 mgCl2 l−1, for the batch method and the sequential injection method, respectively. This is the first paper devoted to grey water from the analytical chemistry point of view.