Firstly, it is necessary to judge the service life of graphite tube clearly, so as to realize correct judgment and replace the graphite tube in time, so as to ensure the safe and stable operation of atomic absorption spectrometer and the authenticity and reliability of the analysis results.
(1) judging from appearance:
The outside of the inlet is obviously thinned after burning; the inlet is enlarged; the surface of the tube is obviously honeycombed; the whole tube is in the shape of a waist drum, and the brightness is obviously higher than that of the initial atomization.
(2) according to the standard solution absorbance value,
When a certain graphite tube is determined, the standard sample with suitable concentration is repeatedly injected after more than ten times of air burning (the performance of the tube has been stabilized), and the absorbance value is recorded as a reference value for the future; when the tube is used for a certain number of times or the appearance of the above-mentioned changes, the absorbance value of the standard sample is compared. If the absorbance value is larger than the reference value and has a decrease in reproducibility, it indicates that the life of the tube has arrived.
Sometimes there is no obvious change in the resistance value of the tube, but the memory effect is significant, which is reflected in the poor reproducibility of the measured value, which is often ignored by the user; the judgment method is: no sample in the tube, at this time the measured value should be less than 0.008Abs, If the value is greater than an order of magnitude and the reproducibility is poor, a new tube is required, but it is worth mentioning that this tube is not necessarily discarded, and other elements may be tested without problems.
(3) According to the reproducibility of the measurement results and the RSD judgment:
Look at the RSD value of the standard curve, if this value is obviously larger, such as >10-15%, and repeat it.
The RSD value of standard solution and quality control solution measured by graphite furnace method should be less than 10% for the atomic absorption work of Daya Bay and Ling’ao nuclear power stations.
(4) judging from the number of times used:
If the sample is single and the analysis frequency is fixed, the service life of the graphite tube can be preliminarily judged according to the number of times the graphite tube is used. According to the experience value of past use, we can preliminarily judge whether it is close to the service life of graphite tube.
(5) according to the peak shape of the analysis results,
If the peak shape of the atomization stage is tailed, the pyrolysis coating inside the graphite tube is damaged and the sample penetrates into the graphite tube wall, the accuracy of the analysis results will be affected. This situation can be combined with the criteria mentioned above to determine whether new graphite tubes need to be replaced.
