Performance Validation for

Explosive Trace Detection

Forensics@NIST 2012,

Gaithersburg, Maryland,

November 28-30, 2012

Certain commercial equipment, instruments, or materials may be identified in this presentation in order to specify the experimental procedure 

adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, 

nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. 

Mike Verkouteren, Research Chemist,

Materials Measurement Division,

NIST-DOC, Gaithersburg, MD USA

“This material is based upon work supported by the Science 

and Technology Directorate of the U.S. Department of Homeland 

Security under Award Number HSHQDC-10-X-00552.”
Forensics@NIST, November 28-30, 2012

Outline

• Trace detection and challenges

• Role of metrology and standards

•Inkjet printing, ASTM limit of detection,

cloud computing, and standard dirt
Forensics@NIST, November 28-30, 2012

Trace 

Detection

Trace detection 

involves 

quantities of 

substance 

invisible to the 

unaided eye... 

typically less 

than a 

microgram.

Most commercial explosive 

trace detectors (ETDs) can 

detect in the low nanogram 

range (a single crystal 

much smaller than the 

width of a human hair!) 
Forensics@NIST, November 28-30, 2012

Trace Detection Challenges:

Sampling

Trace chemical targets are vanishingly small

RDX crystals 

in C4

http://www.itstactical.com/centcom/news/

youll-never-look-at-hay-bales-the-same/

http://showmehowto.net/wpcontent/uploads/2012/07/788suitcase.jpg
Forensics@NIST, November 28-30, 2012

Trace Detection Challenges: 

Specificity/Sensitivity

Contamination is ubiquitous, compositionally variable, 

and can interfere with detection
Forensics@NIST, November 28-30, 2012

0

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800

900

1000

0 20 40 60 80 100 120

ETD Response Curves

Maximum amplitude (a.u.)

Analyte mass (ng)

Vendor-supplied 

test materials
Ink Jet Printing
Forensics@NIST, November 28-30, 2012

Inkjet Metrology and 

Application to Trace 

Explosive Validation

Anal Chem 2009, 81, 8577

Langmuir 2011, 27, 9644

Anal Chem 2010, 82, 8519
Forensics@NIST, November 28-30, 2012

MicroFab Gravimetric Printer (JL4-XLB)

Production of Test Materials

Using Ink Jet Printing

Accuracy 5 %

Repeatability 0.5 %

Deposition 

Range (<1 min)

1 pg to 1 μg

70 pL to 70 μL

Spatial 

Resolution

100 μm
ASTM Limit of Detection

&

Cloud Computing

http://www.v3.co.uk/IMG/473/149473/cloud-computing-security-services-provider-370x229.jpg
Forensics@NIST, November 28-30, 2012

LD: a fundamental yet misunderstood 

analytical metric

We define the LD-90 as the lowest mass of a particular compound –

introduced to the sampling inlet of a well-functioning contraband 

detection system – for which 90 % of independent measurements result 

in true detection, while the true non-detection probability is at least 90 % 

when measuring independent process blank samples.

LD-90 influenced by combination of detector sensitivity, response 

repeatability, and specificity for the analyte against background 

interferences.

ASTM E54.01 Proposed 

Standard on

Limit of Detection for 

ETDs

http://www.chemometry.com/Research/LOD.html
Forensics@NIST, November 28-30, 2012

LOD Method for ETDs

Limit of detection determination for censored samples.

Rukhin, A.L.; Samarov, D.V. (2011) 105, 188-194.

NIST method designed 

specifically for trace 

explosive detectors as 

implemented by ASTM 

E54.01 subtask group*

* S. Leigh, A. Rukhin, J. Yen, J. Staymates, M. Verkouteren 
(1)

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Forensics@NIST, November 28-30, 2012

Web-based LOD Calculator

• http://pubapps.nist.gov:8444/loda

– Input measurement data

– Data quality check

– LD-90 estimate &

 supporting information

ASTM Subtask Group:

A. Heckert,

K. Kwiatek,

M. Verkouteren
Standard 

Dirt
Forensics@NIST, November 28-30, 2012

Standard “Dirts”

Natural Matrix NIST SRMs

• Soils, sediments, dusts, air particulates, sludges, leaves... 

• Immediately and internationally available

• Represent reasonable contamination sources

• Highly characterized

• Certified

• Homogeneous

• Stabilized
Forensics@NIST, November 28-30, 2012

Standard Interferent Material 

(SIMdirt-1)

SRM 2704 (Buffalo River Sediment) 266.5 mg

SRM 2585 (Household Dust) 83.7 mg

SRM 2709a (San Joaquin Soil) 87.5 mg

SRM 1650 (Diesel Particulate Matter) 5.1 mg

2-propanol (HPLC grade) 100 mL

One drop from squeeze dropper deposits 100 μg of SIMdirt-1 (U = 4%) 
Forensics@NIST, November 28-30, 2012

Limit of Detection Comparison

An atypical surprise with SIMdirt-1

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500

1000

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2000

2500

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Dose (ng)

Detector response (a.u.)

0

500

1000

1500

2000

2500

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Dose (ng)

Detector response (a.u.)

Analyses repeated, with 

100 μg SIMdirt-1 added to 

each substrate

Detector responses from 

analyte on clean 

substrates
Forensics@NIST, November 28-30, 2012

SRM Preparers and Analysts

M.M. Schantz

D.L. Poster

S.J. Christopher

J.R. Sieber

D.G. Friend

S.S. Vander Pol

R.M. Lindstrom

R.O. Spatz

S.E. Long

R.S. Popelka-Filcoff

E.A. Mackey

B.E. Tomlin

A.F. Marlow

L.J. Wood

S.A. Wise

R.L. Watters

J.R. Kucklick

S.D. Leigh

M.P. Cronise

C.N. Fales

P. Schubert

J.M. Keller

B.J. Porter

H.M. Stapleton

K.E. Murphy

L.L. Yu

R.L. Paul

R. Zeisler

S.A. Rabb

A.P. Lindstrom

G.C. Turk

L.J. Wood

L.L. Yu

R.R. Greenberg

E.A. Mackey

B.S. McDonald
Forensics@NIST, November 28-30, 2012

Summary

• Several tools have been developed at NIST suitable

for performance testing and validation of trace detectors 

• Inkjet technology for accurate and precise printing

of pg-to-μg of compounds for reliable production of

test materials and reference substrates 

• Proposed ASTM method for determining LD-90,

aided with a web-based calculator 

• Standard interferent material (SIMdirt-1) for

ETD interference response testing

m.verkouteren@nist.gov