A compound (steroidal alkaloid) was isolated by preparative HPLC and is now solved in a large volume of ~20% acetonitrile with 0.1% formic acid. We thought about concentrating the compound after evaporating the acetonitrile by RP18-SPE (500mg of RP18 material per catridge). The expected total amount of the isolated compound is around 50 mg. Is this a realistic approach? What is the approximate sample capacity of such an SPE catridge?
Hello,
you might find THIS helpful: http://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Supelco/General_Information/t402150.pdf (page 5). There the analyte capacity is estimated to be around 5-10% of the bed weight. The amount of analyte is here to be understood as the sum of all substances retained (including matrix).
It strongly depends on the matrix (not the problem in your case) and of course the sorptive properties of analyte, which you will know better than me. As far as I see it you're working near the upper capacity limit which might be fine since you don't have a matrix to speak off.
Hi Jandirk,
We usually use a rule of thumb in our lab whereby you can expect the sample capacity to be about 5% of your SPE bed weight, thus for your 500g SPE cartridge you would be able to isolate 25mg of your product, but this can be increase if you fine tune your SPE eluents strengths and 50mg should be attainable.
Goodluck!
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