Decomposition and solubility of H₂O₂: Implications in exhaled breath condensate

Hydrogen peroxide (H₂O₂) is one of the metabolic end products present in exhaled breath. 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 H₂O₂ 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 H₂O ₂ 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. The experimental results showed the decomposition rate of H ₂O₂ increased as the breath temperature and sampling time increased and the solubility of H₂O₂ 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. These experimental findings need to be further verified with human/animal breath samples.