Analysis of additives and catalyst residues in polyethylene using ADPOL standards

Epsilon 3XLE

Introduction

This data sheet demonstrates that the Epsilon 3XLE – a benchtop energy dispersive X-ray fluorescence (EDXRF) spectrometer – is exceedingly capable of analyzing additives and catalyst residues in polyethylene samples using the ADPOL standards.

ADPOL standards

A set of Certified Reference Materials has been developed for the analysis of additives and catalyst residues in polyethylene (ADPOL), in collaboration with DSM-Resolve. The ADPOL set consists of 5 different standards including a blank and each standard consists of 4 discs. The standards cover the elements and concentration ranges normally required for the calibration of important additive elements in plastic and polymers, such as Na, Mg, Al, Si, P, S, Ca, Ti and Zn.

Instrumentation

Measurements were performed using an Epsilon 3XLE EDXRF spectrometer, equipped with a 50 kV silver (Ag) anode X-ray tube, 6 software selectable filters, a helium purge facility to improve the light-element performance, a high-resolution SDDUltra silicon drift detector, a sample spinner to obtain more homogeneous results, and a 10-position removable sample tray for automated analysis.

Sample preparation

The ADPOL standards are solid discs of 40 mm in diameter and 2 mm in thickness. The samples were rinsed with deionised water and then dried with soft laboratory paper. The samples were put in standard sample holders and loaded in the Epsilon 3XLE spectrometer

Measurement procedure

For each ADPOL standard, 4 disks were stacked to set up calibrations for the 9 elements. Three different measurement conditions were used, each one optimizing the excitation of a group of elements (Table 1). The total measurement time per standard was 14 minutes.

Accurate calibration results

Figures 1 and 2 show calibration graphs for magnesium and titanium in the ADPOL standards and show good correlation between the certified concentrations and the measured intensities. The SDDUltra light-element performance contributes largely to the improved analysis capabilities for sodium and magnesium. Detailed calibration results for all analyzed elements in the ADPOL standards are listed in Table 2. The lower limits of detection (LLD) are based on the measurement times for each of the measurement conditions (Table 1).

Figure 1. Calibration graph of magnesium in ADPOL standards 

Figure 2. Calibration graph of titanium in ADPOL standards 

Precision

To test the instrument stability, one ADPOL standard #4 was measured 20 times consecutively. The certified concentration of the standard, the average concentration of the measurement, RMS (1 sigma standard deviation) and the relative RMS of the repeat measurements for all the elements are shown in Table 3. Except for sodium and magnesium, all elements show a relative RMS of better than 2 %.

Conclusion

The results clearly demonstrate the excellent capability of Epsilon 3XLE  for the analysis of light elements like Na, Mg, Al, Si, P, S, Ca, Ti and Zn in polyethylene using ADPOL standards. Excellent results have been obtained for the calibrations and lower limit of detection. Furthermore, the repeatability of the measurements demonstrate that the Epsilon 3XLE is an ideal instrument for quality control of additives and catalyst residues in polymers and plastics. The high resolution and outstanding sensitivity of the SDDUltra silicon drift detector, combined with powerful software deconvolution algorithms, contribute to this result.