Evaluation of a sample preparation procedure for total-reflection X-ray fluorescence analysis of directly collected airborne particulate matter samples

Highlights: • Airborne particles were hourly collected directly on TXRF substrates. • Vaseline coating of reflectors proves to be more effective than siliconization. • Two quantitative approaches are presented and compared. • Samples show residue-like behavior. • Reproducibility lies within 15–25% for major elemental components. This paper investigates in detail a sample preparation procedure for the total-reflection X-ray fluorescence (TXRF) analysis of airborne particles using a three-stage Dekati™ PM10 cascade impactor. The impactor was modified in such a way, that 30 mm diameter quartz reflectors suitable for TXRF spectrometers can be inserted as collection plates below the impactor's nozzle arrays with cut-off diameters of 10, 2.5 and 1 μm. Smaller particles are collected in a backup filter, which can be analyzed using classical energy-dispersive XRF. As an internal standard 5 ng Y were pipetted centrally onto each reflector after collection. The reflector surface has to be coated in order to reduce particle bounce-off. Two surface coatings, silicone oil and petroleum jelly ("Vaseline"), were compared in this study. Before TXRF analysis this coating layer was removed by low-temperature oxygen plasma ashing. A new approach was introduced, which involves masking of the quartz reflectors in order to remove the outer ring of the spot pattern, which consists of two concentric circles, and to produce a sample, which lies entirely inside the detectable area. Results of this approach were compared to those obtained from unmasked samples and discussed in detail. Angle scans show residue-like behavior of the samples in each stage. Samples were taken on the roof of the Atominstitut building in January 2017 on 10 days during working hours.