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10217 
Journal Article 
Stabilized neutral orthotolidine, SNORT, colorimetric method for chlorine 
Johnson, JD; Overby, R 
1969 
Yes 
Analytical Chemistry
ISSN: 0003-2700
EISSN: 1520-6882 
NIOSH/00154228 
41 
13 
1744-1750 
A colorimetric method for determining chlorine (7782505) was described. A total of 100 milliliters (ml) sample was added to the orthotolidine reagent, 5ml of orthotolidine-dihydrochloride dissolved in 1 liter of 3 millimolar (mM) hydrochloric-acid, stabilized with a bis(2-ethylhexyl)sulfosuccinate/phosphate buffer, pH 7.0. The transmission percent was read at 625 nanometers (nm) in a spectrophotometer or colorimeter. If tetravalent manganese or nitrogen-trichloride were known to be present, 1ml of 1 percent sodium-arsenite was added to the sample and to a blank. The blank was used to set 100 percent transmittance at 625nm. The precision of the method was determined using 10 aliquots taken from a single solution measured over a 2 hour period. The relative standard deviation was 0.39 percent. The precision of the method remained satisfactory up to an analyte concentration of 0.1mM. The sensitivity of the method was determined to be 0.0014 milligram per liter, as free chlorine. The authors note that the orthotolidine/buffer is stable in solution for at least 1 year. 
DCN-143553; Analytical methods; Qualitative analysis; Materials testing; Trace analysis; Electronic equipment; Chemical composition; Equipment design; Sensitivity testing; Laboratory equipment; Quantitative analysis; Spectrographic analysis