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A Guide to Portable XRF Calibrations

The portable XRF has many calibration options, which are designed to analyse a wide variety of materials. With so many on offer it is easy to feel overwhelmed when trying to choose the best calibration option for your application. This is why Portable Spectral Services are going back to calibration basics and looking into what calibrations are, why they are important to consider, and the options available for use on a portable XRF. 

What is a calibration?

A calibration is the process of configuring an instrument to calculate elemental concentrations based on a targeted suite of standards, providing accurate results within an acceptable range.

Calibrations and XRF

When considering the portable XRF, there are so many analytical possibilities. XRF can be used to analyse materials such as glass, wood, paint, various alloys, soil, and rock chips. When considering the large and varied applications for XRF, to analyse everything using one overarching calibration would result in some materials measuring inaccurately due to material variance in elemental composition, concentrations, and density.

Consider low-density plastic to a rock core. Low-density plastic is malleable and contains a higher number of organic components compared to a rock core, which is a denser material of mainly inorganics. If one calibration was used, it would be impossible to accurately target both material types and expect the same level of results. It is therefore more reliable to use targeted calibrations on the XRF that are optimised for the material type being analysed. Most often XRF calibrations do not detect every possible element. Instead, the calibration is set up to target only the elements and concentration ranges that relate to that material. After all, there is no point reporting on iron when targeting lead in paint!

Image 1: Certified reference material are used to check the calibration is working optimally for analysis.

Calibrations QAQC

When a calibration is created, standards are used to check its continued accuracy across time and to monitor for contaminants (image 1). These are most often certified reference materials (CRMs) that have representative concentrations of target elements. By monitoring target elements in an established QAQC analysing procedure, it ensures that the calibration remains functional throughout any given project.  

So what calibrations are out there for portable XRF applications? Outlined below are the most common portable XRF “off-the-shelf” calibrations on the Bruker models (S1 TITAN, CTX, TRACER 5g)*, an explanation of what each are intended to be used for, and what elements each calibration detects**.

In some cases, “off-the-shelf” calibrations may not offer the level of accuracy or capture critical elements at concentrations that is critical for your project. In this case, calibrations can be customised, either by enhancing a pre-existing off-the-shelf calibration or by creating an entirely new calibration from scratch. A custom calibration can greatly improve the accuracy of pXRF results by being fitted to the exact matrix that you are working with and allowing for custom correction due to element overlaps, escape, sum and diffraction peaks and interferences caused by your specific matrix. This will allow increased confidence in the results coming from your pXRF. Portable Spectral Services offers custom calibrations on Bruker portable XRF models.

*Based on calibration sheets for 8mm and 5mm spot size.

**For more information on concentration ranges, please contact Portable Spectral Services

Common XRF Calibrations

GeoExploration    

The GeoExploration calibration targets geological samples (i.e., core, pulp, soil and rock chips) and is a great go-to calibration for those working in the exploration and mining industry. In terms of elements detected, the calibration is very comprehensive, ranging from Mg – U and includes trace and major concentration ranges. Additionally, users can collect information using specialised modes sulphide and oxide dominant mineral samples, although PSS suggest if unsure to utilise the Oxide3Phase option. For best results, the manufacturer Bruker, recommends firmly packing a 4µm prolene XRF cup with homogenous sample.

Elements detected: MgO, Al2O3, SiO2, P, S, Cl, K2O, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Ce, Hf, Ta, W, Pt, Au, Hg, Pb, Ti, Pb, Bi, Th, U. *

Instruments calibrated: Bruker S1 TITAN, Bruker CTX, Bruker TRACER 5g.

portable XRF taking an analysis of rock
portable XRF analysing old clock

Precious Metals 

As precious metals are rare, naturally occurring elements, they have a high economic value. The precious metals calibration targets enhanced platinum-group elements (PGE); Ag, Au, Pd, Pt, Ru, Rh. This calibration provides accurate results of solid precious metal samples such as jewellery. Those working in the positive metal identification (PMI) sector, mining, or in commercial retail areas that need to know the content and amount of precious metal in an object, would suit this calibration.

Elements detected: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, W, Re, Ir, Pt, Au, Hg, Pb.

Instruments calibrated: Bruker S1 TITAN, Bruker CTX, Bruker TRACER 5g.

Lead in Paint    

The 1970s were a critical era in Australia, where commercial paint used for homes was regulated to contain less than 1% lead. This content of lead was further reduced to 0.25% in 1992 and again to its current regulated level of 0.1% in 1997. Despite five decades passing since this initial regulation in Australia, there is still an estimated three million homes that were built prior to the 1970s, that contain paint with high levels of lead. The lead in paint calibration targets these types of homes and other materials of high lead content including drywall, painted metal, concrete, plastic, and wood surfaces. It is well suited to the domestic sector, which our sister company Healthy Homes and Gardens provides services for, in addition to commercial and construction sectors.

Elements detected: Pb.

Instruments calibrated: Bruker S1 TITAN.

portable XRF analysing a wall

Restricted Materials

Restriction of Hazardous Substances also known as RoHS is used to describe chemical elements which can be harmful to humans, especially children when they reach a certain level. The “top” four elements are lead (Pb), arsenic (As), mercury (Hg) and cadmium (Cd). Items that fall under RoHS restrictions include objects like large and small household appliances, such as refrigerators, or hair dryers, computing equipment, electronics such as speakers, various forms of lighting such as fixtures, bulbs and lamps, power tools such as drills and saws, new and old toys, such as grandads old metal train collectible and sports equipment, to list a few. Monitoring RoHS allows for greater health benefits when utilising common objects and reduces contact with hazards.

The restricted materials calibration screens for hazardous elements and can be deployed in manufacturing contexts and sectors that monitor restricted materials. The restricted materials calibration is suited to ROHSII, CPSIA, PROP65, and WHEE compliance application and Cl and Br for halogen free testing. The calibration targets low-density (LD) plastics such as polyethylene (PE), high-density (HD) plastics such as Polyvinyl chloride (PVC), mid-density (MD) objects such as ceramics, glass, aluminium alloys, magnesium alloys and mixed materials and restricted solid metal alloys except aluminium and magnesium alloys.

Elements detected (LD Plastics): S, Cl, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Cd, Sn, Sb, Ba, Hg, Pb.

Elements detected (HD Plastics): S, Cl, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Cd, Sn, Sb, Ba, Hg, Pb.

Elements detected (mid-density): Al, Si, Cl, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Ba, Hf, Ta, W, Pt, Au, Hg, Pb, Bi.

Elements detected (R-Alloys): Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br*, Zr, Nb, Mo, Rh, Pd, Ag, Cd, Sn, Sb, Ta, W, Pt, Au, Hg, Pb, Bi.

Instruments calibrated: Bruker S1 TITAN, Bruker CTX.

* Bruker states that Br does not alloy with metals, if detected, the sample likely has a plastic coating or surface contamination that should be checked.

Limestone

Despite what the name of this calibration suggests, the limestone calibration is intended for analysis of industrial mineral samples. Analysis can be conducted on both on powder and solid rock including on limestone, dolomite, gypsum, cement, clinker, and raw mix materials. The limestone calibration is best suited to those working in construction and can be applied to some exploration and mining contexts.

The manufacturer Bruker suggests for best results samples analysed should be a fine powder, ideally less than 200 mesh. This should be firmly packed into a sample cup using 4µm Prolene or Ultralene film. Bruker also states that this calibration is set up to report MgCO3 and CaCO3 for Limestone and normalizing the result to 100% allowing for semi-quantitative analysis of rockface.

Elements detected (limestone/raw mix): MgCo3, CaCO3, Al2O3, SiO2, P2O5, SO3, K2O, TiO2, MnO,

Fe2O3. 

Elements detected (Gypsum): MgO, CaSO4, Al2O3, SiO2, P2O5, K2O, TiO2, MnO, Fe2O3.

Elements detected (Cement, Clinker, Raw Mix): MgO, CaO, Al2O3, SiO2, P2O5, SO3, K2O, TiO2, MnO, Fe2O3.

Instruments calibrated: Bruker S1 TITAN, Bruker CTX, Bruker TRACER 5g.

Image: A quarry in Siggiewi, Malta. Photo courtesy of Evan Demicoli on Unsplash.

Image: Photo courtesy of Andrew Neel on Unsplash.

Plant Materials

The plant materials calibration targets light and heavy elements in simple matrix plant materials. It is intended to be used on dried and powdered plant material. It is an ideal tool for those working in agriculture and interacting directly with plants, and crops in addition to those in the food safety industry. Bruker recommends for best results that the sample should be packed into a sample cup using 4µm Prolene film.

Elements detected: Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Mo, Cd, Ba, Hg, Pb.

Instruments calibrated: Bruker S1 TITAN, Bruker CTX, Bruker TRACER 5g.

Alloy 2

A portable XRF analyser can remove the guesswork from purchasing steel, alloys and other raw materials used in manufacturing and fabrication, as they provide a reliable chemical composition of the material within seconds. With the Alloy 2 calibration, grade identification of solid metal samples can be determined in as little as 1 minute! This calibration is suitable for all metal samples including low alloy steel, tool steel, stainless steel, nickel alloys, cobalt alloys, zinc alloys, copper alloys, tin-solder alloys, titanium alloys, aluminium and magnesium alloys. Alloys 2 is suitable for those working in manufacturing, construction, and positive metal identification (PMI) sectors.

Elements detected (Low Alloy Steel): Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, W, Pb.

Elements detected (Tool Steel): Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Sn, W, Pb.

Elements detected (stainless steel): Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Sn, Ta, W, Pb.

Elements detected (Nickel Alloys): Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Sn, Hf, Ta, W, Re, Pb.

Elements detected (Cobalt alloys): Al, Si, P, S, Ti, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Sn, Hf, Ta, W, Re, Pb.

Elements detected (Zinc alloys): Al, Si, Mn, Fe, Ni, Cu, Zn, Sn, Pb.

Elements detected (Copper alloys): Al, Si, P, S, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Zr, Nb, Ag, Sn, Cd, Sb, Te, Pb, Bi.

Elements detected (Tin-solder alloys): Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Pb, Bi.

Elements detected (Titanium alloys): Al, Si, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb, Mo, Pd, Sn, Ta, W.

Elements detected (Al and Mg alloys): Mg, Al, Si, Ti,, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn, Pb, Bi.

Elements detected (other alloys; MultiMatrix FP): Mg, Al, Si, P, S, Ti, V, Cr, Mn, Fe, Ci, Ni, Cu, Zn, As, Se, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Hf, Ta, W, Re, Ur, Pt, Au, Hg, Pb, Bi.

Instruments calibrated: Bruker S1 TITAN.

portable XRF analysing metal
portable XRF analysing metal

Images courtesy of Bruker.

CTX analysing oil

Image courtesy of Bruker.

MARPOL / Sulfur in Marine Fuel

Fluids such as oils can be readily analysed by pXRF to detect wear elements, additive and meet regulatory requirements. From 1st January 2020, fuel oil used by ships in Australian water must contain a maximum of 0.5 per cent m/m sulphur. Almost all commercial lubricants contain chemical additives. As part of a preventative maintenance program, analysing oil periodically will reduce the risk of catastrophic failure. The MARPOL calibration is ideal for those working in maritime engineering and oil and gas as it targets sulphur concentration in marine fuels and similar oils. 

As the material is a liquid, Bruker specifies a three layer foil setup for analysis to ensure accurate results:

1st Layer: 4μm Prolene protective Window on the unit.

2nd Layer: 3μm Etnom protective foil on the sample stage / stand for extra leak protection.

3rd Layer: 3μm Etnom foil on the sample cup.

Elements detected: S

Instruments calibrated: Bruker CTX.

Mudrock 

The Mudrock calibration is a great solution for those working in oil and gas who are investigating mudrock and similar matrices. The calibration targets common elements enriched in the laterite and regolith regions. Analysis is intended to be carried out on solid samples or pressed pellets.

 

Elements detected (Air and Helium atmosphere): Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ba, Pb, Th, U.

 

Instruments calibrated: Bruker TRACER 5g.

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