ASTM E2926-17

4.1 µ-XRF provides a means of simultaneously detecting major, minor, and trace elemental constituents in small glass fragments such as those frequently examined in forensic case work. It can be used at any point in the analytical scheme without concern for changing sample shape or sample properties, such as RI, due to its totally nondestructive nature.

4.2 Limits of detection (LOD) are dependent on several factors, including instrument configuration and operating parameters, sample thickness, and atomic number of the individual elements. Typical LODs range from parts per million (µgg^-1) to percent (%).

4.3 µ-XRF provides simultaneous qualitative analysis for elements having an atomic number of eleven or greater. This multi-element capability permits detection of elements typically present in glass such as magnesium (Mg), silicon (Si), aluminum (Al), calcium (Ca), potassium (K), iron (Fe), titanium (Ti), strontium (Sr), and zirconium (Zr), as well as other elements that may be detectable in some glass by µ-XRF (for example, molybdenum (Mo), selenium (Se), or erbium (Er)) without the need for a predetermined elemental menu.

4.4 µ-XRF comparison of glass fragments provides additional discrimination power beyond that of RI or density comparisons, or both, alone.

4.5 The method precision should be established in each laboratory for the specific conditions and instrumentation in that laboratory.

4.6 When using small fragments having varying surface geometries and thicknesses, precision deteriorates due to take-off-angle and critical depth effects. Flat fragments with thickness greater than 1.5 mm do not suffer from these constraints, but are not always available as questioned specimens received in casework. As a consequence of the deterioration in precision for small fragments and the lack of appropriate calibration standards, quantitative analysis by µ-XRF is not typically used.

4.7 Appropriate sampling techniques should be used to account for natural heterogeneity of the material, varying surface geometries, and potential critical depth effects.

4.8 Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) may also be used for trace elemental analysis of glass and offer lower minimum detection levels and the ability for quantitative analysis. However, these methods are destructive, and require larger sample sizes and much longer sample preparation times (Test Method E2330).

4.9 Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) uses comparable specimen sizes to those used for µ-XRF but offers better LODs, quantitative capability and less analysis time. LA-ICP-MS drawbacks are greater instrument cost and complexity of operation.

4.10 Scanning Electron Microscopy with EDS (SEM-EDS) is also available for elemental analysis, but it is of limited use for forensic glass source discrimination due to poor detection limits for higher atomic number elements present in glass at trace concentration levels. However, discrimination of sources that have indistinguishable RIs and densities may be possible.

1.1 This test method is for the determination of major, minor, and trace elements present in glass fragments. The elemental composition of a glass fragment can be measured through the use of µ-XRF analysis for comparisons of glass.

1.2 This test method covers the application of µ-XRF using mono- and poly- capillary optics, and an energy dispersive X-ray detector (EDS).

1.3 This test method does not replace knowledge, skill, ability, experience, education, or training and should be used in conjunction with professional judgment.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.