Measurement of Highly Diluted Aqueous Solutions of Ammonium Persulfate

Raman spectroscopy is traditionally associated with detection limits in the percent range. Anton Paar’s Cora 5001 Raman spectrometers push the limits down to 0.1 wt% for aqueous solutions of the radical starter and oxidation agent ammonium persulfate.

The Challenge of Detecting Small Concentrations using Raman Spectroscopy

Detection of samples in low concentrations is a field of application Raman spectroscopy traditionally struggles with due to the fact that the Raman effect is extremely weak. If the sample is more and more diluted, the measured Raman signature becomes smaller until it vanishes in the noise of the baseline. While this is sometimes overcome by massive averaging, long integration times, or deep detector cooling, the lower detection limit ultimately is a characteristic quality of the spectrometer.

Ammonium Persulfate, a Versatile Oxidizer

Ammonium persulfate (APS), an off-white powder with the chemical formula (NH4)2(S2O8), is a reagent important for many different applications. It is used as starter in radical polymerization of e.g. PTFE (Teflon®), to prepare polyacrylamide gels for electrophoresis, as etching reagent for circuit boards, to graft starch, and as oil decolorizer, to name a few applications.

It is highly important to be able to quickly assess the presence of this reactive compound. Larger amounts of remnant APS from a radical polymerization will degrade the quality of the polymer, especially when exposed to sunlight. Similarly, when using APS in food products, such as starch or edible oil, it is highly important to ensure that no APS is left in the end product.

Thus, there are many situations in which it is important to check for left-over APS or determine the activity of a prepared APS reagent. Since time is a significant factor here, requirements for an analysis method include short measurement times, simple usage, and low sample preparation effort.

Anton Paar’s Cora 5001 Raman spectrometers are the ideal tools to quickly assess the presence of APS in both reagents and finished products. They enable measurements of aqueous solutions directly through the packaging.

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