Materials Included In Kit

Additional Materials Required

Prelab Preparation

Blood Preparation

1. Obtain liver, or other source of raw red meat, from a local butcher.
2. Squeeze the meat to collect as much blood as possible. Alternatively, the meat may be placed in a blender and filtered to obtain the blood sample.
3. Place the blood in a beaker and label it “Evidence 2.”

4. Empty the ketchup packets into a Petri dish. Label it “Evidence 1.”
5. Empty the contents of the tomato paste into a Petri dish. Label it “Evidence 3.”
6. Fill a petri dish with simulated blood and label it “Evidence 4.”

Safety Precautions

Kastle-Meyer reagent is a flammable liquid and vapor. May be harmful if swallowed or in contact with skin. Causes severe skin burns and eye damage. Causes eye irritation. Suspected of causing cancer. Hydrogen peroxide, 3%, causes skin and eye irritation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Kastle-Meyer reagent may be disposed of according to Flinn Suggested Disposal Method #26b. Hydrogen peroxide may be disposed of according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period. The pre-laboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• The easiest way to obtain blood for this activity is from a butcher. It was tested using blood from calf liver. The blood can be collected from the container it sits in or it can be blended and filtered out.

Teacher Tips

• This is an excellent activity to perform as an introduction to forensics studies.
• Flinn Scientific offers several other laboratory kits that further study properties of blood.
  • AP6502 Bloodstains at the Crime Scene—Forensic Laboratory Kit
  • FB1643 Bloodstain Pattern Analysis—Forensic Laboratory Kit
  • AP6292 Forensic Glow—Forensic Laboratory Kit

Answers to Prelab Questions

1. Why is blood a useful piece of forensic evidence?

   It can confirm the presence of someone at a crime scene, support witness testimony, etc.

2. Is the Kastle-Meyer test able to differentiate between human and canine blood? Explain.

   No. Human and canine bood both contain hemoglobin which will produce a positive result in the Kastle-Meyer test.

Sample Data

Answers to Questions

1. Based on the observations of each evidence sample after application of the Kastle-Meyer test, which sample(s) likely contain blood? Record in the data table.

   See Sample Data.

2. If an evidence sample tested with Kastle-Meyer reagent indicated the presence of blood, does that mean it definitely is blood? If not, what else could it be?

   No, it may be blood but it could also be detecting certain enzymes or other metals.

3. What would be the next step in analyzing the blood sample if presumptive blood testing indicated the presence of blood?

   The next step would be to determine the species the blood came from. This is done by tests that reveal species-specific antigens. The next step would be to perform DNA testing to determine the individual the blood came from.

4. Metals, such as copper and nickel salts, produce false positives in the Kastle-Meyer test. Explain why this produces the same result as hemoglobin in blood?

   Hemoglobin contains iron which is another metal so it reacts the same way with phenolphthalein and hydrogen peroxide as copper and nickel.

5. The Kastle-Meyer test can detect blood in extremely low concentrations, such as one drop of blood in 10,000 drops (400 mL) water. Explain why this is useful.

   Oftentimes criminals will try and clean up a crime scene to eliminate evidence. Even if the wall or floor were washed, the Kastle-Meyer test would likely detect the blood presence.

References

Blood Detection by Chemical Methods.

Rohrig, B. (2008, February). The Forensics of Blood. ChemMatters, pp. 4–7.

Tobe, S. S., Watson, N., Daeid, N. (2006). Evaluation of Six Presumptive Tests for Blood, Their Specificity, Sensitivity, and Effect on High Molecular-Weight DNA. American Academy of Forensic Science. Pp. 102–109.

Introduction

After crimes, such as homicides or assaults, blood evidence is usually present at the scene. Blood is useful evidence to solve crimes because it contains DNA. The first step for investigators is to determine whether or not the substance is indeed blood before investing in more expensive tests.

Concepts

• Presumptive blood testing
• Forensics

Background

Blood is one of the most common forms of forensic evidence used by the criminal justice system. Blood evidence is useful to investigators as it can confirm presence of an individual at a crime scene, support witnesses’ testimony or simply aid in solving a case.

First, investigators must determine if a substance present at a crime scene is indeed blood or something similar in appearance. This is done by performing presumptive blood testing. Presumptive blood tests function by detecting a component found in blood that is not commonly found in the everyday environment. The majority of presumptive blood tests rely on the presence of hemoglobin which exhibits peroxidase-like activity. Hemoglobin is a component of blood that is not commonly found in everyday environments.
One type of presumptive blood test is the Kastle-Meyer test. In many forensics television shows a detective is seen collecting a blood sample using a cotton swab, a colorless solution is added and it produces a bright pink color. This is a demonstration of the Kastle-Meyer test. The colorless solution added to the cotton swab contains a reduced form of phenolphthalein and hydrogen peroxide which react with each other to produce a pink solution of water and a phenolphthalein ion. In this reaction phenolphthalein has been modified from its conventional form by being reduced in an alkaline solution. In the presence of hydrogen peroxide in an alkaline solution the hemoglobin in the blood catalyzes the oxidation of this form of phenolphthalein resulting in a pink color.

Experiment Overview

Four unknown samples have been taken from a crime scene. Perform the Kastle-Meyer test on each sample to confirm if they are likely blood.

Materials

Prelab Questions

1. Why is blood a useful piece of forensic evidence?
2. Is the Kastle-Meyer test able to differentiate between human and canine blood? Explain.

Safety Precautions

Kastle-Meyer reagent is flammable, causes severe skin burns and eye damage, may be harmful if swallowed or in contact with skin and is suspected of causing cancer. Hydrogen peroxide causes skin and eye irritation. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Using a cotton swab, obtain a small sample of evidence 1.
2. Using a pipet, add one drop of Kastle-Meyer reagent to the unknown evidence on the cotton swab.
3. Using a clean pipet, add one drop of hydrogen peroxide to the cotton swab.
4. Observe the color change, if any, and record on the Kastle-Meyer Presumptive Blood Testing worksheet.
5. Repeat steps 1–4 for evidence samples 2–4.
6. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12534_Student1.pdf