This invention relates to flameless atomic absorption spectroscopy, and more particularly the invention relates to a graphite tube assembly for use in measuring the flameless atomic absorption, particularly of liquid samples.
For atomic absorption measurements, it is conventional for a sample to be introduced into the interior of the graphite tube, dried at a relatively low temperature, ashed and, subsequently, atomized at a high temperature. The graphite tube is placed in the path of the rays of a spectrometer so that the absorption of light by the atoms present in the interior of the graphite tube can be measured.
It has been found that in measuring the atomic absorption of liquid samples disturbances may occur because the liquids spread out over wide portions of the inner wall of the graphite tube. The liquids also flow to the end portions of the graphite tube where there is incomplete evaporation, because of the relatively lower temperature thereat, so that the sample material is carried over and interferes with subsequent measurements of further samples. Because of the slightly porous structure of graphite, the sample may infiltrate the wall of the graphite tube to such an extent that an uncontrollable portion thereof will pass through the wall to the exterior when the tube is heated, and is thereby lost for the measurement. This results in substantially lowering the sensitivity of the measurement.
It is known, by virtue of German Offenlegungsschrift 23 23 774, that to avoid such problems the graphite tube may be provided with grooves, at least over a portion of its inner wall and extending transversely with respect to the tube axis. However, since the cutting of the grooves causes a substantial roughening of the inner face, additional infiltration of the sample material results therefrom, so that the improvement achieved does not reach the desired degree.
Further, it is known to manufacture graphite tubes of the aforementioned type from so-called pyrolytic graphite instead of from the usual graphite. This pyrolytic graphite is not porous and, therefore, is impervious to gases. Grooves may also be cut in the pyrolytic graphite without the sample infiltrating the walls of the tube. However, the use of pyrolytic graphite for this purpose is undesirable because of the high cost thereof.