An automatic falling drop system based on multicommutation process for photometric chlorine determination in bleach

In this work an automatic photometric procedure for the determination of chlorine in bleach samples employing N,N′-diethyl-p-phenylenediamine (DPD) as chromogenic reagent is described. The procedure was based on a falling drop system where the analyte (Cl2) was collected by a DPD solution drop (50 μL) after its delivery from the sample bulk that was previously acidified. The flow system was designed based on the multicommutation process assembling a set of three-way solenoid valves, which under microcomputer control afforded facilities to handle sample and reagent solution in order to control analyte delivering and solution drop generation. The analyte volatilization was improved by coupling online a little heating device. The detection system comprised a green LED (515 nm) and a phototransistor. Aiming to prove the usefulness of the proposed procedure a set of bleach samples was analyzed. Comparing the results with those obtained with reference method no significant difference at 95% confidence level was observed. Other profitable features such as a linear response ranging from 15 up to 100 mg L−1 Cl2 (R = 0.999); a detection limit of 4.5 mg L−1 Cl2 estimated based on the 3σ criterion; a relative standard deviation of 2.5% (n = 10) using a typical bleach sample containing 25.0 mg L−1 Cl2; a consumption of 55 μg of DPD per determination; and a analytical frequency of 20 determinations per hour were also achieved.