Method for determining calcium and magnesium in alkalis by ICP
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ICP is used as the spike; it is mainly employed for measuring high-salt concentrations (secondary brine, saturated). A rectangular tube is used for high-salt measurements, and a humidifier is also available. Today, we tried to measure 2% alkali using the standard addition method. During the first attempt, direct sampling was carried out, but the calcium curve was not satisfactory. So I added reagent-grade acid to neutralize the solution, without changing to a standard rectangular tube; the curve improved after that. I would like to ask: 1. How should alkali be measured? Is neutralization necessary? 2. Whether direct sampling is used or acid is added for neutralization, should a standard rectangular tube or a high-salt rectangular tube be used? 3. When using the standard addition method, why does the calcium-to-magnesium ratio in sample number 0 end up being higher than that in sample number 1?
This post was last edited by qugd on 2015-9-6 20:36. Under alkaline conditions, calcium and magnesium ions form hydroxides, which greatly affects their solubility. The sample should be acidified, not just neutralized; only through acidification can the calcium and magnesium compounds be completely dissolved in the sample solution in ionic form. When using ICP to detect metal ions, the sample must be dissolved in an appropriate acid to form a solution, in order to ensure the reliability of the measurement results. Both standard samples and actual samples should be acidified. Even after acidifying the sample, since the sodium ion content in the sample remains very high, it is recommended to use a high-salt torch tube to minimize salt deposition that could affect the analysis. The original poster had better refer to the sections on atomic absorption and atomic emission analysis methods in the chemical analysis manual.
Thank you for your answer, academician; I’m very grateful.