USGS-NWQL: O-3127-94:  VOCs in water by purge and trap GC/MS

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
 Determination of volatile organic compounds in water by purge and trap capillary gas chromatography/mass spectrometry
Current Revision
USGS OFR 94-708-W
Media
 WATER
Instrumentation
 Gas Chromatography with Mass Spectrometry Detection
Method Subcategory
 Organic
Method Source
  USGS-NWQL
Citation
 Rose, D.L., and M.P. Schroeder, 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory -- Determination of volatile organic compuounds in water by purge and trap capillary gas chromatogoraphy/mass spectrometry: U.S. Geological Survey Open-File Report 94-708-W.
Brief Method Summary
 Volatile organic compounds are purged from the sample matrix by bubbling helium through a 25-mL aqueous sample. The compounds are trapped in a tube containing suitable sorbent materials and then thermally desorbed onto a Megabore capillary column. The gas chromatograph is temperature programmed to separate the compounds, which then are detected by the mass spectrometer.
Determination of selected compounds is confirmed by analyzing standard reference materials under the same conditions as the samples, comparing retention times and mass spectra.
Scope and Application
 This method is suitable for determining purgeable VOCs. The method may be applied to surface- and ground-water samples, or both. Method detection limits, as well as the linear range of measurement, are dependent on the chemical characteristics of the compound and the ability of the analytical technique to detect and measure the compound.
Applicable Concentration Range
 0.2 to 25 ug/L (undiluted)
Interferences
 (A) Volatile compounds present in the laboratory atmosphere from solvents such as methylene chloride and toluene, and refrigerants such as dichlorodifluoromethane, as impurities in the helium in the trap: Polytetrafluoroethene (PTFE) plastic tubing in the purging device is not used because organic compounds might permeate the tubing, resulting in concentration of the contaminants on the trap. (B) Organic contaminants: Wear laboratory clothing that has not been exposed to methylene chloride vapors. Avoid dichlorodifluoromethane when checking for leaks in the mass spectrometer. To minimize this problem, analyze daily a laboratory blank to quantify any contaminants and to determine if corrective actions are required. Locate the volatiles laboratory far from other laboratories where extractions using organic solvents (particularly, methylene chloride) are conducted. Store laboratory solvents, with the exception of methanol, outside of the VOC laboratory. Moreover, do not store stock VOC solutions near samples. (C) Cross contamination and carryover in low concentration samples analyzed after high concentration samples: Reanalyze the subsequent samples suspected of contamination to verify the results. Replace the purge vessel containing the contaminated sample.
Quality Control Requirements
 Mass spectrometer performance evaluation standard (1-bromo-4-fluorobenzene), Internal standard/surrogate standard solution (SURRIS), Selected compound calibration standard solution, Quality control (QCC) check standard, Matrix spike solution, field equipment blank, trip blank, instrument blank, Continuing calibration verification (CCV) standard, matrix spike, environmental sample duplicate, Limit of quantitation (LOQ) standard.
Sample Handling
 Collect samples in triplicate in clean 40-mL borosilicate amber vials with Teflon-faced silicone septa. Fill the vials to overflowing and cap immediately. Store samples immediately at 4oC. Pack enough ice to ensure the samples remain chilled throughout transit; do not use dry ice for shipment. Do not wrap tape around the vial seal and do not use Freon-puffed Styrofoam pellets when packing the vials for shipment.
Maximum Holding Time
 14 days
Relative Cost
 Less than $50
Sample Preparation Methods
WHO WE ARE
  • NWQMC
  • USGS
  • EPA
LEGAL