PETpla.net Insider 11 / 2016

INSPECTION 24 PET planet Insider Vol. 17 No. 11/16 www.petpla.net Chemical optical sensors determine oxygen permeability of barrier and breathable packaging material Optical sensors for oxygen permeability Based on an article by Christian Huber, PreSens Precision Sensing GmbH; Kajetan Müller, Fraunhofer IVV; Gernot John, PreSens Precision Sensing GmbH The barrier requirements of syn- thetic materials towards oxygen can differ widely, depending on their later use. Unwanted oxygen in packaging, taken up while filling or by permeation through the packaging material, can lead to oxidative deterioration of food, and shorten the shelf-life of certain products. Different methods are cur- rently applied to determine oxygen permeation in packaging materials such as the barometric method or the use of carrier gas. However, these traditional analysing techniques do not guarantee realistic conditions, as they are only applicable for empty packag- ing. A new technique is permeation measurement with chemical opti- cal sensors with a detection limit of 1ppb of dissolved oxygen. They can measure oxygen ingress continu- ously, non-destructively and non- invasively under real conditions over long time periods. The PreSens PSt6 sensor can be applied to meas- ure packaging material for most food applications. It enables the analysis of both barrier and breath- able packaging materials. A recently developed measurement device together with the new low oxygen sensor PSt9, with a detection limit of 0.5ppm and a dynamic range of 0 to 1,000ppm gaseous oxygen, fulfill the requirements of measuring high bar- rier materials which are needed for technical applications. Measurement principle Chemical optical sensors consist of a thin layer containing an analyte sensitive dye. These sensor spots are excited by light of a certain wave- length and emit fluorescence. If the indicator dye in the sensor encoun- ters an oxygen molecule, the excess energy is transferred to oxygen in a non-radiative way; the indicator mole- cule does not show luminescence and the total measurable luminescence signal decreases or is quenched. This principle of decay time meas- urement is used to determine the oxygen concentration in the sample. An optical fibre transfers light to the sensor and the fluorescence signal back to a photodiode integrated in It is very important to determine the barrier properties of packaging and other synthetic materials to protect oxygen sensitive foods, pharmaceuticals and technical applications. New methods in material research are therefore required for oxygen permeation measurements to characterise spe- cial synthetic films. A novel approach is the non-invasive, non-destructive measurement of oxygen permeability with chemical optical sensor technology. Oxygen ingress in filled or empty packaging for most food applications can be deter- mined. Another advantage is that these sensors can be used to measure breathable as well as high barrier films. Fig. 1: Measurement system set-up: The new measurement cell with two gas con- nectors for each of the two chambers; the sensor spot is integrated in the upper chamber and read out via polymer opti- cal fibre by the fibre optic transmitter (source: Fraunhofer IVV).