Knowitall informatics system 8.2 multi technique database

Samples were analysed using a Perkin Elmer Spotlight 400 system (wavenumber range 4000 cm^-1 to 900 cm^-1). Spectra were taken with a 20 μm² aperture and 4 cm^-1 resolution; final spectra were an average of 16 scans. All spectra and maps were background subtracted. Organic peak assignments were made using the Bio-Rad KnowItAll Informatics system 8.2 Multi-Technique database, inorganic peaks by reference values [10 ].

FTIR spectra were collected by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) using a Perkin Elmer Spotlight 400 imaging system. Spectra were taken using a wavenumber range of 4000 to 650 cm^-1, at a resolution of 4 cm^-1 and using an aperture of 100 μm². Sixteen replicate spectra were obtained. Each was background subtracted and then all were summed to produce an averaged, background subtracted, summary spectrum. Organic peak assignments were made using the Bio-Rad KnowItAll Informatics System 8.2 Multi-Technique database. Uroporphyrin I ethyl ester from bovine porphyric urine (CAS number: 54090-85-6) was purchased from Sigma Aldrich and used as a standard for comparison to the shell.