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.
What is a presumptive test for blood?
A presumptive test is a qualitative analysis that allows to identify, or confirm, the presence of a substance in a sample. These determinations usually occur, after a chemical reaction, and a specific colour is produced. A false positive is another substance reacting the same way, producing the expected result.
What is the most common presumptive blood test done in the lab?
The Kastle–Meyer test is a presumptive blood test, first described in 1903, in which the chemical indicator phenolphthalein is used to detect the possible presence of hemoglobin.
What are the three confirmatory test for blood?
Confirmatory tests for blood include identification of blood cells under a microscope [Shaler, 2002], crystal tests such as the Teichman and Takayama tests [Shaler, 2002; Spalding, 2003], and ultraviolet absorption tests [Gaensslen, 1983].
How is a presumptive test performed?
Presumptive testing – is usually colorimetric, meaning the test will indicate that the suspected substance is present or not present by changing color. If the substance is present, the test kit will turn one color, if not, it turns a different color.
What is a presumptive test give an example?
Presumptive tests are not definitive and further confirmatory tests are always required. They are used extensively in forensic science. Examples are the Duquenois-Levine test for marijuana and Scott’s test for cocaine. In general analytical chemistry, presumptive tests are often called spot tests.
How is blood detected at a crime scene?
To detect blood at a crime scene or in the laboratory, an array of tests can be used. The most publicized test by crime shows is the Luminol process in which a chemical is sprayed onto a surface where blood is suspected to be.
What is the difference between a presumptive and confirmatory test?
Presumptive tests, such as those where a color change occurs, are those that usually identify a class of compounds whereas a confirmatory test, such as mass spectrometry, is one that conclusively identifies a specific, individual com- pound.
What is a downfall of utilizing presumptive tests?
However, the disadvantage of many presumptive tests is that they show poor specificity to the human biological/chemical target [1,2] while touch DNA items often fail to produce a corresponding STR profile [3,4] due to low amounts of template material available on these items and/or PCR inhibition.
Which test is used to determine if a blood sample is human?
How it works: The Ouchterlony test is used to determine if a blood sample is human or animal through the comparison of its reactions to specific antibodies. A sample of the unknown bloodstain is placed in a well in an agar gel. Antibodies from human and animal sources of blood are placed in other wells in the gel.
What are the four types of presumptive tests?
Luminol, leuchomalachite green, phenolphthalein, Hemastix, Hemident, and Bluestar are all used as presumptive tests for blood.
Which is a presumptive test for a drug?
Presumptive tests, also known as preliminary tests or field tests, allow drugs to be quickly classified into a particular chemical group, but do not unequivocally identify the presence of a specific chemical compound.
What does presumptive positive mean on a urine test?
A presumptive positive result for any of the tested drugs indicates the possible presence of the drug or metabolites in the urine, but does not measure the level of intoxication. If confirmation is needed for amphetamines, benzodiazepines, cocaine, opiates, or oxycodone/oxymorphone, call the Laboratory at 356-3527.