The Accurate Analysis of Low Levels of Magnesium in PE and PP

For the production of PE and PP polymers catalysts are commonly used for reaction enhancement. Catalyst systems of the Ziegler-Natta type are a mixture of reagents used in the production of polymers of the 1-alkenes type (α-olefins). As the catalyst is very expensive it is not wishful spending it rapidly. In addition the efficiency of the catalysts must be optimised to maximise the output of polymer with a given amount. In order to monitor the catalyst performance, the analysis of magnesium in the final polymer product is important. The aim is to achieve the best accuracy and precision at lowest concentration levels of Mg. Very low levels of Mg can easily be analysed by means of the wavelength dispersive X-ray fluorescence spectrometer S8 TIGER 4K. Brukers (Germany) modern sequential WDXRF spectrometer S8 TIGER delivers optimal light element performance for this task applying an X-ray tube with up to 170 mA current at full 4 kW power. It proves to be an optimal solution for the enhanced accurate and precise analysis of light elements in extreme low concentrations.

The S8 TIGER is the most versatile sequential wavelength dispersive X-ray fluorescence spectrometer. Equipped with an end window X-ray tube with Rh-target and a 10 position beam filter changer the excitation conditions can be easily adjusted to achieve optimum results. To further improve the analysis of traces a broad selection of up to nine different beam filters is available to suppress e.g. Rhodium tube lines and to improve the peak-to-background ratio. With up to four collimators, up to eight analyser crystals and two detectors the S8 TIGER can be adjusted for each element to match the required resolution and sensitivity.

The S8 TIGER is calibrated using certified reference sample in combination with validated process sample. The standard deviation of the calibration is excellent with 0.2 ppm. The accuracy of the method was evaluated with the analysis of two factory samples. Sample 1 contains 5.3 ppm, and sample 2 with 1.5 ppm Mg.The XRF results perfectly fit to the reference values, the deviation is 0.3 ppm for sample 1 and 0.1 ppm for sample 2. To test the precision the two samples were analysed alternated, the results of the 10-fold repeatability test are shown in the table. A precision of 0.1 ppm is obtained for both very low concentration ranges.

The analysis of very low levels of magnesium in PE and PP is accurate and reliable with the S8 TIGER. The achieved detection limit is very low with 0.2 ppm even beside high concentrations of aluminum. Magnesium indicates losses of valuable catalysts during the production process. If analysed precisely It can be easily used to realise savings on catalysts costs giving early warnings in case of catalyst losses. In contrast to ICP-OES the WDXRF spectrometer S8 TIGER is the perfect analytical tool due to its easy operation, quick sample preparation and simple integration into the plant quality and process control regime.