Just go with suggestion provided by Sean Lehman and you'll be okay. Just load different amounts of the analytes unto your SPE cartridge and generate the profile for the amount extracted. The point were it plateaus off is your SPE sorbent capacity.

Alternatively, knowing the mass of the sorbent, your nominal amount loaded and amount you extract after passing it through the SPE cartridge, you can calculate the capacity from the meq 

Start with a known high concentration of your substrate, process it through SPE and then quantify the concentration of the eluent from SPE. Be mindful of two things though:

1. Your instrument has to be calibrated for the concenrations you are projecting.

2. You have to use a Liquid-Liquid extraction step after elution from SPE since you will have to recover your substrate in an organic solvent. Most GC-MS instruments do not tolerate water (neither the column does, nor the MS).

Prepare a set of standards of known concentration of your analyte. Run them through your method and quantify them using calibration from your GC-MS method. You'll see the signal level off at a high enough concentration and that will give you the capacity.

Analytical Method  for volatile organic compounds are the two main methods for the isolation of volatile organic compounds from water are the purge and trap method and headspace method. 

The sorption capacity is an  important factor because it determines how much sor

bent is required for quantitative enrichment of the an analyte from a given solution. In order to evaluate the adsorption capacity of the sorbent, a batch method was used: standards of known concentration of your analyte (mg/L) was added to 100 mg sorbent. After shaking, the mixture was eluted from SPE and, the retained analyte in supernatant solution determined by MS. My be You have to use a microextraction step after elution from SPE.

The capacity of the sorbent was mg of analyte per gram of  sorbent.

Just go with suggestion provided by Sean Lehman and you'll be okay. Just load different amounts of the analytes unto your SPE cartridge and generate the profile for the amount extracted. The point were it plateaus off is your SPE sorbent capacity.

Alternatively, knowing the mass of the sorbent, your nominal amount loaded and amount you extract after passing it through the SPE cartridge, you can calculate the capacity from the meq 

It is meq of analyte sorbed onto unit g of solid phase. you need quantitative gc-fid

or ecd

Dear,

It will be better you prepare different concentration (at least 5 solution), then pass through the SPE column. Then determine the residual concentration (in passed solution). Adsorption capacity will calculate as follow equation: qe=(V/m)*(C0-Ce).

qe is adsorption capacity (mg/g), V is initial volume (mL), m is adsorbent dosage (mg), C0 is initial concentration (ppm) and Ce is residual concentration (ppm).

In this way you will get equilibrium adsorption capacity (qe). For maximum adsorption capacity (qm), the qe must be plot versus Ce, The point were it become plateaus is qm.