In order to determine the background level of volatile organic compounds (VOCs) in Canadian indoor air, a method of identification and quantification at a level of 0.3 μg/m3 using systematic single-ion chromatograms (SICs) has been developed. The compounds selected for measurement included several halogenated compounds, oxygen compounds, terpenes, and C8 to C16 n-alkanes. Air samples were taken in 3-layered sorbent tubes (glass beads, Tenax TA, Ambersorb XE-340) and trapped compounds were thermally desorbed into the helium stream of a gas chromatograph/mass spectrometer (GC/MS) analytical system. Total quantities of volatile organic compounds (TVOCs) were measured using a flame ionization detector (FID). Individual compounds were analyzed by a GC/MS. For the identification of compounds in the main stream GC effluent, both the specific GC retention and mass spectra were used. For the purposes of this study, the specific retention was defined based on two primary reference compounds, benzene and p-dichlorobenzene, and several secondary reference compounds. About 50 selected SICs were routinely extracted from a total ion chromatogram (TIC) to detect and quantify compounds. For each compound, a single representative ion was selected. The specific retention was calculated from the elution time on the SIC. For quantification, ion counts under a peak in the SIC were measured. The single-ion MS response factor for some of the compounds was experimentally determined using a dynamic reference procedure. For compounds whose response factors have not been measured, the total ion counts were calculated from the single ion counts by a regression equation and the total ion counts of a peak were assumed to be proportional to the concentration of the compound in the air.