Question

In the investigation of a crime scene, investigators use phenolphthalein to detect blood. Explain using complete sentences why this indicator would NOT be useful if the crime scene has been cleaned with household ammonia

Answer 1

Answer:

Phenolphthalein is a presumptive test that reacts with the heme molecule present in blood. A positive reaction gives a pink color. While bloodstains normally appear red-brown in color, the color of the substrate or the age of a stain may affect the appearance or visibility of the stain. Phenolphthalein tests are typically conducted on suspected bloodstains prior to collection. While a positive phenolphthalein reaction is indicative of blood, it is only a presumptive test and false positives are possible. Additionally, the reaction is not species specific. Positive reactions are not limited to human blood.