Method Statement VOC Targets by Purge and Trap
@(#) Uncontrolled Document voctargets.html Version 1.3 Last
Revised on 11/20/02
Contents
Introduction
Principle
Performance
Characteristics
Range
of Application
Limit of
Detection
Analytical
Quality Control
References
Introduction
The performance of this method is validated in accordance with
internationally recognised procedures.
This procedure describes the determination of purgeable volatile
organic compounds (VOC) in soils and waters by purge and trap gas
chromatography mass spectrometry.
Principle
Helium is passed through the sample, this carries the volatile
components into a cold trap where they condense. At a predetermined
time the trap is heated rapidly, the condensate evaporates and passes
onto the head of Gas Chromatography (GC) column which separates the
different components. The eluent from the GC column passes into the
ion source of a mass spectrometer which, records mass spectra
continually at a regular interval and with unit mass resolution.
A series of aqueous standards are analysed by this method and the
data are used for reference and calibration. Deuterated internal
standards are added to all samples, spikes and blanks prior to
analysis. An adjustments is made to the results of the quantitation
based on the recovery of these internal standards.
In instances where a compound is not present in the calibration
materiel, a tentative identification and result is produced based
upon a comparison of the mass spectra obtained with those found in
the NIST mass spectral databases. Such tentative results are subject
to confirmation by the analyst.
Soil samples
0.1 to 5 g aliquots are immersed in 10 mls of deionised water,
spiked with the internal standards then analysed.
Water samples
A 1 to 10 ml aliquot is removed directly from the sample vessel,
spiked with the internal standards, then analysed.
Performance
Characteristics
Substances Determined
A range of volatile hydrophobic organic compounds, ranging in
boiling points from circa -10 C to 200 C. Standard target suite
includes chlorinated solvents, 'BTEX' and other priority pollutants.
Note that the purging process is extremely inefficient for
hydrophilic compounds such as alcohols, direct injection GC/MS should
be used if these compounds are to be monitored.
Range of Application
Limit of Detection
Analytical Quality
Control
Analytical quality control is maintained by a number of measures:
Multi-point calibration with
authentic standards (with defined minimum performance
characteristics)
Analysis of control samples within
each analytical batch, such as independent standards, matrix spikes
or reference materials
Analysis of reagent/method blanks
within each analytical batch
Ongoing quality assured by the use
of control charts in conjunction with warning and action limits for
the QC sample data
Participation in external
proficiency testing and interlaboratory schemes such as LGC CONTEST,
HSE WASP, CSL FAPAS
References
US EPA Method 8260,
Revision B, Volatile Organic Compounds by Gas Chromatography-Mass
Spectrometry (GC/MS).
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