Monday, December 10, 2007

How Do CSI's Know If They Are Dealing With Blood?

Whenever a bloodlike stain is establish at the scene of a crime, the forensic man of science must carry on two basic sorts of tests: presumptive and confirmatory. The ground presumptive diagnostic diagnostic diagnostic diagnostic tests are conducted first is because they are more than than cost-efficient than the more cumbrous confirmatory tests.

What is a presumptive test?

Presumptive tests for blood can be establish in two wide categories: those that alteration color, and those that cause a aglow reaction.

Presumptive tests that depend on a colour alteration affect the following:

  • Leucomalachite greenness (LMG) colour test: This chemical reagent have been around since the early portion of the 20th century and undergoes a chemical interaction with blood, yielding a feature greenness color.

  • Tetramethylbenzidine (TMB) colour test: At a law-breaking scene, a CSI technician swabs a suspected bloodstain with a moistened Q-tip and then uses it to a Hemastix strip containing TMB. A Hemastix strip is a dip stick used to prove for the presence of blood. If the Hemastix strip turns blue-green, it might be blood.

  • Kastle-Meyer colour test: Phenolphthalein is the active chemical reagent in this peculiar test. When blood, H peroxide, and phenolphthalein are mixed together, a dark pinkish colour results. This colour alteration is owed to the haemoglobin (the oxygen-containing molecule within reddish blood cells) causing a chemical reaction between H hydrogen peroxide and phenolphthalein.

Other diagnostic tests depend on chemical reactions that cause blood to fluoresce, or glow, under an ultraviolet radiation visible light source, uncovering blood that is unseeable to the bare eye. Offenders many modern times seek to chaparral walls and floorings clean, mistakenly taking for given that if blood is not visible, it can not be found. Fortunately, that is not the case. At the scene of a crime, blood can demo up by spraying a fluorescent chemical over the country suspected of containing blood. The visible lights are dimmed, and ultraviolet radiation visible light is passed over the area, causing bloodstains to fluoresce in the dark just like you see on CSI. Not only is the presence of blood established, but the country of blood statistical distribution is also clearly indicated. This is where blood spurts, retarding force marks, spatter, footprints, and handprints demo up.

The histrions you see on CSI usage fluorescent chemicals to acquire the blood to uncover itself. The most common fluorescent chemicals used are luminol and fluorescein.

  • Luminol--Luminol is highly sensitive and may uncover blood that is present in minute quantities. Luminol is able to expose blood in topographic points that have got got been cleaned repeatedly unless a solvent such as as bleach was used, and even on walls that have been painted to conceal blood. In malice of the fact that it can negatively impact some serologic testing processes, luminol makes not impact subsequent blood typing or deoxyribonucleic acid analysis.

  • Fluorescein--Fluorescein have been around since the early portion of the 20th century. This chemical compound makes not interact with bleach the manner luminol does. Fluorescein is better used over luminol for exposing bloodstains that have got been cleaned up using dissolvents such as as bleach. Fluorescein is advantageous in that it is thicker than luminol and trickles less, therefore, lodges to perpendicular come ups much better than luminol.

What is a confirmatory test?

Teichmann and Takayama diagnostic diagnostic tests are the most commonly used confirmatory tests. Both diagnostic tests depend on a chemical reaction between a reagent and hemoglobin. This reaction outputs crystals, which then can be seen under a microscope. A considerable benefit of these diagnostic tests is that they are more than effectual with aged stains.

The adjacent clip you watch your favourite forensic science/detective show like NCIS or CSI, you will have got a clearer apprehension of the chemicals used in exposing blood at a law-breaking scene.

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