GB1282659A - Atomic fluorescence spectroscopy system - Google Patents

Abstract

1282659 Fluorescence spectroscopy HEWLETT-PACKARD CO 10 Sept 1970 [12 Sept 1969] 43363/70 Heading G1A In an atomic fluorescence system in which a source 21-25 provides radiation having spectral lines characteristic of the atomic species being detected in a sample contained in a chamber 11, the sample is periodically electrically energized to provide a vapour and a photo-detector 43 is gated by the energizing pulse source 59 to provide an output only between pulses. In these betweenpulse periods the output from the detector 43, which may be a photo-multiplier consists of the spectral information regarding the species, superimposed upon unwanted thermal radiation. These two components are separated by chopping, 63, or pulsing the light source at a lower frequency -50Hzthan the sample energizing frequency -500Hz, and employing a switch 49 in synchronism with the light source modulation. Signal averager 51 thereby recieves the component of the detector output corresponding to fluorescence plus thermal radiation, while averager 53 receives the component corresponding to thermal radiation only, i.e. that produced when light from the source is not incident on the sample. These two signals are subtracted and supplied to a log circuit 57 whose output is proportional to the concentration of the species in the sample. The log circuit output may be fed back to a switch 19 of the pulse supply to control the supply of energy to the sample chamber and hence prevent over excitation of the sample. The lamps 21-25 are metallic vapour electrodeless discharge tubes. Each one is characteristic of a particular element and they are employed in sequence for multi-element analysis. Mirrors 39, 41 are provided at each end of the light path to maximize the incident radiation. A lens system may be provided between the sample chamber and the detector, and a monochromator or filter may also be provided in this position for selective attenuation of the emitted light. The gating pulses from the generator 59 are delayed by a one-shot multi-vibrator 61.