In this interview, Wilhelm Sanders, Product Manager at Thermo Fisher Scientific, and Jean-Marc Böhlen, Products Applications Manager at Thermo Fisher Scientific, discuss the advantages of incorporating the Thermo Scientific ARL iSpark Plus high-resolution spark optical emission spectrometer into your routine analysis workflow.
What is Spark OES and how does it contribute to elemental analysis in metal samples?
Wilhelm Sanders:
Spark OES has been the workhorse for elemental analysis of solid metal samples for many years. It is widely used in the complete cycle of metal production, metal processing, and recycling. In OES, atoms are excited. Excitation energy comes from a spark between a sample and an electrode.
The energy of the spark causes the electrons in the sample to emit light, so the light range used for Spark OES is in the visible and ultraviolet (UV) range of the electromagnetic spectrum. The UV range requires special attention since this light is absorbed in ambient air.
The light is then converted into a spectral pattern via the spectrometer. By measuring the intensity of the spectral peaks, the analyzer can produce quantitative concentrations of the elements present in your samples.
What is the ARL iSpark Plus optical emission spectrometer and how is it better compared to its predecessors?
Wilhelm Sanders:
The new ARL iSpark Plus optical emission spectrometer is the ARL iSpark.
The ARL iSpark Plus comes with significant improvements such as improved thermal stabilization, a new patented spark stand design, an improved shutter system, and enhanced communication between the spectrometer software and the instrument for faster analysis.
How does the design of the optics in the ARL iSpark Plus contribute to its exceptional elemental coverage?
Wilhelm Sanders:
One advantage of spark optical emission spectroscopy is that the plasma creates line rich spectra’s and making it possible to analyze most elements of the periodic table, except the noble gases and heavy unstable heavy radioactive elements.
The main contributors to this capability are the optics, and more importantly, its design. Since as mentioned, spark optical emission creates very line-rich spectra, outstanding resolution is needed for optimal separation of the spectral lines’ peaks.
With a one-meter focal length, the optics of the ARL iSpark Plus is the largest on the market and it is set up in Paschen-Runge for the highest resolution. Resolution can be achieved with different parameters, but due to Thermo Scientific’s long-lasting experience, we believe that the focal length is the optimum parameter for the ultimate dispersion and isolation of spectral peaks. The optical system can cover the full interesting spectral range for OES which is from around 120 to 780 nm.
Important elements have their best lines in the ultraviolet (UV) part of the spectrum (e.g. C, P, S N and O among others). As UV light is absorbed in ambient air, a vacuum system is used. This vacuum technology guarantees, compared to alternative ways reaching transmission for UV light (e.g. an argon filled or purged argon system), not only the highest transparency at any time, but also low maintenance and low cost of ownership. It also ensures that parameters like pressure and temperature, which might have a huge influence on dispersion and stability, can be kept ultra-constant, resulting in great stability.
Plasma view and the transmission of light to the optics can be done differently in spark OES. Because optical fibers and mirrors tend to degrade due to photochemical effects, the ARL iSpark Plus use a direct view to the plasma created in the spark chamber, maximizing light throughput. The heavy temperature-controlled cast iron spectrometer provides higher stability. Our optical solutions therefore provide superior resolution and performance for all elements and matrices.
For all these reasons, the ARL iSpark Plus can analyze samples in 14 routine metal matrices and several special matrices and can cover most elements of the periodic table, except the noble gases and heavy unstable heavy radioactive elements.
Why are low detection limits crucial in Spark OES, and how does ARL iSpark Plus fulfill this requirement?
Wilhelm Sanders:
Low detection limits are crucial and become even more important with the transition of the metals industry toward the reduction of CO₂ emissions. Scrap and recycled metals play a key role in this transition. However, a challenge arises from contamination by unwanted elements due to sometimes inadequate sorting of scrap. Elements that cannot be removed during the melting processes, such as tin and copper in steel, may enter the process To control this, the lowest detection limits are of utmost importance on all the elements.
The limit of detection (LOD) is the lowest possible concentration at which the method can detect, but not quantify, the analyte with a certain degree of confidence. It is also defined as the lowest concentration that can be separated from background noise with some reliability.
The LOD significantly influences the limit of quantification, the lowest concentration that can be measured with some high level of accuracy. Thermo Fisher Scientific is one of the few Spark OES manufacturers, if not the only one, that guarantees the detection limits of the elements quantified across all offered applications.
One major contributor to the ultra-low detection limits of the ARL iSpark Plus is the spectrometer optics itself, including the detectors and the readout system. On the ARL iSpark Plus, the best PMT (photomultiplier tube) is selected for each element. Each PMT benefit from programmable high-voltage settings, that ensure optimal conditions for different applications. Every PMT allows perfoming time-gated acquisition (TGA), which allows the signal to be acquired only during specific time windows, enhancing the signal-to-noise ratio and reducing interference from other elements.
PMT's also offer the fast read-out that is necessary for single-spark acquisition, a pre-requisite for our Spark-DAT ultra-fast inclusion analysis methods.
How does the ARL iSpark Plus ensure good accuracy and high precision in elemental analysis?
Wilhelm Sanders:
Ensuring good accuracy and high precision is essential in analytical processes. Precision means how close the measurements are to each other, while accuracy refers to how close a measured concentration is to the true or the reference value. The achievable accuracy of a Spark OES depends on the quality of the reference material used for the calibration and their certification.
For precision and accuracy, the excitation source plays a key role. Thermo Scientific’s intelliSource is an innovative current controlled OES spark source that helps our application specialists design the most efficient spark current shapes in terms of sample surface preparation, material ablation, and light emission in each metal matrix. This is very important, for example, for the effectiveness of the pre-integration which aims at remelting the sample prior to signal acquisition, in order to minimize the effects of both the matrix and the metallurgical structure. This is also important in the integration phases, where well-designed current shapes help obtaining the best performance for trace, as well as minor and major elements.
Since OES is not an absolute measurement technology, the instrument must be calibrated with reference material. Each ARL iSpark Plus metal analyzer is individually calibrated by hand at our factory. The calibrations are performed using large sets of reference samples, mainly CRM's (certified reference materials), and establishing the calibration curves with the help of a powerful multi-variable regression tool that corrects for matrix effects as well as spectral interferences and ensures, the highest possible accuracy.
How does the ARL iSpark Plus address the crucial factors of stability and fast result delivery in routine elemental analysis?
Wilhelm Sanders:
These are the most important improvements of the ARL iSpark Plus. The stability of an instrument is of utmost importance when performing routine analysis. High stability reduces the frequency of maintenance and drift correction operations, increasing the availability of the instrument for routine analysis of process and production samples. This parameter is also important if the sample load is high and results are required extremely quickly, for example, in steel process control. A fast analysis, on its side, allows concentrations of critical elements to be available faster, better control the process, and save energy. It also helps more samples to be analyzed.
We have put a lot of effort into the ARL iSpark Plus in order to maximize the stability. On the one hand, we have improved the thermal regulation of the optics. This includes optimization of the ventilation and the air flows and of the regulation algorithm of the oven to respond quickly to ambient temperature changes. On the other hand, we have also implemented a new shutter system to provide better protection of the PMT's against over-illumination during the high-energy pre-integration phase of the analysis
In terms of stability, the most impactful enhancement is, however probably, the new and patented spark stand design, with two additional argon channels inside the spark stand. This allows for better evacuation of metal vapors, dust and particles from the stand, resulting in a 45 % reduction in dust and a 30 % increase in maintenance intervals. It also contributes strongly to improving long-term stability and it virtually eliminates any memory effect.
In terms of delivering fast results, communication between the spectrometer software and the instrument firmware has been improved, leading to a global 15 % reduction in measurement time per analysis. For example, one analysis run (one measurement) of a low-alloy steel sample, including nitrogen and inclusion analysis now takes 18 seconds, positioning the ARL iSpark Plus as one of the fastest optical emission spectrometers
How does the ARL iSpark Plus prioritize user-friendliness, ease of maintenance, and optional software tools in its design?
Wilhelm Sanders:
User-friendliness, easy maintenance, and optional software tools are of paramount importance, especially in laboratories with limited resources. OXSAS is the most comprehensive spectrometer software, offering numerous tools and features to streamline the analytical workflow.
For example, the maintenance management system uses a traffic light system. If the light is green, no maintenance operation is needed. The orange light indicates upcoming maintenance, while the red light signifies that a maintenance operation is due.
As another example, easyOXSAS is the ideal software module for inexperienced operators of the instrument. It allows defining the tasks he is allowed to perform and not to perform, for example, performing analyses, but not standardization, and simplifying routine operations, while the lab manager can still switch to the full OXSAS for advanced tasks.
Another interesting feature is the possibility to calculate the measurement uncertainty for every element at the end of an analysis. This is important for preparing reports according to ISO 17025.
There are also other software tools that further enhance the capabilities of the ARL iSpark Plus. One noteworthy tool is SPC (statistical process control), which is vital for industries with strict quality control requirements, such as automotive and aerospace. SPC provides control limits, trends, process warnings, and capability information. It is also useful for audits because it allows the storage of control sample results, which can help demonstrate that the instrument is working in proper conditions.
Total Materia is another tool, worth mentioning for those who need to validate elemental composition for verifying if the results are matching a specified grade. This database contains information on all the grades existing globally. Instead of manually entering grade specifications, Total Materia allows users to seamlessly add the grades they need in just a few clicks, simplifying and ensuring faultless verification.
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How does Spark-DAT in the ARL iSpark Plus provide a cost-effective solution for non-metallic micro-inclusion analysis?
Jean-Marc Böohlen:
The ARL iSpark Plus allows ultra-fast check of non-metallic micro-inclusions using Spark-DAT, a technology introduced more than 25 years ago with ARL spectrometers. With Spark-DAT, the instrument is transformed into a two-in-one analyzer that combines inclusion analysis and elemental analysis without increasing the analysis time. In steel, This means that less than one minute is needed for a two-run analysis of a low-alloy steel sample.
Instrument operation and maintenance are unchanged, and the instrument remains as easy to use as a normal ARL iSpark Plus. Usual sample preparation methods, such as milling or, in some cases, paper grinding, can still be used.
The benefits are substantial: it has a low cost and it enables huge savings and fast instrument payback. Rich inclusion data, like the number per unit volume of many different inclusion types, their size and their concentration, is available for close to real-time for quality and process control, with the capability of analyzing hundreds of samples per day.
What are the main differences between the spark inclusion analysis and an inclusion analysis technique like SEM/EDX?
Jean-Marc Bohlen:
The first difference is related to the dimensionality of both methods. With SEM/EDX instruments, a two-dimensional analysis is performed. In contrast, the Spark-DAT inclusion analysis is three-dimensional, ablating material and looking for inclusion in the volume of the sample.
The second difference is that SEM/EDX instruments can determine the composition, shape, and location of the inclusion. This is not possible with a spark OES instrument, which can evaluate the composition and number of inclusions, but not their shape or their location.
Another difference is the time required for sample preparation and analysis. The SEM/EDX method requires sample polishing, which is much longer than sample milling or grinding with paper as used in the spark OES method.
The last difference is the number of samples that can be analyzed. Spark-DAT inclusion analysis can analyze up to hundreds of samples a day, while SEM/EDX, may be limited to a few tens of samples only.
About the interviewees:
Wilhelm Sanders studied Physical engineering at the Rheinische Akademie in Cologne where he gained his first experience with optical emission spectrometers, which also ignited his passion for this technology. Since then, for more than 30 years, Wilhelm has worked in this field for various companies and roles. First in applications, then in automation, and later in service and sales and finally as Product Manager.
Since 2021, Wilhelm is working in this role for Thermo Fisher Scientific, as the task of developing high-resolution "high-end" spark spectrometers really appealed to him. What he likes about this role is that it enables close contact with our customers and interaction with research and development.
Jean-Marc Böhlen holds a master's degree in chemistry and a PhD in NMR spectroscopy from the University of Lausanne. He joined the optical emission marketing team at Thermo Fisher Scientific in Ecublens, Switzerland, 23 years ago.
After many years as Application Manager and Product Manager for OES spectrometers, he is currently Product Applications Manager, responsible among other things for applications of the inclusion analysis and collaborations with partners in the metallurgical industry.
This information has been sourced, reviewed, and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.
For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers and Phase Analyzers.
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