Son cartuchos para SPE que es una técnica preparativa. Solid Phase Extraction.
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http://www.strataspe.com/gs_bedvolume.asp

Selecting the Proper Sorbent Mass
The sorbent bed mass determines the maximum amount of analyte that can be retained by the sorbent.
Sorbent Bed Mass = Analyte Capacity
(i.e. 30mg, 50mg, 60mg, 100mg, 150mg, 200mg, 500mg, 1g, 2g, 5g, 10g, 20g, 50g, 70g)


As a general rule for selecting the proper bed mass
Silica-based sorbents:
Non-ionic sorbents retain a mass of solute (analyte plus retained contaminants) that is equivalent to approximately 5% of the sorbent mass. Therefore, a 100mg cartridge can retain approximately 5mg of total solute mass.
Polymeric sorbents
The large surface area of polymers give a higher capacity that is approximately 10-15% of the sorbent mass.
Ion exchange sorbents
Capacity is determined by the number of charged sites on the sorbent available to interact with the analyte. The mean capacity ranges from 0.8-1.3 meq/g.


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Note added at 1 hr (2008-02-25 20:06:05 GMT)
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masa de sorbente en mg.