Jennifer Verkouteren, Jessica Grandner,

Kirsten MacIsaac, Nicholas Ritchie 

National Institute of Standards and Technology, 

Gaithersburg, MD 20899 USA

Presented at : Forensics@NIST 2012, Gaithersburg, MD, November 29, 2012

Portions of this material are based upon work supported by the Science and 

Technology Directorate of the U.S. Department of Homeland Security under Award 

Number HSHQDC-11-X-00420
Applications of Wipe Sampling

(Collection of Contaminants from Surfaces)

 Environmental sampling

Heavy metals, beryllium, pesticides, molds, etc.

 Industrial/occupational/residential hygiene

Work and home place exposure

 Post-remediation/decontamination

Clandestine methamphetamine laboratories

 Security/forensics

Trace detection of explosives, controlled substances, 

biohazards, nuclear material
0

2

4

6

8

10

12

0 5 10

Force, N

time, s

100 kPa

> 0 kPa

http://www.inspection.gc.ca

http://www.industrysearch.com.au http://www.cdc.gov

Wipe Sampling Materials

Gauze, cotton, polyester, nylon, PVA, paper, cellulose sponge, foam 

swab, clean room wipes, glass fiber filters ......
Agency use of Trace Detection

 Transportation Security Administration – airport explosives screening

 US ARMY Criminal Investigation Laboratory – forensics analysis of 

explosives and narcotics

 Department of State –US Embassy trace explosives screening

 Federal Protective Services – federal building trace explosives screening

 Customs and Border Protection – drug screening at borders

 Arizona Department of Corrections – drug interdiction

 Bureau of Prisons – prisoner/mail drug screening

 USSS – mobile trace explosives detection
Wipe Sampling for Trace Detection

Direct Introduction of Sample Wipe to Explosive (or Narcotic) Trace 

Detector (ETD)

dry collection, wipe heated to ~ 200°C, sample confined to specific area 

cotton Nomex (aramid polymer) Teflon-coated fiberglass
Current State-of-Knowledge:

Wipe Sample Collection

In general, no overwhelming consensus can be drawn 

from the current literature on how to collect a wipe 

sample ......... EPA/600/R-11/079 January 2007

 Factors

Wipe material, solvent, applied force, sampled area, 

surface characteristics, physical/chemical nature of 

contaminant 

 Goal

Maximum - or at least repeatable - collection efficiency
A

B

C

D

E

F

A. Sled

B. Plane

C. Sampling surface

D. Wipe

E. Particulate sample

F. Tow line

Collection Efficiency of Sampling Wipes: Method

Particle Counting

Fluorescent Microspheres Wipe Comparison

Friction/slip tester

Standard Practice in 

development ASTM E54.01

With Jayne Morrow and Sandra 

Da Silva (NIST)

force

sample

wipe

velocity

surface
Collection Efficiency of Wipes: Results

Different Wipes

0

10

20

30

40

50

60

surface 

1

surface 

2

CE, %

40 um

10 um

2 Particle Sizes

0

10

20

30

40

50

60

70

10 um 40 um

CE, %

325 gforce

1275 gforce

2 Forces

Wipe material, surface characteristics, particle 

size, applied force - all significant factors

Source: J. Staymates, NIST

Source: Verkouteren et. al (2008) Meas. 

Sci. Technol, 19, 115101.
Development of Standard Sampling Method

Factors

 Force (Force Sensitive Resistors – FSRs)

 Area (sampling path)

 Surface

 Particles

 Wet wipe vs dry

FSR

Microspheres RDX

0

2

4

6

8

10

12

0 5 10

Force, N

time, s

Applied Force
FSR Measurements of Operator Performance

0

2

4

6

8

10

12

14

16

18

20

1 7 1 4 1 9 9 1 0 1 1 1 8 1 3 2 2 0 1 6 1 2 8 6 7 3 1 4 5 1 5

Force, N

operator

Average “firm” force = 7 N (1.5 lb)

a

relative path length

0.75

0.8

0.85

0.9

0.95

1

4

1815171220

26

141916

39857

11

1

1310

coverage factor

operator

exp 1

exp 2

exp 3

ideal 

Area Coverage

80% to 98%

Population size: 20

Sample with “firm” force

Follow sampling pattern

Significant Inter-operator Variability

In Press: Verkouteren et al. Environmental Science: Processes & Impacts, 

DOI: 10.1039/c2em30644a
FSR Use for Operator Training

0

5

10

15

20

average force, N

start train test

Train for 7 N

92

88

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

area coverage

op 10

op 14

op 20

start train test

98

94

Train for >95% coverage

Currently training NIST Physical Security

(NIST Test Bed)

Technology transfer to Transportation 

Security Administrations for airport 

screener training
-80

-70

-60

-50

-40

-30

-20

-10

0

0 20 40 60 80 100

distance, mm

distance, mm

y = 4.2807x - 1.3729

R2 = 0.8763

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

0 5 10 15

collection efficiency, %

force, N

a b

start

end

10 m fluorescent 

microspheres

“dry transfer” RDX particles

~ 20 m diameter

0

20

40

60

80

100

120

Normalized Intensity

mass RDX (log scale) 

ETD Sensitivity to RDX

Count Microspheres

Particle Collection Efficiency: Method

Explosive Trace Detector (ETD)

Particle Test Materials
0

20

40

60

80

100

0 5 10 15

CE, 

%

force, N

Dry or Wet Wipes

Microspheres

wet dry

force, N

CE,%

Dry Wipes

RDX

Particle Collection Efficiency: Results

0

5

10

15

20

25

30

35

40

0 5 10

CE %

force, N

• modify microsphere adhesion 

 better simulant for explosive particles

• Increase force

• Use wet wipes (maybe in future)

Plain sphere

Sticky sphere

RDX
0

2 0

4 0

6 0

8 0

100

7N 4N ~1N

90

30

0

80

60

20

Alarm Rate (%)

Approximate Testing Force (N)

ETD 3--Alarm Rate

MD

UD

Field Testing using ETD Alarm Rate

Success measure for correct sampling:

ETD Alarm rate > 67 % (2/3 trials)

Unidirectional

(UD)

Multidirectional

(MD)

3 Trials

Apply Dry Transfer Material

Sample at force > 4 N

No FSR
0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15

Force, N

time, s

oper 3

oper 7

oper 20

operator flat surface hand

force, N force, N

3 10.5 (±1.4) 2.3 (max 3.3)

7 11.4 (±2.4) 1.3 (max 1.8)

20 7.4 (±1.8) 1.2 (max 1.8)

Dermal Sampling

Reduction in force for wiping 

hands compared to wiping flat 

surface of 80% or more

Applied Force Depends on the Scenario
Field Use of FSR-Integrated Wands

Green light when force threshold 

exceeded

Force threshold set at 6 N

Test ability to achieve required force in operational environment

Source: M. Staymates, NIST
Conclusions

 Standard practice for evaluating wipes

 Controls wipe, force, particle size, surface 

 Development of standard sampling method

 FSR based

 Control of same factors, and area coverage and path

 Determine best practices for wide range of contaminants

 Training of operators to reduce variability

 Average 7 N force

 >95% area coverage

 Integration of FSR in wand