Infrared Spectroscopy - Varied Applications

Concrete Staining

In a more investigative role Infrared spectroscopy has been used to examine a concrete sample with a heavy pink staining. Due to the nature of the sample, a direct analysis was not possible, so an infrared spectra had to be obtained using a solvent extraction and cast film technique. The resultant infrared spectrum when compared with our own library data of infrared spectra was found to be very similar to phenolpthalein, as can be seen in figure 5, so the staining on the concrete sample was probably the result of spillage by a careless operative.

Figure 5 Infrared spectra of heavy pink staining on concrete and phenolpthalein.

In a similar investigative vein a ceramic tile had surface markings that may have originated from a paint product or an adhesive material. Comparison of the infrared spectra obtained from the three materials in question soon identified the source of the markings to be the paint product, rather than the adhesive.

Using Infrared Spectroscopy to Investigate Cable Damage

Both of the previous two examples show how the technique of infrared spectroscopy can be used in a comparative way to identify unknowns. However in a less obvious scenario some cabling had been accidentally immersed in an inhibitor solution containing sodium nitrite. The purpose of the analysis was to determine if the inhibitor solution had penetrated the outer sheath of the cable thus posing a threat to the high purity copper conductors within.

Due to the small quantity of water and therefore even smaller quantity of sodium nitrite that may have penetrated the cable, classical analytical techniques could not be employed. Water is however infrared active and so employing the technique of infrared spectroscopy spectra could be obtained for the outside face of the cable, inside surface of the cable, and by paring the cable at a shallow angle with a scalpel, the middle of the cable.

Lengths of cable were variously subjected to immersion over a range of time spans, heating in water and immersion with a vacuum being applied to the inside of the cable. Infrared spectra were then obtained of the three positions and compared one to another. The results did not show any evidence of water penetration into or through the outer sheath, so therefore it was felt unlikely that a short term immersion would have had any dramatic effect.