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 8C 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 l1 can not be accurately
analysed using these methods. However, samples with a TOC lower than 60 mgC l1 gave 1009/3% recoveries. The
linear range of the methods was 0/3.0 and 0/5.0 mgCl2 l1, and the limit of quantification 0.2 and 0.5 mgCl2 l1, 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.
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