Issues with copper content determined by different methods
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Yesterday, the laboratory analyzed a solid waste sample; flame atomic absorption spectroscopy indicated a copper content of around 4.5%. In order to obtain more accurate figures, the laboratory used the conventional iodometric method, and the results showed that there was almost no copper present. For flame atomic absorption, they are digested with aqua regia, made up to volume, filtered, diluted, and then directly analyzed using the instrument. The iodometric method also involves digestion with aqua regia; after routine operations such as pH adjustment, potassium iodide is added for the titration of iodine. They are all experienced inspectors, and there will be no issues with the testing procedures or the pre-treatment process. And the results remained similar after repeating the tests, indicating that the sample was also correct. They asked me why, and I said that this sample is a blind sample whose source of production is unknown; perhaps copper exists in a special form, and after conventional pretreatment it may not be in the form of divalent copper that can be titrated I suggest trying to calcine the sample at high temperature first, and then seeing if copper can be determined to be around 4% using titration Is it possible to have false copper absorbance in flame atomic absorption? According to them, about 0.2 g of sample is used, diluted to 100 mL, and then further diluted 100-fold before being analyzed. I think at such a dilution factor, the possibility of interference isn’t very high, right?
A possible reason for this difference is that copper may exist in a special form, not in the form of divalent copper that can be directly titrated. Flame atomic absorption spectroscopy may detect other forms of copper, whereas the iodimetry method may not be able to detect such forms of copper, resulting in significant differences in the measurement results. Attempting high-temperature calcination of the sample followed by titration may help determine the existence form of copper. The possibility of false copper absorbance occurring in flame atomic absorption spectroscopy is relatively low, but the possibility of interference from other factors cannot be completely ruled out. .
This post was last edited by qqgd on 2024-7-15 at 11:48. Why not process the samples under the same conditions and then distribute them to two analysis stations, where different analysis methods are used for testing? Additionally, a qualitative test should first be conducted on any copper elements or compounds that may be present in the sample; those with knowledge of analytical chemistry in the laboratory should be familiar with the qualitative testing for copper. If the laboratory has an XRF analyzer, solid samples can be used to test for copper. In short, the two different methods yielded significantly different results; it is necessary to look for reasons in aspects such as method operation, sample processing, and sample origin. This is not an analytical bias, but rather a problem that exists clearly throughout the entire analysis process yet went unnoticed.
Atomic absorption is generally less affected by metal interferences, resulting in high accuracy; titration methods have their own limitations, and it is necessary to carefully identify the sources of interference. If that doesn’t work, other methods can be used for comparison.