Neutralisation of False Positives using Presumptive Tests

Neutralisation of False affirmatives victimization seeming TestsJasnique TiwanaThe Neutralisation of False Positives victimization Presumptive Tests for logical argumentAbstractIntroductionThis construe emphasis upon neutralising presumptive footraces for crosscurrent, this differs from other studies as they bonny test for inconclusive confident(p)(p)s, instead of attempting to neutralise these cognise fake positives. This project was conducted as there atomic number 18 no current pellucid projects on the neutralisation of irrational positives. This is a crucial topic beca wont it testament save time at crime medical prognosiss when looking at a suspected cable blemish, m both false positives ar cognize to interfere with the presumptive tests kits. However, if these goat be eliminated at the scene, then it will save lots of time conducting positive tests for a bell ringer that is non blood. It will be interesting to discover whether one and only(a) neutrali zer can neutralise all or the majority of the unknown false positives.The aims of this project are to find out which substance/ products produce false positives, and whether or not these false positives can be neutralised. In amplification, how many of these false positives work for two Kastle-Meyers and Leucomalachite jet plane. as well whether the type of surface these false positives are found upon affects the ability for them to be detected.There are numerous amounts of different bodily fluids that can be found at a crime scene. Blood is one of the well-nigh common and important bodily fluid found at a crime scene as it can give an insight to a desoxyribonucleic acid profile and much more. The blood can either be from the offender this can help corroborate stories and give a deeper insight into what in truth happened (The Forensics Library, n.d). In the criminal justice system blood is defined as a vital labyrinthian biological fluid containing red blood cells, which is p resent in vertebrate and may be wander during an accidental, intentional and/or criminal acts. (Wonder,2001). Blood consist of erythrocytes, leucocytes and platelets, hence presumptive assays test for the presence of hemoglobin located in the erythrocytes (Jackson and Jackson, 2007).However, at a scene it may not al panaches be obvious as to whether or not the stain is actually blood, thus, presumptive tests are required to attend whether the stain could be blood or not. There are various different presumptive tests designed to make out whether the stain is blood, although, these are not a confirmatory test for blood. Blood found at a crime scene is essential as it can provide a DNA profile from two the victim and the suspect. (Gupta, et, al. 2016). This can then be collected for supercharge analysis in the laboratory, to obtain DNA profiles etc. (Tobe, et, al. 2007). Over centuries various different attempted clean-up orders arouse been apply for blood, including bleach, th erefore, it is important to use a presumptive test which can detect microscopic blood stains.Presumptive testsPresumptive tests with the exception of luminol are not use transportly to a stain, instead, the suspected stain is lifted victimization a stereotypical swab or filter make-up, the presumptive test is then carried out on the filter paper or the swab. This is to gibe that the suspected stain is not damaged. In certain cases, such as where the surfaces have been washed down, it becomes more appropriate to use luminol due to its high take of detection (Jackson and Jackson, 2007).Presumptive tests are used by forensic scientists worldwide to aid in the identification of unknown substances such as blood. However, a presumptive test does not provide definitive identification instead it provides useful reading which helps to decide what further action if any is needed.There are numerous presumptive tests for blood, historically with the most common be benzidine which was fir st introduced in 1904 (after Kastle-Meyers) which was introduced in 1901). Moreover, this is no longer widely used in forensics as it was discovered to have carcinogenic effects. Tetramethylbenzidine has in addition been recognised as a carcinogen and caution should be applied when employ either test (James,1998).Presumptive tests are not specific to Human blood as they will alike give a positive issue for animal blood. Commonly, a tinct interpolate is observed to determine whether it is positive for that substance, due to these presumptive tests are subject to false positives and false negatives. In screening tests for blood, the heam group is observed as this acts as a catalyst which is involved in the chemical chemical receptions.False positive results can be obtained from chemicals containing ironlike oxidants such as bleaches and household cleaners. do peroxidases such as red cole can also affect presumptive tests such as sawhorseradish as they contain peroxidases th ey catalyse oxidation reactions thus ca employ a false positive. They are known to be sensitive to heat so heating up a plant peroxidase can demobilize it. A false positive is place as a discolor permute before the addition of heat content peroxide (Li,2008). Li (2008) states that although uncommon false negatives can also occur, this happens when a affectionate reducer is present, this hinders the oxidation reaction.Luminol Luminol is referred to a chemiluminescent reaction which is oxidised by hemoglobin. It was a very early method used in 1937 to detect microscopic amounts of blood at a crime scene as it has a very small detection limit (in nanograms). Although, the test is sensitive it is also prone to false positives as with the other presumptive tests of blood. atomic number 11 Hypochlorite is in bleach based substances commonly used for a clean-up, this would be detected by the luminol test (Quickenden and Cooper 2001). A limitation to luminol is that it must be used in total darkness to be able to see the reaction. It is different from the other presumptive tests as it involves illumination with a bright light (blue) (Webb, et al, 2006).Kastle-MeyersThe phenolphthalin Assay is referred to as the Kastle Meyers test, it differs from phenolphthalein which is a class of dye indication commonly used in titrations. Phenolphthalin is a act uponless compound (the reduced form), the oxidized derivative is phenolphthalein which turns bug (Li, 2015). The Kastle-Meyers (KM) test is one of the most best-selling(predicate) presumptive test used by forensic scientists, it is contingent to detect blood up to 100,000x dilution (Bell, 2012). identification number 1 aims the oxidation of phenolphthalein causing a pink intensity change when reacting with a peroxide.The Kastle-Meyers test is a presumptive test used to identify blood stains it contains phenolphthalein, which reacts with the haemoglobin in blood with the addition of hydrogen peroxide leading to a pink colour change for a positive test. This test, however, is not specific for blood and can be subject to false positives, it is also not specific to human beings blood and will react with animal blood. Therefore, it is not a confirmatory test of blood. Leucomalachite green (LMG) is also a presumptive test of blood, however it is not as popular as the Kastle Meyers test (Bell, 2012). A positive result for Leucomalachite green is a green-blue colour change.Leucomalachite green (LMG)Figure 1 to show the chemical structure of Leucomalachite green (Sigma Aldridge, 2017)Leucomalachite Green chemical symbol C23H26N2 (PubChem, 2005), this is also a colour change test it is not as widely used as Kastle Meyers but it is just as useful. Leucomalachite green is oxidised by haem causing a bluish green colour change it is colourless when in its reduced state. The reaction is usually carried out in acetic acid and hydrogen peroxide which acts as an oxidiser (li, 2015). It is used in a v ery similar way to Kastle-Meyers, as the test is almost identical, this test as with the Kastle- Meyers, therefore, it is also prone to a false positive, hence further analytical tests are required to confirm if its blood. Due to the false positives, it cannot be called a confirmatory test for blood. These tests are also not specific as they do not react to just human blood but other animal blood.Neutralising agents Various different neutralisers are available for bleach. discolor is known to be a common false positive detected with Presumptive tests. The active ingredient in Bleach is Sodium Hypochlorite, therefore, research into is neutralisation was looked into. The most common one used is Sodium Thiosulphate another(prenominal) is Ascorbic acid which is used more commonly in water storage tanks to climate all stay bleach making the water safe to drink (Tanguay,2013). Due to the neutralisation of peroxide both these neutralisers will be used to see if they neutralise all the fal se positives.MethodPreparation of the reagentsThe Kastle-Meyers test The reagent is do by weighing out 12g of phenolphthalein, 120g of potassium hydroxide and 30grams of Zinc dust and 600ml of di fluented water should then be added. This is then put onto a hot plate and moved(p) for 3 hours. (Langford et,al).The Kastle-Meyers was used as follows, the stain was moistened with ethanol (optional depending on how the stain was lifted) and this is rubbed over the stain, then two drops of the Kastle-Meyers is then added onto the stain, at this stage a colour change is indicative of a false positive, if there is no false positive at this point then continue to the next stage, and add two drops of 3% hydrogen peroxide, if there is an ready pink colour change this indicates blood could be present as it is a positive result for blood. If there is no colour change then it can be almost certainly verbalise that no blood is present, this is due to its high level of predisposition.Leucomalac hite green solution was make up using 0.11grams of Leucomalachite green powder, 66mL of glacial acetic acid and 33mL of distilled water, this was mixed together to form the colourless Leucomalachite green (cox, 1991). The alike method mentioned above is used for Leucomalachite green with a blue-green colour change being a positive result for blood and a blue-green before the addition of hydrogen peroxide being a false positive. The initial Leucomalachite green solution is clear.Defibrinated horse blood was used due to its proportion to human blood, also because presumptive tests cannot differentiate between blood types. The swabs used were all in aseptic packaging and all the pipettes had been autoclaved prior to use to ensure that all equipment used was sterile as not to allow any cross contamination. Blood was placed straight onto a sterile swab this was subjected to the presumptive tests to ensure no other contaminants caused a colour change this acted as a positive control. proscribe controls were created using a sterile swab and adding each of the reagents to make sure no liaison else was interfering with the test. A positive control was also taken by swabbing blood from jean to see if it would still react or if there was an interfering ingredient.To determine the levels of sensitivity for both KM and LMG blood was thin and put into test subways. Blood was pipetted into test tubes using Finn pipettes in order to determine accuracy. Different concentrations of blood were made up using distilled water and blood. The solutions made up were 110, 1100, 11000, 1 10,000, 1 100,000 were prepared. This was done by pipetting 1mL of blood into 9mL of water, from this solution 1mL was added into 9mL of water and so on. This method was used to determine the level of sensitivity of the presumptive tests used a sterile swab was dipped into each of these solutions and the Kastle -Meyers test was performed. The time taken for these to turn and the shade of pink i n which they turned were recorded. Each swab was taken 3 times in order to determine accuracy, but also each test tube was made up 3 times, this gave a total of 15 test tubes, to make sure no extra or no less blood was added each time, and to check the reliability of the method as the blood had begun slightly clotting. This was done over a series of days to see if the results differed in anyway.A series of household items and known false positives obtained from previous literature reviews were determined and these were placed onto the denim real(a), by rubbing the item onto the material. The items used were, horseradish, bleach, red onion, lemon, tomato, tomato ketchup (Heinz) and potato. These were then allowed to dry on the material before dampening the stain with distilled water. This was repeated three times and also repeated after 3 days when it had more time to dry.With a fresh batch of false positives, horseradish, bleach, ketchup and tomato were re well-tried to see if the y reacted to the new Kastle Meyers and Leucomalachite green solutions. erst the false positives were established such as the use of bleach, then sodium thiosulphate and Ascorbic acid were added to the stains to see if they affected the tests and gave a new negative reaction.Sodium thiosulphate was made up using 0.25g of Sodium Thiosulphate and 5ml of water and mixed to make a 5% solution, the crystals were stirred and the be solution was colourlessAscorbic acid was made up using 0.25g of ascorbic acid in 10ml of water, this was then stirred and gives a clear solution.Firstly, a sterile was dipped into bleach and a few drops of the leucomalachite green were applied using a disposable sterile pipette each time, the colour change was then observed. Once this was established another swab was dipped into bleach but this time sodium thiosulphate was first added to the swab, (again using a disposable sterile swab) the sodium thiosulphate was applied all the way around the swab to ensure a ll areas were covered. In addition, lecucomalachite green was then pipetted onto the swab and observed for a colour change, the equivalent thing was then repeated using ascorbic acid. The swab was held up against a white background to see if It had a slight reaction or not. It was tried with pure bleach and weaken bleach to see if the reactions were the same. The neutralising agents were also used with pure blood to see if it reacted the same with blood and caused a colour change, hydrogen peroxide was added to the pure blood stain. This was to determine whether or not it is a true false positive or not.The next stage was to repeat the following steps using Kastle -Meyers on pure bleach and thin out bleach.In addition, to determine whether or not the false positives worked on all peroxides, both Ascorbic acid and Sodium Thiosulphate were also used on horseradish, in an attempt to neutralise it, this was repeated three times.ResultsFirstly, a positive and negative control were tak en to ensure a positive result was obtained for pure blood and a negative result for water, indicating there was no contamination.A serial dilution was made for the Kastle-Meyers to determine the level of sensitivity. It was metric to a 1 in 100,000 dilution as this is the results obtained from previous literature as to the level of sensitivity. give in 1 shows the intensity of the colour change from the dilution of blood, this was repeated three times. hold over 1 a tabularize to show the level of sensitivity of the Kastle-Meyers solutionDilution factor assume 1Repeat 2Repeat 3X10Bright pinkBright PinkBright PinkX100PositivePositivePositiveX1,000PositivePositivePositiveX10,000Faint pinkFaint pink no(prenominal)X100,000NoneNoneNoneFalse positives were first tested on denim to see if they reacted. The blood sample was placed onto the denim material first this was to determine whether the Kastle-Meyers kit was working correctly. The results of the false positives can be seen in tab le 2, each sample was firstly loaded onto the swab and the denim material, this was too see if there was a difference between the two methods. The highlighted results in table two show the false positives which differed on the denim and the swab. Table 2 shows the first experiment to test for false positives comparing it to the reaction it had on denim.Table 2 false positives using Kastle-Meyers on denim and straightway to swab, with* meaning inconclusive result as it is the same colour in which the test kit changes, the samples reacted after 5 mins of the addition of Kastle-Meyers reagentFalse positiveNegative/positive reaction on denim materialAdded directly to swabHorse radish plant rootBleach(Sodium Hypochlorite)+ ablaze(p) onionPotato tomato sauce+Red OnionLemon+Tomato*Red radishLeucomalachite green was also tested for its sensitivity of bloodThis was then tested on pure blood with the addition of hydrogen peroxide. This was to check if the solution made up gives a blue-green colour change. Table 3 shown below shows a serial dilution for Leucomalachite green, the serial dilution was performed in the same way as in the Kastle-Meyers test and the colour change and intensity of the change was recordedTable 3 a table to show the dilution factor of Leucomalachite green after the addition of hydrogen peroxideDilution factorRepeat 1Repeat 2Repeat3X10 immobile cobalt ultramarineStrong TurquoiseStrong TurquoiseX100Blue green thinly Blue-greenBlue-greenX1,000Light Blue-greenFaint Blue-greenLight Blue-greenX10,000No reactionNo reactionNo reactionX100,000No reactionNo reactionNo reactionTable 4 shows the false positives on the denim material and direct application to the swab, the first repeat the same method applied as that in Leucomalachite greenTable 4 false positives using denim material and direct application to the swab, this shows the first attempt using Leucomalachite greenFalse positiveNegative/positive reaction on denim materialAdded directly to swabHor se Radish root+Bleach(Sodium Hypochlorite)+Red onionPotatoTomato sauceRed OnionLemonTomatoRed radishA fresh set of Known false positives were then used, this was tested with both Kastle Meyers and Leucomalachite green respectively, this is shown in table 5 and 6, each one was tested three times and the reaction and the intensity of the reaction are shown. This time instant colour changes were recorded, using a new Kastle- Meyers test Kit, this was done under a fume hood. This time a diluted bleach sample was used to see if it affected the results of bleach.Table 5 False positives tested using Kastle -Meyers where + means a positive reaction and is a negative reaction, instantaneous resultsFalse positiveRepeat 1Repeat 2Repeat 3 horseradish+ strong pink+ pink+ strong pinkTomatoTomato KetchupBleach+ Strong Pink+strong Pink+ Strong PinkDiluted bleach+ weak pink+ pink+ weak pinkTable 6 false positives tested using Leucomalachite green where + indicates a positive reaction and indicates a negative reaction instantaneousFalse positiveRepeat 1Repeat 2Repeat 3Horseradish+ light green+ light green+ dark greenTomatoTomato KetchupBleach+ Strong blue/green+strong green+ Strong greenDiluted bleach+ strong green+ strong green+ strong greenTable 7 shows the neutralisation of the false positives identified in table 5 and 6 using ascorbic acid and thiosulphateTable 7 neutralising agents of the false positives for both Kastle-Meyers and Leucomalachite green. where + indicates a positive reaction (colour change) and indicates a negative reaction (no colour change)False positiveKastle- MeyersLeucomalachite greenSodium thiosulphateAscorbic acidSodium thiosulphateAscorbic acidHorse radish++Bleach+++Diluted bleach discussion The test was repeated three times to see if the results were the same each time. Kastle -Meyers has a level of sensitivity up to 1 in 100,000. This was found to be the level of sensitivity by other authors. Blood was diluted with water this was not only to te st the level of sensitivity but blood is likely to be cleaned up with water of some kind.Leucomalachite green is not as widely used as Kastle-Meyers, as it has a lower level of sensitivityThis was diluted in blood to check its level of sensitivity it got a reaction up to 1 in 1,000 rather than 1 in 10,000 as suggested by other literature reports.Denim material had ketchup, tomato, horseradish and blood added to it, however, it did not yield any results as the false positives did not change colour with the addition to lecuomalachite green. Bleach was tested with lecuomalchite green, this gave an instant colour change, bleach was then diluted in water to see if watered down bleach gave the same effect and this also gave a positive reaction.Sodium thiosulphate neutralised the effect of bleach as the reaction was barely visible using the Leucomalachite green, however, the ascorbic acid worked but not as well as the thiosulphate. This is because it was sticky to tell whether the entire swab had been neutralised as it appeared a very faint green colour around the sides, compared to other swabs which appeared unaffected by the neutralising agent chosen. It was only tested on the bleach and horse radish because they were the only substances which had given a false positive reaction,None of the substances on denim gave a false positive, this leads to further research into indigo dye as a neutraliser.