HIGHLY SENSITIVE MICROWAVE TEMPERATURE-JUMP APPARATUS

A temperature-jump apparatus with repetitive microwave heating and spectrophotometric detection is described. Temperature jumps of 1.5°C are achieved in a flow microcell within 1.5 μs (two shorter heating times of 0.5 and 0.25 μs are also available) at a repetition rate up to 50 Hz. On-line accumulation of the relaxation signals is performed with a PDP 11 processor, leading to very short recording times (more than 1000 signals accumulated in less than 50 s) and to a sensitivity better than 10-4 optical density (OD) units. Nonlinear identification treatment permits processing the summed signal even when it is strongly blurred by noise. To demonstrate the capabilities of our apparatus, highly shifted fast prototropic equilibria in aqueous solutions of pyrimidine base have been studied.