CHAPTER 7
A QUALITATIVE AND QUANTITATIVE ANALYSIS OF ARSENIC SULPHIDE
IN POTASSIUM CHLORATE BASED CRUDE BOMB RESIDUE SAMPLES OF
CASE STUDIES USING EDXRF, SEM EDX AND ICP AES INSTRUMENTAL
METHODS
Introduction:
Blasting has become a common phenomenon in the increasing era of terrorist
activities, when it happens it is creating panic and fear among the public. In such
activities a variety of explosives are used. An explosive is a chemical which stores in
itself large amount of potential energy which when released suddenly either knowingly or
unknowingly causes explosion by which it releases heat, light, pressure and sound. In
such explosions locally made gun powder, flash powder and pyrotechnic compositions or
ammonium nitrate containing explosives are used. Explosive debris or fragments
collected from the spot are sent by the investigating agency to forensic laboratory are
subjected to analysis for their compositions and nature. This will in turn help the
investigating agency to trace back to find the culprits. High explosives explode only
when connected to a detonator whereas low explosives explode by subjecting them to
friction or flame under confinement. Explosives also find their use for killing wildboar
and other animals to prevent crop damage from them [V.Vasudeva Rao et al, 2015].
Farmers have to adopt many measures to control such wild animals. One such way of
control is to keep low explosive or a pyrotechnic composition which gets exploded with
bite by the wild boar in the vicinity of crops.
A mixture of arsenic sulphide and
potassium chlorate will ignite even with a small friction [John A.Conkling and Chris
Mocella, 2011] and expolode with an impact [Bernard Martel, 2004].
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63 parts of
potassium chlorate and 37 parts of arsenic sulphide is also termed as red explosive and
should be mixed when they are wet as they are very sensitive pyrotechnic mixture
[K.L.Kosanke et al., 2012]. There are reports to say that pressed mixture of potassium
chlorate with arsenic sulphide ignites even at room temperature [John A Conkling] and
an arsenic sulphide is more than 30% weight of chlorate device explodes on impact if the
mixture is in fine powder form [Bernard Martel, 2004]. Arsenic sulphide (As 2S3) was
found to be one of the chemicals present in low explosive combinations [D.K.Kuila et al.,
2006]. Being cheap and easily available, inorganic salts may favor for its use in
homemade or crude explosives [Cameron Johns et al., 2008].
Low pyrotechnic residues analysis was evaluated by characteristic particles
produced during explosion using SEM EDS [Susan A Phillips, 2001].
Ion
chromatographic analysis of low explosives was carried out to know the anions in post
blast samples [Umi Kalthom Ahmad et al., 2001]. About 1000 post blast low explosive
residues containing arsenic sulphide were analysed and identified using SEM EDX
analyzer and Ion Chromatograph [D.K.Kuila et al., 2006] in such residues other ions like
chloride, chlorate, nitrite, nitrate, aluminium are frequently found in those debris [CJ.
Johns et al., 2008 and Susan A. Phillips, 2001, UK Ahmad et al., 2011]. Other than
explosive context, a vast number of literatures are available on arsenic sulphide which are
about environmental and health concern and its presence in drinking water, soil and food
[Michael F. Hughes et al., 2011] it may be from mining and industrial process producing
affect symptoms nausea, pain in abdominal pain, vomiting and severe diarrhea [RN
Ratnaike, 2003] in addition to affecting skin and lung [Victor D. Martinex et al., 2011].
Among the methods available in literature for arsenic estimation include EDX RF [M.Ali
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and S.Tarafdar, 2004] using spectrophotometric method [M.Pandurangappa and
K.S.Kumar, 2012], Atomic Absorption Spectrometeric method [Ahmad Shraim et al.,
2008], surface plasmon resonance technique [Y. Choi et al, 2014], ICP AES method
[I.I.Evdokimov et al., 2015], ion chromatographic methods [Adrian A. Ammann, 2011,
Nicole S. Keller et al., 2014] but there appears no method for its estimations with
explosive mixtures. It is therefore in the present study an attempt is made spectroscopic
methods that provide elemental profiles helping in identifying the elements and their
quantities in them for the identification and estimation of arsenic ion in presence of other
ions and expecting method to be an important helping aid to decide the kind of low
explosive used by analyzing the post explosion debris.
Brief history of the cases:
Case 1: A dog was found dead with its mouth and head portion blasted and when it was
keenly observed, yellow colour stains were noticed on the teeth. Swabs, said to have
been collected from the teeth were referred to the lab for analysis.
Case 2: In a crowded market place, a low explosive got blasted when a person stamp on
an object similar to cow dung. The shoes gets fragmented, the person who stamped on
the object got injured and admitted to the hospital. Another person also stamped on a
similar such object and person got injured because of the blast of the object. The
fragmented shoes, socks, remnants samples of exploded object, soil were received in the
laboratory for their analysis.
Case 3: Fifty four numbers of crude bombs were claimed to be used to target wildboars
were seized by the local police while transportation. Each of them was about a lemon
size, thread tied, round shaped objects with about 25 grams of orange yellow colour
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powder along with small stones wrapped with cloth and paper. They were carefully
opened and separated and sent to forensic laboratory for further analysis.
Case 4: A case was reported where in the roof of a house made of asbestos blasted
producing huge sound. Fragmented pieces of asbestos, collapsed wall and burnt garments
were observed when visited the spot. Yellow colour stains were noticed on the floor and
also on some parts of the wall. A child and her father were admitted to a hospital for
treatment of their burn injuries. Pieces of asbestos sheets, cement and stone pieces, some
clothes with yellow stains were forwarded to the laboratory for analysis.
Objectives:
Attempts made to develop suitable methods for easy identification of kind of
explosives with or without processing from post blast debris.
Spectroscopic identification and semi-quantification based on EDX RF profiles
by taking intensity ratios of two elements namely arsenic of arsenic sulfide and potassium
of potassium chlorate.
Identification of arsenic used crude bombs and quantification of arsenic present in
the post blast debris with help of yellow colour stains as a marker for sample collection.
Experimental:
Materials and Methods:
Inductively Coupled Plasma Atomic Emission Spectrometer, model JY 2000 (Jobin
Yvon Horiba, France), provided with ICP JY v 5.1 software, Energy Dispersive X-Ray
Fluorescence spectrometer (Oxford, UK), provided with ExperEase software, Scanning
Electron Microscope-Energy Dispersive X-Ray spectroscope (Tescan, UK) with Team
software, Arsenic trisulphide from Sigma Aldrich, TraceCertArsenic solution (1000
130
mg/L, Sigma Aldrich) and all other reagents used were of analytical grade and water used
was distilled water.
Preparation of stock solution of arsenic (III) sulphide, 1000 µg ml-1:
An accurately weighed amount of 1.6403 g of arsenic trisulphide (MW=246.04 g
mol-1) was dissolved in hot concentrated nitric acid, diluted to 1000 ml with distilled
water. Diluted 1 ml of this solution to 100 ml with water to obtain 100 µg ml -1 arsenic
solution.
Preparation of synthetic mixture of arsenic sulphide with potassium chlorate:
Synthetic mixtures of arsenic sulphide and potassium chlorate were prepared in the
ratios, 1:0.5, 1:1, 1:2, 1:3, 1:4 and 0.5 g of each sample was mixed with 5 g of soil
samples and 1 g of this soil was subjected to EDX RF spectroscopic studies.
Preparation of samples of cases and spiked soil samples:
For EDX RF spectroscopic analysis: 1 g of soil sample collected from respective
explosion sites were placed inside the cups meant for the analysis, Swabs in cotton were
collected and analyzed similarly.
For SEM EDX Analyzer studies: Particles adhering to the blasted items, sieved from the
soil and other debris recovered from blast sites were directly mounted on the conducting
tape and subjected to SEM EDX analysis.
For ICP AES studies: 1 g of the soil sample or 0.2 g of yellow colour particles adhering
to the debris were extracted with 5 ml of 1M sodium hydroxide, thrice, neutralized with
nitric acid, diluted to 100 ml and subjected to ICP AES studies. To check the proposed
extraction procedure, 5 g of soil samples were spiked with different volumes of 100 µg
131
ml-1 arsenic sulphide solution, and mixed well. The parameters followed for ICP AES
estimations was given below [Gerd H. Brunner, 2004].
Inductively Coupled Plasma Atomic Emission Spectrometer parameters:
Power
Plasma gas flow rate
Sheath gas flow rate
Sheath gas stability time
Nebulization flow rate
Nebulization pressure
Sample uptake
Rinsing time
Rinsing pump speed
Transfer time
Stabilization time
Transfer pump speed
Auxilary flowrate
Wavelength
1000W
10 (PL1) L/min
0.1(G-1) L/min
3.0 s
0.02 ml/min
45 psi
1 ml/min
5.0 s
High
10.0 s
0.5 s
1 ml/min
0 l/min
193.695 nm
Results and Discussion:
The articles referred to FSL were contained blood stained swabs pertaining to
Case 1 wherein the mouth portion of the dog was blasted, Fig. 1. After collection of the
sample, the investigating agency forwards the sample to forensic lab and was keen to
know the kind of chemical in it. Even though, arsenic sulphide containing crude bomb
compositions could be identified with smell, the blood present in the sample masks the
typical smell or colour that could be used as a parameter to decide the use of arsenic
sulphide. After looking at the photographs, as in Fig. 2, yellow colour stains were
noticed on the teeth portion of the dog. Initially arsenic was tested by Gutzeit method as
explained using mercuric bromide paper [Jyotsna Cherukuri and Y. Anjaneyulu, 2005].
Other ions present along with arsenic sulphide were also analysed without separation
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using the chemical tests as detailed in Table 1 and the reagents added to perform the spot
tests [Alexander Beveridge, 2011, G.Svehla, 2009 ] are detailed in Table 2.
Table 1: Preliminary (spot) tests conducted to check the presence of possible ions to
know the type of explosive in the four cases
Major Ions/element found with chemical tests
Case 1
K+, S2-, Fe2+, ClO3-, S, As3+, SO42-, Cl-
Case 2
Case 3
Ca2+,K+, S2-, Fe2+, ClO3-, S, As3+, SO42-,
Cl-, NO3K+, S2-,ClO3-, S, As3+, Fe2+
Case 4
K+, S2-, Fe2+, ClO3-, S, As3+, SO42-, Cl-
Table 2: Name of the tests performed to check the presence of the ions / element present
in the case studies
Ions / element
Name of the reagent used performed
Potassium
Calcium
Arsenic
Chlorate
Sulphate
Chloride
Sulphide
Nitrate
Nitrite
Sulphur
Sodium cobaltinitrite
Ammonium carbonate
Mercuric bromide paper (Gutzeit test for arsine gas)
Aniline sulphate + Conc. sulphuric aicd
Barium chloride
Silver nitrate
Lead acetate
Ferrous sulphate + Conc. sulphuric aicd
Alpha naphthylamine+Sulphanilic acid
Pyridine + Sodium hydroxide (with ether extract)
The fragmented shoes, socks, remnants of exploded object, soil collected in Case
2 and swabs and debris collected in Case 4 were also subjected to chemical tests as
shown in Table 1.
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Fig. 1: Photo of a dog, whose mouth portion was blasted as a consequence of crude bomb
explosion
Fig. 2: Close-up view of the dog’s blasted mouth with yellow colour stains on the teeth,
134
Fig. 3 shows the crude bomb which were not blasted and recovered as such by the
investigating agency and Fig. 4 shows the materials found inside the crude bomb after
carefully opening it. Orange yellow colour powder, some stones, cloth pieces have been
used to make a crude bomb and lot of thin threads were used to wound them.
Fig. 3: Country made crude bomb before opening, photo obtained in Case 3
Fig. 4: Thread pieces, stones and chemical found in the crude bomb of case 3 indicating
the use of arsenic sulphide
135
Fig. 5 and 6 are the photographs of collapsed house wall after the explosion showing
fragmented asbestos and yellow colour stains.
Fig. 5: Scattered household items in an explosion with collapsed wall and asbestos roof,
photo of case 4
Fig. 6: Photo at the wall edge showing noticeable yellow stains indicating the probable
use of sulphur or arsenic sulphide in case 4
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Analysis using EDXRF Spectrometer:
Using ExpertEase software, the spectra were acquired for all the samples. Control
samples of soil collected away from the explosion site and swabs used to collect the post
blast residues were subjected to analysis in the similar way and same were presented in
Fig. 7 and 8, with trace quantities of copper, iron, sulphur and calcium. Since the
transition of electrons produces unique peaks which do not interfere, profiles obtained for
case samples will represent on the composition of explosive only. Table 3 shows the
binding energies of the detected elements of importance.
Line due to sulphur and
chlorine was not considered to take the ratio in synthetic mixture since line due to sulphur
may appear because of transitions of either elemental sulphur or sulphide present in
arsenic sulphide.
Similarly, peak of chlorine might have originated by chlorate or
chlorine ions cannot be distinguished. The ratios of intensities of Kα line for arsenic to
potassium chlorate were tabulated for synthetic mixture. The intensity ratios obtained for
case samples were compared with the synthetic mixture to get an idea of composition of
arsenic sulphide and potassium chlorate as indicated in Table 4. The ratios of peaks in
the profiles corresponding to arsenic and potassium are found to be indicate a
composition of arsenic to potassium chlorate in the debris as 1:3. The profiles of case
samples obtained from EDX RF spectrometer analysis are shown in Fig.9 to 13.
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Fig. 7: Control swab used to collect the specimens
Fig. 8: Control soil sample near the blast site
138
Fig. 9: Soil sample collected from the explosion spot of Case 2
Fig. 10: Particles collected from the stone of Case 4 not showing presence of any arsenic
139
Table 3: K-shell emission lines for the detected elements with EDXRF Spectrometer
Element
Electron binding energies in
keV
Kα line
Kβ line
Arsenic
10.54
11.72
Potassium
3.31
3.59
Sulphur
2.30
2.46
Chlorine
2.62
2.82
Table 4: Semiquantitative analysis and ratios of intensities of synthetic mixture and case
samples
Intensity of
Intensity of
Ratio of
Type of sample
Kα line for
Kα line for
intensities of
arsenic,
potassium,
arsenic to
a
b
Wt%
Wt%
potassium
1g As + 0.5 g K
37.56
4.84
7.76
1g As + 1 g K
35.44
6.11
5.80
Synthetic
1g As + 2 g K
34.34
8.54
4.02
mixture
1g As + 3 g K
36.22
10.55
3.43
1g As + 4 g K
32.88
15.77
2.08
1g As + 5 g K
32.14
28.76
1.11
Case 1
Swab of dog’s teeth 1
22.34
7.76
2.87
Swab of dog’s teeth 1
9.22
3.03
3.04
Case 2
Soil collected as blast site
12.76
3.91
3.26
Fragmented shoes 1
43.61
13.80
3.16
Fragmented shoes 2
24.81
8.37
2.94
Case 3
Powder sample recovered
41.34
12.84
3.22
Case 4
Wall swab
14.54
4.76
3.05
Particles adhering to
16.88
stone
Particles adhering to
18.42
6.40
2.88
asbestos pieces
a and b – mean value of three determinations of arsenic and potassium respectively
140
Fig. 11: Swab No. 1 of the dog’s teeth encountered in Case 1
Fig. 12: Swab from the collapsed wall of Case 4
141
Fig. 13: Explosive powder found inside the ball type objects recovered in Case 3
SEM EDX Analyzer studies:
Fig. 14 to 17 are the profiles obtained from SEM EDX Analyzer for sulphur,
potassium chlorate and arsenic sulphide respectively. Similar to EDX RF spectrometer, in
SEM EDX Analyzer also produces characteristic peaks of X-rays are obtained from the
samples. The microscopic image from SEM showing characteristics spheroidal particles
those could be used for identifying pyrotechnic residues collected from the explosions
occurred under metal confinements [S.A.Philips, 2001].
142
Fig. 14: SEM image of focused particle of arsenic sulphide (top) and EDX profile for the
same (bottom)
143
Fig. 15: SEM image of focused potassium chlorate particle of Case 2 (top) and EDX
profile for the same (bottom)
144
Fig. 16: SEM image of focused sulphur particle (top) and EDX profile for the same
showing sulphur (bottom)
145
Fig. 17: SEM image of focused chemical sample of Case 3 (top) and EDX profile for the
same showing arsenic, potassium, sulphur and chlorine (bottom)
ICP AES analysis:
Extraction of arsenic sulphide from samples referred to forensic labs is the most
important step before subjecting them to the actual analysis. It was suggested in the
literature that the solubility of arsenic sulphide increases with increasing pH [Zheng Yi et
146
al., 2009]. Arsenic sulphide dissolves in alkali hydroxides with the formation of water
soluble AsS33- ions [G.Svehla, 2009]. Known quantity of arsenic sulphide was added to 1
g of soil samples as shown in Table 5. Extractions were done using 0.1M sodium
hydroxide solution to separate it from soil. The solution extract was acidified so as to
produce a residual mass of arsenic(III) sulphide. It was filtered and to the residue left on
the filter paper was treated with hot conc. nitric acid to dissolve the arsenic(III) sulphide.
It was transferred to 100 ml volumetric flask and diluted to volume with water. It was
done in acid medium since alkalis are known to clog the automizer. It is therefore, the
recovery experiments were performed in acidic medium for arsenate ion with ICP AES
instrument under optimized conditions [Gerd H. Brunner, 2004] and determined with
calibration graph as given in Fig. 18. The recovery experiment results are indicated in
Table 5. Samples of soil and related were from the above cases were subjected to
extraction and later performed experiments with ICP AES and the results obtained are
given in Table 6.
Table 5: Recovery studies with ICP AES instrument for arsenic from spiked soil samples
and other samples of case studies.
Sample Spiked level
Amount
Amount
% Recovery
a
Amount of As expected (mg)
Recovered (mg)
added to soil
2 mg/ 10 g
2
1.77 (1.22)
88.5
Soil
5 mg/ 10 g
5
4.38 (0.88)
87.6
10 mg/ 10 g
10
9.24 (1.35)
92.4
a - values are average of three determinations with RSD % in parenthesis
147
Fig. 18: Spectrum obtained for Arsenic with ICP AES showing maximum absorbance at
193.695 nm (top) and calibration graph obtained for the concentration range 2-10 ppm
TraceCert ICP standard arsenic solution.
148
Table 6: Quantification of arsenic in case samples
Type of sample
Quantity of arsenic
founda
%
13.86 (0.34)
Case 1
Swab of dog’s teeth
Case 2
Shoes with yellow stains
22.41(0.26)
Case 2
Soil extract
7.32(0.45)
Case 2
Shoe without yellow stains
0.96(0.71)
Case 3
Chemical found inside the crude bomb
37.64(0.49)
Case 4
Swab of the collapsed wall
7.77(1.21)
Case 4
Swab of the stone with yellow stain
12.33(0.84)
Case 4
Swab of the stone without yellow stain
0.63(0.81)
a - values are average of three determinations with RSD % in parenthesis
Conclusion:
There are many chemicals which are considered to be safe like magnesium and
aluminium powders. They do produce same effects, therefore, arsenic sulphide could be
used by such metal powders in pyrotechnics. Also, arsenic sulphide in the form of
realgar or orpiment when undergoes explosion will produce arsenic oxide which is an
environmental hazard. Considering the toxic nature of arsenic sulphide it is desirable to
avoid it in the making of explosives. The frequently asked question by the investigating
agency in case of explosion or any crime is the nature of the chemical, which can be
easily answered by confirming its presence with explosive residues by the EDX RF, SEM
EDX and ICP AES spectroscopic techniques that are successfully used in this work.
The semiquantitative analysis of post explosive residue samples were carried out
with EDX RF spectroscopy and the results obtained in the form of profiles are revealing
149
that arsenic sulphide to potassium as chlorate are present in them in the ratio 1:3
respectively.
It is based on the ratio of peak intensities of the emitted x-rays
corresponding to arsenic of arsenic sulphide and potassium of potassium chlorate present
in various compositions of their synthetic mixtures. And these peaks ratios are the basis
for ascertaining the composition of arsenic of arsenic sulphide and potassium of
potassium chlorate present in post blast residues of cases samples. The SEM EDX
Analyser helps in obtaining the profiles of residue samples indicating composition of
elements present in them and also provides information about particle structures present
in the residues. Structure based analysis is an aspect that is not followed here. The ICP
AES analyses have provided the results that could reveal the successful use of extraction
procedure adopted for extracting arsenic sulphide. Yellow/orange stain on the destroyed
part of the animal or on object is due to high concentration of arsenic in the post residual
debris. Therefore, orange/yellow colour stain can be conveniently considered as an
indicator of arsenic containing explosive produced debris collected from the spot of
explosion. The spot with yellow stains when collected it will be better for arsenic results
and this observation is expected to guide in sample collection for obtaining assertive
arsenic content from the debris.
150
Summary:
Identification of type of chemicals used in explosive as obtained from post blast
residues is of prime importance for a forensic scientist. It is in this context EDXRF, SEM
EDX and ICP AES methods are adopted for identifying chemicals present in such post
explosive residues. In EDXRF spectroscopy, identification of elements based on their
binding energy values and also library marking from the instrument software were
providing the basis of sample analysis. Here, these methods are specifically used in
establishing the ratio of two selected peaks originating from arsenic and potassium
present in their synthetic mixtures of various composition of these two chemicals from
which they are prepared. Ratio of peak intensities corresponding to arsenic from arsenic
sulphide and potassium from potassium chlorate are basis for establishing the
composition of arsenic sulphide and potassium chlorate present in the case study samples
collected from post explosive debris of the respective cases 1 - 4. The results of arsenic
from arsenic sulphide and potassium from potassium chlorate as determined semiquantitatively from post blast residue samples compared with the standard synthetic
mixtures and are accounting for 1:3 ratio of arsenic sulphide and potassium chlorate.
SEM EDX analysis was carried out to confirm the use of arsenic present in the post blast
residues obviously accounting for their use in the making of explosives. Procedure
adopted for extraction of arsenic from soil of residues initially with sodium hydroxide
followed by hot, concentrated nitric acid is satisfactory as revealed by recovery results.
ICP AES results are also revealing that yellow/orange colour stains on the materials
recovered from the blast sites could serve as a marker to collect the evidence materials
for analysis in forensic labs.
151
References:
[1] V. Vasudeva Rao, B. Naresh, V. Ravinder Reddy, C. Sudhakar, P. Venkateswarlu and
D. Rama Rao. International Journal of Modern Research and Development, 2015, Vol. 2,
No. 2, pp 32-36.
[2] John A. Conkling and Chris Mocella, Chemistry of Pyrotechnics: Basic Principles and
Theory, 2nd Ed., CRC Press, USA, 2011.
[3] Bernard Martel, Chemical Risk Analysis: A Practical Handbook, Kogan Page
Science, UK, 2004.
[4] K.S.Kosanke, Barry T. Sturman, Robert M. Winokur and B.J.Kosanke, Encyclopedic
Dictionary of Pyrotechnics, Pyrolabs Inc., USA, 2012.
[5] D.K.Kuila, A. Chakrabortty, S.P.Sharma, S.C.Lahiri, Forensic Science International,
2006, Vol. 159, No. 2-3, pp 127-131.
[6] Cameron Johns, Robert A. Shellie, Oscar G.Potter, John W.O’Reilly, Joseph P.
Huchinson, Rosanne M. Guijt, Michael C. Breadmore, Emily F. Hilder, Greg W.Dicinosk
and Paul R. Haddad, Journal of Chromatography A, 2008, Vol. 1182, pp 205-214.
[7] Susan A. Phillips, Problems of Forensic Sciences, 2001, Vol. 46, pp 301-316.
[8] Umi Kalthom Ahmad, Ong Shin Tze, Muhammad Fauzi Ghazali, Yew Chong Hooi
and Mohd Koey Abdullah, Malaysian Journal of Analytical Sciences, 2001, Vol. 15, No.
2, pp 213-226
[9] Michael F. Hughes, Barbara D. Beck, Yu Chen, Ari S. Lewis and David J. Thomas,
Toxicological Sciences, 2011, Vol. 123, No. 2, pp 305-332.
[10] R N Ratnaike, Postgraduaate Medical Journal, 2003, Vol. 79, pp 391-396.
152
[11] Victor D. Martinez, Emily A. Vucic, Daiana D. Becker-Santos, Kionel Gil and Wan
L. Lam, Journal of Toxicology, 2011, Article ID 431287.
[12] M.Ali, and S.Tarafdar, Journal of Radioanalytical and Nuclear Chemistry, 2003,
Vol. 256, No. 2, pp 297-305.
[13] M. Pandurangappa and K.S. Kumar, American Journal of Analytical Chemistry,
2012, Vol. 3, No. 1, pp 455-461.
[14] Ahmad Shraim, Imad A.Abu-Yousef, Sifian M. Kanan, Naser Abdo, Henry
Olszowy, Stephan Petry and Jack NG, Journal of International Environmental
Application and Science, 2008, Vol. 3, No. 4, pp 215-223.
[15] Y. Choi, H. Kwak and S. Hong, 2014, Analytical Methods, Vol 6, pp 7054-7061.
[16] I.I.Evdokimov, V.G.Pimenov and D.A.Fadeeva, Analytics and Control, 2015, Vol
19, No. 1, pp 13-20.
[17] Adrian A. Ammann, American Journal of Analytical Chemistry, 2011, Vol. 2, pp
27-45.
[18] Gerd H Brunner, Supercritical Fluids as Solvents and Reaction Media, 1 st Ed.,
Elsevier B.V., Netherlands, 2004.
[19] Nicole S. Keller, Andri Stefensson and Bergur Sigfusson, Talanta, 2014, Vol. 128,
pp 466-472.
[20] Jyotsna Cherukuri and Y.Anjaneyulu, International Journal of Environmental
Research and Public Health, 2005, Vol. 2, No.2, pp 322-327.
[21] Alexander Beveridge, Forensic Investigation of Explosions, 2 nd Ed., CRC Press,
USA, 2011.
153
[22] G.Svehla,Vogel’s Qualitatative Inorganic Analysis, 7 th Ed., Pearson Education Ltd.,
India, 2009.
[23] Zheng Yi, Xu Yuan and Wang Hui, Journal of Environmental and Health, 2009,
Vol. 26, No. 12, pp 1064-1066.
154