Determination of isoprene in human expired breath using solid-phase microextraction and gas chromatography–mass spectrometry

An analytical method for determination of isoprene in expired breath as a marker of body cholesterol synthesis was developed with a special emphasis on breath sampling. Patients were breathing controlled air using respiratory masks for 2 min (washout period) and then their expired breath was collected in 8-l Tedlar bags. The bags were heated to 40°C and the solid-phase microextraction fiber Carboxen–polydimethylsiloxane 75 μm was inserted through the septum. Extraction time was 10 min. Analytes were desorbed in the GC injector for 2 min at 270°C. Analyses were performed on a Q-PLOT column and fragment ions 68, 67 and 53 were quantified. The concentration range was 1–40 nmol/l, limit of detection was 0.25 nmol/l, the calibration curve was linear. Precision, expressed as RSD, was 5.5–12.5%. These tests are non-invasive, feasible and relatively inexpensive.