Validation of a sensor system for the measurement of breath ammonia using selected-ion flow-tube mass spectrometry.

The measurement of trace breath gases is of growing interest for its potential to provide non-invasive physiological information in health and disease. While instrumental techniques such as selected-ion flow-tube mass spectrometry (SIFT-MS) can achieve this, these are less suitable for clinical application. Sensitive sensor-based systems for breath ammonia could be more widely deployed, but have proven challenging to develop. This work demonstrates the sequential analytical validation of an electrochemical impedance-based sensor system for the measurement of ammonia in breath using SIFT-MS. Qualitative and relative responses between the two methods were comparable, although there were consistent differences in absolute concentration. When tested in artificial breath ammonia, sensors had a relative impedance sensitivity of 3.43x10^-5ppbv^-1for each breath in the range of 249 to 1,653 ppbv (r²=0.87,p<0.05). When correlated with SIFT-MS using human breath (n=14), ammonia was detected in the range of 100 to 700 ppbv (r=0.78,p<0.001), demonstrating acceptable sensitivity, reproducibility and dynamic range for clinical application.