AN AUTOMATIC SYSTEM FOR THERMAL LENS SPECTROMETRY AND FLOWING SAMPLES

A computer-controlled pulsed-flow system for thermal lens spectrometri c detection, is developed. Flow pulses are synchronized with the laser pumping and data acquisition periods, measurements being made in stat ic conditions at the end of the stopped-flow half-cycles. A comparativ e study of the measurement of FIA peaks in continuous and pulsed flow conditions is made. Using the pulsed-flow system, the dependence of se nsitivity and noise on the flow and on the presence of turbulences or irregular pump pulses in the flow, is reduced. With a methyl red solut ion injected into a 1:1 ethanol-water carrier at a flow rate of 2.7 mL min-1, limits of detection and peak area repeativities were 2.1 x 10( -8) M and 6.0%, and 6.2 x 10(-9) M and 4.3%, for the continuous and pu lsed flows, respectively. Linear dynamic range extended up to 5 x 10(- 7) M.