The effectiveness of biofilters in removing volatile organic compounds (VOCs) in complex mixtures is often difficult to evaluate due to the presence of numerous unknown compounds. A study was undertaken to determine if a simple, accurate, and useful method could be developed for the quantification of complex mixtures of VOCs. The study compared results from an external standard calibration with several primary components, an internal standard calibration with deuterated ethylbenzene (EB-d10), and an external total hydrocarbon calibration. The EB-d10 internal standard calibration resulted in quantifications of both area sum and individual compounds in the VOC stream which were within 12% of the two external calibrations. This technique allows technicians to monitor the concentrations of all analytes individually and as a group without complicated calibration techniques or preparation of multi-component standards. Finally, this method has proved useful in the quantification of air VOC samples which were incorporated into a commercially available toxicity assay system.