Outline+of+Blood+Detection+by+Chemical+Methods

__Blood Detection by Chemical Methods__

Three categories of chemical methods used to detect blood: - Crystal tests- use derivative crystals such as haematin, haemin, and haemochromogen. o Best-known version of this test is when an alkaline solution of pyridine is added to the stain and if the stain is blood, the pink crystals of a complex between pyridine and haem form as the slide is warmed. o A negative result doesn’t necessarily mean there isn’t blood, it could be a fault technique o 20 yr-old blood stains have been tested positive with this - Catalytic tests o Common substrates are benzidine, ortho-tolidine, leucomalachite green, leucocrystal violet and phenolphthalein (Kastle- Meyer test) o Kastle- Meyer test- if it turns to bright prink (using phenolphthalein) o “Sangur” test ticks are used to find blood in urine in clinical situations but are just as useful for dried bloodstains. Change from yellow to green-blue tells that it is blood o Not totally specific for blood because there can be a number of interferences o If test is negative, it isn’t blood, but if it is positive there is probably but not definitely blood. o Confirm that visible stains are blood (probably) - Instrumental methods o HPLC (high performance liquid chromatography) is used to identify blood using the absorbance of haemoglobin as the method of detection o Identify species of origin, distinguish child from adult, and give estimate for age of the bloodstain - Luminol for non-visible bloodstains and can be used for enhancement of blood stains