Precise 13 CO 2 / 12 CO 2 isotopic ratio measurements for breath diagnosis

ABSTRACT A laser spectrometer based on a distributed-feedback semiconductor diode laser at 2  m is developed to measure the changes of 13 CO 2 / 12 CO 2 isotope ratio in exhaled breath sample with the CO 2 concentration of ~4%. It is characterized by a simplified optical layout, in which a single detector and associated electronics are used to probe CO 2 spectrum. The cell has 10 cm long base length with 26.4 m optical path length in total and 330 cm 3 volume. The cell pressure and temperature are controlled at 50 Torr and 28 , respectively. The best 13 / precision of 0.06‰ was achieved by using wavelet denoising and Kalman filter. Keywords: Stable isotopes, Laser spectroscopy, Human breath, Wavelet denoising, Kalman filter. 1. INTRODUCTION Exhaled breath testing, as a non-invasion and safe diagnostic method, is an ideal approach to evaluate health status and disease types. The bacterium Helicobacter Pylori , being able to dissociated the urea molecule by the urease producing ammonia and carbon dioxide, is believed to cause peptic ulcer in humans while infecting the gastric mucous layer. The carbon dioxide produced by the b acterium is expelled through the expired breath. It means that an infected people will expire more