How much sample can I load onto my SPE device? Is it linked to the concentration of my analyte of interest?

When considering the mass of sorbent required to perform a solid phase extraction it is critical to consider the sample matrix (serum, plasma, urine, saliva, food, river water, soil etc). This information will allow you, with the use of a suitable look up table to determine the mass of SPE sorbent to use. The tables are produced to reflect the relative levels of interfering endogenous material present in the samples. 

The SPE device must have enough capacity to retain all analytes of interest together with any endogenous materials capable of retaining on the sorbent with the same type of interactions as the analyte. If there is insufficient sorbent, it is possible some analyte may pass unretained through the SPE device during sample loading, leading to lower recoveries and a loss of consistency of recovery between samples.

Sample Volume

Determines Bed Mass/ Solvent Volumes

Phenomenex: How much sample can I load onto my SPE device? Is it linked to the concentration of my analyte of interest?

Generic Loading Capacities:

Polymeric: 10 - 15% of Total Bed Mass | Silica: 5% of Total Bed Mass

If we compare plasma and urine, we can load 500 µl of plasma onto a 60 mg polymeric sorbent such as Strata™-X. Using the same 60 mg SPE tube 2 mL of urine could be loaded, indicating that urine contains significantly less endogenous material than plasma.

For sample types not included in the table, the use of generic loading capacity, 5% of sorbent mass for silica materials, or 10-15% for polymeric materials are advised. The difference between silica and polymeric sorbent loading capacity is a function of available surface area, which is higher for polymeric materials and also ligand density – the entire surface of a polymeric material is essentially stationary phase, while on a silica material only the phase bonded to the silica takes part in the extraction mechanism for reversed phase or ion exchange extractions.