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General Description
At Supelco, we generate almost all of our SPME applications using manual SPME units. For reliable quantitative results from these extractions, we follow these guidelines:
The sample volume must be consistent among samples. For direct immersion applications, completely fill the sample container. For headspace applications, fill the container between 1/2 and 3/4 full.
When extracting semivolatiles, use a consistent stirring rate. If the rate is inconsistent, precision drops, particularly for analytes with high distribution constants.
Keep the amount of organic content in the samples minimal (<1%) and consistent among all samples. Large amounts of organic solvent can greatly affect the distribution constants. Some solvents, such as methanol, act as co-solvents with the water, and can reduce the number of analytes extracted.
Use internal standards that are similar to your analytes. Internal standards help to offset extraction variables. Standard preparation is important. Prepare standards at 1-2mg/mL solvent, then spike 0.05-5uL of the standard into the water sample prior to the extraction.
Keep extraction time and temperature consistent among samples. The extraction time generally is 10 minutes for volatiles, 20-30 minutes for semivolatiles.
For more information about consistent results from SPME, refer to Bulletin 923.
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