Ion trap liquid chromatography/tandem mass spectrometry analysis of leukotriene B4 in exhaled breath condensate

The objective of this study is the measurement of leukotriene B₄ (LTB₄), a potent inflammatory mediator, in exhaled breath condensate by using liquid chromatography/mass spectrometry (LC/MS and LC/MS/MS). Condensation of exhaled breath is a non-invasive method to collect airway secretions. Deuterated (d₄)-LTB₄ was used as internal standard. The MS and MS/MS behavior of LTB₄ and LTB ₄-d₄ was studied by electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in both positive and negative ion polarity mode. Preliminary results show that monitoring negative ions in ESI mode has the best sensitivity for both LTB₄ and LTB ₄-d₄. Therefore, negative ESI was chosen, and the [M-H]^- ions at m/z 335 and 339 were selected for quantification. The lower limit of quantification for LTB₄, expressed as the lowest point of the calibration curve, was 100 pg/mL. Using this technique, we measured LTB₄ in exhaled breath condensate in two healthy subjects, four asthmatic patients on anti-inflammatory treatment, and four asthmatic patients who were not on anti-inflammatory drugs. Exhaled LTB₄ concentrations were detected only in asthmatic patients who were not on anti-inflammatory therapy. This method is potentially useful for non-invasive assessment of airway inflammation, but the sensitivity of the technique needs to be improved.