Natural carbon isotopes (carbon-12 (12C) and carbon-13 (13C)) contained in human respiration can be used to detect various diseases (cachexia, helicobacter pylori). Isotope mass spectrometry (IRMS), which is widely used to determine carbon isotopes in human respiration has a high level of accuracy and sensitivity, but is a very complex and expensive technique. There is a less expensive way to detect carbon isotopes using an isotope-selective non-dispersive infrared spectrometer (NDIRS), but it is only suitable for simple breath tests when a small number of samples is required. Raman spectroscopy is well suited for the simultaneous detection of various gases in the analysis of human respiration, but the Raman signal from the carbon isotopes has a very low intensity, what makes their detection difficult. In this work, we demonstrate an effective system for detecting carbon isotopes 12CO2 and 13CO2 in human breath with an extremely low concentration level of ~ 0.01%. The Raman detector consists of a 5 W CW narrow-linewidth single-frequency solid-state laser at 532 nm, a focusing system with compensation for a spherical aberration, a gas cell which can withstand pressures up to 100 atmospheres and a high-resolution Czerny-Turner based spectrometer with a matrix, cooled by a Peltier element down to -40 °C. Such a system has a lower cost in comparison with analogues and can be used the medical diagnosis of various diseases.
|