Effects of measurement technique and sample preparation on NIR spectroscopy analysis of livestock effluents and digestates

The purpose of this study was to evaluate different measurement technique as sample treatments, probes used and sample temperature during NIR scan, in order to obtain accurate and reproducible values of Total Solids (TS), Total Kjeldahl Nitrogen (TKN), Total Ammonia Nitrogen (TAN) and Volatile Fatty Acids (VFA), contained in dairy and swine slurry and digestate. In particular, three sample treatments were tested as filtration, homogenization and a raw control, two types of probes (petri dish and optical fiber) and three different sample temperature during NIR scan (10-25-35°C). We studied the possible significant influences on predictive capability of analyte contents and which experimental condition, allow to obtain the best results. The results show that spectral acquisition through petri dish was more accurate respect to optical fiber. The better sample treatment was represented by filtration. We did not observe any effect of the temperature in the reported range.