How to choose the operating current of the hollow cathode lamp of atomic absorption spectrometer?

Technical Knowledge 2018-12-12 16:31:12
The quality of the element lamp selected by the atomic absorption spectrometer directly affects the sensitivity of the measurement and the linearity of the standard curve. Some of the lamp backgrounds are too large to be used normally. The lamp emits a trace of hydrogen in the lamp during use, and the light emitted by the hydrogen is a continuous spectrum, which can be called the background emission of the lamp.

When the shutter is turned off, then the shutter is turned on, and the wavelength is changed to leave the wavelength of the emission. Where there is no emission line, if there is still a reading, this is the background continuous spectrum. The background reading should not be greater than 5%, preferably equal, and the ratio should be less than 1%. Therefore, check the quality of the lamp before selecting the lamp current.

The hollow cathode lamps are marked with the maximum operating current. For most elements, the working current of daily atomic absorption spectrometer analysis should be 40%~60% of the rated current, which can ensure stable and suitable sharp line light output. Generally, a hollow cathode lamp having a high melting point of nickel, cobalt, titanium, zirconium or the like can be used with a larger current, and for a hollow cathode lamp of a low melting point and easily sputtered bismuth, potassium, sodium, cesium, cesium, gallium or the like, an electric current is used. Small is appropriate.

The magnitude of the operating current of the lamp directly affects the stability of the lamp placement point and the output intensity of the sharp line light. The lamp current is small, and the spectral line of the sharp line that enables radiation is narrow, which makes the measurement sensitivity high. However, if the lamp current is too small, the transmitted light is too weak, and the gain of the photomultiplier tube sensitivity needs to be increased. At this time, noise is increased and the signal-to-noise ratio is lowered; if the lamp current is too large, the spectrum of the radiation is thermally broadened and the collision is widened. The self-absorption in the lamp increases, the intensity of the radiation sharp light decreases, the background increases, the sensitivity decreases, and the consumption of inert gas in the lamp is accelerated, and the service life of the lamp is shortened.

In general, both sensitivity and precision should be considered. The choice of the atomic absorption spectrometer lamp current can be determined experimentally by measuring the absorbance of a standard solution at different lamp currents and plotting the relationship between lamp current and absorbance. The curve is usually a lamp current with higher sensitivity and better stability.

Tags aas spectroscopy absorption spectroscopy atomic absorption spectroscopy instrumentation atomic absorption spectroscopy principle atomic spectrometry
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