A cavity ring-down spectrometer for study of biomedical radiocarbon-labeled samples.

A compact cavity ring-down spectrometer aimed at the detection of trace amounts of radiocarbon (¹⁴C) in biomedical samples is demonstrated. Rapid sampling, as required for large scale studies, is made possible by modifications to a CHNS elemental analyzer. After conversion of the carbon content of a sample into CO₂, spectral analysis using a high-finesse cavity in conjunction with a quantum cascade laser system reveals the ratio of ¹⁴CO₂ in relation to the stable isotopologues of ¹²C and ¹³C. Cooling and temperature stabilization of the cavity is achieved by a combination of liquid cooling and thermo-electric elements. The system is studied in terms of reproducibility, linearity, and sensitivity as well as contamination and memory effects of the sampling process. While the performance of the system is still limited mainly due to etaloning and other systematic effects, first spectra of biomedical samples, such as urine and feces, have been analyzed at ¹⁴C concentration levels above ten times natural abundance. Results are compared with those from a traditional liquid scintillation counter system. Possibilities for improvement of the sensitivity are discussed. [ABSTRACT FROM AUTHOR]