Kastle-Meyer test
The Kastle Meyer test (short: KM test ) is a forensic pre-test for the indication of suspected blood traces . The detection reagent is phenolphthaline , which is reduced phenolphthalein .
History
The foundation stone for the Kastle-Meyer test was laid by Louis Jacques Thénard and Christian Friedrich Schönbein . Thenard discovered in 1818 that hydrogen peroxide is broken down by blood . From this discovery in 1863 Schönbein developed the first test for blood. The decomposition of hydrogen peroxide by the heme- containing protein hemoglobin in the blood (in the erythrocytes ) is observed. The result of this reaction is foaming, with oxygen bubbles rising. Schönbein concluded from this that an unknown stain that is foamed up by H 2 O 2 probably contains hemoglobin and is therefore blood.
In early 1900 ( 1901 ) the chemist Joseph Hoeing Kastle (1864–1916) developed a pre-test for hemoglobin that contained phenolphthalein as a color indicator . A few years later ( 1903 ) the internist and chemist Erich Meyer (1874-1927 ) refined and improved the reagent, which is why it is also known as the Kastle-Meyer test.
Strengths and Detection Limits
When talking about pre-test reagents, one should become familiar with two terms: sensitivity and specificity .
sensitivity
The sensitivity relates to the dilution factor of a substance that the test can still detect. The sensitivity of the contrast medium test is around 1: 10,000: a drop of blood can still be detected after dilution with 10,000 drops of water.
Specificity
Specificity relates to the ability of the test to react to substances other than blood. So far, a true positive reaction could only be demonstrated in the presence of hemoglobin. False-positive reactions can occur in the presence of chemical oxidants; vegetable peroxidases can also react with the test. But these reactions could only occur after phenolphthalein has been applied, before the addition of hydrogen peroxide. A true-positive statement can only be made after hydrogen peroxide is added. The KM test therefore reacts specifically to blood.
Alternatives
A newer method, in which luminol is sprayed onto a suspected area, is more reliable : if the trail begins to glow, the suspicion of blood is confirmed.
Kastle-Meyer reagent
The stock solution consists of
- 20 g of potassium hydroxide
- 2 g phenolphthalein and
- 30 g zinc powder,
which are suspended in 100 ml of water and refluxed for 2 h (or left to stand for 48 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 .
To prove this, two drops of Kastle Meyer reagent and two drops of a 3% hydrogen peroxide solution are added to the trace. A red color within seconds indicates a positive reaction.
swell
- ^ Joseph Hoeing Kastle, Oliver March Shedd : Phenolphthalin as a Reagent for the Oxidizing Ferments . In: American Chemical Journal . tape 26 , no. 6 , 1901, pp. 526-539 ( Internet Archive ).
- ↑ Erich Meyer: Contributions to the leukocyte question . Ferments of the leukocytes. In: Münchner Medizinische Wochenschrift . tape 50 , no. 35 , 1903, pp. 1489-1493 .
- ↑ a b Joanne L. Webb, Jonathan I. Creamer, Terence I. Quickenden: A comparison of the presumptive luminol test for blood with four non-chemiluminescent forensic techniques . In: Luminescence . tape 21 , no. 4 , 2006, p. 214-220 , doi : 10.1002 / bio.908 , PMID 16645959 .