Decomposition and solubility of H₂O₂: Implications in exhaled breath condensate collection

Hydrogen peroxide (H₂O₂) is one of the metabolic end products present in exhaled breath and exhaled breath condensate. High levels of H₂O₂ found in breath condensate are an indicator of airway inflammation and could be used for monitoring the condition of patients with chronic obstructive pulmonary disease. However, sampling conditions such as breath temperature, condensing temperature, flow rate and collection time can affect the intrinsic properties of H₂O₂ - its solubility, volatility, and decomposition rate. Sudden decreases to H₂O ₂ concentration may be due to the sampling conditions instead of the patient's health status. The decomposition rate and Henry's law constant for saturated H₂O₂ vapor (RH > 95%) within 22-42°C, which correlates to room temperature and range of human breath temperatures, are needed for better understanding and standardization of breath collection. In this study, we determined the effects of initial H₂O₂ concentration, temperature, and sampling time on the decomposition rate by comparing electrochemical measurements of H2O2 in simulated breath samples. Results showed the decomposition rate of H₂O₂ increased as the breath temperature and sampling time increased and the solubility of H ₂O₂ increased with increasing flow rate and condensing temperature during sampling. Prediction models for H₂O₂ sensing in exhaled breath sample were developed that could be used in the standardization of exhaled breath condensate collection.