FRTR Field Sampling and Analysis Technologies Reference Guide

7 SAMPLE ANALYSIS TOOLS for METALS

7.1 EX-SITU ANALYSIS

7.1.3 X-Ray Fluorescence

Use:

X-ray fluorescence (XRF) spectrometry is a non-destructive, analytical method used primarily to detect heavy metals in soil/solids samples.

Description:

XRF spectrometry uses primarily x-rays to irradiate a sample, which causes elements in the sample to emit secondary radiation of a characteristic wavelength. Two basic types of detectors are used to detect and analyze the secondary radiation:

Wavelength-dispersive XRF spectrometry uses a crystal to diffract the x-rays, as the ranges of angular positions are scanned using a proportional or scintillation detector (an extremely sensitive instrument that can be used to detect alpha, beta, gamma, and x-radiation).
Energy-dispersive XRF spectrometry uses a solid-state, Si(Li) detector from which peaks representing pulse-height distributions of the x-ray spectra can be analyzed.

The elements in the sample are identified by the wavelengths of the emitted x-rays while the concentrations of the elements are determined by the intensity of the x-rays. Sample preparation is minimal compared to conventional analytical techniques. XRF spectrometry allows for simultaneous determination of several elements. Portable energy-dispersive XRF instruments are now available, and the more accurate wave length XRF instruments can be used in mobile laboratories. The portable energy-dispersive XRF instruments can be used for scanning the ground surface to determine the prescence of metals without collecting a sample for analysis.

Analytes:

7. Metals

Media:

Soil/Sediment	Water	Gas/Air
BETTER	BETTER	Requires extraction

Selectivity:	Technique measures the contaminant directly.
Susceptibility to Interference:	Low.
Detection Limits :	10-100 ppm (soil); 0.5-10 ppm (water). Detection limits range from 20 - 1,000 ppm depending on vendor, unit type, and element analyzed. For portable instruments, detection limits typically are an order of magnitude higher than ICP-AES.
Turnaround Time per Sample:	Minutes.

Applicable To:
Screen/Identify	Characterize Concentration/Extent	Cleanup Performance	Long-Term Monitoring
BETTER	ADEQUATE	BETTER	ADEQUATE

Quantitative Data Capability:	Produces quantitative data.
Technology Status:	Commercially available and routinely used field techonology.
Certification/Verification:	Technology has participated in CalEPA certification and/or CSCT verification program.
Relative Cost per Analysis:	Least expensive.

Limitations:

Laboratory use with liquid samples requires preconcentration or precipitation, which is time consuming.
Soil texture and moisture content may affect performance.
Target analytes next to each other on the periodic table may not be separated adequately because they emit similar x-ray wavelengths.
Unsuitable in ambient temperatures outside 30 to 100° F range.
Surface scanning does not indicate whether metals of interest are present under the surface due to shallow depth of penetration. Collection and processing of soil by obtaining a vertical profile and grinding samples is generally required to obtain reproducible reading using a portable probe.
Does not differentiate between different valences.

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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