Sample preparation
Sample preparation - contextSample preparation - motivationPurpose of sample preparationOverview of preparation methods
Liquid liquid extraction (LLE) Solid phase extraction (SPE) Solid phase microextraction (SPME) Purge and trap (PT) (Accelerated) Solvent extraction ((A)SE) 
Supercritical fluid extraction (SFE) Filter Techniques (FT)
Box 10 FiltrationBox 11 SorbentsBox 12 Preconcentration
Selftest 1) Polar organic solvent Answer 2) Ideal extraction procedures Answer 3) SPME Answer 4) Extraction efficiency Answer 5) Sorption capacity Answer 6) Use as little of an extraction medium as possible Answer 7) Should soil samples be grinded? Answer 8) Solvent volume Answer 9) Extracting an air sample AnswerProblems
End of chapter2) Ideal extraction procedures
Answers:
Which of the following points are "must haves" and which are "nice to haves" for ideal extraction procedures?
Ideal extraction procedures should...
(1) ...extract a well defined percentage of the target compound out of the sample.
A clear "must have": note that the extraction does not necessarily have to be quantitative (quantitative = phase transfer of close to 100% of the chemical). If it is not quantitative, then a requirement is that the extraction efficiency is highly reproducible, such that calibrations are possible (i.e., set of standards with different concentrations of analyte extracted by the given extraction procedure).
(2) ...extract close to 100% of the target compound out of the sample.
Often a "must have"! Many extraction systems rely on a quantitative transfer. Yet, there are certain extraction procedures (e.g., SPME) in which no quantitative transfer is achieved. In these cases the extraction efficiency MUST BE highly reproducible (see (1)).
(3) ...extract the target compound in as little solvent or sorbent as possible.
It is often desirable to minimize the use of solvent or of an adsorbent. So, the analyte of interest should have a high distribution coefficient to the phase out of the phase that composes the environmental samplee (e.g., air or water). Not really a "must have", but clearly a "nice to have".
(4) ...extract as many compounds out of the sample as possible.
Sometimes it is desirable to extract many organic compounds out of a sample. However, sometimes the opposite is true. If one uses the extraction step to preferentially pre-concentrate one analyte over others, it is necessary to avoid co-extraction of other analytes than the target analyte. So, if (4) is proposed as a general statement, the answer must be NO.
(5) ...be cheap and can be automated.
That is a clear "nice to have". Some extraction procedures may be very expensive and labor intensive. Yet, that is justified if the extraction procedure is working well and if there are no alternatives.
(6) ...be quick and safe.
Similar to (5) a clear "nice to have".
(7) ...cause as little toxic waste as possible.
Similar to (5) a clear "nice to have".
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