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Effectiveness of oxidizing reagents in removal of blood stains

Akademische Arbeit 2019 45 Seiten

Chemie - Analytische Chemie

Leseprobe

Table of Contents

1. Topic

2. Introduction

3. Background information
3.1 Oxidizing reagent
3.2 Mechanism and Detection of Chemiluminescence

4. Research Variables

5. Expectation

6. Chemicals required

7. Apparatus required

8. Cautionary Principles

9. Methodology of Experimentation:
9.1 Preparations of the chemicals
Synthesizing of luminol stock solution
Preparation of Iron stock solution imitating blood
Synthesis of sodium per borate monohydrate
Preparation of 3% H2O2
9.2 Using the spectrophotometer

10. Qualitative analysis

11. Data collection and Graphical analysis
11.1 Absorbance pattern shown by 0.1g of the reagents in visible light region
11.2 Absorbance pattern shown by 0.2g of the reagents in visible light region
11.3 Absorbance pattern shown by 0.3g of the reagents in visible light region
11.4 Absorbance pattern shown by 0.4g of the reagents in visible light region
11.5 Absorbance pattern shown by 0.5g of the reagents in visible light region

12. Explanation of results and discussion

13. Evaluation

14. Conclusion

15. Limitations and improvements

16. Future scope and Extension

17. Bibliography

18. Appendix

1. Topic

Effectiveness of oxidizing reagents in removal of blood stains

2. Introduction

Adjustments, amendments and concealing of the crime evidences have resulted in an increment in the world’s crime rate. One such recurring hindrance can be seen with the most vital forms of evidence; bloodstains. Bloodstains are considered to be one of the most difficult stains to remove and even after cleaning them off the clothes through the detergents available in the market, there are some colored traces left which do not disappear completely and can be detected. The red color present in the blood is due the pigment called hemoglobin which basically comprises of ‘Hem which means Iron and globins which means protein.’1 Forensic scientists use luminol to detect bloodstains which when reacted with iron in blood stains exhibit chemiluminescence.2 This led to a thinking of till what extent were these criminals able to manage the escape by washing the stains and hinder the evidences. Thus the desire to study more about the mystery led to this investigation on bloodstains removal. After researching about the detergents from journals like ‘ Surface active agents: Advances in research and application- Ashton Acton’ and websites like ‘ The Science of Stain Removal, Study of Oxyper- H2O2, and Study of sodium per borate ’ and also studying3 the effect of various compounds present in them, it was found out that the active oxygen reagents were the sources through which bloodstain removal was possible. This helped in framing a research idea:

To what extent does the change in mass (1- 5g) of the oxidizing reagent, sodium per borate (NaBO3 ·H2O), sodium per carbonate (Na2 CO3 ·1.5H2O2) and hydrogen peroxide (H2O2 )found in detergents is effective in removing bloodstains, measured by spectro-photometric analysis of change in chemiluminescence intensity of luminol due to the oxidation of ferrous (Fe[2]+ ) to ferric ions (Fe[3]+) in stock solution containing oxidizing agents and iron solution (120 µg/dL) imitating blood at room temperature (30°C)?

In this essay, the correlation between removal of the stains and the extent to which it depends on the amount of reagent was measured. The decrease in chemiluminescence signifies the extent to which the stains are removed. On this basis, the cleansing action of various oxidizing agents like hydrogen peroxide, sodium per borate and sodium per carbonate were compared. Seeing the competence of the strongest oxidizing reagent, it can be considered that this research will be useful for forensic science departments to detect the extent to which evidences were tried to be concealed as all the oxidizing agents contain H2O2 and even after washing the clothes, some content of H2O2 is left. Using peroxide test strips it can be identified whether the criminals have tried to clear the evidences or not. It will also be valuable for the detergent manufacturers because through this research, they will opt for a better oxidizing agent to yield a better cleansing action.

3. Background information

3.1 Oxidizing reagent

Oxidizing agents work on the phenomena of releasing oxygen molecules through the process of oxidation which helps in breaking the bonds of chemical compounds- chromophores which produce color reflecting a definite region of the visible light spectrum.4 These oxidizing agents change the molecular shape of chromophores which leads to reflection of no color or color outside the visible spectrum. After researching from organic chemistry portal 5, two commonly used highly active oxidizing reagents ‘ Sodium per Carbonate (2Na2CO3·3H2O2)6 and S odium per Borate Monohydrate (NaBO3·H2O)7 ’ were selected as they can be easily prepared in the laboratory. Sodium per Carbonate is a colorless crystalline adduct which is denser than water. Due to its polarity, it is easily soluble in water and has the tendency to dissociate into Hydrogen Peroxide (H2O2) and sodium carbonate (Na2CO3) which together act as a complete detergent.

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A long time exposure to this chemical might cause burns, skin irritation, eye irritations, blindness, throat irritation and coughing; however the amount used for households isn’t harmful for humans. The long time exposure can be avoided by wearing gloves while handling the detergents.

The second reagent Sodium per Borate Monohydrate was manufactured by Deutsche Gold- und Silber-Scheideanstalt by dehydrating sodium per borate tetra-hydrate. Unlike sodium per carbonate and per phosphate, sodium per borate is not simply an adduct8 with hydrogen peroxide. Instead, it forms a cyclic structure with a B2O4 core and four hydroxide groups surrounded by two boron atoms. 9

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This makes the bond weaker, increasing the oxidizing capacity and causes the stain to be removed. A long time exposure to this may cause dermatologic manifestations10. This can be avoided by wearing gloves and avoiding inhalation or direct contact.

To compare the activity of the other two reagents, the third reagent chosen is Hydrogen Peroxide which is commonly used as a bleaching agent in detergents due to its excessively high oxidizing quality, easy availability and cheap rate.11

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The side effects of the reagent are that if directly used or used in excess, then it may damage the skin. To prevent this, a diluted solution of H2O2 should be used in the detergents.

3.2 Mechanism and Detection of Chemiluminescence

H.O. Albrecht discovered Luminol (technically 5-Amino-2, 3-dihydro-1, 4-phthalazinedione)12. When blood (containing hemoglobin) and luminol mixture (containing H2O2) come in contact, hemoglobin initiates an oxidation reaction between luminol and hydrogen peroxide.13 During this reaction, luminol undergoes oxidation by gaining oxygen atoms and losing nitrogen atoms and hydrogen atoms forming an energized compound 3-aminophthalate. In it, the electrons of oxygen atoms jumps to higher orbital which when fall back into lower energy state emit photons producing blue light. This exhibits the chemiluminescence property of luminol14.

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Image 1- Mechanism of Luminol Activation

The chemiluminescence of luminol can be measured through several methods like thermo- luminescence or through the light emitted by the reaction between iron and luminol in presence of H2O2. The method used in this experiment is spectro-photometer 16 which works by passing a light beam through a sample to measure the absorbance/transmittance of a sample. The wavelength emitted by luminol when in contact with iron is in the blue region i.e. 420nm- 445nm but in this experiment 428nm of wavelength was used as it showed the highest transmittance during the experimentation. (Shown in the appendix- Graph 13)

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Image 2 - Working mechanism of spectrometer

4. Research Variables

The amount of sodium per borate, hydrogen peroxide and sodium per carbonate was chosen as the Independent Variable as varying the amount of reagent used would show different extents of the activity of oxidizing agent on bloodstain stain removal. The absorbance pattern emitted by the usage of oxidizing agent was chosen as the Dependent Variable as the absorbance pattern shown at the 428nm of wavelength by the all three reagents depends on the mass of reagent used. This was measured by the spectro-photometric analysis of luminol. The amount of sodium silicate and sodium carbonate used was kept Controlled as Sodium silicate moves in prevention of deposition of mineral at the surface resulting in hardness and sodium carbonate was used to avoid bonding of hard water with the detergent. The two chemicals were used as a complimentary detergent ingredient to obtain better results and hence had to be constant for all the trials. Amount of luminol stock solution and iron stock solution used were chosen as the Controlled Variable as luminol helps in detection of blood stains and it was taken in proportionate amount to iron stock solution. More the iron solution, more detergent will be required to remove the stain which will result in hindrance of the results which is why it was necessary to control both the quantities. The third controlled variable was temperature which was kept at 30°C because changing the temperature of solutions will change the cleansing action is detergents

5. Expectation

When luminol reacts with bloodstains (specifically Fe[2]+ (ferrous ions in blood)), it emits a blue light indicating the presence of blood. Blood has red color due to hemoglobin and the oxidizing agents present in detergents easily break the bonds present between the chromophores. Chromophores have an ability to possess color. Due to breaking of the bonds, they will emit light which does not have a wavelength in the visible light spectrum. So using the above stated phenomena, the experiment was conducted to demonstrate the effect of oxidizing reagents on removal of the red pigment from the bloodstains. It is assumed that when iron (Fe[2]+) present in hemoglobin reacts with the oxidizing reagent, they get oxidized into ferric ions (Fe[3]+). Ferrous ions have the ability to bind with luminol producing chemiluminescence which helps in detecting bloodstains whereas the oxidized form ferric ions can no more bind with luminol. It implies that the oxidizing strength of the reagent is directly proportional to the ability of the reagent to work on stain removal. This change in oxidizing strength can be measured by the absorbance spectrum obtained by photo-spectroscopy of a particular wavelength (428nm) in visible region.

[...]


1 "Definition of Hemoglobin." www.medicinenet.com, May 13, 2016, https://www.medicinenet.com/script/main/art.asp?articlekey=15738. Accessed Jan 2, 2018.

2 "What Is Chemiluminescence? | www.scienceinschool.org." www.scienceinschool.org, 5 undefined. 2011, http://www.scienceinschool.org/2011/issue19/chemiluminescence. Accessed Jan 2. 2018.

4 "How Does Bleach Work?." wonderopolis.org, https://wonderopolis.org/wonder/how-does-bleach-work. Accessed Jan 3, 2018.

5 "Oxidizing Agents." www.organic-chemistry.org, http://www.organic-chemistry.org/chemicals/oxidations/. Accessed Jan 3, 2018.

6 "PubChem Search." pubchem.ncbi.nlm.nih.gov, https://pubchem.ncbi.nlm.nih.gov/search/. Accessed 3 Jan, 2018.

7 "Sodium Perborate - Oxygen Bleaching Chemical For Laundry Detergents." Runyoutech.com. 2017. Web. 4 Jan. 2018.

8 "Acid-Base Reaction - Dissociation Of Molecular Acids In Water | Chemistry." Encyclopedia Britannica. 2017. Web. 4 Jan 2018

9 "Preparation of Sodium Peroxoborate- Equations." chemistry.stackexchange.com, March 8, 2017, https://chemistry.stackexchange.com/questions/44911/preparation-of-sodium-peroxoborate-equations. Accessed Jan 6, 2018.

10 "SODIUM PERBORATE - National Library of Medicine HSDB Database." toxnet.nlm.nih.gov, May 12, 2017, https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+1676. Accessed Jan 8, 2018.

11 "Hydrogen Peroxide - the Evonik History Portal - the History of Evonik Industries." history.evonik.com, http://history.evonik.com/sites/geschichte/en/inventions/hydrogen-peroxide/pages/default.aspx. Accessed Jan 8, 2018.

12 Luminol - Dictionary Definition of Luminol | Encyclopedia.com: FREE Online Dictionary." www.encyclopedia.com, Feb 25, 2018, https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/luminol. Accessed Jan 11, 2018.

13 Harris, Tom. "How Luminol Works." science.howstuffworks.com, June 11, 2002, https://science.howstuffworks.com/luminol2.htm. Accessed Jan 11, 2018.

14 https://eic.rsc.org/exhibition-chemistry/chemiluminescence-the-oxidation-of-luminol/2020040.article

15 "BLUESTAR Forensic - Chemistry and History." www.bluestar-forensic.com, http://www.bluestar-forensic.com/gb/bluestar-chemistry.php. Accessed 12 Jan. 2018.

16,16 "Principle of Spectrophotometer and Its Applications| Chemistry| Byjus." byjus.com, Jan 20, 2017, https://byjus.com/chemistry/spectrophotometer-principle/. Accessed Jan 11, 2018.

Details

Seiten
45
Jahr
2019
ISBN (eBook)
9783668927414
ISBN (Buch)
9783668927421
Sprache
Englisch
Katalognummer
v456043
Note
A
Schlagworte
effectiveness bloodstains removal luminol sodium per borate sodium per carbonate hydrogen peroxide crime

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Titel: Effectiveness of oxidizing reagents in removal of blood stains