A portable, fast gas chromatographic method for the direct measurement of part-per-billion level of ethylene oxide in medical work place atmospheres is introduced. Ethylene oxide is a chemical of significance in life science for its critical role as a highly effective sterilizing agent for heat sensitive surgical instruments. However, ethylene oxide is highly flammable, a suspected human carcinogen, is mutagenic, and henceforth, requires close monitoring. The approach incorporates a temperature-programmable silicon micromachined gas chromatograph for the fast separation of ethylene oxide from airborne organic interferences. The separation approach is hyphenated to a micromachined differential mobility detector, improving targeted analyte detection, and enhancing the overall selectivity obtained. A complete analysis can be conducted in less than 60s. Further, ethylene oxide in the matrix mentioned can be measured directly with low possibility of false positives and without the need for any sample pre-treatment, such as pre-concentration or derivatization. A relative precision of less than 5% RSD (n=20) over a range from 5 parts per billion (v/v) to 500 parts per billion (v/v) was obtained.