A new generation chemiluminometer allowing measurements of chemiluminescence in atmosphere of defined humidity with non-destructive sampling.

THE INSTRUMENT (Fig. 1) is designed for commercial applications and enables us to monitor the chemiluminescence signal intensity, which is assumed to be proportional to the rate of the sample degradation, in dependence on temperature (from room temperature to max. 150 °C), humidity (the limits of humidity flow 0.1 – 5 g of water/h) and concentration of oxidizing gas (oxygen). The limits of gas flow are 0 – 10 l/h, any pre-mixed gas can be used. ¶ The sample is inserted in the external chamber (Fig. 2), through the door. The size of the chamber allows for insertion of bigger samples, even of bound volumes (books).

The sample is gas-tightly clamped (Fig. 3) between two gold-plated copper ovens so that the temperature gradient between the detector and the site of reaction is minimal. One oven is situated on an arm, which can be moved in the vertical plane and can approach the light-collecting part of the CL probe. ¶ The movable oven serves only for sample heating, while the fixed one surrounds the outlet of the optical cable through which the chemiluminescence signal is transferred to luminometric part of the instrument (Lumipol 3) via fibre optics (Fig. 4).

In the light-collecting part of the probe, there is also an inlet and outlet of water vapour and gas mixed and preheated to the same temperature as that of both ovens. The atmosphere is pre-prepared in a Bronckhurst mixer and if working with higher water vapour mass-flow the condensed water is lead away from the reaction space. The instrument displays a high degree of regulating precision and the probe (reaction space) and luminometer function independently. If needed, long term measurements of CL of samples can be performed in the humidifying unit with a pre-set temperature, relative humidity and gas flow, while the luminometer itself can be used for instantaneous testing of reactions in progress or for measurements of other samples in a destructive fashion, which enables high productivity.

A typical experiment is performed in the following way. The arm with the heater approaches the part of a sample to be examined (e.g. a page of a book) and the sample is gently pushed towards the light-collecting end of the fibre optics, which is not covered with the sample, but in fact a few milimeters away from it, thus forming the reaction compartment into which humid atmosphere is introduced (Fig. 5). The sample is locally heated (the diameter of the heated area being 2 cm) to the desired temperature and is slowly equilibrated with the surrounding atmosphere, while the light can be collected. ¶ The clamping mechanism is constructed in the way that there is no possibility of sample destruction. The position of the sample is easily adjusted by adjusting the vertical position of the shelf on which the book (or any other sample) is placed, so that any part of the artefact can be subjected to the experiment.

Coupling of both units together (external dark chamber and luminometer) is achieved via an optical cable (Fig. 6). While the light-collecting end is in the vicinity of the sample in the dark chamber, the other end is fashioned in the way to allow easy insertion into the light-sensing part of the instrument. Thus, the extremely weak light collected in the dark chamber is detected by the photomultiplier located in the Lumipol 3 instrument. Via the photon counter and an appropriate software interface (as provided already in the Lumipol 2 instruments), the signal can be observed in the form of a curve representing emmited light intensity vs. time.

The optical cable interface can easily be dismounted (Fig. 7). In such position, light from the sample in the dark chamber is not collected, while on a separate heater, simultaneous experiments can be performed, albeit with destructive sampling. ¶ The provided software permits the control of atmosphere, the mass-flow of water vapour (from which relative humidity can easily be calculated) and the temperature of the sample in the chamber. Additionally, the software provides control over the internal heating oven, the photomultiplier and the photon counter, and provides a user-friendly interface for data acquisition and handling. Features such as high-voltage switching, data acquisition interval and additional security features are provided. The later are needed in order to protect the photomultiplier from a non-desirable exposition of the sensitive photomultiplier to daylight.

The prototype is a highly accomplished instrument and permits examinations not only of paper-like materials, but also of any sheet-formed material, e.g. many other polymeric materials that can be cast into thin films. This feature makes the prototype even more important achievement, as its use can be extended into areas of research other than protection of cultural heritage.