激光原子荧光光谱分析仪及其分析性能

Laser Excited Atomic Fluorescence Spectrometer and Its Application in Trace Metal Analysis

介绍了自行研制的激光激发原子荧光光谱分析系统。该系统采用激光作为激发光源，电热石墨棒作为原子化器。用聚焦透镜将激光光束聚焦于石墨棒上部２ｍｍ处激发该空间的原子，并用一石英透镜在垂直于激光光束的方向上收集该空间的原子荧光。利用原子荧光和原子化器背景光在空间和时间上不同的特点，在荧光收集光路上加一适当的小孔，用时间门技术除去背景发射噪声。该系统对Ｇａ、Ｉｎ、Ａｕ、Ｐｄ和Ｐｂ的检测限为１０－１～１０－４μｇ／Ｌ。

A high sensitive detection system for trace metal element analysis, based on laser excited atomic fluorescence spectrometer (LEAFS) combined with graphite electrothermal atomization was reported. A 20 μL sample solution was poured into a graphite rod crucible and was heated by an alternating current to produce a neutral atomic beam. The pulsed laser beam with appropriate wavelength, which was produced by a dye laser pumped by an excimer laser, intersected the atomic beam perpendicularly to excite the atoms selected from the ground state to an intermediate state. Then fluorescence photons emitted by the atoms were collected at 90° relative to laser beam. Passing through a diaphragm in the collection optics and a monochromator, the fluorescence photons were separated from background emitted by atomizer and were detected by a fast response photo multiplier tube (PMT). Then the current pulse signal from PMT was coincided with a delayed time gate signal in synchronism with the laser pulse. The residual background light caused by the furnace was almost eliminated by the time gate technique, because only the current pulse signal in synchronism with the laser pulse can be integrated into a charge, and then was converted to a digital by a charge to digital converter (QDC). Finally the data were acquired and processed automatically by a microcomputer. The analytical performance of the LEAFS system, built up by our laboratory, was tested. The detection limits for Ga, In, Au, Pd and Pb were in the range of 10 -1 ～10 -4 μg/L with precision of less than 7% RSD( n =8).