the invention describes the process by which a standard mixture of organic compounds are spiked and retained onto a composite sorbent matrix for the controlled generation of a standard in fluid above the spiked matrix either in gas or aqueous phase which is contained in portable vials . the novelty of the aforementioned composite matrix stems from the combination of an immobilizing liquid phase such as silicone oil or a polyacrylonitrile solution , and solid , porous particles such as polystyrene - co - divinylbenzene or hydrophilic / lipophilic balance particles to strongly retain the spiked standards facilitating high capacity which translates into prolonged use as a source of calibrant . these novel composite mixtures exhibit sorptive capabilities greater than the sum of their individual components producing a standard analyte generator far superior to those described in the prior art . in addition swelling of the particles with the liquid phase facilitates immobilization of the composite sorbent matrix in the vial . immobilization of said particles has also been achieved by cross - linking of a liquid polymeric solution such as polydimethylsiloxane , allowing the composite sorbent matrix to be uniformly distributed on the vessel wall . with thermodynamic equilibrium strongly favoring the sorbent phase for a wide range of chemical compounds , this invention allows for the reproducible generation of an ultra - low concentration standard analyte mixture in fluid . if the fluid is gaseous , extractions from this headspace can be performed via solid phase microextraction , needle trap devices , or direct headspace extraction for injection onto various hyphenated gas chromatography systems . if the fluid is aqueous , extractions may be performed directly from the standard water for injection onto hyphenated gc or liquid chromatography systems . the invention can be used for a variety of applications ranging from integrated gc - ms or lc - ms tuning , automated instrument quality control , preparation of reusable external calibration mixtures and , addition of internal standards wherein the method provides long - term stability , inter - batch reproducibility , repeatable analyte loading of the fluid , and quantifiable low concentrations at given temperatures .