Spectrophotometer aging and prediction of total soluble solids

There is a trend to take instrumentation from the laboratory to the field, e.g., a range of spectrophotometers are commercially available for in field assessment of fruit attributes. Unfortunately, field users tend to place less emphasis on instrument maintenance, so understanding performance issues is important. Deterioration of lamp output quality over time and degradation of detector signal to noise ratio are some of the issues associated with aging of an instrument. To document the effect of instrument aging on fruit quality prediction, an experiment was conducted with three handheld spectrophotometers, with repeated spectra of a reference Teflon tile, and spectra of 20 apple fruit acquired at yearly intervals. Fruit TSS was also assessed, and used in development of a PLS regression models. The repeatability of each instrument was assessed as the standard deviation of absorbance, typically around 0.1 mAbs. Instrument changes were identified in performance and in PCA plots, but performance (apple TSS model) was not related to instrument repeatability.