Rapid XRD Screening of Asbestos Reference Samples on Aeris Using the 1Der High-Energy-Resolution Detector

Abstract

This note summarizes a feasibility study measuring two JAWE asbestos reference samples (amphibole and serpentine) on an Aeris benchtop X-ray diffractometer equipped with the 1Der energy-dispersive solid-state strip detector. With ~340 eV energy resolution, 1Der uses programmable energy windows to suppress unwanted radiation (white radiation, Kβ, and sample fluorescence). This reduces background to levels close to an empty zero-background holder, improving visibility of low-level asbestos peaks. A single 5-minute short-range scan enabled detection of 0.17 wt.% amphibole and 0.30 wt.% serpentine above the limit of detection (LOD) criterion, a 15-minutes scan was sufficient to reach limit of detection (LOD) for both amphibole and serpentine in compliance with the recently released USP <901>.

1. Background and objective

The need to identify and quantify trace amounts of asbestos within materials such as talc has become increasingly important in recent years, with the requirement for quantification found in both the mining and pharmaceutical industries, the latter now having USP <901> in place. This regulation is explicitly mentioning X-ray diffraction (XRD) as a mandatory technique to detect presence of asbestos in pharmaceutical talc.

XRD identification of asbestos phases can be limited by elevated background from fluorescence and other parasitic radiation components. The objective of this study was to assess whether high-energy-resolution detection on Aeris can electronically reject these contributions and improve detection performance for low-level asbestos presence in a crystalline matrix.

2. Instrumentation and concept

• Aeris benchtop XRD with 1Der detector (127 channels)
• Energy resolution (~340 eV) enables programmable energy windows acting as an electronic secondary monochromator
• Unwanted radiation suppressed from (i) the source (white radiation/Kβ), (ii) the sample (fluorescence), and (iii) background contributions - eliminating the need for a Kβ-filter increasing the intensity of the signal!

3. Sample preparation

Two JAWE reference samples containing the phases in question were used: JAWE 1113 - amphibole (0.5 wt.%) and JAWE 1213 - serpentine (0.8 wt.%).

Sample preparation:

• A small amount of sample was filled using top-loading technique into the holder cavity of a 16 mm silicon zero-background plate.
• A glass slide was gently pressed onto the powder to make sure no loose powder is on the surface of the sample holder.
• The glass slide was removed, and the plate was mounted into the sample ring.

4. Measurement methods

Parameter	Setting
Geometry	Reflection mode (Bragg Brentano)
Primary optics	No Kβ-filter, 1/4° divergence slit; 0.04 rad Soller slits, beam mask 13 mm; beam knife in “low” position
Secondary optics	Anti-scatter slit 7 mm; Soller slits 0.02 rad
Detector	1Der high energy resolution detector
Tube	Cu anode; 40 kV, 15 mA (600 W)
Scan range / step (overview scan)	3° to 70° 2θ; step size 0.0138°
Scan range / step (short-range scan)	7.5° to 15° 2θ; step size 0.0138°
Time (full range)	33 min per scan (5 scans total; 165 min)
Time (zoomed range)	5 min per scan (5 scans total; 25 min)

5. Results

Measured diffractograms showed very low background in the crystalline matrix, reported to be close to an empty zero-background holder measured under identical conditions. Both amphibole and serpentine peaks were visible in a 33-minute overview scan. Figure 3 shows the overview scan (3° to 70° 2θ) as well as the short-range scans (7.5° to 15° 2θ) of the two measured samples.

According to USP <901>, following limits of detection are expected to be achieved with the XRD measurements:

• Amphiboles (amphibole and anthophyllite): 0.2%
• Serpentine (serpentine) with no chlorite interference: 0.2%
• Serpentine with 1% chlorite interference: 0.5%
• Serpentine with >1% to 15%-20% chlorite interference: 1%, with resolution of the two phases confirmed using a 2θ range of 23.5-25.6

To assess whether XRD measurements using benchtop XRD Aeris can fulfill these requirements, Signal-to-noise (S/N) ratio for amphibole and serpentine phases was calculated using the following formula:

S/N = Signal height / Noise at background level

Furthermore, in order to assess what quantities of two minerals in question can be detected, following criterion were used: Limit of detection (LOD) when S/N > 3.

The LODs found in this study are summarized in Table 1. For the amphibole sample LOD is achieved with a 5-minute short scan, for the serpentine sample a scan time of 15 minutes was sufficient to satisfy USP <901>.

Table 1: LODs observed for amphibole and serpentine

Measurement	Amphibole LOD	USP met	Serpentine LOD	USP met
Overview 33 min	0.17 w%	Yes	0.30 w%	No
Short-range 5 min	0.17 w%	Yes	0.30 w%	No
Overview 99 min	0.12 w%	Yes	0.17 w%	Yes
Short-range 15 min	0.12 w%	Yes	0.17 w%	Yes
Overview 165 min	0.09 w%	Yes	0.15 w%	Yes
Short-range 25 min	0.09 w%	Yes	0.15 w%	Yes

6. Practical guidance for routine screening

• Use a short overview scan to confirm matrix/background behavior; then focus on specific diffractogram regions (containing high-intensity reflections of the phases in question) to reduce total measurement time.
• With 1Der detector’s background suppression, detection limits below 1 wt.% are readily achievable for the demonstrated reference materials.
• For improved confidence at very low levels, combine repeated short scans or extend counting time in the selected 2θ ranges.

7. Conclusions

• Aeris equipped with 1Der detector provides strong electronic suppression of unwanted radiation, lowering background and improved trace phase visibility.
• In this feasibility study, we demonstrate that with the Aeris benchtop XRD the required limits of detection for USP <901> for asbestos:
  • 0.2 wt.% of amphibole can be achieved within a 5-minute short-range measurement
  • 0.2 wt.% of serpentine can be achieved within a 15-minute short-range measurement

These results demonstrate that the benchtop XRD Aeris is on par with the floor standing XRD systems which were used for generating the norm.