"EPA 800-R-71-009." Includes bibliographical references.

In this study each participant was shipped four sealed glass ampoules of concentrated solution which when diluted according to instructions, provided two samples containing free chlorine and one containing combined chlorine. Each analyst was requested to use two preselected methods from the seven being studied but unfortunately not all complied and although 71 participants submitted results, only seven were submitted for the leuco crystal violet method; whereas sixteen to thirty results were obtained for each of the other methods. Statistical analysis of these results indicated that the best accuracy and precision was obtained by leuco crystal violet and the stabilized neutral orthotolodine (SNORT) procedures, followed by DPD-titrimetric, amperometric titration, DPD-colorimetric and methyl orange. By far the poorest was the orthotolidine-arsenite (OTA) procedure.