Analysis of Low Dilution Fusion Rock Samples Using a Low Powered WDXRF System

This paper was derived from an application request requiring good accuracy and suitable LLDs for rock analysis but still using a borate fusion preparation and excluding the pressed pellet method commonly used for trace analysis. Fusion was requested to eliminate the typical problems with pellets – particle size, major matrix effects, etc. The request originated from the owner of a WDXRF benchtop system. Because of the system involved, a low dilution fusion was used in view of the power available for excitation in order to maintain as low a detection level as possible for all elements requested.

Rock type materials are one of the more complex matrices to analyze. With potential element ranges from ppm to high %, whole rock analysis (WRA) has required various methods of preparation from pressed pellets to fusions. This discussion describes a low dilution fusion method (2:1 flux to sample) encompassing a variety of matrices to produce good reproducibility while maintaining favorable lower limits of detection using a low powered (50W) bench top WDXRF system. Besides the 10 common major elements, 11 traces were also analyzed.

Even though the benchtop XRF system used here is small and utilizes a low power tube it is still able to produce good lower limit of detections (LLD). Light elements such as sodium respond with enough signal to produce an LLD of just less than 0.1% while the majority of the trace component LLDs are about 10 ppm or less.