Measurement of Highly Diluted Aqueous Solutions of Ammonium Persulfate

Raman spectroscopy is traditionally associated with bulk measurements and detection limits in the percent range. These limits are being pushed by technological advancement: Anton Paar’s Cora Raman systems with their high sensitivity and throughput allow for the detection of small fractions of the radical starter and oxidation agent ammonium persulfate (APS) in water with concentrations down to 0.005 M (≈ 0.1 wt%) within less than 10 seconds.

The challenge of detecting small concentra-tions using Raman spectroscopy

Detection of samples in low concentrations is a field of application Raman spectroscopy traditionally strug-gles with. This originates mainly from the fact that the Raman effect produces extremely small signals. If the sample is more and more diluted, the measured Ra-man signature becomes smaller until it vanishes in the noise of the baseline. While this is sometimes over-come by massive averaging, long integration times, or deep detector cooling, the lower detection limit ulti-mately is a characteristic quality of the spectrometer.

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