U.S. Department of Justice 

Office of Justice Programs 

National Institute of Justice 0 

National Institute of Justice 

SMOKELESS POWDER RESIDUE ANALYSIS BY 

CAPILLARY ELECTROPHORESIS 

NIJ Report 600-91 

¢D 

t~ 

gl. 

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AND TESTING PROGRAM 

The Law Enforcement and Corrections Standards and Testing Program is sponsored by the Office of Science and 

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U.S. Department of Justice 

Office of Justice Programs 

National Institute of Justice 

Smokeless Powder Residue Analysis by Capillary Electrophoresis 

NIJ Report 600-91 

David M. Northrop, M.S.ES., Ph.D. 

Washington State Patrol 

Crime Laboratory 

Kennewick, WA 99337 

and 

William A. MacCrehan, Ph.D 

Chemical Science & Technology Laboratory 

Analytical Chemistry Division 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-0001 

February 1997 
National Institute of Justice 

Jeremy Travis 

Director 

The technical effort to develop this report was conducted 

under NIST Award 60NANB-9D0926 and 

NIJ Interagency Agreement LEAA-J=IAA-021-3, 

Project No. 9001. 

This report was prepared with the assistance of the 

Office of Law Enforcement Standards (OLES) 

of the National Institute of Standards and Technology (NIST) 

under the direction of Kathleen M. Higgins, Director of OLES. 

This work was sponsored by the National Institute of Justice, 

David G. Boyd, Director, Office of Science and Technology. 
FOREWORD 

The Office of Law Enforcement Standards (OLES) of the National Institute of Standards and Technology (formerly 

the National Bureau of Standards) furnishes technical support to the National Institute of Justice program to strengthen 

law enforcement and criminal justice in the United States. OLES's function is to conduct research that will assist law 

enforcement and criminal justice agencies in the selection and procurement of quality equipment. 

OLES is: (1) Subjecting existing equipment to laboratory testing and evaluation, and (2) conducting research 

leading to the development of several series of documents, including national standards, user guides, and technical 

reports. 

This document covers research conducted by OLES under the sponsorship of the National Institute of Justice. 

Additional reports as well as other documents are being issued under the OLES program in the areas of protective 

clothing and equipment, communications systems, emergency equipment, investigative aids, security systems, vehicles, 

weapons, and analytical techniques and standard reference materials used by the forensic community. 

Technical comments and suggestions concerning this report are invited from all interested parties. They may be 

addressed to the Office of Law Enforcement Standards, National Institute of Standards and Technology, Gaithersburg, 

MD 20899. 

David G. Boyd, Director 

Office of Science and Technology 

National Institute of Justice 

°.. 

lU 

CONTENTS 

FOREWORD ................................................................................................ 

1. PURPOSE .............................................................................................. 

2. SCOPE ................................................................................................. 

3. DEFINITIONS .......................................................................................... 

4. TEST EQUIPMENT AND ANALYTICAL PROCEDURES ........................................... 

4.1 RESIDUE COLLECTION AND PREPARATION ................................................ 

4.2 RESIDUE GENERATION ....................................................................... 

4.3 RESIDUE PERSISTENCE AND COMPONENT AGING ........................................ 

4.4 CAPILLARY ELECTROPHORESIS EQUIPMENT .............................................. 

4.5 CHROMATOGRAPHY DATA STATION ......................................................... 

4.6 MECE OPERATING CONDITIONS .............................................................. 

5. DISCUSSION .......................................................................................... 

5.1 RESIDUE COLLECTION AND SAMPLE PREPARATION ...................................... 

5.2 MINIMUM DETECTION LIMITS ............................................................... 

5.3 INTERFERENCES AND FALSE POSITIVES ................................................... 

5.4 GUNPOWDER IDENTWICATION .............................................................. 

5.5 PERSISTENCE OF RESIDUES AFTER FIRING ............................................... 

5.6 ENVIRONMENTAL EXPOSURE AND RESIDUE DECOMPOSITION ........................ 

5.7 FREQUENCY OF RESIDUE DEPOSITION ..................................................... 

5.8 MECE ANALYSIS VERSUS SEM/EDX ANALYSIS ............................................ 

5.9 CASEWORK RESULTS ......................................................................... 

6. CONCLUSION ........................................................................................ 

7. REFERENCES ........................................................................................ 

Page 

111 

1 

1 

1 

5 

5 

6 

6 

6 

8 

9 

9 

9 

9 

10 

10 

10 

14 

14 

14 

15 

15 

15 

FIGURES 

Figure 1. 

Figure 2. 

Figure 3. 

Figure 4. 

Schematic of MECE Separation ................................................................ 

MECE Analysis of Gunpowder Constituent Standards .......................................... 

Schematic of Capillary Electrophoresis System ................................................. 

Diode Array UV Spectra of Dinitrotoluene Isomers ............................................. 

3 

4 

7 

8 
LIST OF ACRONYMS USED IN THIS REPORT 

CE 

DBP 

DEP 

DNT 

DPA 

EC 

MC 

MECE 

NC 

nDPA 

NG 

NGU 

N-nDPA 

SDS 

SEM 

SEM/EDX 

OLES 

NIST 

capillary electrophoresis 

dibutylphthalate 

diethylphthalate 

dinitrotoluene 

diphenylamine 

ethyl centralite 

methyl centralite 

micellar electrokinetic capillary electrophoresis 

nitrocellulose 

nitrodiphenylamine 

nitroglycerin 

nitroguanindine 

N-nitrosodiphenylamine 

sodium dodecylsulfate 

scanning electron microscopy 

scanning electron microscopy/energy dispersive X-ray analysis 

Office of Law Enforcement Standards 

National Institute of Standards and Technology 

vi 
COMMONLY USED SYMBOLS AND ABBREVIATIONS 

A 

ac 

AM 

cd 

cm 

CP 

c/s 

d 

dB 

dc 

°C 

OF 

diam 

emf 

eq 

F 

fc 

fig. 

FM 

ft 

ft/s 

g 

g 

gr 

ampere 

alternating current 

amplitude modulation 

candela 

centimeter 

chemically pure 

cycle per second 

day 

decibel 

direct current 

degree Celsius 

degree Fahrenheit 

diameter 

electromotive force 

equation 

farad 

footcandle 

figure 

frequency modulation 

foot 

foot per second 

acceleration 

gram 

grain 

H henry 

h hour 

hf high frequency 

Hz hertz (c/s) 

i.d. inside diameter 

in inch 

ir infrared 

J joule 

L lambert 

L liter 

lb pound 

lbf pound-force 

lbf-in pound-force inch 

lm lumen 

In logarithm (natural) 

log logarithm (common) 

M molar 

m meter 

min minute 

mm millimeter 

mph mile per hour 

m/s meter per second 

N newton 

N.m newton meter 

area=unit 2 (e.g., ft 2, in 2, 

nnl 

No. 

o.d. 

f~ 

p. 

Pa 

pe 

PP. 

ppm 

qt 

tad 

ff 

rh 

s 

SD 

see. 

SWR 

uhf 

uv 

V 

vhf 

W 

k 

wt 

etc.); volume,=unit 3 (e.g., ft a, m 3, etc.) 

nanometer 

number 

outside diameter 

ohm 

page 

pascal 

probable error 

pages 

part per million 

quart 

radian 

radio frequency 

relative humidity 

second 

standard deviation 

section 

standing wave radio 

ultrahigh frequency 

ultraviolet 

volt 

very high frequency 

watt 

wavelength 

weight 

d 

c 

m 

p, 

n 

P 

deci (10 -I) 

centi ( 10 -2) 

milli (10 -3) 

micro ( 10 -6) 

nano ( 10 -9) 

pico (10 -'2) 

PREFIXES 

da deka (10) 

h hecto (102) 

k kilo (103) 

M mega (1 (f) 

G giga (109) 

T tera (10 '2) 

COMMON CONVERSIONS 

(See ASTM E380) 

ft/s x0.3048000=m/s 

ftx0.3048=m 

ft.lbfX 1.355818=J 

gr × 0.06479891 =g 

in×2.54=cm 

kWh × 3 600 00(~J 

lb×0.4535924=kg 

Ibf×4.448222=N 

Ibf/ft × 14.59390=N/m 

lbf.inX0.1129848=N.m 

lbf/in2x 6894.757=Pa 

mph x 1.609344=km/h 

qt×0.9463529=L 

Temperature: (T*F-32)X5/9=T*c 

Temperature: (TocX9/5)+32=Tv 

vii 

NIJ Report 600-91 

SMOKELESS POWDER RESIDUE ANALYSIS BY 

CAPILLARY ELECTROPHORESIS 

David M. Northrop 

Washington State Patrol, Crime Laboratory, Kennewick, WA 99337 

and 

William A. MacCrehan 

Chemical Science and Technology Laboratory, Analytical Chemistry Division, 

National Institute of Standards and Technology, Gaithersburg, MD 20899-000/ 

A procedure is presented that can be used for the analysis of residues generated by the combustion of ammunition and explosives 

prepared with smokeless gunpowder. The bases of the test are the qualitative and quantitative identification of characteristic organic 

components present in the post-combustion residues. The residues are collected by adhesive film lift and/or alcohol swabbing of hands, 

clothing, spent shell casings, and explosive debris, and analyzed using mieellar electrokinetic capillary electrophoresis (MECE). The 

MECE technique provides identification of organic additives in the smokeless powder. The procedure described here may provide positive 

identification of the use of materials containing smokeless powder. 

Key words: explosive residue; gunshot residue; micellar electrokinetic capillary electrophoresis; organic constituents; plasticizers; 

primers; propellants; stabilizers. 

1. PURPOSE 

The purpose is to provide evidence in crimes involving the use of firearms and improvised explosive devices (such 

as pipe bombs), based on the analysis of residues from fired smokeless powder collected from the hands of shooters, 

clothing, spent shell casings, or explosive remains. 

2. SCOPE 

The test is based on the compositional analysis of gunshot and explosive residues left on surfaces that (1) provide 

limited interferences from complex matrices such as soil, blood, sweat, etc., and (2) are easily sampled using adhesive 

film lifts or by swabbing with solvent. Quantitative compositional data on more than 100 commercially available 

smokeless powders provides the framework for a data base for matching purposes. The possible occurrence of 

characteristic smokeless powder components that could result in false positive tests has been extensively evaluated. 

Samples were collected from 100 people in the general population to identify interfering components for the MECE 

analysis. Results obtained by the MECE method are compared to the results obtained by scanning electron microscopy/ 

energy Dispersive X-ray analysis (SEM/EDX). Finally, this procedure is used to evaluate forensic casework samples for 

the presence and composition of gunpowder residues. MECE analysis of residues left on the hands of a suspect may 

provide a link to a shooting. The composition of these residues may also provide a link to a weapon. 

3. DEFINITIONS 

3.1 Adhesive Film Lift 

An adhesive film lift is a method used for the collection of gunshot residues from surfaces, such as skin, and 

clothing. This method uses an adhesive tape to collect the residue. Residues are recovered from the tape by physical 

removal of visible particles with tweezers, or solvent extraction for microscopic residues. 
3.2 Capacity Factor 

An indexing term that allows normalization for random variations in migration times for a given component in 

multiple MECE analyses. The capacity factor, k, is defined by the following equation: 

k - tr-- to 

t0(1 -- t,/tm) 

where tr is the migration time of a solute, to is the migration time for ethanol, which migrates with the electroosmotic 

flow, and tm is the migration time for dibutylphthalate (DBP-a compound that moves with the micellar agent). 

3.3 Capillary Electrophoresis 

Capillary electrophoresis (CE) is an analytical technique in which chemical compounds are separated based on 

their relative movement through a conductive liquid (buffer) in a small diameter capillary tube under the influence of a 

high voltage electric field. Compounds separate as a result of differences in size and positive or negative charge. 

3.4 Characteristic Residue Components 

These are smokeless powder additives that are good markers for the MECE identification of gunshot residues. 

These compounds are typically present in amounts greater than 0.1 percent in the unfired powder, can be detected by 

optical absorbance, and occur in many types of ammunition powders. These may include, but are not limited to, 

nitroglycerin, dinitrotoluene isomers, diphenylamine, and ethyl centralite. Although alkyl phthalate esters are present in 

most smokeless powders, they are also present in many plastic and adhesz've materials. Therefore the phthlate esters are 

not suitable for consideration as characteristic components of gunshot residue. 

3.5 Electroosmotic Flow 

Electroosmotic flow is the bulk flow of buffer towards the detector end of the capillary, caused by electrostatic 

interactions of the buffer with the charged walls of the capillary under the influence of the high voltage field. 

3.6 Explosive Residue 

Explosive residue is defined as the traces of material that remain on fragments of an explosive device and/or are 

deposited on other objects as a result of the detonation of such a device. The sources of these materials are the propellants, stabilizers, and plasticizers used in the explosive device as well as the compounds formed from the decomposition 

of these materials as a result of detonation. 

3.7 False Positive Results 

A false positive result is the erroneous identification of characteristic residue components in a sample that by 

definition should not contain any of these components. 

3.8 Gunshot Residue 

Gunshot residue is defined as the traces of material that remain after the use of a firearm using smokeless gunpowder ammunition. The major sources of these materials are the primer, propellant and associated stabilizers, and plasticizers that are used in ammunition, as well as any decomposition products of these materials formed during detonation. 

3.9 Micellar Electrokinetic Capillary Electrophoresis 

Micellar electrokinetic capillary electrophoresis (MECE) is a CE method in which electrically neutral compounds, 

not possessing a positive or negative charge, may be separated based on differences in their interaction with a charged 

micellar agent (such as sodium dodecylsulfate--SDS) added to the buffer. See figure 1. 
f 

Micellar Electrokinetic Separation 

//~-GSR -I- ~ ~c~ 

I ,~ ~ ,.".'--" 

/ Hydrophilic(~°~,(~ ~?~ ~'oo~ 

! Phase eo 

1 °o° 

,.... 

0 

:#e 

0 ¢ 0 

~~clric Field 5 to 30 kV ~:. - • ® 

J 

Figure 1. Schematic of MECE Separation. 
3.10 Migration Time 

Migration time (tin) is the unique time required for the electrophoretic movement of a single organic component to 

travel from the beginning of the capillary to the detector. Using current MECE instruments, small variations in the 

migration time for a given component occur from test to test as a result of system instability. Computing capacity factors 

and normalizing to an internal standard substantially eliminates these variations. See figure 2. 

E3 

<: 

E 

50 

40 

30 

20 

10 

0 

0 

Gunpowder Constituent Standards 

I I I 

1 - Nitroglycerin 

2 - 2,4-Dinitrotoluene 

3 - 2,6-Dinitrotoluene 

4 - 3,4-Dinitrotoluene 

5 - 3,3-Dinitrotoluene 

6 - 2-Naphthol 

7 - Diethylphthalate 

8 - Diphenylamine 

9 - N-nitrosodiphenylamine 

10 - Methlycentralite 

11 - 2-nitrodiphenylamine 

12 - 4-nitrodiphenylamine 

13 - Ethylcentralite 

14 - Dibutylphthalate 

I I I I I 

8 

10 14 

13 

ntema II 

ii ii 

, JUL 

tot tm 

I I I I I I I 

2 3 4 5 6 r 7 8 9 

MINUTES 

10 

Figure 2. MECE Analysis of Gunpowder Constituent Standards. 

3.11 Plasticizers in Smokeless Powders 

Plasticizers are organic materials added during manufacture of propellant and explosive mixtures to aid in their 

fabrication. These materials may include, but are not limited to, short chain aliphatic phthalic acid esters, of which 

dibutylphthalate is the most common. 

3.12 Primers 

Primers are devices used to initiate the propellant in ammunition, and may consist of a single component or a 

mixture of various inorganic and organic materials. Primer ingredients may include, but are not limited to, lead azide, 

lead styphnate, tetracene, diazodinitrophenol, barium nitrate, strontium nitrate, and antimony sulfide. 

3.13 Propellant Components of Smokeless Powder 

Smokeless powder propellants are organic materials that undergo rapid combustion when initiated with a primer. 

In smokeless gunpowder, the bulk material is nitrocellulose (NC). Propellant materials found in double-and triple-base 

smokeless gunpowders may also include, but are not limited to, nitroglycerin (NG), nitroguanidine (NGU) (rare in small 

arms propellants), and the isomers of dinitrotoluene (DNT). 

4 
3.14 Residue Extract 

The residue extract is prepared by taking either an adhesive film lift or collection swab and extracting with an 

organic solvent to remove the residue. 

3.15 Scanning Electron Microscopy/Energy Dispersive X-Ray (SEM/EDX) Analysis 

SEM is an analytical technique that uses an electron beam to examine microscopic particles. In the SEM/EDX 

technique, an x-ray detector provides additional information of the chemical composition of selected particles. This 

technique has been used to identify gunshot residues based on the selective detection of primer compounds containing 

lead, and/or barium, and/or antimony. 

3.16 Stabilizers 

Stabilizers are organic materials that are added to propellants and explosives to retard their decomposition during 

storage. These materials may include, but are not limited to, diphenylamine (DPA) and ethyl centralite (EC). Both 

decomposition and combustion of the propellants results in the formation of nitrated stabilizer derivatives such as 

N-nitrosodiphenylamine (N-nDPA), 2-nitrodiphenylamine (2-nDPA), and 4-nitrodiphenylamine (4-nDPA). 

4. TEST EQUIPMENT AND ANALYTICAL PROCEDURES 

4.1 Residue Collection and Preparation 

The MECE test relies on preparing a liquid extract of the fine particles that remain following the use of ammunition and explosives. Both adhesive film lift and swabbing methods can be used for residue collection. Gloves and 

tweezers rinsed with alcohol are used to handle all materials. 

4.1.1 Adhesive Lift Method 

The adhesive material used for sample collection should be a masking-type tape with an adhesive that does not 

dissolve in alcohol. The tape should be precleaned using methanol in an ultrasonic bath to eliminate any alcohol-soluble 

material on the tape. Samples are collected by using a 2.5 cm X 2.5 cm section of masking tape held by tweezers and 

pressed onto the surface to be examined. This method can be adapted for analysis by both SEM/EDX and MECE by 

using a double-sided masking type adhesive tape placed on an aluminum SEM/EDX sample stub. Samples are then 

collected by holding the aluminum stub while pressing the adhesive onto the surface to be examined. 

Samples from the hands of a suspected shooter should be collected using a separate adhesive lift for both back and 

palm of each hand. Samples from clothing should be collected using a separate adhesive film lift pressed onto the 

clothing near any bullet hole or area suspected of being exposed to gunshot residue. All samples are placed in capped 

vials and refrigerated until analyzed. 

A blank sample also should be collected as a part of the crime scene protocol. A blank sample tests both the sample 

collection and preparation systems for interferences or contamination. To collect a blank sample, an adhesive film lift 

should be collected from the skin of a suspected shooter in an area that could not be exposed to gunshot residue, e.g., a 

foot, leg, back, etc. From clothing samples, the blank should be collected from an area of the clothing that could not have 

been exposed to any gunshot residue. The blank sample should then be tested in the same manner as evidence samples. 

The following protocols are used for MECE analysis: 

Sample Preparation for Residue Samples 

Place a 2 mm × 2 mm section of adhesive lift in 50 p,L of methanol, 

Agitate in an ultrasonic bath for 15 min, 

Add 5 p,L of ethylene glycol to prevent complete evaporation, 

Evaporate methanol under a stream of dry nitrogen, 

Reconstitute residue in 50 t~L of MECE buffer. 
Sample Preparation for Unfired Powder 

Place 0.050 g of powder in 5.00 mL of methanol, 

Agitate in an ultrasonic bath for 15 min, 

Add 5 IxL of the methanol extract to 50 I~L of MECE buffer. 

4.1.2 Swab Residue Collection Method 

Cotton used for swabbing is precleaned in an ultrasonic bath with high purity ethyl alcohol. Alcohol-cleaned 

cotton, moistened with ethanol and held with tweezers, is used for swab collection of residues from the surface to be 

sampled. 

Samples are collected from shell casings or debris from improvised explosive devices by swabbing each surface of 

interest with a separate swab. The swabs are placed in capped glass vials and refrigerated prior to analysis. 

As with the adhesive lift method, a blank sample also should be collected for the swab method. A swab should be 

made of a surface that could not have been contaminated with gunshot residue. 

Samples for MECE analysis are prepared as follows: 

Place swab in 500 IxL of ethanol, 

Agitate in an ultrasonic bath for 15 min, 

Add 5 I~L of ethylene glycol to prevent complete evaporation, 

Centrifuge sample through a 1 I~m fluoropolymer filter, 

Evaporate ethanol under a stream of dry nitrogen, 

Reconstitute residue in 50 I~L of MECE buffer. 

4.2 Residue Generation 

Controlled firing range studies were used to generate test residue samples for method validation. Eight handguns, 

varying from 22 to 45 caliber, with both revolver and semiautomatic mechanisms, were used to generate residues. The 

hands of the individual firing the weapons are thoroughly washed with soap and water and dried with paper towels 

before firing. A blank sample is then collected to verify that the hands are free of any residues prior to firing the 

weapon. This procedure is repeated before each test. Gunshot residues for this test are generated by firing three rounds 

of commercial ammunition from the test weapon. Examination of gunpowder composition before and after firing is 

achieved by analysis of unfired powder and the residues generated by firing a single round of commercial ammunition 

with the same powder through a 15 cm × 15 cm section of sterile 100 percent nylon cloth placed over a white paper 

target from a distance of about 20 cm (muzzle-to-target distance). These tests are repeated with each weapon and 

ammunition studied. 

4.3 Residue Persistence and Component Aging 

In casework, it is important to establish how long residues from a particular weapon will persist on the hands or 

clothing of a shooter after deposition. This persistence may be studied by firing ammunition from the weapon and 

collecting residues at hourly intervals. In this study, adhesive film lift samples were collected at hourly intervals from 0 h 

to 6 h from hands used to fire'three rounds from a semiautomatic handgun. Individuals were involved in normal 

activities during the time period of this study. 

In order to simulate the effect of environmental exposure on gunpowder components, bulk gunpowder was placed 

in glass test tubes, positioned outside in direct sunlight, and sampled every hour for 28 h. 

4.4 Capillary Electrophoresis Equipment 

Commercially available apparatus for capillary electrophoresis, providing controlled voltage to 30 kV and using 

on-column ultraviolet absorbance detection, is required. A schematic of a typical capillary electrophoresis system is 

shown in figure 3. The capability to select the exact detection wavelength is required. Wavelength programming or 

simultaneous multiwavelength detection is advantageous, permitting measurement of component spectra to enhance the 

certainty of component identification. Table 1 lists information on the wavelength maxima for the gunpowder component standards studied. An example of the diode array display for four gunpowder components is shown in figure 4. 

6 
f 

Capillary Electrophoresis 

Instrumentation 

25 - 1 O0 pm~ 

\ 

\ : 

\\ 

[ 

I 350 pm 

Capillary Length 

20-100 cm 

High Voltage Power 

.......... ....... 

J Optical J~ Absorbance JJ 

Detection ll 

_I_ 

Destination 

Electrolyte 

II 

Chromatography 

Data System 

J 

Figure 3. Schematic of Capillary Electrophoresis System. 
TABLE 1. Information values of wavelength maxima of residue components 

Sample Wavelength maxima in nm i Sample Wavelength maxima in run i 

DBP 200, 235 DEP 200, 235 

DPA 200, 285, 235 2-nDPA < 190, 275, >450 

4-nDPA < 190, 410, 260 2,3-DNT 210, 265 

2,4-DNT 260, 200 2,6-DNT <200, 240 

3,4-DNT <190, 220, 270 EC < 190, 250 

MC < 190, 250 N-nDPA < 190, 230, 300 

NG < 190 NGU 270, 220 

t Maxima estimated to the nearest 5 nm on an uncalibrated spectrometer, first value is largest maximum, with 

succeeding values in descending order of intensity. 

2.6-DNT 

FIGURE 4. Diode array UV spectra of dinitratoluene isomers. 

4.5 Chromatography Data Station 

A chromatography data system, capable of precise measurement of peak retention time, peak height and peak area 

is required. The capability to edit graphically the peak measurements and to overlay multiple sample runs is desirable. 
4.6 MECE Operating Conditions 

The operating conditions used for the MECE analysis are as follows: 

SDS buffer: 10 mmol/L sodium tetraborate decahydrate (adjusted to pH 8.50 with boric acid), 25 mmolFL 

sodium dodecylsulfate (SDS), 

Sample preparation buffer: SDS buffer with 1 × 10 -4 mol/L 2-naphthol as an internal standard, 

Sample injection: samples are injected using pressure injection at 300 Pa (30 mbar) for 1.5 s, 

Separation column: 75 I~m diameter capillary of 82 cm length with an extended path length optical cell, 

Separation voltage: analyses are conducted at 30 kV, 

Detection mode: diode array ultraviolet absorbance monitored at 200 nm. 

Typical results for a mixture of standards at 10 -4 mol/L are shown in figure 2. 

5. DISCUSSION 

In this work, the MECE method for use in forensic gunshot residue and explosive cases has been validated by 

collecting the following information: 1) a reliable and reproducible residue collection and sample preparation protocol 

has been developed; 2) the minimum detection limits of the characteristic smokeless powder components using the 

MECE apparatus have been determined; 3) the occurrence of false positive results in the general population was studied 

and was determined to be unlikely; 4) a database of the composition of more than 100 commercially available smokeless 

powders has been generated; 5) the persistence of characteristic residue components on sample surfaces and the loss of 

residues from the shooter's hands over time has been investigated; 6) changes in characteristic residue component 

composition resulting from environmental exposure have been determined; 7) multiple firings of two weapons were 

performed to determine if residues would be deposited each time a given weapon was fired; 8) MECE analysis of firing 

range samples was compared to those obtained using SEM; and, 9) casework samples were examined using both the 

MECE method and SEM/EDX. 

5.1 Residue Collection and Sample Preparation 

Adhesive film lifts, as evidenced by this study, provide a reliable method for sample collection of gunshot residues 

from the hands of individuals who have fired a weapon and from clothing. The adhesive used for the film lift must be 

evaluated for method interferences by extraction using the residue protocol and analysis by MECE before being used for 

collection. Adhesives that do not dissolve in methanol must be used. Various commercially available solvent resistant 

masking tapes (both single-and double-sided tapes) are most likely to meet these requirements. The double-sided tape 

may be used on a SEM/EDX sample holding aluminum stub so that gunshot residue samples can be collected for both 

MECE and SEM/EDX. This is the collection method of choice. 

Alcohol swab collection can be used to recover residues from spent cartridges and bomb fragments. However, it 

was found that recovery of characteristic residue components from cotton swabs is less than 50 percent using solvent 

extraction. Swabbing is not suitable for residue collection from the hands since the alcohol recovers large quantities of 

fats and oils from the skin that can interfere with quantitative residue recovery and analysis. 

Ultrasonic agitation of residues in methanol for 15 min was found to be sufficient to completely extract the 

characteristic residue components from gunpowder. This was determined by performing a second extract on all commercial gunpowders examined. Negligible quantities of the components were detected in the second extract. An evaluation of solvents found that methanol was more efficient than ethanol as a residue extraction agent. The addition of 

ethylene glycol, when used at a volume fraction of 5 percent, was found to pre~cent losses of the residue constituents 

during the evaporative concentration of the extract, and did not alter the quantitative analysis by MECE. 

5.2 Minimum Detection Limits 

The minimum detection limits for gunshot residue constituents using four commercially available CE instruments 

were found to be in the picogram mass range using the MECE method. Detection limits were approximately 1 pg to 2 pg 

for the components with aromatic functionalities and 4 pg for nitroglycerin. Future improvements in detection technology may improve the sensitivity of the test. 
5.3 Interferences and False Positives 

Using the outlined protocols and MECE analysis, no false positive tests for the characteristic residue components 

were found on the adhesive film lifts from the hands of I00 volunteers representing a wide variety of occupational 

backgrounds. The individuals sampled included law enforcement officers, mechanics, teachers, construction workers, 

farmers, chemists, secretaries, and many other professions. The sample group included men, women, right-handed, 

left-handed, employed, and unemployed individuals, as well as people with visibly clean hands and dirty hands. No 

peaks were identified with capacity factors that match any of the characteristic residue components. 

All blank samples collected during this study were also found to be negative for the characteristic residue components. Hand washing with soap and water was determined to effectively remove all MECE-detectable residue components. 

These results indicate that the identification of the characteristic residue components by MECE can only occur if 

an individual has been exposed to a recently fired weapon. False positive results because of occupational duties or 

environmental exposure were not found to occur. 

5.4 Gunpowder Identification 

In order to provide evidence to identify a gunpowder or its residues, including the type Of propellant, manufacturer, and lot, it is necessary to identify and quantitate the characteristic components of both the residues and the unfired 

powder. In determining a match between a residue sample and unfired powder, it is also necessary to take into account 

any chemical compositional changes that may result from the firing of the gunpowder. 

Information values on the approximate composition of 106 commercially available cartridges and reloading powders as determined by MECE are provided in Table 2. These results are provided as a first step in identifying the source 

of an unknown residue or powder sample so that subsequent tests can provide final identification. 

5.4.1 Factors to Be Considered in Matching of Smokeless Powders 

There are several factors that need to be considered in the identification of a smokeless powder or residue sample 

based on matching known and unknown materials. In a matching Study of the residue composition of 17 smokeless 

powders before and after firing, clear matches were not always obtained. The matching criteria consisted of a qualitative 

test and a quantitative test. Both tests had to be satisfied for a match to be obtained. The qualitative test identified the 

characteristic residue components in the residue and compared them to the components in the unfired gunpowder. The 

quantitative test compared the measured value of each component in the residue to the measured value of those components in the unfired powder. For this exercise, a match was considered to be achieved if the relative amount of a 

component in the residue was within one standard deviation of the measured value of that component in the unfired 

powder. In this test, residues obtained from 5 of the 17 powders met this match criteria, while 12 of the powders did not. 

In addition, multiple sub-samples from the same residue gave significantly different quantitative results. Therefore, there 

may be a number of factors that need to be considered in interpreting the results. 

Some of the factors that should be considered in comparing pre- and post-firing composition are: 1) nonuniformity 

in the manufactured composition of the unfired powder; 2) nonuniformity in the individual residue particles collected; 

3) nonuniformity resulting from changes in composition from burning or partial burning of the gunpowder, 4) nonuniformity from changes in composition that may result from environmental exposure; and, 5) nonuniformity resulting 

from the use of different ammunition in the same weapon. 

The relative contribution of each of these 5 factors to the interpretation of matches between known and unknown 

materials has yet to be determined. 

5.5 Persistence of Residues After Firing 

The persistence of post-firing residues on shooters' hands was studied to evaluate the effect of normal activity on 

the MECE test results. The residues from a weapon discharged at a firing range were studied to examine residue 

persistence. Samples were collected immediately after the weapon was fired (time zero), and test samples were taken to 

correspond to hourly collections up to 6 h. One hour after firing, no residues were found on any of the subjects. 

Subsequent samples at 2 h to 6 h also were found to be negative for gunshot residues. Initial residues (at time zero) were 

at low concentrations, thus it is possible that weapons that deposit higher concentrations of residues may result in longer 

residue persistence. As discussed previously, all residues can be deliberately removed from the hands by washing with 

soap and water. 

10 
Table 2. Information Values of Gunpowder Composition 

AMMUNITION 

ISmm 

3-D Inv. Inc. 

CCI Blazer 

Eldorado Starfire 

Federal 

Federal Am. Eagle 

Federal JHP 

Federal Parabellum 

Makarov (9X18) 

Norinco 

Norma No. 19026 

Remington 

Remington Kleanbore 

S&W 

S & W Nyclad 

Sellier & Bellot 

Sellier & Bellot 

Speer "Lawman" 

Speer Blount 

SuperVel 

Winchester 

LOT # 

Winchester Luger Cartridge #10 

Winchester Luger Cartridge #30 

Winchester Luger Cartridge #10 

Winchester Luger Cartridge #30 

Winchester Luger Cartridge # 10 

Winchester Luger Cartridge #30 

Winchester Luger Cartridge # 10 

Winchester Luger Cartridge #30 

Winchester Luger Cartridge # 10 

Winchester Luger Cartridge #30 

NG dev ° 2,4-DNT 

80317941 12.5% 0.3% 0.063% 0.007% 

3509 41.8% 0.7% 

ELD95FA-008 24.4% 1.4% 

431572H067 45.2% 0.6% 

2310812592 17.3% 0.2% 

43A-5106 47.6% 1.5% 

9AP 

NA 0.72% 0.06% 

NA 42.2% 2.0% 

11308Y 0.42% 0.01% 

Y07YC8501 42,9% 2.7% 

Tl10 40.9% 0.9% 

41041 44.1%! 1.8% 0.05% 0.002% 

AE0441 48.3% 1.2% 

891 0.84% 0.05% 

891 0.86% 0.01% 

4100T4 36.1% 2.5% 

D05Z23 13.7% 2.4% 0,064% 0,010% 0.52% 0.13% 

ME173 44.8% 2.1% 

28MC473 50.9% 2.1% 

56HN61/86 19.2% 0.6% 

56HN61/85 19.0% 0.3% 

36HE10/64 19.5% 0.1% 

36HE10/64 19.0% 1.5% 

56HN61/85 20.3% 0.9% 

56HN61/85 20.2% 0.5% 

46HN61/98 18,7% 0.1% 

46HN61/98 18.5% 0.3% 

36HE10/64 20.6% 0.9% 

36HE10164 19.3% 0.5% 

dev DPA dev N-nDPA dev 

0.44%1 0.01% 0.40% 0.01% 

0.34% 0.04% 0.43% 0.05% 

0.05% 0.01% 0.08% 0.01% 

Winchester Subsonic 73FN11 

Winchester Suoer-X 66HA91 

Suoreme 54HF30 

0,28% 0.003% 

14.6% 1.6% 0.061% 0.009% 

15.8% 0.4% 0.079% 0.004% 

0.11% 0.02% 

0.26% 0.01% 

0.08% 0.01% 

0.12% 0.01% 

0.10% 0.0001% 

0.23% 0.06% 

0.80% 0.02% 

0.71% 0.02% 0.34% 0.01% 

0.71% 0.004% 0.33% 0.01% 

0.76% 0.01% 0.35% 0.01% 

0.74% 0.05% 0.32% 0.03% 

0.75% 0.03% 0.36% 0.02% 

0.75% 0.02% 0.36% 0.01% 

0.71% 0.01% 0.34% 0.01% 

0.72% 0.01% 0.33% 0.01% 

0.81%1 0.04% 0.38% 0.01% 

0.76% 0.01% 0.34% 0.01% 

0.42% 0.05% 0.24% 0,03% 

0.64% 0.02% 0.30%! 0.01% 

MC dev 2-nDPA dev 4-nDPA dev EC dev :)BP • dev 

0,041% 0.002% 0.024% 0.002% 0.98% 0.03% 0.18% 0.01% 

0.72% 0.02% 

0.040% 0.003% 0.019% 0.003% 0.041% 0.006% 0.19% 0.02% 

0.86% 0.06% 0.15% 0.02% 

0.78% 0.04% 

0.77% 0.04% 

1.6% 0.03% 0.020% 0.01% 

0.034% 0.004% 0.096% 0.010% 0.41% 0.01% 

0.80% 0.08% 0.25% 0.02% 

0.95% 0.08% 

0.61% 0.03% 0.022% 0,004% 

0.82% 0.01% 0,059% 0.01% 

0,038% 0.003% 0.039% 0.01% 

0.60% 0.05% 

0,033% 0.008% 0,019% 0.006% 0,021%: 0.005% 

0.87% 0.01% 

0.20% 0.05% 

0.25% 0.03% 

0,038% 0.004% 0.021% 0.003% 0,025% 0.004% 0.18% 0.02% 

0.043% 0.003% 0,025% 0.001% 0.024% 0,002% 0.25% 0.01% 

* Represents the uncertainty of deviation of 9 replicates and does not reflect the uncertainty in the measured value. 
Table 2. Information Values of Gunpowder Composition Continued 

38 caliber 

3-D Inv. Inc. 

CCI- Blazer 

CCI- Speer 

CCI-Blazer 

Eldorado PMC 

Eldorado Starfire 

Federal Lot 

Federal Lot 

LOT # NG dev 2,4-DNT dev DPA dev N-nDPA dev 

150929931 24.4% 1.2% 0.050% 0.009% 0.45% 0.03% 0.54% 0.03% 

L04M2 41.8% 2.2% 

210014 25.6% 2.3% 0.35% 0.04% 0.071% 0.01% 

G20N4 50.2% 1.0% '~ 

38G-582 . 27.9% 0.4% 0.61% 0.01% 0.18% 0.004% 

38SFA-014 24.2% 0.7% 0,075% 0.009% 0.37% 0.01% 0.44% 0.03% 

12A-4670 55.9% 2.9% 

12B-4634 55.0% 0.2% 

5330223610 59.0% 4.8% 

38.0% 0.5% 

31.9% 0.8% 0.43% 0.007% 0,072% 0.01% 

33.3% 1.5% 

18.6%! 0.3% 

39.6% 7.2% 

31.8% 6.7% 

44.7% 0.7% 

1.1% 0,01% 

0.44% 0.01% 0.45% 0.01% 

0.27% 0.02% 0.34% 0.03% 

0.21% 0.01% 0.13% 0.01% 

0.082% 0.001% 0.72% 0.02% 

Fiocchi 

G&S 3 

Hornady's Frontier 5937915 

Lapua 6011FJSU950 

Norma NA 

Remington LE03H 

Remington Kleanbore RA5169 

Remington LA08R 

Remington LA08R 

S&W 7230321 

Scorpion Hydra-Shok X13456 

SuperVel GC09228 

USAC 2030593 

WAHIB 

Winchester 

Winchester • 

29.7% 0.3% 0.41% 0.01% 0.17% 0.01% 0.97% 0.02% 

16.3%1 0.5% 0.18% "0.01% 0.18% 0.01% 

13.3% 0.2% 0.67% 0.02% 0.53% 0.02% 

MAR 5, 1982 22.8% 0.2% 0.35% 0.01% 0.11% 0.01% 

60VM62/2 26.3% 1.1% 0.20% 0.02% 0.44% 0.02% 0.24% 0.01% 

36UM92/95 48.4% 1.3% 

60VM62/2 30.9% 3.0% 0.19% 0.006% 0.40% 0.02% 0.61% 

LOT # NG dev 2,4-DNT 

100314941 24.4% 0.60% 

NA 48.9% 1.8% 

090534Hl16 36.4% 0.60% 

949663600 52.7% 1.4% 

333008N137 63.9% 1.3% 

J17T5114' 47.7% 0.50% 

R18U 50.2% 1.5% 

7210682 44.6% 1.0% 

8050981 45.7% 0.20% 

042HB42/99 43.3% 0.99% 

05SL62/49 51.3%10.60% 

46KD1103 30.7% 0.40% 0,38% 

73GK70/56 49.2% 2.7% 

dev 

MC 

0.05% 

DPA dev N-nDPA dev MC 

0.46% 0.006% 0.52% 0.01% 

0.089% 0.002% 

0.17% 0.006% 0.034% 0,004% 

0.071% 0.003% 0.070% 0.004% 

0.031% 0.001% 0.13% 0.004% 

0.47% 0.005% 0.37% 0.02% 

Winchester 

380 auto 

3-D Inv. Inc. 

CCI - Blazer 

Federal 

Federal Am. Eagle 

Fiocchi 

Remington 

Remington Kleanbore 

S&W 

S&W 

Winchester 

Winchester 

Winchester 

Winchester 

0.15% 0.006% 0.98% 0.007% 

0.54% 0.029% 0.55% 0.02% 

dev 2-nDPA dev 4-nDPA dev EC dev DBP .dev 

0.037% 0.003% 0.021% 0.003% 0.075% 0.01% .0.20% 0.01% 

0.53% 0.05% 

0.055% 0.005% 0.023% 0.003% 

O.58% O.0O2% 

0.029% 0.002% 0.015% 0.002% 0.064% 0.05% 

0.043% 0.005% 0.021% 0.002% 0.045% 0.004% 0.19% 0.01% 

0.91% 0.06% 

1.0% 0.02% 

1.5% 0.4% 

0.49% 0.01% 

0.51% 0.06% 

0.17% 0.011% 

0.12% 0.004% 

0.38% 0.01% 

0.058% 0.005% 0.024% 0.003% 0.40% 0.04% 0.068% 0.01% 

0.026% 0.001% 0.043% 0.004% 

2.9% 0.5% 

2.2% 0.5% 

0,69% 0.02% 

0,094% 0.004% 0.031% 0.006% 

0.097% 0.004% 0.071% 0.001% 2.1% 0.07% 

0.35% 0.04% 

0.077% 0.002% 0.031% 0,002% 0.23% 0.02% 0.21% 0.09% 

1.0% 0.04% 

0.34% 0.03% 0.20% 0.004% 

dev 2-nDPA dev 4-nDPA dev EC dev DBP dev 

0.037% 0.002% 0.019% 0.002% 0.026% 0.002% 0.16% 0.01% 

0.71% 0.03% 

0.59% 0.02% 

0.93% 0.04% 

1.5% 0.04% 

0.59% 0.01% 

0.72% 0.02% 

0.61% 0.02% 

0.64% 0.002% 

0.63% 0.02% 

0.12% 0.002% 0,081% 0.002% 

0.045% 0.003%! 0.021% 0.002% 0.026% 0.002% 

0.15% 0.005% 
25 auto LOT # 

CCI - Blazer K15R6 

Daisy & Heddon RF-U/Lo101 

Dynamit GECO NA 

Dynamit Sinoxid 43 MA 

Eldorado PMC 25A-089 

Federal 17A-3250 

Table 2. Information Values of Gunpowder Composition Continued 

NG dev 2,4-DNT dev DPA dev N-nDPA dev MC dev 2-nDPA dev ¢.nDPA dev EC dev DBP dev 

48.3% 1.2% 0.72% 0.029% 

0.26% :).002% 0.79% 0.006% 0.069% 0.005% 0.18% 0.002% 

0.30% 0.006% 0.13% 0.003% 

0.27% 0.02% 0.12% 0.004% 

28.9% 0.80% 0.51% 0.02% 0.32% 0.02% 0.027% 0.002% 0.013% 0.002% 0.073% 0.004% 

48.6% 2.0% 0.66% 0.026% 

Fiocchi 

Remington 

winchester 

Winchester ACP 

W'mchester 

~ELOADING POWDERS 

Dupont IMR SR4756 

Dupom IMR SR7625 

704001-075 26.3% 1.4% 0.15% 0.004% 

Dupont IMR 4198 

Dupont IMR 4350 

DupontlMR 3031 

Dupont IMR 4064 

Hercules Rx7 

Hercules Unique 

Hodgdon H414 

Hodgdon H100 

Hodgdon H322 

Norma 1010 

Norma 2120 

LB20D 41.4% 0.30% 

65SH62/97 48.7% 1.4% 

03GA41/37 37.4% 0.60% 

11GF03/1190 39.5% 0.70% 

LOT # iNG dev 2,4-DNT 

P73JY22B 2.3% 

P71 MY03C 2.3% 

OE11/3087 4.3% 

P75MA10B 4.6% 

P73A1323 6.1% 

P75JA25C 6.3% 

11 8.28% 0.6% 

0.19% 0.004% 

0.30% 0.006% 0.56% 0.01% 

0.14% 0.008% 0.072% 0.003% 

dev 2,6-DNT dev 

0.1% 0.028% 0.002% 

0.1% 0.035% 0.001% 

0.2% 0.055% 0.001% 

0.1% 0.076% 0.002% 

0.3% 0.069% 0.003% 

0.4% 0.10%! 0.02% 

DPA dev 

0.44% 0.01% 

0.47% 0.02% 

0.34% 0.02% 

0.11% 0.003% 

0.10% 0.004% 

0.10% 0.01% 

0.33% 0.01% 

1.82% 0.16% 

0.54% 0.018% 

0.62% 0.012% 

0.13% 0.01% 

0.64% 0.023% 0.18% 0.02% 

N-nDPA dev 2-nDPA dev 4-nDPA dev EC dev DBP dev 

0.17% 0.01% 0.021% 0.002% 0.068% 0.001% 

0.17% 0.02% 0.021% 0.001% 0.083% 0.009% 

0.16%1 0.01% 0.057% 0.004% 0.069% 0.005% 

0.22% 0.003% 0.070% 0.070% 0.071% 0.002% 

0.32% 0.03% 0.072% 0.006% 0.10% 0.01% 

0.30% 0.02% 0.061% 0.002% 0.088% 0.007% 

0.17% 0.004% 0.030% 0.002% 0.021% 0.001% 3.0% 0.1% 

winchester 680 

Winchester 748 

Winchester 760 

Winchester 748 

Winchester 296 

Winchester 452AA 

Winchester 473AA 

Winchester 231 

winchester 540 

Winchester 571 

Winchester 630 

UN294 28.0% 0.9% 

NA 10.3% 0.4% 0.24% 0.01% 

50685 13.7% 0.3% 0.26% 0.01% 

50484 

NA 34.8% 1.6% 

NA 38.9% 1.8% 

680081H5 12.2%= 0.2% 0.61% 0.01% 

748018NE91 12.9% 0.5% 0.38% 0.004% 

760010HG2 12.9% 0.5% 0.57% 0.01% 

748018NE91 13.3% 0.5% 0.39% 0.01% 

296003KH72 13.8% 0.4% 0.56% 0.01% 

452KB81 17.7% 0.6% 0.52% "0.02% 

473009KB42 18.5% 0.5% 0.51% 0.01% 

27092NBll 28.9% 1.1% 0.25% 0.01% 

540080822 30.1% 0.4% 0.14% 0.002% 

500094 E61 30.2% 2.2% 0.49% 0.03% 

63000XE21 53.3% 0.3% 0.32% 0.01% 

0.44% 0.004% 0.056% 0.002% 

0.54% 0.02% 0.30% 0.004% 0.092% 0.004% 0.041% 0.002% 

0.65% 0.01% 0.44% 0.01% 

0.16%; 0.01% 0.11% 0.00% 0.081% 0.007% 0.16% 0.02% 

0.63% 0.01% 0.34% 0.01% 

0.40% 0.01% 0.59% 0.01% 0.18% 0.004% 0.13% 0.001% 

0.20% 0.01% 0.51% 0.02% 0.14% 0.014% 0.061% 0.006% 

0.50% 0.02% 0.56% 0.02% 0.18% 0.004% 0.12% 0.006% 

0.45% 0.01% 0.34% 0.01% 0.13% 0.005% 0.64% 0.005% 

0.18% 0.004% 0.79% 0.02% 0.070% 0.005% 0.050% 0.002% 

0.27% 0.01% 0.73% 0.01% 0.087% 0.002% 0.066% 0.003% 

0.41% 0.02% 0.83% 0.03% 0.082% 0.004% 0.036% 0.003% 

0.51% 0.003% 0.74% 0.01% 0.12% 0.002% 0.054% 0.003% 

0.051% 0.001% 0.64% 0.02% 

0.85% 0.01% 

3.0% 0.03% 

1.5% 0.2% 

1.2% 0.1% 

2.2% 0.03% 

1.8% 0.03% 

0.35% 0.02% 

4.2% 0.1% 

3.2% 

4.6% 

4.1% 

4.5% 

2.4% 

0.1% 

0.1% 

0.1% 

0.1% 

0.1% 
Based on this experiment, residues found on the hands of a suspect are a clear indication that a weapon has been 

fired or handled within a short period of time prior to the collection of the sample. These results also indicate that 

sampling for gunshot residues from the hands must occur as soon as possible. A suspect that is not captured until several 

hours after a shooting is not likely to be found to have residues present on his/her hands at that time, as determined by 

the MECE test. 

Clothing was found to retain residues for a long period after firing. Residues may persist for days, weeks or months 

if the clothing is not washed or involved in significant frictional contact with other objects. 

5.6 Environmental Exposure and Residue Decomposition 

Changes in the chemical composition of a given gunpowder might be expected to occur over time, particularly 

when exposed to heat and/or light. However, when an unfired powder was exposed to direct summer conditions over a 

28 h period, no significant change was found in the measured value of the following characteristic gunpowder components: NG, 2,4-DNT, DPA, N-nDPA, 2-nDPA, and 4-nDPA. Although unfired powder composition appeared to be 

unchanged in this simple experiment, the decomposition of the characteristic components when deposited as residues 

might be expected to be more rapid. We evaluated whether this compositional change could be used to provide an 

estimate of the time of firing. 

Samples of post-firing residues on cloth targets obtained by point blank firing of a handgun were stored in the 

laboratory and examined over a 2-month period of time. Residue composition immediately after firing, in some cases, 

was different from the unburned powder and varied from sample to sample as determined by replicate analyses, as noted 

previously. Very slow loss of nitroglycerin was seen over the 2 months of the study. However, the measured variation in 

composition is similar in magnitude to the particle-to-particle variability both of unfired gunpowder particles and 

collected residue particles. Thus, a determination of when a weapon was discharged based on the change in residue 

composition does not appear to be possible. The decomposition rate is too slow relative to the measurement uncertainty. 

5.7 Frequency of Residue Deposition 

In cases where a positive MECE test for gunshot residues is obtained, it is a strong implication that the individual 

has been exposed recently to a discharged weapon. We evaluated the frequency of positive MECE test results by firing 

two weapons. Multiple firings were made using two different 9 mm semiautomatic weapons. Each weapon was fired 

multiple times with each hand. The first weapon, a Mac 9, has an ejection port on the right side of the weapon. The 

second weapon, a Walther P38, has an ejection port on the top of the weapon. Samples collected from the Mac 9 were 

positive for gunshot residues 53 percent of the time when the weapon was fired with the right hand and 20 percent of the 

time when fired by the left hand. Samples collected from the Walther P38 were positive for gunshot residues 93 percent 

of the time when the weapon was fired with the right hand and 71 percent of the time when fired by the left hand. 

These results indicate that, even in controlled conditions, detectable gunshot residues may not be deposited on the 

hands of the shooter every time the weapon is fired. Deposition may be dependent on the caliber of weapon, type of 

weapon (e.g., semiautomatic versus revolver, etc.), configuration of ejection port, mechanical condition of the weapon, 

how clean the weapon is, the ammunition composition, completeness of the ammunition combustion, wind conditions, 

perhaps weapon temperature, random trajectories of residue particles, and which hand the shooter used to fire the 

weapon. Thus, a negative residue test does not prove that a weapon was not fired. 

5.8 MECE Analysis Versus SEM/EDX Analysis 

If MECE analysis is to augment the current technology for gunshot residue detection, it is necessary to compare the 

results obtained by MECE to those obtained using SEM/EDX on the same sample. Firing range samples examined 

using both MECE and SEM/EDX were found to be positive for gunshot residues by both methods. Some samples found 

to be positive by SEM/EDX were found to be negative by MECE. However, all samples that were positive by MECE 

were positive by SEM/EDX. Some false positive SEM/EDX results were obtained on blank samples. Since multiple 

firings were conducted by the same volunteer, it was assumed that hand washing would remove the inorganic residues 

as efficiently as the organic residues. This was not always the case with all blank samples. The false negative MECE 

results obtained on these identical samples could be caused by a difference in the quantities of inorganic versus organic 

residues. However, the most important result is that no false positive results were obtained by MECE analysis, and 

SEM/EDX analysis confirmed the positive results. 

14 
5.9 Casework Results 

MECE and SEM/EDX has been conducted simultaneously on samples collected from the hands of individuals 

suspected of having fired a weapon in seven criminal investigations. No gunshot residues were conclusively identified 

by MECE in any of these cases. However, SEM/EDX analysis has conclusively identified gunshot residues in two of 

these cases. MECE analysis in one of those cases suggested the presence of nitroglycerin, but at quantities too small to 

confirm. The negative MECE results for the five other cases were confirmed by SEM/EDX. This would indicate that the 

organic gunshot residues were either not deposited, or were not present at high enough concentrations to be detected. 

MECE analysis has been performed on a total of 16 samples from two cases involving the examination of clothing 

for the presence of gunshot residues. Gunshot residues were conclusively identified in seven of the samples from these 

cases using MECE analysis. SEM/EDX analysis of the samples confirmed the presence of gunshot residues on five of 

these samples and three additional samples that were negative by the MECE method. The results on five of the samples 

were the same using both MECE and SEM/EDX analysis. However, three samples were positive by SEM/EDX and 

negative by MECE, and two samples were positive by MECE and negative by SEM/EDX. 

6. CONCLUSION 

The results of this research suggest that MECE analysis is a valid analytical method for gunshot residue analysis. 

MECE analysis has been achieved on adhesive film lifts from hands and clothing, and these same lifts are compatible for 

SEM/EDX of the inorganic residues. Risk of false positive tests from occupational exposure to characteristic residue 

components does not appear to be a concern. Positive MECE results are not always obtained when a weapon is fired. 

This could be due to a number of factors, including low efficiency of residue deposition, low residue persistence, and 

lack of sensitivity of the MECE test. Recoverable residues do not appear to persist on skin for more than an hour. Thus, 

residues must be collected immediately from skin. However, residues on clothing are stable for a long period of time. 

Quantitative analysis for the purpose of generating a "chemical fingerprint" to match residues to known gunpowders 

must be interpreted with great care. Compositional variations of unfired and fired gunpowder particles has been noted. 

However, the presence or absence of components may provide valuable information for the inclusion or exclusion of an 

ammunition type or manufacturer. Residue decomposition over time resulting from environmental exposure is slow 

compared to the time that residues persist on samples. Thus, time of firing information cannot be obtained from 

quantitative analysis of the residues. 

Sample preparation and analysis can be achieved in about 2 h per case. Qualitative and quantitative information is 

generated concerning the characteristic organic constituents in gunshot residues. The cost of instrumentation is four to 

five times less than the cost of an SEM/EDX system. MECE analysis does provide a rapid and complimentary analytical 

tool for gunshot residue analysis. 

7. REFERENCES 

[1] Northrop, D. M.; Martire, D. E.; and MacCrehan, W. A. "Separation and Identification of Organic Gunshot 

and Explosive Constituents by Micellar Electrokinetic Capillary Electrophoresis," Analytical Chemistry, 63, 

1038-1042 (1991). 

[2] Northrop, D. M. Ph.D. Thesis, Georgetown University (1991). 

[3] Northrop, D. M.; and MacCrehan, W. A. "Sample Collection, Preparation, and Quantitation in the Micellar Electrokinetic Capillary Electrophoresis of Gunshot Residues," Journal of Liquid Chromatography, 15(6), 1041-1063 

(1992). 

[4] Northrop, D. M.i McCord, B. R.; and Butler, J. M. "Forensic Applications of Capillary Electrophoresis," Journal 

of Capillary Electrophoresis, 1 (2), 158-168 (1994). 

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