LASER PHOTOACOUSTIC TRACE GAS-DETECTION, AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL-RESEARCH

The use of infrared laser based photo-acoustic trace gas detection equ ipment in biological research is discussed on the basis bf two example s. A CO2 laser based photo-acoustic trace gas detection system is empl oyed to follow the time-dependent pattern of the nitrogen fixation pro cess by the cyanobacteria Nodularia Spumigena on a one-minute time sca le. Due to the high sensitivity of the detection system for ethylene ( detection limit 6 part per trillion; 6.10(12)), the fixation process c an be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a c ertain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation.