FRTR Field Sampling and Analysis Technologies Reference Guide

6 SAMPLE ANALYSIS TOOLS for VOCs, SVOCS, and PESTICIDES

6.2 EX-SITU ANALYSIS

6.2.1 Photo Ionization Detector

Use:

Photo ionization detectors (PIDs) are used to detect aromatic hydrocarbons (a PID can detect most VOCs with a carbon range of 6 (such as benzene) to 10 (such as naphthalene)).

Description:

The PID is comprised of an ultraviolet lamp that emits photons (a quantum unit of light energy) which are absorbed by the analyte in an ionization chamber. Ions (atoms or molecules that have gained or lost electrons and thus have a net positive or negative charge) produced during this process are collected by electrodes. The current generated provides a measure of the analyte concentration.

PIDs are commonly used as detectors in portable gas chromatographs (which separate the specific analyte types). Because only a small fraction of the analyte molecules are actually ionized, this method is considered nondestructive allowing it to be used in conjunction with another detector to confirm analysis results. This is easily accomplished by connecting the exhaust port of the PID to a flame-ionization detector (FID) or electron capture detector. In addition, PIDs are available in portable hand-held models.

Analytes:

1. Non-Halogenated VOCs
3. Some Halogenated VOCs

Media:

Soil/Sediment	Water	Gas/Air
Requires extraction to liquid or gas phase	Requires extraction to liquid or gas phase	BETTER

Selectivity:	Technique measures the contaminant indirectly.
Susceptibility to Interference:	High.
Detection Limits :	10-100 ppm (soil); 0.5-10 ppm (water).
Turnaround Time per Sample:	Minutes.

Applicable To:

Screen/Identify	Characterize Concentration/Extent	Cleanup Performance	Long-Term Monitoring
BETTER	SERVICEABLE	BETTER	SERVICEABLE

Quantitative Data Capability:	Does not produce quantitative data.
Technology Status:	Commercially available and routinely used field technology.
Certification/Verification:	Technology has not participated in CalEPA certification and/or CSCT verification program.
Relative Cost per Analysis:	Least expensive. Rental: $150 - 300 per week. Purchase: $4,000 - 6,000.

Limitations:

Not suitable for detection of semi-volatile compounds.
Indicate if VOCs are present but do not identify type (unless combined with GC).
May give false positive readings for water vapor.
Rain may affect operational performance.
High humidity can cause lamp fogging and decreased sensitivity. This can be significant when soil moisture levels are high or when a soil gas well is actually in ground water.
High concentrations of methane can cause a downscale deflection of the meter.
Rapid variations in temperature at the detector, strong electrical fields, and naturally occurring compounds, such as terpenes in wooded areas, may affect instrument response.
Hand-held PIDs are not compound-specific.

ASTM Standards/EPA Methods:

No applicable ASTM standards or EPA methods are cited for this technology.

Sample Access/Collection Matrix

Sample Analysis Matrix

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