CALTEST INFORMATIONAL BULLETIN
Written by Peter Halpin - August 30, 2005
CURRENT LIMITATIONS IN PYRETHROID ANALYSIS
Reporting Levels
Two pyrethroids of interest have a water quality goal below current method capabilities. They are cypermethrin with a CVRWQCB water quality goal of 0.002 μg/L, and permethrin with goals of 0.03 μg/L in freshwater and 0.001 μg/L in saltwater. Caltest's current reporting level for cypermethrin is 0.005 μg/L and 0.005 μg/L for permethrin. Reporting limits are supported by calibration standards and MDLs. Reporting limits should be at or below the goal, and preferably 10 times lower than the goal.
Sediment reporting limits for pyrethroids should be sub μg/kg. These levels have been obtained by government and academic labs, and at Caltest in Napa California.
Hold Times
USGS and the California Dept. of Food and Agriculture hold time studies indicate hold times as short as 3 days to 13 days depending on the analyte. Such short hold times require coordination with the lab to extract the samples in time. Spiked sediment samples by Weston and Lydy have shown reproducible recoveries after several months frozen. California Dept. of Pesticide Regulation has sponsored studies using hexane as a 'keeper' to be added at the time of sampling to extend hold time in water.
Co-Reporting
Esfenvalerate and fenvalerate are not distinguishable, and are reported by some including Caltest combined. Deltamethrin thermally degrades in the GC to tralomethrin causing the two to be indistinguishable. They are reported together.
APPROACH TO EXISTING METHODS
Normalization of Results
USGS and some others normalize data to reflect extraction efficiency. Caltest follows EPA style (Clean Water Act and SW-846 manual methods) adding the internal standard at the instrument and not normalizing sample results according to extraction process recovery. Extraction surrogates are reported but the data is not normalized to that recovery.
Total Analyte Reporting
Caltest calibrates and quantitates samples based on the sum of the analyte's detectable isomers. Unless otherwise noted then, results are 'total'.
Extraction
Water samples can be analyzed with or without coarse sediments and solids. Some drinking water analysis for pyrethroids include SPE (solid phase extraction) with pre-filtering. This may suit the needs of drinking water raw water surveys but has been considered inappropriate for environmental analysis. Because pyrethroids have a strong affinity for solids, most water analysis for pyrethroids is based on 'whole water', that is water with all sediments/suspended solids included. Alternatively total 'whole water' and 'dissolved' fractions can be collected. When whole water samples are analyzed by liquid-liquid extraction, results will include pyrethroids bound to the solids as well as any dissolved fraction present. Pyrethroids are easily lost to surfaces they come in contact with. Sample bottles are solvent rinsed (with lids screwed on) to try to recover all analyte possible from the sample container walls.
APPROVED METHODS
Accreditations
There are no regulatory approved methods for these analytes. The draft EPA method suffers from lack of sensitivity relevant to the environmental levels of interest. Caltest’s approach has been to run the GC/MS method exactly like all other EPA methods used for environmental compliance.
Instrument calibrations include more than 5 points. The reporting limit is supported by the low calibration standard and MDL. Second source calibration check standards are employed. Batch QC matches EPA style of Method Blank, Laboratory Control Standard, Matrix Spike and Matrix Spike duplicate for each and every batch of samples, with a maximum batch size of 20 samples. Extraction surrogates are included, but results of surrogates are reported as is, results of extraction surrogates are not used to normalize the results. Internal standard is added to the sample at the instrument. Instrument tune is checked every 12 hours. Control limits are established based on lab in-house data.
Method Modifications
Caltest runs the EPA GC/MS method 8270 in the narrow range selected ion monitoring mode similar to the USGS and California Dept. of Food and Agriculture methods. These vary from EPA promulgated methods in that instead of employing the method full scan, a short list of the most abundant ions per analyte are scanned in the selected ion monitoring mode. Running the Mass Spectrometer in this narrow range scan provides greater sensitivity. This sensitivity is required to get into the range of the environmentally relevant. By requiring the most abundant ions to be present and observed in the correct ratio, a high degree of confidence of analyte identification is still maintained.
Revised June 2008
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