X-Ray Fluorescence
The JMU XRF Lab analyzes major and minor elemental oxide concentrations of rocks, sediments, and soils on fused beads.
Elements analyzed currently: Al2O3, CaO, Fe2O3, K2O, MgO, MnO, P2O5, Na2O, SiO2, TiO2, ZrO2
Trace element analysis is planned for the future...
Note: this is not a for-fee lab. The information below is provided for students, collaborators, and anyone interested in how we rock out in the lab.
Methods
Sample Powder Preparation
Kaliyah Booker (Earth Science B.A., Fall '22) and Joslyn Herold (Geology B.S., '24) providing elbow grease for the sake of science!
Samples (10-50 g) are ground to a homogeneous powder in a Spex Shatterbox using a zirconia ceramic grinding vessel.
Sample powders are dried in an oven at 105-110°C for a minimum of 2 hours.
Oven-dry powders are cooled to room temperature in a desiccator.
Oven-dry samples are then divided into two aliquots:
Split 1 is prepared as a fused bead.
Split 2 is prepared for loss-on-ignition (LOI) analysis.
Fused Beads
Fused beads are prepared with the following procedure.
6.3000 ± 0.0002 g of flux is weighted into a 95 / 5 (Pt / Au) crucible. Flux is 49.75 / Li-metaborate / 49.75 Li-tetraborate / 0.5 LiBr mix of pre-fused microbeads.
0.7000 ± 0.0001 g of oven-dry powder is weighed onto the flux and gently mixed to homogeneity.
The flux-sample mixture is placed in the Katanax 300 electric fluxing furnace. The fluxing program has a bathing temperature of 1050°C for roughly 12 minutes. The entire process takes roughly 20 minutes with loading, ramping, fluxing, and cooling.
Spex Katanax 300 electric fluxing furnace. This model can hold up to three samples at a time; we a currently set up for one.
Oven-dry powder (Silurian paleosol, left) and corresponding fused bead (right). Darkening of fused bead is due to radiation damage during XRF analysis.
Standard powders, flux, and fused beads are stored in cabinet desiccators.
LOI
Katanax 300 fluxer (left) and muffle furnace (right).
Loss-on-ignition is calculated with the following procedure (Neydon et al., 2022).
A sterile porcelain crucible is weighed and recorded.
Approximately 5 g of oven-dry powder is weighed into the crucible. Total weight (sample + crucible) is recorded. Be sure to use > 3 g of sample to avoid static-induced uncertainty from the analytical balance.
The sample is placed in a preheated Ney 525 muffle furnace at 950°C for 105 min (1 hr 45 min). Bathing time is started when the furnace reaches full temperature after sample loading.
Samples are removed from the muffle furnace and cooled to room temperature in a desiccator.
The porcelain crucible and roasted sample are weighed and recorded.
LOI is calculated as:
LOI % = [(oven-dry sample wt. - roasted sample wt.) / oven-dry sample wt.] x 100
Oven-dry sample powders (left) and roasted samples (right). Sample positions do not correspond to each other between images. These samples consist of basalt, schist, and shale prepared by the Fall 2021 GEOL 390: Lab Techniques in Geology class. Oxidation of Fe-bearing minerals can result in slight gain-on-ignition (negative LOI values).
XRF Analysis
Fused beads are analyzed on a Malvern PANalytical Zetium spectrometer.
Instrument specifications
1-kW power
Wavelength-dispersive analysis
Rh (rhodium) X-ray tube
Two detectors:
Scintillation detector for Na to Mn (with Be window)
Gas-flow detector for Fe to Zr (uses P10 gas: 90 / 10 ratio of Ar / methane)
Five crystals:
LiF200, LiF220, Ge, PE, PX1
Quantitative Analysis
Calibration curves for 11 elemental oxides are constructed using 23 analytical standards, mostly from the USGS and Geological Survey of Japan.
No corrections are currently used in SuperQ software.
An Ausmond drift monitor (silicates and general) is analyzed at the start of every batch.
Up to 16 samples + standards can be analyzed in each batch.
Two standards are analyzed at the beginning and end of each batch as unknowns to assess accuracy and precision for each run (14 samples + 2 check standards per run).