23May2012
23rd May 2012 XRF User Meeting - University of Leicester.
A joint BCA/RSC Atomic Specroscopy Group Meeting.
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24th May XRD Meeting Report
Morning Session speakers, from left to right:
Rainer Schramm, Phil Potts, Ros Schwarz(Chair), Frederic Davidts, Marc Reichow and Andy Saunders.
Morning Session.
The future of XRF in geochemical analysis lies in the field not the laboratory: Thoughts on the capabilities and limitations of hand-held instrumentation
Phil Potts, Open University.
Phil briefly summarised the current status of XRF techniques. The two important advances have been; i) flexibility to analyse with a wide range of major and trace elements: ii) measurement precision. Recently, XRF developments have focused on XRF portable instruments to respond to the need of carrying measurement into the field, especially for Earth Sciences projects.
Can XRF portable measurement fit the purpose? To answer this questions two study cases were assessed: a) Concentration profile of Pb at Bole-Hill in Derbyshire b) Individual outcrop identification in Preseli Mountains in Wales. Both studies included the investigation of factors such as conditions of the measurement, sample nature, precision, reproducibility and sampling, which has a great influence on the evaluation of measurement uncertainty. In addition, the comparison between XRF field and laboratory measurements has been used to demonstrate the relevance of information provided by XRF field measurement.
XRF Fusion: Development and application of internal standard methods for high accuracy
Frederic Davidts, SOCACHIM, Brussels, Belgium
The most common sample preparation techniques, pressed pellet, fused beads and loose powder were presented. During the discussion, fused bead preparation was shown to be the technique most suitable to produce high quality results. However, this preparation methodology is subjected to variation of results due to the physical condition of platinum-ware, especially flat-side curvature of casting dishes. This curvature is mainly due to fast cooling cycles.
The use of fluxes doped with an internal standard (eg. Tb, Tm, Rb etc.) has led to a great improvement in the precision of results from fused beads as it will correct for the casting dish’s curvature effect. The selection of the internal standard in the doped flux is dependent on avoiding line overlaps in the samples being analysed.
The use of XRF in the Earth Sciences: Understanding Volcanic Super-Eruptions.
Prof. A.D. Saunders or Dr. M. Riechow, University of Leicester.
We were entertained by a double act for this presentation with Andy first taking us through the use of XRF for understanding flood basalt ‘super-eruptions’. XRF is an ideal analytical technique because of its convenience, ease of use (especially preparation of samples), and accurate and precise analysis of the elements of interest. Analysis of heavy elements in ocean island and mid-ocean ridge basalts show that the concentrations of Nb, Zr and Y provide excellent discrimination between the different sources of magmas. A plot of Nb/Y versus Zr/Y ratios clearly distinguishes between the different types of mid-ocean ridge and ocean island basalts, and provides geologists with a key to a better understanding of flood-basalt eruptions and their devastating effects on the planet.
Marc went on to talk about the devastating super-eruption in Yellowstone Park some 600,000 years ago and the role XRF chemical data has played in differentiating between different eruptions over time and estimating the 2000 km3 volume of ejected material (e.g., the eruption of Mt St. Helens, USA in 1980 produced a mere 0.25 km3). He demonstrated the usefulness of incompatible trace element data (e.g., Nb) obtained by the XRF method in order to distinguish between separate eruptions in samples from the Snake River plain. The two speakers combined to give a very interesting and informative presentation, with the help of some excellent slides, on the use of XRF data from field samples to convey an understanding of super-eruptions.
Practical Use of New Version of ISO 12677:2011 - Chemical Analysis of Refractory Products by XRF.
Dr. Rainer Schramm, Fluxana.
This 2011 revision updates a previous 2003 version and introduced some descriptive corrections, sample preparation, additional ceramics, reproducibility and repeatability, limit of detection and check samples with precision data. This is essential reading for anyone setting up XRF methods in a wide range of refractory and ceramic materials and their source minerals (17 material types). To cover this wide range of materials 14 flux combinations are recommended and for each flux a list of materials it can be used for is given. Lithium Tetraborate at 10:1 dilution is suitable for 13 of the 17 and a special flux (75.6% Lithium Mretaborate, 20.9% Lanthanum Oxide and 3.5% Boron Oxide) at 16.67:1 dilution was suitable for all 17 types. Calibrations are made using pure chemicals and a series of CRM’s (appendix E) with a list of suitable control standards in appendix D. are also covered. The need for measurement error to be at least 10 times lower than preparation error, LoI correction for tungsten contamination, line overlaps, matrix correction, drift correction and validation techniques are also covered. For anyone involved in the analysis of these materials this document is essential reading. The results of a proficiency test of two materials using the ISO 12677 will be published at the end of September 2012 at: www.fluxana.com
Belen Morales, LSM Analytical Services et al.
Afternoon Session.
Afternoon Session speakers, from left to right:
Nick Marsh(local organiser), Simon Lawes, Jean-Philippe Gorse, Owen Butler and Andy Scothern(Chair)
Afternoon session.
After a very tasty lunch, (the mini cheesecakes were particularly appreciated) we began again with a talk from Dr Mike Norry from the University of Leicester with the title ‘So we’ve got some numbers from the XRF – what can we do with them to understand rocks?’ After pointing out that analyses presented as tables of concentrations of elements can be difficult to interpret, Mike showed some of the plots geochemists use to look at the results for rocks formed in different environments. He started with some trends for rare earth elements in basalts, which depend on the minerals present during partial melting. When the individual element results are normalised to their concentrations found in chondritic meteorites, different patterns can clearly be seen for different sources. Turning to sedimentary rocks, using examples from the Oxford Clay deposits, he illustrated how plots of SiO2/Al2O3 against Na2O+K2O/Al2O3 could be interpreted in terms of settling rate of the sediments, and hence used to give information about comparative levels of hydrodynamic energy through the deposits. Lastly, he concentrated on molybdenum as an element that indicates quiet, anoxic conditions during deposition.
Next, Owen Butler of the Health and Safety Laboratory gave some interesting examples of the way groups of laboratories can cooperate in his talk on Development of Laboratory Reference Materials at the Health and Safety Laboratory. First he described the cross-certification of national reference materials for respirable quartz against an established (matrix-matched) material, NIST SRM 1878a. Filters with a range of loadings of NIST SRM and of national quartz material were supplied to the laboratories and the resulting straight line graphs were used to derive a ratio for each national material to the quartz content of the SRM. Secondly he discussed the use of spiked samples in the analysis of welding fume dusts where there are no reference materials available as a control, mentioning the guidance in ISO Guide 35 and the availability of software such as ‘Soft CRM’. His final example concerned reference slides for counting of asbestos fibres, a test frequently carried out on-site. Here new slides are included in each round of proficiency testing so that they are counted by a number of practising analysts.
Following our break for tea, Dr. Simon Lawes from the University of Leicester gave a talk showcasing the capabilities of X-ray Computer Aided Tomographic Scanning – the newest x-ray toy on the block. Describing development from the kind of two dimensional imaging used in medical x-rays and in airport security, he likened the technique to CAT or MRI scanners. Magnification is obtained by using a small spot size (3 - 4 µm), a short source-sample distance and high energy bremsstralung x-rays to give cross sectional ‘slices’ which are subsequently assembled to give an image. Contrast is provided by density and atomic number differences, with dense regions being brighter. Donning 3-D glasses, we saw that the technique gives views inside a manufactured part without the need to dismantle it. These images can also be used for criminal investigations, as illustrated by a study of tool marks on bones that gave clear evidence of dismemberment of a body with a saw.
In the final talk of the day, Jean-Philippe Gorce of the Health and Safety Laboratory discussed the Validation of Portable X-Ray Fluorescence Spectrometry for the Quantification of Lead Dust on Workplace Surfaces. He told us that sampling of surfaces for lead in industrial environments is important for many reasons, including identifying the origin and extent of contamination, checking for cross-contamination and as an educational tool. PXRF has several advantages over the use of wipes (which are followed by ICP analysis); pXRF will give on-site real time results, can measure up to 39 elements and can be used on a wide range of surfaces such as towels and clothes that are not suitable for wipes. Its disadvantages are that the substrate is also measured, that the area sampled is comparatively small and that the limit of detection is substrate dependent and generally higher than for wipes. By comparing the difference in pXRF measurements before and after a wipe was used with the concentration on the wipe determined by ICP, he showed that there was a one-to-one correspondence, although the data was quite scattered.
To finish the day, we thanked all the speakers and organisers for a very good meeting.
Ros Schwarz, University of Sheffield
Delegate Photograph
