This Application Note shows the rapid, non-destructive identification of isopropyl alcohol from two manufacturers using Raman spectroscopy following the creation of a suitable library. The measurements with the handheld Raman spectrometer Mira M-1 require no sample preparation and provide immediate results that identify the samples unambiguously.

Organic solvents like isopropyl alcohol are required in the production of many beauty and cosmetic products, paints, fragrances, and in synthesis reactions – the latter in particular in pharmaceutical applications.

In this work, isopropyl alcohol samples from two different suppliers were analyzed and the differences in the spectra were investigated. Unexpectedly, the spectra showed some differences, allowing a supplier-specific identification.

All spectra were measured using the Mira M-1 Raman spectrometer in auto-acquisition mode, i.e., integration times were determined automatically. A laser wavelength of 785 nm and the Orbital-Raster-Scan (ORS) technique were used. The isopropyl alcohol samples were analyzed in vials using the vial holder attachment of the Mira M-1.

Two different suppliers of isopropyl alcohol were evaluated. Due to the visible differences in the spectra indicating a possible contamination of the samples the Raman spectroscopic distinction was possible (see Figure 1).

Figure 1. Spectra of isopropyl alcohol (Supplier 1 and 2) superimposed with a spectrum of ethyl alcohol

The peaks at 1400–1470 cm-1 correspond to the asymmetric vibrations of δ(CH2) and δ(CH3). Between 600–1300 cm-1, aliphatic chain vibrations for υ(CC) can be found. In both samples of isopropyl alcohol, peaks in those areas can be observed.

Changes come up when focusing on the peaks at 883, 1049, 1095, and 1276 cm-1, since those peaks, according to literature, suggest the presence of ethyl alcohol in the sample (see Figure 2).

Figure 2. Differences between the isopropyl alcohol spectra.

Comparing the spectra of the two isopropyl alcohol samples, it becomes obvious that there is ethyl alcohol in the isopropyl alcohol sample of supplier 2. With Mira M-1, it was possible to distinguish the different suppliers, proving that Mira M-1 is suited for the identification of incoming raw materials such as solvents and alcohols.

Author

Metrohm AG

Ionenstrasse
9100 Herisau

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