NIR spectroscopy comes out top in washing powder challenge

Washing powder may be a fairly mundane household item, but it is still regularly tested by manufacturers, both for quality control purposes and to see what their competitors are up to. This testing is mainly done using techniques such liquid chromatography and capillary electrophoresis, which involve taking physical samples, even though non-invasive techniques such as NIR spectroscopy potentially offer a more convenient alternative.

So Christian Huck and his colleagues at Leopold-Franzens University in Innsbruck, Austria, decided to test the ability of NIR spectroscopy to distinguish between eight different washing powders and determine their chemical compositions. They also compared NIR spectroscopy with two other non-invasive vibrational spectroscopy techniques: Raman spectroscopy and attenuated-total-reflection infrared (ATR-IR) spectroscopy.

As reported in Talanta, they quickly discovered that NIR and ATR-IR spectroscopy were much more effective than Raman spectroscopy at analysing washing powders. Whereas NIR and ATR-IR spectroscopy could distinguish between all eight brands, with the spectral data forming distinct clusters for each brand when analysed by principal components analysis, the Raman spectral data didn’t cluster in the same way.

Similarly, when used with partial least squares regression models, NIR and ATR-IR spectroscopy could accurately determine the concentration of all 22 ingredients, including bleaching agents, surfactants and enzymes, making up the eight brands of washing powder. This did require a separate model for each ingredient, though, because a single model that covered every ingredient wasn’t accurate enough. Raman spectroscopy, on the other hand, could only accurately determine the concentration of two ingredient: a dye transfer inhibitor and a surfactant.

Although NIR and ATR-IR spectrometry were broadly similar in their analytical abilities for washing powder, Huck and his colleagues conclude that the availability of portable, handheld NIR spectrometers means that NIR spectrometry is probably the best choice.

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