I have carried out an acid persulfate digest (sulfuric acid + potassium persulfate) for total phosphorus extraction on freshwater samples, but can't find a reference for recommended holding time post digestion. Many sources say that the sample can be initially preserved with sulfuric acid and then held for 28 days in the cold before digestion/analysis. Can I assume that the same holding time would be suitable post-digestion? Many thanks.
My experience with digested samples is that the composition is typically stable for long periods if they are sterile and acidic
The holding time for a digested water sample for total phosphorus analysis can vary depending on the specific analytical method and the laboratory's standard operating procedures. Holding times are typically defined to ensure sample integrity and minimize potential changes in analyte concentrations due to sample preservation or storage.
For total phosphorus analysis, it is common to follow holding time guidelines as per the analytical method recommended by regulatory agencies or standards organizations. In the United States, for example, the U.S. Environmental Protection Agency (EPA) provides guidelines for sample preservation and holding times for various environmental analyses, including total phosphorus.
The EPA's recommended holding time for total phosphorus analysis in water samples was typically 28 days at 4°C (39°F) or lower. However, it's important to note that these guidelines can change over time, so it's essential to consult the most recent EPA or relevant regulatory agency guidance for the specific holding time requirements.
In addition to regulatory guidelines, laboratories may establish their own standard operating procedures (SOPs) for sample holding times based on factors such as the analytical method used, the stability of the analyte in the sample matrix, and the specific laboratory's quality control protocols. Therefore, it's advisable to check with the laboratory conducting the analysis for their specific holding time requirements and procedures, as they may differ from regulatory guidelines.
@all The holding time for a digested water sample for total phosphorus analysis can vary depending on the specific analytical method and the preservation techniques used. However, in general, it is recommended to analyze the digested samples as soon as possible after digestion to minimize potential changes in the phosphorus concentration. Here are some considerations:
In summary, while the holding time for digested water samples for total phosphorus analysis may not be as critical as for some other analytes, it's still essential to minimize delays between digestion and analysis to obtain accurate results. Follow the guidance provided by your specific analytical method or laboratory, and if in doubt, consult with the experts or resources associated with your analysis to ensure you are following the best practices for your particular situation.
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