EFFECT OF STRAY LIGHT IN MONOCHROMATORS ON DETECTION LIMITS OF FLAME ATOMIC-FLUORESCENCE SPECTROMETRIC MEASUREMENTS

Quantitative results are described that demonstrate that the use of a double monochromator to reduce stray light originating from strong thermal emission in the flame gives significant reductions in noise on the background of the fluorescence measurement. This leads to worthwhile improvements in detection limit for all elements with analytically useful resonance lines at wavelengths shorter than approximately 250 nm. The degree of improvement depends upon whether water or a real sample is being aspirated. For the determination of cadmium in urine the detection limit is improved by a factor of three and for the determination of selenium in water the improvement is a factor of 5-6. Scatter of excitation source radiation is also shown to have a small but significant effect on detection limits when using electrodeless discharge lamps as source. Scatter is more serious in the air - hydrogen flame than the air - acetylene flame.