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ANALYSIS OF INORGANIC CATIONS IN LOW EXPLOSIVE RESIDUE
USING SOLID PHASE EXTRACTION AS A PRE-
CONCENTRATION TECHNIQUE
ANIZAH BINTI MAHMOD
UNIVERSITI TEKNOLOGI MALAYSIA
ANALYSIS OF INORGANIC CATIONS IN LOW EXPLOSIVE RESIDUE USING SOLID PHASE EXTRACTION AS A PRE-
CONCENTRATION TECHNIQUE
ANIZAH BINTI MAHMOD
A dissertation submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Science (Forensic Science)
Faculty of Science
Universiti Teknologi Malaysia
APRIL 2016
x
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Statistics of Explosive Cases in Malaysia 6
2.2 Reasons of the criminals to use explosives 7
4.1 Limit of detection and correlation coefficient of analytes 42
under study
4.2 Relative standard deviation for within-day and day-to-day for 43
each analyte
4.3 Pre-concentration factor for each analyte 50
4.4 Concentration of cations in pyrotechnic samples 53
xi
LIST OF FIGURES
FIGURE NO. TITLE PAGE 2.1 SPE operations 20
2.2 SPE adsorbent packing for ion-exchange 21
2.3 Schematic diagram of CE system 24
2.4 Basic IC components 26
3.1 Physical appearance of all explosive samples 35
3.2 Flow chart for experimental design 38
4.1 IC chromatogram for 1 mg/L standard cations 40
4.2 Calibration graph of the cations for 1 to 5 mg/L of
standard solution 41
4.3 Effect of flow rate on SPE recoveries of target cations using
Supelco MCAX, benzenesulphonic acid (H+) 500 mg cartridge 45
4.4 Effect of eluent type using Supelco MCAX, benzenesulphonic
acid (H+) 500 mg cartridge 46
4.5 Effect of the eluent volume using Supelco MCAX,
benzenesulphonic acid (H+) 500 mg cartridge 48
xii
4.6 IC chromatogram of blank SPE extract 51
4.7 Comparison of IC profiles of pre-blast samples for (a) MB,
(b) MK, (c) MS and (d) HB 52
4.8 IC chromatogram of target cations in (a) post-blast with
cotton swab method and (b) post-blast with cotton
swab followed by SPE method of MB sample 56
4.9 IC chromatogram of target cations in (a) post-blast with
cotton swab method and (b) post-blast with cotton
swab followed by SPE method of MK sample 57
4.10 IC chromatogram of target cations in (a) post-blast with
cotton swab method and (b) post-blast with cotton
swab followed by SPE method of MS sample 58
4.11 IC chromatogram of target cations in (a) post-blast with
cotton swab method and (b) post-blast with cotton
swab followed by SPE method of sample HB 59
xiii
LIST OF ABBREVIATIONS
CE – Capillary Electrophoresis
DDDW – Double Distilled Deionized Water
FTIR
– Fourier Transform Infrared
GC
– Gas Chromatography
HPLC
– High Performance Liquid Chromatography
IC – Ion Chromatography
IED
– Improvised Explosive Device
MCAX
– Mixed Cation Acidic Exchange
ND – Not detected
RSD – Relative Standard Deviation
RMP – Royal Malaysia Police
SPE – Solid Phase Extraction
SPME – Solid Phase Microextraction
xiv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Abstract for National Convention Forensic Science 2015 68
iv
ACKNOWLEDGEMENT
In completion of my dissertation, I wish to thank the supervisor, Dr Umi
Kalthom binti Ahmad for her support and guidance throughout the years. I would
like to thank my co-supervisor, DSP Satwant Singh A/L Karam Singh for his help
and support. I am truly indebted to both of you.
Special thanks to the lab staffs, Madam Mariam Hasan and Madam Linda for
their endless support and for all the opportunities and resources they has given me in
order for me to complete this dissertation. Thank you for everything, both of you
have taught me about IC and answering all of my questions.
Thanks to my sponsor, MyBrain15 under Ministry of Education for financial
aids. I appreciate my family that always give supports through my ups and downs.
Thanks to all my friends especially my classmates for your help, supports and joy
during my graduate studies.
v
ABSTRACT
Solid Phase Extraction (SPE) is a very powerful technique for clean-up and
pre-concentration of the sample. Even though there is no universal method for SPE,
there have been an increasing demand for a reliable and accurate forensic trace
analysis. Samples received by a forensic laboratory are often in small amounts and
there is a need to develop methods that are capable to detect lower concentration. The
objectives of this study were to develop, evaluate and compare an SPE procedure as a
pre-concentration step with conventional cotton swabbing method for analysis of ions
in explosive residue. Four samples of pyrotechnics were analysed in this study. The
samples were Mercun Bola (MB), Mercun Ketupat (MK), Happy Bomb (HB) and
Monster Bomb (MS). The results of this study showed that all six standard cations
(lithium, sodium, ammonium, potassium, magnesium and calcium) were successfully
separated within 45 minutes using Metrosep C4 column (250 x 4 mm i.d) with 5 µm
particle size. The eluent used were 0.7 mmol/L dipicolinic acid and 1.7 mmol/L nitric
acid with a flow rate of 1.0 mL/min and pressure of 9.5 MPa. The calibration graph
gave a good linearity with r2 ≥ 0.992. The detection limits were 0.32 µg/L to 1.32 µg/L
and quantitation limits in the range of 1.26 µg/L to 4.4 µg/L. The SPE method was
optimized using several parameters before the method was applied to post-blast
residues. The SPE cartridge used was Supelco MCAX with 500 mg sorbent bed packed
with sulfonilic functional group. The SPE parameters that have been chosen were
sample flow rate, type of eluents and volume of eluent. The results indicated that SPE
procedure gave good pre-concentration of the analytes of interest with the pre-
concentration factor in the range of 7 to 74.
vi
ABSTRAK
Pengestrakan fasa pepejal (SPE) adalah suatu teknik pembersihan dan
prapemekatan yang baik. Walaupun tiada kaedah yang universal untuk SPE, keperluan
untuk menghasilkan keputusan analisis forensik yang baik dan tepat sentiasa
diperlukan. Sampel yang diterima oleh makmal forensik kebiasaannya adalah pada
kepekatan yang rendah dan adanya keperluan untuk membina kaedah yang dapat
mengenalpasti kepekatan sisa bahan letupan pada kepekatan yang rendah. Objektif
kajian ini adalah untuk membentuk, menilai dan membuat perbandingan antara SPE
sebagai kaedah prapemekatan terhadap kaedah konvensional sapuan kapas bagi
analisis sisa bahan letupan. Empat sampel piroteknik dianalisis di dalam kajian ini iaitu
Mercun Bola (MB), Mercun Ketupat (MK), Happy Bomb (HB) dan Monster Bomb
(MS). Hasil kajian ini mendapati kesemua enam piawai kation (litium, natrium,
amonium, kalium, magnesium dan kalsium) berjaya dipisahkan dalam masa 45 minit
menggunakan turus Metrosep C4 (250 x 4 mm i.d) dengan saiz zarah 5 µm. Eluen yang
digunakan adalah 0.7 mmol/L asid dipikolinik dan 1.7 mmol/L asid nitrik dengan
kadar aliran 1.0 mL/min dan tekanan 9.5 MPa. Graf penentukuran menunjukkan garis
lurus yang bagus dengan r2 ≥ 0.992. Had pengesanan adalah 0.32 µg/L hingga 1.32
µg/L dan had kuantitasi adalah antara 1.26 µg/L hingga 4.4 µg/L. Kaedah SPE
dioptimumkan dengan beberapa parameter terlebih dahulu sebelum diaplikasikan
kepada residu bahan letupan. Kartrij SPE menggunakan Supelco MCAX dengan 500
mg penjerapan dan kumpulan berfungsi asid sulfonilik. Parameter yang dipilih adalah
kadar aliran sampel, jenis eluen dan isipadu eluen. Keputusan menunjukkan prosedur
SPE memberikan analisis yng bagus dengan faktor prapemekatan antara 7 hingga 74.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xiii
LIST OF APPENDICES xiv
1 INTRODUCTION 1
1.1 Background of Study 1
1.2 Problem Statement 2
1.3 Research Objectives 3
1.4 Scope of Study 3
1.5 Significant of Study 3
2 LITERATURE REVIEW 5
2.1 Preamble 5
2.2 Explosives 6
viii
2.2.1 Classification of Explosive 7
2.2.2 Types of Explosive 8
2.2.2.1 High Explosive 9
2.2.2.2 Low Explosive 10
2.2.2.3 Pyrotechnics 11
2.3 Forensic Sampling of Explosive Residue 14
2.4 Sample Preparation of Explosive Residue 15
2.4.1 SPME 15
2.4.2 Solid Phase Extraction 16
2.4.2.1 Basic Principle of Solid Phase
Extraction 19
2.4.2.2 Types of Solid Phase Extraction 19
2.4.2.3 Off-line vs On-line SPE 21
2.5 Analytical Techniques for Inorganic Analytes 22
2.5.1 Capillary Electrophoresis 22
2.5.2 Ion Chromatography 24
2.5.2.1 Basic Principle of IC 27
2.5.2.2 Suppressor and Non-Suppressor
Ion Chromatography 28
2.5.2.3 Single Column and Double
Column 30
2.6 Trace Detection Challenges 31
3 EXPERIMENTAL 33
3.1 Introduction 33
3.2 Apparatus 33
3.3 Chemicals and Materials 33
3.4 Sample Preparation 34
3.4.1 Explosive Sampling 34
3.4.2 Unexploded Explosive Sample 35
3.4.3 Cotton Swab Method 35
3.4.4 Solid Phase Extraction 36
3.5 Optimization of Experimental Parameters 36
ix
3.5.1 Effect of Type of Eluent 36
3.5.2 Effect of Eluent Volume 37
3.5.3 Effect of Flow Rate 37
3.6 Preparation of Eluent 37
3.7 Preparation of Standard 37
3.8 Instrumentation 37
3.9 Flow Chart of Research Design 38
4 RESULTS AND DISCUSSION 39
4.1 Introduction 39
4.2 IC Separation of Cations 39
4.3 Calibration Graph and Detection Limits 41
4.4 Method Validation 43
4.5 Optimization of SPE 44
4.5.1 Effect of Sample Loading Flow Rate 44
4.5.2 Effect of Eluent Type 46
4.5.3 Effect of Eluent Volume 47
4.6 Determination of Cation from Spiked Cotton Ball 49
4.7 Identification of Inorganic Cations in Explosives
Sample 50
4.7.1 Analysis of Pre-blast Pyrotechnic Samples 51
4.7.2 Analysis of Post-blast Residue 54
4.7.3 Comparison of Post-Blast Extracts with and
without SPE Preconcentration 59
5 CONCLUSION 61
5.1 Conclusion 61
5.2 Suggestion for Future Work 63
REFERENCES 64
Appendix A 68
CHAPTER 1
INTRODUCTION
1.1 Background of Study
Identification of ions in post-blast residues at crime scenes generally helps the
investigator to know the type and source of explosives used by the criminals. There
are two types of explosives, which are high and low explosives. Low explosives are
usually modified by using improvised explosive device (IED) to give explosion of high
impact.
There are several techniques of ion determination in ion chromatography (IC);
ion-exchange chromatography, ion-exclusion chromatography, and ion-pair
chromatography. A number of selected cations and anions can be determined by using
ion-exchange chromatography with high sensitivity. For explosives, determining the
type of ions is very valuable in forensic science since it can help the crime scene
investigator to detect the source of the explosives
Cotton swabbing is the most universal method commonly used for sample
extraction in explosives analysis. There are two types of cotton swabbing, which are
dry and wet swab. Water is a good extraction solvent for inorganic substances. There
has been much research that focuses on different kind of solvents for extraction of
organic and inorganic substances rather than finding another method for pre-
concentration of samples. Normally after cotton swabbing, the sample is analysed
directly by using ion chromatography. Detection of explosives types becomes more
2
challenging with the advent of more IEDs by the criminals. This makes the quest for
the details of the crime more difficult. Hence, more research is needed to solve this
problem.
In most cases, sample preparation steps take up most of the required analysis
time, contributing substantially to the analysis costs (Weiss, 1995). Manipulation of
the sample can falsify the analytical result. Therefore, sample preparation can directly
affect the quality of the results. Pre-concentration of samples by using solid phase
extraction (SPE) has been proven to help in the development of better methods for
analysis of explosives due to its selectivity and sensitivity.
1.2 Problem Statement
The conventional cotton swabbing has several weaknesses in samples
preparation. Sometimes, the amount of samples, such as the real field samples, is not
enough for analysis purpose. Therefore, forensic laboratory needs to develop methods
with low limit of detection (LOD). They are needed to improve detection method for
explosives to get the most accurate results. Currently, there is a lack of analytical
method for inorganic analytes since most research focuses more towards the organic
substances.
Cotton swabbing is still a commonly used method for extraction of inorganic
explosives. However, this method does not clean up the sample and causes the sample
to be not pure. The interferences and unknown peaks may appear in the chromatogram
during analysis, making the data interpretation and peaks identification to become
harder. Hence, a new method that can clean up and remove interferences may be useful
to solve this problem.
3
1.3 Research Objectives
The objectives of this study are:
i. To develop an SPE procedure as a pre-concentration step for analysis of
cations in explosive residues.
ii. To evaluate the SPE procedure by comparison with the current cotton swab
method.
iii. To apply the developed SPE procedure for post-blast pyrotechnic residues.
1.4 Scope of Study
This study focused on the inorganic components of hand-made low explosives.
Li+, Na+, NH4+, K+, Ca2+, and Mg2+ were detected by using IC. The accuracy of SPE
was tested and compared with the conventional method of cotton swab extraction
protocols.
1.5 Significance of Study
Identification of explosives becomes crucial due to the need of the investigators
to determine its source every time the crimes occur. There are several high and low
explosives that are usually used by the criminals. The SPE method provides fast and
reliable result in determination of various samples including forensic sample. It is
necessary to develop a sample preparation method that enables determination of the
targeted ions at lower concentration level.
This study can be used by Royal Malaysia Police (RMP) to improve the accuracy
of explosive types detection. This is useful for the RMP in tracking the criminal by
getting the accurate data regarding the explosives. Furthermore, profiling and database
are really crucial for RMP due to the increasing number of criminal cases using low
4
explosives in this country. Further method development is always needed in order to
keep up with the advanced technology and well-educated criminals.
64
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