False Positives In Presumptive Blood Testing Biology Essay

Blood is a unstable medium that is found within the cardiovascular system-which comprises of the bosom and blood vass ( Jackson and Jackson 2008 ) . It consists of 55 % blood plasma and 45 % cellular stuff ( Jackson and Jackson 2008 ) . Blood plasma consists of dissolved stuffs such as antibodies, endocrines, waste merchandises and foods, whereas the cellular stuff consists of red blood cells ( ruddy blood cells ) , leucocytes ( white blood cells ) and platelets ( thrombocytes ) ( Jackson and Jackson 2008 ) .Blood is transported through the organic structure by the pumping action of the bosom. It has legion maps including ( Jackson and Jackson 2008 ) :Acting as an internal conveyance system-including the remotion of waste merchandises for elimination and traveling foods for metamorphosis.Keeping organic structure temperature.

Defending against infection.Protecting the organic structure from effects of hurt.Blood is one of chief beginnings of Deoxyribonucleic acid found at offense scenes, and is crucially of import in set uping a nexus between a suspect and a victim of a offense ( Jackson and Jackson, 2008 ) . To observe the presence of blood at a offense scene, a presumptive trial is used. These can, nevertheless, merely detect whether a substance is blood and can non separate between human and carnal blood-a serological trial is needed to make this.The Erythrocytes ( ruddy blood cells ) are the most common type of blood cell and contain hemoglobin ( Jackson and Jackson 2008 ) .

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!

order now

They contain haemoglobin- a protein incorporating Fe. Haemoglobin is responsible for the passenger car of O, and it is this belongings that presumptive blood trials are based on. Most of the presumptive trials rely on the ability of hemoglobin to catalyze the oxidization of a reagent, usually hydrogen peroxide ( H2O2 ( aq ) ) ( Jackson and Jackson 2008 ) . The consequence of oxidization usually produces a coloring material alteration in the presumptive trial.Bantam sums of blood nowadays as a scene can be observing utilizing a coloring material alteration trial. Some old and dried discolorations look similar in visual aspect to blood – which can take to a scenes of offense officer carry oning a presumptive trial.

Other substances that could hold contaminated suspected blood or other substances on their ain at a scene could take to a presumptive blood trial falsely demoing a positive consequence for blood. This is known as a false positive.Once a discoloration has been determined as blood, so two procedures must be completed.

The first is to construe any bloodstain forms, so that a Reconstruction of events can be established ( Langford et al 2005 ) . Second, bloodstains must so be recovered for farther analysis ( Langford et al 2005 ) . Recovery of bloodstains varies harmonizing to whether the discoloration is wet or dry. Once recovered, the blood can so be sent to a Forensic Science Service research lab, where it will be ab initio tested to determine whether it is human or carnal blood. To make this a serological trial will be conducted, which involves placing the presence of proteins specific to worlds and analyzing for DNA sequences specific to worlds ( Jackson and Jackson 2008 ) .

The blood will so be used for DNA profiling, which will hopefully set up whether the blood belongs to the suspect or the victim.I.II Aims and AimsThe purpose of my undertaking is to make a unequivocal list of false positives for four different presumptive blood trials. Within this purpose I have six aims to finish:To compare the false positives of four different presumptive trials.To prove substances that are known false positives- as reported by other writers.To prove unknown substances allied to those already known.

To enter the clip taken for a substance to respond with a presumptive trial.To snap the consequences of from each substance.To make a unequivocal list of false positives for each presumptive trial.I am traveling to compare four different presumptive trials, as some trials are more practical to utilize in some state of affairss than others.

Consequently, analyzing more than one trial will let a wider scope of consequences.I shall besides be proving known false positives as reported by other writers, as it is of import to demo how the presumptive trials react. Unknown substances allied to those that are known will so be tested to see whether similar substances react likewise. This will so let me to set up whether an unknown substance has reacted or non, as I can compare the reaction times and coloring materials alterations from both the known and unknown substances.It is of import to enter the clip taken for a substance to respond with a presumptive trial, as blood should demo a consequence directly off. An unobvious consequence that takes clip to develop could bespeak that the substance being tested is a false positive. Photographing consequences will let me to document the differences in the coloring material alteration in each reaction with each substance.

I feel that it is of import to make a unequivocal list of false positives as it can cut down the hazard of utilizing valuable resources at a offense scene. For illustration, if a scenes of offense officer is informed that a possible blood discoloration has been contaminated with horseradish ( a known false positive ) , so they can utilize a presumptive trial for blood that is non known to bring forth a false positive with horseradish. If the consequence is positive for blood, so serological trials for blood can be carried out.Overall, I hope that this undertaking will help the work of a scenes of offense officer to take the right presumptive trial to utilize in different situations-minimising clip spent and resources used.Chapter II. Literature ReviewII.I Background InformationThe scientific analysis of blood was ab initio mentioned in thirteenth century Chinese texts, but it was Karl Landsteiner who discovered the modern scientific discipline of blood typewriting, which categorises different types of blood into the “ ABO blood typing system ” ( White 2010 ) . In 1901 it was reported that blood could be determined in two hebdomad old serum stains on linen, and by 1902 the four blood types – Angstrom, B, O and AB had been discovered ( White 2010 ) .

This system is based on types of antigen on the ruddy blood cell ‘s membrane. An antigen is a “ protein molecule capable of adhering on to an antibody ( Erzinclioglu 2004 ) . The ABO system uses two antigens which are known as A and B ; and the four blood groups are determined harmonizing to this system ( Erzinclioglu 2004 ) . Peoples that have the blood group A have the A antigen, those that are group B have the B antigen ; those in the AB class have both antigens and those who belong to the O group have neither antigen ( Erzinclioglu 2004 ) . A individual ‘s blood contains the opposite group of matching antibodies, so people with blood group A have b antibodies, people with blood group B have a antibodies, those with blood group AB have neither a or B antibodies and those with blood group O have both a and B antibodies ( Erzinclioglu 2004 ) . If the incorrect antibodies are introduced into the incorrect blood group so decease can be a consequence due to the ruddy cells cloping together.

The first suspect to hold been convicted mostly on the footing of DNA analysis of blood samples was found guilty at Leicester Crown Court on 22nd January 1988 ( White 2010 ) . This instance marks an of import milepost, and DNA engineering has become platitude in forensic research labs and is now instrumental in set uping both guilt and artlessness in tribunal instances ( White 2010 ) .II.II Physical Properties of BloodBlood constitutes about 7.7 % of the organic structure weight of a individual ( White 2010 ) . This equates to 5-6 liters in males and 4-5 liters in females ( Tortora and Anagnostakos 1987 ) . Viscosity is opposition to flux, which in fluids is compared to H2O which has a viscousness of 1.

( Bevel and Gardner 2002 ) . Blood viscousness normally ranges between 4.4 and 4.7 ( Tortora and Anagnostakos 1987 ) .

Blood besides has a higher specific gravitation ( denseness ) than H2O, which is the weight of a substance relation to the weight of an equal volume of H2O ( James and Nordby 2005 ) .Blood is a fluid that circulates throughout the organic structure by manner of the bosom, arterias, venas and capillaries-known as the circulatory system ( James and Nordby 2005 ) . A primary map of blood is to transport O, electrolytes, nutriment, endocrines, vitamins and antibodies to tissues and to transport waste merchandises from tissues to the excretory variety meats ( James and Nordby 2005 ) .Tortora and Anagnostakos ( 1987 ) ( in Bevel and Gardner 2002 ) say that when 4-6 liters of blood is present in the circulatory system, it is distributed as follows:Figure 1- Blood Distribution in the Circulatory System ( Tortora and Anagnostakos 1987 )As a medium, blood is composed of 55 % plasma and 45 % cells ( White 2010 ) .

A individual bead or big volume of blood is held together by strong cohesive molecular forces that produce a surface tenseness ( James and Nordby 2005 ) . Surface tenseness is defined as “ the force that pulls the surface molecules of a liquid toward its inside, diminishing the surface country and doing the liquid to defy incursion ” ( James and Nordby 2005 ) .Bevel and Gardner ( 2002 ) province that plasma is the pale xanthous fluid constituent of blood, which is broken down by volume into 91 % H2O, 8 % protein, 1 % organic acids and 1 % salts. Fibrinogen is one of the proteins, and this plays an of import function in the curdling of blood ( Bevel and Gardner 2002 ) . Blood serum is blood plasma minus its protein content ( Jackson and Jackson 2008 ) . The cellular constituent of blood consists of red blood cells ( ruddy blood cells ) , leukocytes ( white blood cells ) and platelets ( thrombocytes ) ( Bevel and Gardner 2002 ) . Red blood cells are heavier than plasma, which can be seen in organic structures as lividity-which is where ruddy cells settle to the lowest appendage of a organic structure after decease ( Chmiel and Walitza 1980 ) .hypertext transfer protocol: //people.

eku.edu/ritchisong/301images/Red_White_Blood_cells.jpgFigure 2- A ruddy blood cell, thrombocyte and white blood cell ( University of Eastern Kentucky 2010 ) .There are approximately 4.

8 to 5.4 million ruddy blood cells per three-dimensional millimeter of blood ( Tortora and Anagnostakos 1987 ) . They are bioconcaved phonograph records in form. The chief function of the ruddy blood cells is “ to transport O from the lungs via the arterial system and return C dioxide to the lungs for termination via the venous system ” ( James and Nordby 2005 ) . Red blood cells contain hemoglobin which is a ruddy pigment that gives blood its coloring material ( Bevel and Gardner 2002 ) . Haemoglobin is composed of hematohiston, which is made up of four folded polypeptide ironss, and four heme groups that join with Fe ( University of Eastern Kentucky 2010 ) .hypertext transfer protocol: //www.

ul.ie/~childsp/CinA/Issue64/Images/TOC36_2.gifFigure 3- Haemoglobin, incorporating four heme groups ( University of Limerick, 2010 ) .As the O content additions in the blood, the bright ruddy pigment of the hemoglobin besides increases ( Bevel and Gardner 2002 ) . A ruddy blood cell does non incorporate a karyon.Red blood cells are expressed as a per centum of the “ jammed ( ruddy ) cell volume ( PCV ) ” , besides known as the hematocrit ( Wonder 2001 ) .

Nelson and Rodak ( 1983 ) province that the hematocrit in worlds is variable between persons.HematocritPossible people with scope of hematocrit15-29 %Chronic alkies or drug maltreaters, steroid maltreaters, adult females after traumatic kid birth or illegal abortion, malnourished homeless, elderly.30-48 %Normal scope for nontraumatic venipuncture ( blood drawn in a clinic or infirmary ) samples.49-75 %Dehydrated persons, people in daze, those populating at high height, impending and active bosom onslaught victims, newborn babes, people enduring from hypothermia, and people after utmost exercising.Table 1- Table to demo the scope of hematocrit ratios ( Wonder 2001 ) .White blood cells act to contend infections, destroy old cellular stuff and to destruct other occupying bugs ( Bevel and Gardner 2002 ) .

White blood cells can be farther subdivided into scavenger cells – which are responsible for the gaining control and consumption and foreign substances, and lymphocytes- which are responsible for the production of antibodies ( Jackson and Jackson 2008 ) . They make up less than 1 % of the cellular constituent of blood, which equates to 5000 to 9000 white blood cells per cubic millimeter ( Tortora and Anagnostakos 1987 ) . The karyon of white blood cells are the beginning of DNA in the blood ( James and Nordby 2005 ) .

The other portion of the cellular constituent of blood is the thrombocytes. Like ruddy blood cells, thrombocytes besides lack a karyon ( Bevel and Gardner 2002 ) . Bevel and Gardner ( 2002 ) say that there are by and large approximately 250,000 to 400,000 thrombocytes per three-dimensional millimeter of blood. Platelets are major constituents of the coagulating mechanism of blood, and this is their primary map ( James and Nordby 2005 ) . Platelets have irregular forms and are usually rather little, nevertheless when they encounter a damaged blood vas they increase their size and their forms alterations ( Bevel and Gardner 2002 ) . They besides become gluey and adhere to environing fibers in the vas wall, which consequences in the accretion of thrombocytes called the “ thrombocyte stopper ” ( Bevel and Gardner 2002 ) .II.

III Blood at a Crime SceneBlood is usually found at a offense scene due to a individual prolonging an hurt either by accident or on intent. When a breach in the circulatory system occurs- due to an injury- the organic structure reacts in different ways to command the loss of blood ( Bevel and Gardner 2002 ) . Initially the vascular cramp occurs, which is which the “ smooth vass in the blood vas wall contract to diminish the size of the vas ” , which reduces the flow of blood through it ( Bevel and Gardner 2002 ) . Tortora and Anagnostakos ( 1987 ) say that this reduces blood loss for up to 30 proceedingss following hurt, which gives clip for the other blood loss mechanisms to prosecute. The thrombocyte stopper so follows which reduces, if non stops, the blood loss ( Bevel and Gardner 2002 ) . The concluding measure is curdling, or coagulating.

This is what is usually seen at offense scenes, where the clogged mass of fibrin fibers and blood cells is surrounded by blood serum ( Bevel and Gardner 2002 ) .There are three types of shed blooding that can happen from harm to blood vass ( BUPA 2009 ) :Arterial BleedingVenous BleedingCapillary Bleeding.Arterial hemorrhage normally is spirting bright ruddy blood, due to the blood holding come from the bosom and lungs-so it is oxygen rich ( Walter et al 2004 ) . The pumping action of the bosom adds rhythmic rushs to travel blood vass off from the bosom ( Wonder 2001 ) . It is the most serious type of hemorrhage, and the most hard to command due to the blood in the arterias being under force per unit area from the bosom ( Walter et al 2004 ) . Arterial lesions consequences in “ volume discolorations ” ( Wonder 2001 ) . Loss from the carotid arteria or the aorta can quickly take to decease ( Wonder 2001 ) .

Examples of arterial hurts, and how they may happen are listed in Table 2.ArteryLocationProbable HappeningFacialMouth/lipsBeatingTemporalHead/templesGunshot, OppressingCarotidNeck, forepart pharynxStab lesion, Gunshot, DecapitationSubclavianUnder neckband boneGunshot, OppressingAortaChestGunshot, Stab lesionBrachialArm/elbowBone interruptionRadialWristSlit carpuss, Bone Break, Stab lesionFemoralGroinGunshot, Stab lesionTibialAnkleBone Break, OppressingDeltoidUpper arm musculusStab lesionTable 2- Areas and actions that may affect arterial harm ( Wonder 2001 )External venous hemorrhage is usually as a consequence of wounding, as venas are closer to the tegument than arterias ( Walter et al 2004 ) . It consequences in the steady flow of dark ruddy ( about brown ) blood, and is darker than arterial blood as it has released O to the tissues in the organic structure and is fluxing back to the bosom and lungs for more O ( Walter et al 2004 ) .Capillary wounding is common in minor lesions as capillaries are really little vass that are under really small force per unit area with a low volume of blood ( Walter et al 2004 ) . Capillary hemorrhage consequences in the seepage of either bright or dark ruddy blood, which will usually halt on its ain ( Walter et al 2004 ) .Equally good as the three chief types of hemorrhage, there is a farther class which is traumatic hemorrhage. There are different types of lesions which can do traumatic hemorrhage, and these can be categorised as follows:Abrasion- besides known as a graze, where an object coppices on the tegument but does non interrupt it.

Hematoma- where blood vass are damaged, doing blood to roll up under the tegument.Laceration- where a blunt impact to soft tissue causes a deep lesion.Incision- where a precise cut is made into the tegument.Puncture Wound- where an object penetrates the tegument and deeper beds.

Contusion- besides known as a contusion, where a blunt injury causes harm under the tegument, but does non interrupt it.Oppressing injuries- where a great sum of force is applied over a period of clip, doing ab initio internal hemorrhage.Ballistic trauma- where a missile arm has entered and exited the country of the organic structure, doing a lesion between the two.Scenes of Crime officers attend many types of offense scene where blood is present. These include:Burglary- When an wrongdoer breaks a glass window or door to derive entry to a premises, they risk cutting their hands/arms. This leads to blood being left on fragments of glass in the window and on the floor.

Assault/Wounding- Open lesions are usually the consequence of an onslaught on a victim. Blood can be left at an assault scene on the arm that was used in the assault, on the land, on the wrongdoer and on the victim. If the victim is shed blooding to a great extent so blood will be left whenever the victim comes into contact with another surface.Manslaughter/Attempted Murder/Murder- Blood left at these scenes is non merely of import for swobing intents, but the form in which the blood is left can find the order of events at a major scene.

Road Traffic Crash- Blood at this scene can be found in the victims auto and, if involved, the wrongdoers auto. This is of import as it can put people in their several cars- leting research workers to work out the places of people at the clip of the incident.The aggregation, packaging and saving of blood grounds at a offense scene should non take topographic point until the scenes of offense officer has documented the bloodstain forms ( Lee, Palmbach and Miller 2001 ) . Whenever biological fluids are encountered at a offense scene, protective vesture, baseball mitts and masks should be worn due to the biohazard nature of blood ( Lee, Palmbach and Miller 2001 ) .To retrieve dry blood, an country near the blood that is unstained should be swabbed utilizing a unfertile swab, as a control sample ( Derbyshire Constabulary 2008 ) .

Then, the discoloration should be swabbed utilizing a unfertile swab that has been moistened utilizing unfertile H2O ( Derbyshire Constabulary 2008 ) . The remains of the discoloration should so be dry swabbed utilizing a unfertile swab ( Derbyshire Constabulary 2008 ) . The swabs should be returned to their tubings instantly and stored frozen every bit shortly as possible ( Derbyshire Constabulary 2008 ) . A “ batch control ” of both the H2O and swabs should ever be made, and should be exhibited individually to the swabbed discoloration and background control ( Derbyshire Constabulary 2008 ) . Items that have countries of dried blood on them should be packaged in paper bags which are sealed firmly and clearly marked as biohazard.

Blood and bloodstained grounds should ne’er be packaged in air-tight containers ( Lee, Palmbach and Miller 2001 ) .To retrieve wet blood, a control swab of the environing country of the discoloration should be taken utilizing a unfertile swab ( Derbyshire Constabulary 2008 ) . The wet discoloration should so be swabbed utilizing a dry, unfertile swab ( Derbyshire Constabulary 2008 ) . The swabs should be returned to their tubings instantly, and should be stored frozen every bit shortly as possible ( Derbyshire Constabulary 2008 ) . Again, a “ batch control ” of the swab should be exhibited individually ( Derbyshire Constabulary 2008 ) . If a removable point has an country of wet blood on it, so the full object should be exhibited and left to dry in a drying room at the constabulary station.Frequently at offense scenes, discolorations that are composed of unknown substances can easy be confused with blood. Identifying whether a substance is blood allows further analysis to corroborate species, and the person ( Spalding 2006 ) .

II.IV Presumptive Trials for BloodJames and Nordby ( 2005 ) say that a presumptive trial is one which allows the scenes of offense officer to do a qualified decision that blood is present in the tried sample, when positive. They besides say that when a trial is negative, stains that demand no farther consideration are eliminated. Presumptive trials may be recognised as those that produce a seeable color reaction or those that result in the release of visible radiation ( James and Nordby 2005 ) . Both of these rely on the catalytic belongingss of blood to drive the reaction ( James and Nordby 2005 ) . Lee, Palmbach and Miller ( 2001 ) compose this as a chemical reaction:

AH2 + H2O2 i? A + 2H2O

Oxidisable chemical Hydrogen peroxide Haeme Oxidised( colourless ) ( peroxidise )James and Nordby ( 2005 ) province that catalytic trials involve the “ chemical oxidization of a chromogenic substance by an oxidising agent catalyzed by the presence of blood ” . They besides say that the accelerator of the reaction is the peroxidise-like activity of the haeme group of hemoglobin.Cox ( 2004 ) describes the properties that a good presumptive trial for blood should be sensitive, specific, speedy, simple and safe.

In order for presumptive trials for blood to work decently, they must observe a constituent of blood ( Tobe, Watson and Daeid 2007 ) . Most presumptive trials therefore act on the peroxidise activity of hemoglobin. This constituent is non found in the mundane environment, but other substances found in points such as fruit and veggies execute a similar map ( Tobe, Watson and Daeid 2007 ) .A really popular presumptive method is the phenolphthalein trial, which is besides known as the Kastle- Meyer trial ( Virkler and Lednev 2009 ) . Lee, Palmbach and Miller ( 2001 ) say that the Kastle-Meyer trial was introduced in 1901 by Kastle. Phenolphthalein will do an alkalic solution to turn pink after it has been oxidised by peroxide when blood is present ( Spalding 2006 ) . The reagent consists of decreased phenolphthalein in alkalic solution, which is oxidised by peroxide in the presence of hemoglobin ( James and Nordby 2005 ) .

The trial consequence is usually immediate, and a positive consequence a minute or more after the trial is performed is normally non considered as dependable ( James and Nordby 2005 ) . It has a sensitiveness of 1:100,000 ( Lee, Palmbach and Miller 2001 ) .James and Nordby ( 2005 ) say that Adler and Adler in 1904 investigated the reduced or colorless signifier ( leuco ) of the dye malachite viridity, which is besides referred to as McPhail ‘s reagent. This trial involves the Leuco base of malachite viridity ( Lillie 1969 ) . Leucomalachite Green oxidization is catalyzed by haeme to bring forth a green coloring material ( James and Nordby 2005 ) .

The reaction is normally carried out in an acerb medium with H peroxide as the oxidant ( James and Nordby 2005 ) . It has a sensitiveness of 1: 20,000 ( Lee, Palmbach and Miller 2001 ) .“ Bluestar is a luminol readying developed by Professor Loic Blum in France that is highly sensitive and stable and produces a really bright, long lasting chemiluminescence ” ( James and Nordby 2005 ) . The utmost sensitiveness of Bluestar Forensic allows sensings of bloodstains down to 1:10,000 dilutions ( Bluestar Forensic 2004 ) . It does non necessitate entire darkness to be seeable, and works good on either fresh blood or old bloodstains ( Bluestar Forensic 2004 ) .

Bluestar plants by blending the Bluestar Forensic solution with Bluestar Forensic tablets, which is so left to fade out. This is sprayed onto the country of suspected blood. A positive consequence will do a blue luminescence ( Bluestar Forensic 2004 ) .The Hemastix trial, created by Miles Laboratories in 1992, is peculiarly utile when solutions can be risky, or inconvenient ( James and Nordby 2005 ) . The trial consists of a fictile strip with a “ reagent treated filter check at one terminal ” ( James and Nordby 2005 ) . The check contains TMB, diisopropylbenzene, dihydroperoxide, buffering stuffs and non reactants ( James and Nordby 2005 ) . A bloodstain is tested by washing a swab with distilled H2O, trying the discoloration, and touching the swab onto the reagent check on the strip ( James and Nordby 2005 ) .

The check is usually xanthous, and turns form orange to green or blue when positive.Quality control testing is necessary and should be completed with known blood samples on every new batch of trial reagents to verify that the reagents are working as expected ( Lee, Palmbach and Miller 2001 ) .II.V False PositivesSutton ( 1999 ) points out that a false positive is “ an evident positive trial consequence obtained with a substance other than blood. James and Nordby ( 2005 ) say that misdirecting consequences can be attributed toChemical oxidizers ( frequently bring forthing a reaction before the application of peroxide )Plant stuffs ( vegetable peroxidises are thermolabile )Materials of carnal beginning ( that contain hints of blood ) .Substances that produce false positives by and large take detectably longer to respond and, hence, may be eliminated through experimental reading ( Tobe, Watson and Daeid 2007 ) .

False positives were ab initio noted merely with Cu salts ( Glaister 1926 ) .Tobe, Watson and Daeid ( 2007 ) province that “ spit, seeds, murphy, tomato, tomato sauce, tomato sauce with meat, ruddy onion, ruddy kidney bean, horseradish, 0.1 ascorbic acid, 5 % bleach, 10 % cuprous sulfate, 10 % ferrous sulfate and 10 % nickel chloride ” are all known false positives.Bluestar False Positives ( 2008 ) say that Bluestar has false positives that include oil based pigment, alkyd varnish, Brassica rapa, banana, scallion, green bean, carrot, ginger, manganese sulfate, Cu sulfate, Fe sulfate and K permanganate.Lee, Palmbach and Miller ( 2001 ) write that many family cleansing merchandises contain oxidizing agents that can bring forth false positives.

Many fruit and veggies produce false positives including apples, horseradish and Brassica oleracea italica ( Lee, Palmbach and Miller 2001 ) .Bleach is a false positive that provides an ( immediate and intense reaction ) harmonizing to Gardner ( 2005 ) . Hunt et Al ( 1960 ) say that fecal matters frequently gave a false positive depending on the nutrient that had been eaten antecedently.Ponce and Pascual ( 1999 ) province that lemon juice added to a bloodstain can do a positive consequence due to its sourness.A false negative is when “ there is some intervention with the oxidation-reduction reaction ” , usually in the presence of a strong reduction agent, which consequences in a hold of the oxidization reaction ; therefore ensuing in a colored formation ( Lee, Palmbach and Miller 2001 ) .

False negatives are less common but debatable as an existent blood sample may be overlooked or left at the scene ( Lee, Palmbach and Miller 2001 ) .Many of the false positive reactions can be identified during the presumptive testing process if any alterations observed and the exact point in the reaction of these alterations is recorded and compared to that of blood ( Lee, Palmbach and Miller 2001 ) .Chapter III. Experimental MethodologyI will be look intoing known substances antecedently reported by other writers that show a false positive and so analyzing other substances similar to those already known to see if these besides produce a false positive.III.I Project DesignEach of the substances will necessitate to be repeated to guarantee a broad adequate scope of consistent consequences. Therefore, a grid will be drawn on a piece of Perspex mensurating 1.5m2, and a piece of filter paper placed in each of the grid infinites, to let the even distribution of substances and to let the easy designation of false positives.

BloodKnown FalsePositivesUnknowns12312ANew technique to observe metabolites from a individual bead of bloodBacillusNew technique to observe metabolites from a individual bead of bloodCNew technique to observe metabolites from a individual bead of bloodFigure 4- A diagram to exemplify an illustration of the undertaking layout.For each of the presumptive reagents tested, the filter paper in each grid infinite will be exposed to a substance to be tested. This will be allowed to dry for a lower limit of 1 hr. Each substance will so be tested with a reagent. Each substance will be repeated three times to give a just indicant of public presentation. The clip taken for a substance to register a positive consequence will be recorded. If a coloring material alteration occurs so the trial will be classed as positive.

If no coloring material alteration is noted within 5 proceedingss of the reagent being added, so the trial will be classed as negative.III.II Sample PreparationThe substances that I have chosen to analyse are known false positives as reported by other writers and so substances allied to cognize false positives.Known false positives to be tested:Horseradish.Tomato Sauce.Red Onion.

Turnip.Lemon Juice.Bleach Solution ( 5 % ) .Unknown substances to be tested:Brown Sauce.

BBQ Sauce.Radish.Dark Chocolate.Orange Juice.Bleach Solution ( less than 5 % ) .III.

III Choice of Presumptive TrialsI have chosen to utilize the undermentioned presumptive reagents to prove substances for false positives:Kastle-Meyer.Hemastix.McPhail ‘s.Bluestar.III.IV Control TestsI will prove all of the presumptive trials on clean filter paper before continuing to prove with substances. This ensures that there is no reaction from the filter paper to the presumptive trials.

I shall besides prove all of the presumptive trials with Equus caballus blood before continuing to prove with substances. This shows that the trials do recognize a sample of blood.I have chosen to utilize 2.5g of each substance as I feel this is an sum that is representative of a discoloration at a scene.Blood is reported to hold been diluted to 1:10000 in old trials, and as this dilution has proved the most successful, I have chosen to utilize this dilution.



I'm Ruth!

Would you like to get a custom essay? How about receiving a customized one?

Check it out