Bromophenol Blue as a Chemical Enhancement Technique for Latent Shoeprints

Technical Note Bromophenol Blue as a Chemical Enhancement Technique for Latent Shoeprints Katelyn McNeil 1 Wade Knaap 2 Abstract: The enhancement of...
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Technical Note

Bromophenol Blue as a Chemical Enhancement Technique for Latent Shoeprints

Katelyn McNeil 1 Wade Knaap 2 Abstract: The enhancement of two-dimensional shoe impressions, where the matrix is soil, may best be approached using chemistry. Potassium thiocyanate, which reacts with iron particles in soil, is a generally accepted development medium used by forensic investigators. Bromophenol blue, a pH indicator that reacts with carbonates in soil, is used, but with less frequency, particularly in North America. This study compared both chemistries and their ability to enhance two-dimensional shoe impressions deposited from a variety of soil samples on varying substrates. Bromophenol blue, although determined to be an inappropriate enhancement technique for brown paper samples, provided significantly more detailed enhancement than potassium thiocyanate with other tested substrates, including plastic and linoleum.

Introduction The documentation and preser vation of two-dimensional shoeprint impressions can be difficult. Impressions can be left in various substances (e.g., dust, blood, mud), which makes details difficult to detect. Before a shoeprint can be processed, it must be photographed, but often this photograph lacks suff icient contrast. Chemical enhancement techniques provide increased contrast between the shoeprint and the background, allowing photographs to document more detail. These enhancement techniques can be valuable, but there is little research available to assess their effectiveness. 1 2

University of Toronto Mississauga, Ontario, Canada Forensic Identification Services, Toronto Police Services, Ontario, Canada Received December 13, 2010; accepted April 12, 2011 Journal of Forensic Identification 62 (2), 2012 \ 143

Potassium thiocyanate was first introduced in the United States in 1994 [1]. Someha acknowledged Junichi Murao as the individual who developed the technique in 1957. This technique is regarded as the most effective chemical en hancement technique for dusty and muddy footwear impressions regardless of the substrate on which it is deposited [2]. Potassium thiocyanate, routinely used by the Ontario Provincial Police, reacts with metal ions in soil, particularly iron, to cause a bright red coloration, depending on ferric ion concentration in the soil [3]. Bromophenol blue, developed as a forensic identif ication technique in 1996, has been used with great success in Israel as a chemical enhancement technique [4]. Bromophenol blue is a pH indicator with a transition range of pH 3 to 4.6. In the acidic form, it appears yellow and in the basic form, it appears blue. The enhancement of bromophenol blue can be improved by applying steam [4]. Bromophenol blue reacts with carbonates in the soil [4] as well as with amino acids [3] and has been found to be more effective than other chemical enhancement techniques when calcium carbonate is a major component in the soil [5]. Other studies have used gel lifters to recover shoeprints and have then treated them with bromophenol blue. Because the white adhesive lifter provides better contrast between the background and developed impression, it is easier to apply vapor directly after if required, and this removes the issue of enhancement of the background as well [5]. The aim of the current study is to assess the usefulness of bromophenol blue on soils from several locations in Ontario, Canada. Also, the present study examines the enhancement abilities of bromophenol blue and compares them to potassium thiocyanate. It is hypothesized that bromophenol blue is an effective chemical enhancer for soil shoeprint deposit. The enhancement chemistries – bromophenol blue and potassium thiocyanate – were tested on various soil samples and substrates. Method Ten soil samples were collected f rom several locations throughout southern Ontario to allow for comparison: Ottawa, Mississauga, Brampton, Scarborough, Port Perry, Oak Ridges, and four areas in Toronto (Lakeshore at Sunnyside Park; St Clair Avenue West and Keele Street; Toronto Iron Works at Eastern Avenue and Caroline Avenue; and banks of the Don River). The soil samples were all placed in separate cardboard hand-gun boxes, air-dried, and broken into smaller dustlike particles. Journal of Forensic Identification 144 / 62 (2), 2012

The left shoe of a pair of size 8 women’s Sketcher shoes was used to make all shoe impressions. Individual characteristics were created by the researcher by cutting the outsole and by the insertion of a thumb tack. For comparison purposes, a control shoeprint (Figure 1) was created by dusting a greasy shoeprint impression with black magnetic fingerprint powder. The enhanced impression was then analyzed, with eight individualizing characteristics being noted. The control print was then copied onto an acetate overlay. For all test impressions, the same individual (wearer) deposited each impression with a similar stepping technique (i.e., rolling from heel to toe) and application force to provide replication consistency. Experimental impressions were made by stepping into a hand-gun box containing a sample soil collection. Excess soil was shaken off of the outsole prior to stepping on each substrate. All experimental impressions were deposited in the same fashion as to approximate a realistic walking pattern. All impressions were photographed before enhancement using lighting techniques to capture maximal detail. This was completed to ensure that there were no significant differences in detail in the latent shoeprint impressions. If experimental impressions were smudged or had an otherwise inappropriate level of detail, impressions were excluded from the study before treatment with enhancement chemistries.

Figure 1 Control shoeprint with the eight individual characteristics identified.

Journal of Forensic Identification 62 (2), 2012 \ 145

Impressions on brow n paper were photog raphed using overhead f luorescent lighting; impressions on plastic and on linoleum were photographed with oblique white light generated from a Luma-Lite (Payton Scientific Inc., Buffalo, NY). For brown paper and plastic substrate samples, six impressions were made, whereas only four impressions were made on linoleum. Half of the impressions were sprayed with bromophenol blue and the other half were sprayed with potassium thiocyanate. All enhanced prints were photographed. Prints enhanced with bromophenol blue were steamed for maximal contrast and then re-photographed. This technique added extra moisture to the soil so that the enhancement could occur. Both of the enhancement chemistries were prepared at the Toronto Police Forensic Identification unit. To make potassium thiocyanate, 15 g of potassium thiocyanate (Alphachem Ltd. Mississauga, Ontario) was added to 120 mL of acetone and 15 mL of water. In a separate beaker, 1 mL of concentrated sulfuric acid was added to 9 mL of water. Upon mixing the dilute acid and potassium thiocyanate mixture, a solute formed. Once the solute settled, an eye dropper was used to transfer the top layer to a spray bottle. For the purposes of this study, a fine mist was necessary to be produced. To generate this spray, the Kitchen Spritzer (Pampered Chef, Addision IL) was used (Figure 2). This spray bottle uses a hand pump to create pressure so that a fine mist can be generated. The bottle was pumped until there was resistance against the pumping (approximately three full pumps). A small amount of mist was released before being sprayed onto the experimental impressions. The bromophenol blue (Alphachem Ltd. Mississauga, Ontario) was prepared using as a solution of 1% (w/v) bromophenol blue in a solution of 5% water in methanol. For the analysis of the experimental prints, the acetate overlay was used to make pointwise comparisons on a four‑point scale: 0 to 3. A score of 0 was used to denote the absence of the individual characteristic or if the enhancement obscured the detail, and 1 was used to denote the presence of the individual characteristic but that it lacked identifying detail. Both 0 and 1 lacked sufficient detail to make an identification and were classed as nonconclusive. A score of 2 was used when the individual characteristic was present and defined, and a score of 3 was assigned when individual characteristics were present, well defined, and showed clear enhancement. Both a 2 and a 3 had sufficient detail for an identification to be made. A paired t-test was used to test the means of between nonconclusive and Journal of Forensic Identification 146 / 62 (2), 2012

Figure 2 Kitchen Spritzer.

identification between potassium thiocyanate and bromophenol blue. For the t-test, a score of 0 or 1 was given a score of 0, and a score of 2 or 3 was given a score of 1 for statistical purposes. Qualitative obser vations were also made about the level of enhancement. Because of the nature of the enhancement techniques, they may not have worked on all of the soil types. A classification of “enhanced” or “did not react” was made with each soil type for each enhancement method (potassium thiocyanate and bromophenol blue). A scale from -1 to 3 was used to assess the enhancement. A score of -1 was given if there was a deterioration of the print (e.g., the enhancement chemistry reacted with the substrate, obscuring the detail of the shoeprint impression). A score of 0 was given when the print was not enhanced (e.g., the shoeprint impression appeared the same before and after the enhancement chemistry was applied). A score of 1 was given for a somewhat enhanced shoeprint impression (e.g., the chemistry reacted with the soil but resulted in limited enhancement). A score of 2 was given when the shoeprint impression was enhanced (e.g., there was contrast between the background and the enhanced shoeprint impression). A score of 3 was given when the print was very much enhanced (e.g., there was very strong, clear, distinct enhancement of the shoeprint impression). Also, because of the nature of the substrates, a judgment about whether the enhancement technique was approJournal of Forensic Identification 62 (2), 2012 \ 147

priate also was made. For the bromophenol blue, the substrate was deemed to be acceptable if the background turned yellow and the soil turned blue, but if the background turned blue, then it was unsuitable. For potassium thiocyanate, if the soil turned a red to pink color and the background did not turn significantly red to pink, then it was considered to be appropriate for the substrate. Also, any particular characteristics or interactions between liquid and substrate were also noted. Results and Discussion Both bromophenol blue and potassium thiocyanate reacted with all of the soil samples from the Toronto areas. Bromophenol blue reacted with the brown paper substrate, causing the brown paper to turn blue, which obscured the footwear impression. It has been previously noted that a formulation of bromophenol blue that consists of too much water can cause the background to enhance [4]. Perhaps a different formulation of bromophenol blue would be effective in enhancing shoeprints on paper samples, though it is noted that white paper has previously been found to react [4]. Also, the steaming step of the enhancement of bromophenol blue may be unnecessary in humid climates because it introduces extra moisture, which may cause it to overreact. The soil samples in the present study lacked moisture and, as a result, adding extra moisture benefited the enhancement, but often the samples reacted before the steam was applied. Bromophenol blue used on the plastic and on the linoleum ranged from “somewhat enhanced” to “very much enhanced”, whereas when it was used on brown paper, there was a deterioration of detail. Potassium thiocyanate was effective at enhancing all substrates tested, but it tended to have a weaker contrast compared to bromophenol blue. Potassium thiocyanate ranged from a level of “unaltered” to a level of “ver y much enhanced” but often gave minimal enhancement. Table 1 lists the qualitative ratings of level of enhancement. Although qualitative analysis is subjective and different conclusions can be drawn even among experts [6], the trend of bromophenol blue having a stronger enhancement contrast is evident.

Journal of Forensic Identification 148 / 62 (2), 2012

Bromophenol Blue

Potassium Thiocyanate

Soil

Paper

Plastic

Linoleum

Paper

Plastic

Linoleum

St Clair and Keele

0.67

2.5

2

1.67

2

0.5

Don River

0.33

2.67

1.5

1.33

1.67

0.5

Toronto Iron Works

-1

1.33

1

1

1

1

Port Perry

-1

2

1.5

1.67

1

1

Scarborough

-1

1.67

2

1.33

1.33

1

Ottawa

-1

1.33

1

1.33

1.67

1

Lakeshore

-1

2

1

2

2

1

Mississauga

-1

1.67

1.5

2.33

1.67

1

Oak Ridges

-1

1.33

1.5

1.67

2

2.5

Brampton

-1

1

1

1.33

1

1

Average

-0.7

1.75

1.4

1.67

1.53

1.05

Table 1 Average qualitative ratings of level of enhancement.

From paired t-test analyses it was found that when all of the substrates were considered, the levels of enhancement of bromophenol blue and potassium thiocyanate were not significantly different [t(78) = 0.49, P < 0.622], but when the brown paper was excluded, bromophenol blue enhanced individual details significantly better than potassium thiocyanate [t(47) = 4.78, P < 0.001]. When analyzing specific substrates, potassium thiocyanate enhanced detail significantly better than bromophenol blue on brown paper [t(28) = 7.29, P < 0.001], but bromophenol blue had a significantly higher level of detailed enhancement than potassium thiocyanate on linoleum [t(19) = 3.09, P < 0.006] and plastic [t(26) = 4.27, P < 0.001]. Plastic gave the best level of detail for both bromophenol blue and potassium thiocyanate, whereas the enhancement of latent shoeprints on brown paper treated with bromophenol blue had the lowest level of enhancement. These results are depicted in Figure 3. Overall, bromophenol blue had more three-point enhancements, identifying level of detail, than the potassium thiocyanate. See Figure 4 and Figure 5 for examples of enhancement on the plastic substrate using the same soil sample with bromophenol blue and with potassium thiocyanate, respectively. An analysis of individual detail enhancement of each of the soils was also conducted. The level of enhancement of individual detail from the pointwise comparisons was not significantly different between soils from Mississauga, Lakeshore, Ottawa, Brampton, Don River, St Clair Avenue and Keele Street, and Toronto Iron Works even when the overenhanced paper samples treated with bromophenol blue were removed from the analyJournal of Forensic Identification 62 (2), 2012 \ 149

sis. Potassium thiocyanate had a significantly higher level of individual detail enhancement on the pointwise comparison than bromophenol blue [t(7) = 2.45, P < 0.05] for the Oak Ridges soil. When the overenhanced bromophenol blue on paper samples were removed from the analysis, bromophenol blue and potassium thiocyanate performed equally. The enhancement of soil from Scarborough was approximately equal when overenhanced bromophenol blue brown paper samples were included, but when they were removed from the analysis, then bromophenol blue gave a significantly better enhancement of detail than potassium thiocyanate [t(4) = 5.31, P < 0.006]. Port Perry soil was not found to have significantly different ratings of enhancement of individual detail until the overenhanced bromophenol blue on paper samples were removed from the analysis, and then bromophenol blue performed significantly better than potassium thiocyanate [t(4) = 8.55, P < 0.001]. See Table 2 for a list of means of enhancement rating for each soil sample. All Substrates

Plastic and Linoleum Only

Soil

Bromophenol Blue

Potassium Thiocyanate

Bromophenol Blue

Potassium Thiocyanate

St Clair and Keele

0.542

0.208

0.750

0.208

Don River

0.469

0.594

0.650

0.550

Toronto Iron Works

0.250

0.281

0.375

0.275

Port Perry

0.391

0.250

0.625*

0.225*

Scarborough

0.453

0.281

0.725*

0.275*

Ottawa

0.313

0.375

0.500

0.375

Lakeshore

0.297

0.500

0.475

0.500 0.350

Mississauga

0.359

0.422

0.525

Oak Ridges

0.359*

0.594*

0.575

0.700

Brampton

0.359

0.359

0.575

0.300

* Indicates significant difference

Table 2 Mean of individual detail enhancement of soil samples.

Though a variety of chemistries can be valuable tools when it comes to enhancing impressions left at crime scenes, they also have inherent limitations that have to be acknowledged so that they can be minimized. When administering the chemistry to the substrate in question, sufficiently fine mist is necessary to ensure that water droplets do not form. This is especially important on nonporous surfaces, such as plastic or linoleum, because if droplets form, the detail of the shoeprint is obscured. Also, caution has to be taken that too much of an enhancement chemistry is not sprayed onto the shoeprint impression because this can cause running, which can obscure detail in a print. Journal of Forensic Identification 150 / 62 (2), 2012

Figure 3 Comparison of enhancement between chemistries and substrates. (* Indicates significant difference.)

Figure 4 Bromophenol blue enhancement of soil from St Clair and Keele on plastic.

Figure 5 Potassium thiocyanate enhancement of soil from St Clair and Keele on plastic. Journal of Forensic Identification 62 (2), 2012 \ 151

Some limitations of the present study are that the formulation of the bromophenol blue reacted with the brown paper, which caused the background to enhance as well. A commercially made aerosol container of bromophenol blue (Bromphenol Mix, #36729, Evident, Inc., Union Hall, VA) is available and preliminary tests of it showed that it did not react with the brown paper substrate. The aerosol container would be ideal in that it emits a fine mist that does not cause water droplets to form. It is easily transportable and premixed, which makes it practical to use. One drawback of the commercial bromophenol blue spray is that it is costly. It costs approximately $90 CDN, whereas buying the bromophenol blue crystals and mixing it in the lab costs approximately the same but yields 25 times the amount. Bromophenol blue is easily prepared, whereas the potassium thiocyanate formulation is more complex, involving a separation step. A second limitation of the study is that the same shoe was used for each impression made. This allows the individual characteristics of the print to be consistent across all the samples, but it introduces the possibility of contamination of the soil types. The bottom of the shoe was cleaned thoroughly before a new soil sample was used in attempts to reduce contamination. Another limitation of the study is the limited number of substrates used. Although a textured linoleum, a nonporous plastic surface, and a porous surface (paper) were used, other common substrates should also be tested. Suggestions for future research include testing the effectiveness of bromophenol blue on a variety of substrates so that potential deleterious reactions between the chemistry and substrate are established. Also, although the soil samples were thought to be representative of Toronto and surrounding areas, other areas may have different soil compositions that may not react appropriately with the bromophenol blue. Even though a sample was used from Ottawa, it was only a single sample and may not be representative of that area. Conclusion Overall, bromophenol blue is an effective chemical enhancement technique for use on soils in the area tested. The current research suppor ts that of Glattstein et al. [4]. Bromophenol blue performs equally or better than potassium thiocyanate on enhancing individual details and gives a better level of contrast. The contrast given from bromophenol blue is clear because the background turns yellow and the latent shoeprint, the soil, turns Journal of Forensic Identification 152 / 62 (2), 2012

blue. One drawback of bromophenol blue is that it is not suitable for use on all substrates. For further information, please contact: Katelyn McNeil 88 Mapleburn Drive SE Calgary AB T2J1Y6 Canada [email protected]

References 1.

2. 3.

4. 5. 6.

Someha, S. Chemical Techniques for the Enhancement of Footwear and Tire Impressions in Japan. In Proceedings of the International Syposium on the Forensic Aspects of Footwear and Tire Impression Evidence. Federal Bureau of Investigation, Laboratory Division, U.S. Department of Justice, U.S. Government Printing Office: Washington D.C., 1994. Davis, R. J. A Systematic Approach to the Enhancement of Footwear Marks. Canadian Society of Forensic Science Journal 1988, 21, 98–105. Theeuwen, A. B.; van Barneveld, S.; Drok, J. W.; Keereweer, I.; Lesger, B.; Limborgh, J. C.; Naber, W. M.; Schrok, R.; Velders, T. Enhancement of Muddy Footwear Impressions. For. Sci. Int. 2001, 119 (1), 57–67. Glattstein, B.; Shor, Y.; Levin, N.; Zeichner, A. pH Indicators as Chemical Reagents for the Enhancement of Footwear Marks. J. For. Sci. 1996, 41 (1), 23–26. Shor, Y.; Vinokurov, A.; Glattstein, B. The Use of an Adhesive Lifter and pH Indicator for the Removal and Enhancement of Shoeprints in Dust. J. For. Sci. 1998, 43 (1),182–184. Majama, H.; Ytti, A. Survey of the Conclusions Drawn of Similar Footwear Cases in Various Crime Laboratories. For. Sci. Int. 1996, 82 (1), 109–120.

Journal of Forensic Identification 62 (2), 2012 \ 153

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