Chemical Stability and Compatibility - Stability of diluted iodide standards
Your iodine solutions come in 1% TEA - if we are diluting the solution we get from you (from 1 ug/mL down to 10ng/mL), should we use a 1% TEA solution? Will that help stabilize those lower concentrations or is it only needed for higher (1000ug/mL) concentrations?
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The TEA stabilizes the iodide primarily by keeping the pH relatively high (>7), as iodide stability suffers at lower pH values (particularly when the solutions are stored in plastic). What we can’t answer with great certainty is “how low can the pH be for a given iodide concentration and container material before I should worry?”. De-ionized water in equilibration with the atmosphere will have a pH of about 5.5, so you could probably just dilute in water only, particularly for your working range (10 ng/mL) and if you’ll use the standard immediately. If you plan on using your working standard for several days or weeks, then we’d recommend adding 0.1% TEA just to be safe and help ensure stability. |