Will storing for more than 24 hours lead to inaccuracy of results?
My concentration ranges from 20-80mg/L of zinc.
My study also takes into consideration pH (as zinc speciation occurs as pH changes). Would storage of more than 24 hours affect it considerably? What would be the maximum storage time?
If the pH is below 2, these solutions can be stored for much longer than 24 hours without a significant change in concentration. You can check this by recording the absorbance of the standards in dependence of storing time.
If the pH is neutral or alkaline, zinc could precipitate more or less immediately. The pH is hence crucial to know. Aqueous and solid zinc species/precipitates can affect the pH and vice versa.
If you need to make zinc standards at pH above 2, you can use chemical speciation modelling to determine if all zinc is in solution at a certain pH and solution composition.
Just after collection of water sample if acidify and make around pH 2, as suggested by Dr. Yolanda, is well recommended and widely in practice. sample should be stored in glass bottle and keep in cool and dark place. Duration to keep the sample is depend upon type of water samples. If sample is high in TDS or chances for precipitation/colloidal solution/ deposition, it is always safe to analyse earliest
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