Kastle–Meyer test

The Kastle -Meyer test (short: KM - Test) is a forensic pretest for the indication of suspected traces of blood. The detection reagent is phenolphthalin, where it is reduced phenolphthalein.

History

The foundation stone for the Kastle -Meyer test was established by Louis Jacques Thénard and Christian Friedrich Schönbein. Thenard discovered in 1818 that hydrogen peroxide is decomposed by blood. Schönbein developed from this discovery in 1863 the first test for blood. The decomposition of hydrogen peroxide is monitored by the blood contained in the ( in RBCs ) heme-containing protein hemoglobin. The result of this reaction is a foaming, with oxygen bubbles rise. Schönbein concluded that an unknown spot, which is foamed by H2O2, probably contains hemoglobin and thus is blood.

Beginning of 1900 (1901) developed the chemist Joseph Hoeing Kastle (1864-1916) a pre-test for hemoglobin containing phenolphthalein as a color indicator. Some years later (1903 ) refined and improved the internist and chemist Erich Meyer ( 1874-1927 ), the reagent, which is why it is also called Kastle -Meyer test.

Strengths and detection limits

When talking about the pre-test reagents, one should be familiar with two terms: the sensitivity and specificity.

Sensitivity

Sensitivity refers to the dilution factor of a substance that can not demonstrate to the test. The sensitivity of the KM - test is approximately 1:10,000: A drop of blood can still be detected so after dilution with 10,000 drops of water.

Specificity

Specificity refers to the ability of the test reaction to substances, which are different from blood. So far, as far as one could detect a true positive reaction only in the presence of hemoglobin. False-positive reactions may occur in presence of chemical oxidants, also vegetable peroxidases can react with the test. However, these reactions may only occur after phenolphthalein was applied before the addition of hydrogen peroxide. A true - positive statement can only occur after hydrogen peroxide is added. Thus, the KM - test reacts specifically to blood.

Alternatives

Reliable is a newer method, is sprayed on a suspect area in which luminol: When the track begins to shine, the blood suspicion is confirmed.

Kastle -Meyer reagent

The stock solution is made

• 20 g of potassium hydroxide
• 2 g of phenolphthalein and
• 30 g of zinc powder,

( leave or 48 h) are suspended in 100 ml of water and boiled under reflux for 2 h until the solution is colorless. Store in a brown bottle with zinc powder. The working solution consists of 10 ml of this stock solution in 40 ml of ethanol.

For the detection of the track is mixed with two drops of Kastle -Meyer reagent and two drops of a 3 % hydrogen peroxide solution. A red coloring matter of seconds indicates a positive reaction.

Swell

• Biochemical detection reaction
• Forensic Medicine