Portable Headspace Sampling for Field 

Applications in Forensic Science

Megan E. Harries, Ph.D.

University of Colorado Boulder

Fluid Characterization Group

Applied Chemicals and Materials Division

This work is funded by the NIST Special Programs Office
Vapor (= headspace) sampling

Cleaner: which is why we use it 

for fire debris analysis and many 

environmental analyses

Safer: does not require direct 

contact with sample (like a 

fentanyl) or even close proximity 

to a sample, with the right 

sampling probe

Non-destructive: a big advantage 

in evidence analysis or when 

sample availability is limited

Static Dynamic

Analyze this

To characterize this
150

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250

0 0.2 0.4 0.6 0.8 1

Temperature, C

mol fraction

If we have a thermodynamic model and 

the vapor composition, we can predict 

the liquid composition.

y (vapor) x (liquid)

Example:

An 80-proof spirit is 40% ethanol, by definition, in the liquid.

The headspace of an 80-proof spirit is >40% ethanol, because of mixture 

effects and the variable vapor pressures of the components.

V

L

L + V

Thermodynamics: vapor and liquid phase composition differ

y = 56%

x = 40%
Bruno, T.J. J. Chromatogr. Sci., 47, 569-574, 2009.

sample

A preconcentration headspace method that uses an 

adsorbent capillary trap and cryoadsorption to 

enhance efficiency

Adsorbers are eluted with solvent and analyzed

Advantages

• Small sample quantities (mg)

• Fast

• Temps 30-300 °C

• Fast, cheap, flexible setup

• Good for low-volatility compounds (TNT, 

plasticizers)

• Adaptable to the situation

• Lower measurement uncertainty (in progress)

Lab PLOT-cryo and applications
A preconcentration headspace method that uses an 

adsorbent capillary trap and cryoadsorption to 

enhance efficiency

Past applications:

• Decomposition (rat graveyard)

• Fire debris

• Spoiled poultry

• Vapor pressure of explosives and cannabinoids

Many unexplored field applications!

Lovestead, T. M., Bruno, T. J., Detecting gravesoil with headspace analysis with adsorption on 

short porous layer open tubular (PLOT) columns. Forens Sci Int 2011, 204, 156-161.

Lovestead, T. M., Bruno, T. J., Determination of cannabinoid vapor pressures to aid in vapor 

phase detection of intoxication. Forensic Chemistry 2017, 5 (Supplement C), 79-85.

Nichols, J. E., Harries, M. E., Lovestead, T. M., Bruno, T. J., Analysis of arson fire debris by low 

temperature dynamic headspace adsorption porous layer open tubular columns. Journal of 

Chromatography A 2014, 1334, 126-138.

Lovestead, T. M., Bruno, T. J., Trace Headspace Sampling for Quantitative Analysis of Explosives 

with Cryoadsorption on Short Alumina Porous Layer Open Tubular Columns. Anal Chem 2010, 

82, 5621-5627.

Lovestead, T. M., Bruno, T. J., Detection of poultry spoilage markers from headspace analysis 

with cryoadsorption on a short alumina PLOT column. Food Chem 2010, 121, 1274-1282.

Lab PLOT-cryo and applications
Portable device development

• Robust, sturdy, hand-portable

• Withstands extreme temperature or humidity

• A probe to enable sampling from a distance

• Capable of rapid sampling times (higher flow rate)

• Field-based sample elution and PLOT reactivation

11 cm

4 cm

100 mL/min!
First tested using

• Naphthalene inside a suitcase: 3 sec 

detection

• Coumarin

• Trinitrotoluene (TNT)

• Low-volatility gas turbine kerosene 

(JP-5)

• Diesel fuel

Lab studies

suction

Harries, M.E., Bukovsky-Reyes, S., Bruno, T. J., Field portable low temperature porous layer open tubular cryoadsorption 

headspace sampling and analysis part II: Applications, Journal of Chromatography A, 1429, 72-78, 2016.
EPA 40 CFR 136 B: determining a method’s detection limit (MDL)

1. Prepare and analyze at least 7 sample replicates at the same 

concentration

2. Select concentration estimated 2-10x the actual MDL

3. MDL = s * tn-1, α

where s is the population standard deviation and t is the Student’s t value for the 

given α-level

PRO: The method is designed to reflect all variability from sample 

prep through analysis... not just the TOF’s detection limit.

CON: The result is expressed in terms of signal, not concentration, 

and we can only estimate the MDL in ppm from the signal result.

Testing the limits with a diesel fuel spill

TMB

Harries, M.E., Bukovsky-Reyes, S., Bruno, T. J., Field portable low temperature porous layer open tubular cryoadsorption 

headspace sampling and analysis part II: Applications, Journal of Chromatography A, 1429, 72-78, 2016.

GC-QTOF analysis

Neat diesel fuel

Result

MDL = 32378 AU 

1 ppm = 53997 AU

MDL <1 ppm
• 55 gallon (220 L) volume allows multiple headspace 

samples without changing the overall concentration

• Reduces sample uncertainty and matrix effects 

(single-phase mixture)

• Isolates variability due to portable vapor collection 

from variation among individually prepared samples

What we found:

In the MDL study, COV (σ/xx̅) included sample 

variation: 

COV = .28 (n=16)

Using the chamber to eliminate sample-to-sample 

variability: 

COV = .05 (n=7)

Assessing sampling uncertainty

0

0.5

1

0 50 100

Normalized response

Conc C6, ppm
Portable PLOT-cryo setup in the field

Bunker exterior

Bunker study

Bunker interior

Challenges: 

• Mother Nature

• Not well mixed, no guarantee of equilibration

• Open system

• 13600 L = Largest test bed by 100x
Four experiments

Test compound volatility 5* 10-4 kPa to 5 kPa

Bunker study

Naphthalene Pure compound Check device functioning

Explosives-related 4-part mixture Solvents and plasticizers

Vapor pressures 4 x 10-3 – 0.63 mm Hg

Gravesoil-related 8-part mixture Sulfur compounds

Diamines putrescine and cadaverine

Vapor pressures 3 – 38 mm Hg

Gasoline Highly complex ≈ ruptured fuel tank

Test conditions ranging:

Tambient = 3 to 37 °C

Tbunker = 2.2 to 43 °C

RH = 9 % to 92 %

Sample times = 30 s – 20 min

Compressed air testing:

• House air

• Diesel compressors

• Canister from SCBA
Findings

• Strong bunker background signal: degrading polyurethane foam insulation

• Diethyl phthalate (challenge compound)

• Gasoline in 3 s

• Higher temps eased detection

• Humidity > 90% increased sampling time; humid compressed air caused interruption to refrigeration

0

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0.1

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0.14

0.16

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2 3 4 5 6 7

Relative abundance

Retention time, min

neat

vapor sample

Gasoline (10 s sample)

Bunker study

Harries, M.E. Field Demonstration of Portable Headspace Sampling in a Simulated Cargo Container, in: Vapor-Liquid Equilibria 

Pertaining to the Study of Alternative Fuels and the Forensic Analysis of Chemical Evidence, available September 30,2018.
• Profs. Joost de Gouw and Jose Jimenez (CU Boulder) 

• Online MS and field GC-MS teamed with 

portable PLOT-cryo preconcentration

• Breath sampling to detect intoxication

• Monitoring disease biomarkers in animal 

agriculture

• Investigating indoor air quality as a route of exposure 

to occupational hazards

Future work

Vocus PTR-TOF

Lamplugh, A., Harries, M., Xiang, F., Trinh, J., Hecobian, A., Montoya, L. Occupational Exposure to Volatile 

Organic Compounds and Health Risks in Colorado Nail Salons, Environmental Pollution, submitted.
Thank you

Platon Science and Technologies

Licensed patents for portable PLOT-cryo

Chris Gray, Ph.D.

platonscitech.com

chris.gray@platonscitech.com

ACMD Fluid Characterization Group

Boulder Fire and Rescue Department

NIST Special Programs Office

megan.harries@nist.gov