Abstract
A criminal investigation laboratory is sometimes asked to identify chlorine bleach on damaged clothes of pedestrians in a criminal case. However, it is difficult to prove the detection of sodium hypochlorite, the main component of chlorine bleach, because it decomposes in a short time. In this study, decomposition of sodium hypochlorite was investigated to decide whether the ratio of chloride and chlorate ions produced through the decomposition of hypochlorite ion could be an effective indicator for the use of chlorine bleach. A sample was prepared by making a piece of filter paper or fabric absorbed with 25 µL of sodium hypochlorite solution or chlorine bleach and by drying it from one minute to 25 days. Chloride and chlorate ions in the sample were extracted into 100 mL of H2O and determined by using ion chromatography. These two ions are stable and no significant change was observed in the ratio of them after the solution was dried. Therefore decomposed products can be detected from fabrics which had dried over a period of time and it is possible to show that chlorine bleach was used. The ratio of these ions exhibited separated ranges among bleach products by different manufacturers. In addition, the ratio of these ions was affected not only by the time after the bottle of bleach was opened but also the types of fabric material, even if bleach of same manufacturer was used. Comparing the ratio of two ions allows the discrimination of bleach products on the clothes, if two fabrics are made from the same material.
