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Fabric softeners and laundry perfumes (concentrated fragrances) are a category of personal care/laundry products used for their ability to make textiles softer, smoother, and more pleasantly scented after the washing cycle. A variety of raw materials is necessary to manufacture these products, and different analytical methods are often required before production can commence. Traditional analysis requires time-consuming methods. This Application Note describes how viscosity, dry matter content, and pH level of fabric softeners and laundry perfumes are measured with near-infrared spectroscopy. Near-infrared spectroscopy (NIRS) is a fast, chemical-free analysis technique for quality control of fabric softeners and laundry perfumes without sample preparation.

Figure 1. OMNIS NIR Analyzer Solid with transflection vessel and large reflector

Fabric softener and laundry perfume samples were measured with an OMNIS NIR Analyzer Solid (Figure 1) in transflection mode (1000–2250 nm) using a 1 mm gap size reflector and 28 mm disposable vials.

Reference values of dry matter were measured by loss on drying, and pH and viscosity were determined with a pH meter and viscometer, respectively.

OMNIS Software was used for all data acquisition and prediction model development

The obtained NIR spectra (Figure 2) were used to create prediction models for quantification of dry matter, pH value, and viscosity. The quality of the prediction models was evaluated using correlation diagrams (Figures 3–5) which display a very high correlation between the NIR prediction and the reference values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.

Figure 2. NIR spectra of fabric softeners and laundry perfumes analyzed on OMNIS NIR Analyzer Solid

Result pH in fabric softeners and laundry perfumes

Figure 3. Correlation diagram and the respective FOMs for the prediction of pH value in fabric softeners and laundry perfumes using an OMNIS NIR Analyzer Solid. The correlation set is shown in blue, and the external validation set is in green.
R2 SEC SECV SEP
0.997 0.11 0.14 0.15

Result dry matter in fabric softeners and laundry perfumes

Figure 4. Correlation diagram and the respective FOMs for the prediction of dry matter in fabric softeners and laundry perfumes using an OMNIS NIR Analyzer Solid. The correlation set is shown in blue, and the external validation set is in green.
R2 SEC (%) SECV (%) SEP (%)
0.995 0.09 0.10 0.09

Result viscosity in fabric softeners and laundry perfumes

Figure 5. Correlation diagram and the respective FOMs for the prediction of viscosity in fabric softeners and laundry perfumes using an OMNIS NIR Analyzer Solid. The correlation set is shown in blue, and the external validation set is in green.
R2 SEC (cp) SECV (cp) SEP (cp)
0.994 17.16 20.25 22.18

This Application Note shows the feasibility of the analysis of dry matter, pH, and viscosity in laundry perfumes and fabric softeners with near-infrared spectroscopy. Measurement of all three quality parameters can be conducted within seconds without using any chemicals.

NIRS can be used in several steps of the production chain or during quality control of the final product, saving manufacturers time and money. Additionally, with NIRS only one technology is required, compared to the standard analytical techniques often used for these determinations (Table 1).

Table 1. Overview of standard methods used for the determination of different reference values in fabric softeners and laundry perfumes.
Parameter  Method Time to result
Dry matter Loss on drying 30 min
pH pH meter 5 min
Viscosity Viscometer 15 min (sample preparation + measurement)
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Metrohm ANZ

56 Buffalo Road
2111 Gladesville

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