EXECUTIVE OVERVIEW

Perform like a PRO: Robust ICP-OES Analysis with the iCAP PRO Series ICP-OES by Nora Bartsch and Sukanya Sengupta (Thermo Fisher Scientific)

Introduction Every inductively coupled plasma-optical emission spectrometry (ICP-OES) instrument has a series of common components starting with the sample introduction system, the most common of which converts liquid samples into an aerosol which can be transported to the plasma, hosted in the torch. The plasma, which is sustained by a radio frequency (RF) generator, is an ionized gas at approximately 8,000 °C. This allows the sample to be processed and causes light to be emitted from the sample. The light is collected from the plasma, separated into its wavelengths, and focused onto a detector where it is measured. The Thermo Scientific iCAP PRO Series ICP-OES (Figure 1) is a new platform that has been designed with customer feedback in mind. One of the most important new features is improved speed, achieved through new high-light throughput optics that allow for capture of the entire spectrum in one measurement, such that all elements of interest are measured at the same time. The new charge injection device (CID) detector has fast electronics meaning that overhead time is kept to a minimum, ensuring no wasted time during analysis. In addition, enhanced robustness is delivered with the new iCAP PRO Series ICP-OES. All instruments in the series have an optimized vertical torch design that is extremely robust to ensure long-term stability. The torch box has been designed with ease of use in mind, and with an inner torch box which can be easily removed, for cleaning when required.

New FeaturesThe iCAP PRO Series ICP-OES can be either a dual view, or a dedicated radial-only instrument, with the new vertical torch design enabling simple, high-matrix and organic measurements on a Duo instrument without compromising the detection limits. The innovative inner torch box design prevents any corrosion of the instrument, and is easy to use and maintain. The whole torch box has been optimized to ensure plasma stability and minimize any sample deposition on the torch, inside the instrument or the interface. The optical system is protected by a series of windows that can be easily removed, to aid simplicity of any required maintenance. Both the radial and axial views are purged, ensuring good sensitivity, especially for elements that emit light in the UV

region of the spectrum. The iCAP PRO Series ICP-OES optical system consists of a polychromator that allows for simultaneous analysis of the spectrum between 167 and 852 nm, ensuring fast analysis speed. The separation of the orders achieved ensures minimal interferences in the sample, and the optimized purge allows high-light throughput for excellent detection limits. The optical system is sealed, meaning that any purge gas is used efficiently and also it has a beam blocker installed to protect the fore-optics mirrors from UV degradation. The CID detector has a large active surface for full wavelength coverage and uses fast electronics to ensure the fastest possible measurements, typically up to 40% faster than possible on the Thermo Scientific™ iCAP™ 7000 Series ICP-OES. The iCAP PRO Series ICP-OES has several features that improve ease of use. The easy access door ensures unhindered access to the torch box. If the peristaltic pump tubing comes undone, the drain sensor can shut the instrument down and prevent sample loss. In addition, the fully adjustable radial viewing height allows optimal measurement of all samples (provided on some models). The instrument has the smallest footprint on the market and requires only a standard power plug and minimal extraction flow rates, making positioning in the laboratory very easy. The sample introduction system is based on that of the iCAP 7000 Series ICP-OES, which has proven

Learn about the benefits and applications of the new Thermo Scientific™ iCAP™ PRO Series ICP-OES, and how to improve speed of analysis and ensure accuracy in complex sample analysis.

Figure 1

to be simple to use. The ceramic torch has an extended life, reducing consumable costs. Selected instruments in the iCAP PRO Series ICP-OES also have features that improve laboratory productivity, such as reduced warmup time. The instrument optics are kept at a consistent temperature, even in standby mode, and with the boost purge function, the instrument is ready within five minutes of plasma ignition, direct from standby mode. The standby approach can be chosen for different laboratory needs, to ensure low gas consumption and fast startup times. Figure 2 shows the different instrument models of the iCAP PRO Series ICP-OES. Moving through the range, from Thermo Scientific iCAP PRO ICP-OES to Thermo Scientific™ iCAP™ PRO XPS ICP-OES, the analysis time decreases - this has a direct impact on cost of ownership, as less argon is used per sample, ensuring maximum return on investment. In addition, flexibility increases from the iCAP PRO ICP-OES through to iCAP PRO XPS ICP-OES instruments. There are many common features available across all models of the iCAP PRO Series ICP-OES. All instruments are easy to install and use because of minimal installation requirements and the user-friendly design of sample introduction. The complete series benefits from an innovative design to ensure the ultimate reliability. The new optical design allows for optimal light transmission, which when coupled with the new CID delivers a high-resolution spectrum ensuring interferences can be easily resolved.

ApplicationsIn this section we will look at specific applications to give an overview of the performance of the iCAP PRO Series ICP-OES, starting with the robust and fast determination of major and trace elements in lubricating oils using the Thermo Scientific™ iCAP™ PRO XP ICP-OES and iCAP PRO XPS ICP-OES Radial instruments. Analysis of organic matrices by ICP-OES can be more challenging than aqueous ones. This is mainly because of interferences caused by high-carbon emission and the viscosity of the sample, which has an impact on the plasma and, therefore, on the instrument settings. Most used or in-service lubricating oil samples have particles which can block the nebulizer or the sample

introduction transfer line, and the homogeneity of the sample has an impact on the result. Speed of analysis is also key for most laboratories dealing with this type of sample. For measurement time, the sample transport speed and washout time is important. In addition, instrument downtime must be factored in, and so maintenance resulting from challenging samples needs to be considered.

Lubricating Oils: The first example is the analysis of lubricating oil in accordance with the standard ASTM test method for ‘Determining of Additive Elements, Wear Metals, and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by ICP-OES’. Here the iCAP PRO XP ICP-OES Radial instrument was used because of its high matrix tolerance and its reduced matrix interferences. The Teledyne CETAC ASX-7400 stirring autosampler was used to ensure good mixing of the solution analyzed. The ASX-7400 autosampler helps to overcome the challenges of particulate matter which settles out over time, causing problems with large batches of samples. A stirring paddle mounted next to the sample probe effectively mixes the next sample prior to analysis, and a drip-cup prevents sample-to-sample contamination between analyses. Another benefit of the ASX-7400 autosampler is that it has a dual pump rinse station to aid with the analysis of oil and coolant samples with the same automation. One rinse line is flushed with white spirits, while the other one is used with nitric acid. The samples for the measurements of the lubricating oils were diluted by weight with xylene. The organic sample introduction kit was used, consisting of a baffled spray chamber and 1.5 mm center tube. For this measurement the intelligent full-range (iFR) mode was used to speed up analysis. The recoveries, seen here in Table 1, show very good values in the range of ±5%. The method detection limits also show values in low µg/kg range. To increase the sample throughput of the iCAP PRO XP ICP-OES and iCAP PRO XPS ICP-OES systems, the Teledyne CETAC ASXPRESS valve can be used. The principle of the valve is based on the switching six-port vacuum valve with two positions (Figure 3). In position one, the loop of the sprint valve is loaded with the sample and in position two, the sample is injected from the loop into the nebulizer, while the rinse step is already started on

Figure 2

be reduced to 50s. Furthermore, the use of the ASXPRESS Plus can reduce the measurement time to 35s per sample. Compared with the iCAP 7400 ICP-OES Radial, the time saved per sample can be up to 50s with the iCAP PRO XPS ICP-OES. In summary, the iCAP PRO XPS ICP-OES Radial instrument is ideal for high-matrix samples. High speed of analysis is accomplished by covering the whole wavelength range within one simultaneous acquisition, and the removable and easily cleaned interface parts reduce downtime through minimal maintenance. The ASX 7400 stirring autosampler ensures good mixing of the sample, and in conjunction with the ASXPRESS Plus sprint valve, the sample throughput can be increased.

High Total Dissolved Solids: These samples require a robust system in order to perform long-term measurements with little maintenance. There are several challenges when trying to analyze samples that have very high total dissolved solid contents. In this instance, high refers to >3% for typical ICP-OES systems. For example, a brine sample with a high concentration of alkaline elements such as sodium, potassium, etc., is not good for a standard ICP-OES system with a quartz glass torch. Under the high temperatures of the plasma, alkaline elements become incorporated within the structure of the quartz. This causes crystallization in the quartz glass material, in a process known as devitrification, causing damage to the glass, and leading to premature failure of the torch. Another problem is salt deposition and clogging of the ICP torch center tube, or clogging of the normal glass nebulizer tip. Both of these lead to loss of sample signal and failed analysis. To overcome these issues, a higher RF power, or higher nebulizer gas flow, etc., could be used, but these solutions lead to increased consumption of consumables and higher costs. The data

Table 1

Table 2

Figure 3

the autosampler end. With this, the sample delivery, the stabilization, and washout time can be reduced. For speed comparison, four analysis methods were set up to trial the capabilities of the iCAP PRO XPS ICP-OES (Table 2). With 2s integration time, a total analysis time of 55s can be achieved. With 1s integration time this can

might not be as expected, and there is typically poor data stability or even failure seen over long runs. To develop a method that would help overcome these problems, it was decided to run experiments using 25% NaCl aqueous solutions, with a special sample introduction system on the iCAP PRO XP ICP-OES. To run high salt content samples, a ceramic ICP torch is perfectly suitable. Ceramic is very robust and can tolerate such samples, even over long experimental runs, without suffering any degradation. The iCAP PRO XP ICP-OES is equipped with a fully demountable vertical torch in both Radial and Duo designs, which makes both instruments robust enough for this kind of analysis. A Buergener Mira Mist nebulizer was used to minimize salt deposition at the nebulizer tip. A baffled spray chamber ensures that the plasma loading is controlled, as is the amount of sample in the plasma, and in this way less sample material and only the very small aerosol particles make their way to the torch, leading to a minimal chance of salt deposition. Figure 4 shows a

sheath gas adapter - this is another important addition to the introduction system. To overcome the problem of crystallization of salt from high TDS solutions at the tip of the injector tube, a sheath gas adapter, together with additional gas, can be used. The sheath gas or additional gas is a constant flow of argon introduced between the spray chamber and the torch, using the sheath gas adaptor. The sheath gas envelopes the sample aerosol tangentially, preventing it from coming in contact with the inner injector tube of the ICP torch. In this way, little or no sample deposition occurs, and the need for extended washing phases between samples is negated. Less sample dilution is required, and improved method detection limits are obtained. The method detection limits (MDLs), of the different elements analyzed for both Radial and Duo instruments are provided in Figure 5. Note that these are for the specific experimental setup and instrumental parameters that were used for this kind of a challenging experiment. On the right-hand side of Figure 5, is a plot displaying the stability of relative concentrations of analytes over 18 hours of continuous measurements of 25% NaCl solution, with the iCAP PRO XP ICP-OES Radial instrument. The relative concentrations of the elements are within ±10% over the entire 18 hours. Very good stability was obtained over long measurement sessions, without any interruptions. Very good stability and robustness are also seen on the iCAP PRO XP ICP-OES Duo instrument, while analyzing solutions with high TDS (Figure 6). These plots of the stability data from the Duo instrument show experiments that were run for 10 hours, and data was acquired in both radial and axial viewing modes. The analytes remained very stable, within ±10% over all 10 hours for both viewing modes. As such, customers can benefit from stable and robust data with very good sensitivity provided by the axial mode. The data here are as a good as on the Radial instrument, shown in Figure 5, demonstrating that both dedicated Radial and Duo instruments may be used for such analysis. Laboratories that must run hundreds of such challenging samples daily can benefit from the increased operation time and minimal downtime of the iCAP PRO XP ICP-OES systems. Maintenance requirements are extremely low, together with improved robustness over long time periods, providing a cost-effective solution for users. The ceramic ICP torch is mechanically stable and does not suffer any damage. In addition, no cleaning of the torch, center

Figure 4

Figure 5

tube or injector, nebulizer, or the cones is necessary. The data shown here demonstrate that there is no problem analyzing high matrix samples such as 25% NaCl solutions (i.e., brine samples), over uninterrupted time periods of at least 10 hours.

Rare-Earth Elements (REEs): Massive amounts of electronic waste, or e-waste, is generated globally each day, and with rapid technological advances, this amount will likely increase with time. Several recycling industries, especially in China, have started targeting e-waste as a potential resource for recovering valuable or precious elements for reuse in other industries. Another aspect of the ever-increasing amounts of e-waste is waste management, particularly when it comes to managing and responsibly disposing of toxic elements. So, an application for element detection and analysis of e-waste is important for both recycling and waste management industries. Electronic waste can be composed of a variety of complex chemicals and materials. Different elements in various concentrations are to be expected within them, which is why an instrument with high matrix tolerance and reduced matrix interferences is an absolute must for this kind of application. Consequently, the iCAP PRO XP ICP-OES Duo was used for this application. A Teledyne CETAC ASX-560 autosampler was also used in conjunction for remote and unsupervised operation. REEs are 17 elements of the modern periodic table, out of which 15 belong to the lanthanide series found in the second last row of the periodic table, from lanthanum to lutetium. The remaining two elements are scandium and yttrium, which commonly occur in close geological association with lanthanides in ores. Thorium is also found closely associated with REEs in nature and, thus, it is also reported in this study. Ores from which REEs might be mined in an economically viable fashion are often hard to find. Nevertheless, REEs have important industrial applications: cerium, lanthanum and yttrium in glass and metallurgy industries; neodymium in permanent magnets; gadolinium in medical image visualization; and different REEs in various components of electronic devices, such as magnet, screens etc. This

contributes to the high market demand and price of REEs. The choice of e-waste type for this application was mobile phone waste. The thin-film transistor screens (TFTs), printed circuit boards (PCBs), and magnets in speakers, of two mobile phones were selected as samples representing electronic mobile phone waste. Analytes of interest included the RREs - commonly expected in these types of samples are neodymium, cerium, etc., different precious metals including gold, silver, etc., and some poisonous or toxic elements, such as cadmium and lead, were also included in the list of analytes or elements of interest. A relatively straightforward and simplified cost-effective sample preparation method was used for this application. The mobile phones were manually disassembled and crushed using a grinder. Magnets from the speakers were separated out and left whole. 1-2g of sample powder was digested overnight in concentrated acids, in HCl and HNO3. Magnets were digested whole in aqua regia. Samples were filtered and final solutions contained 10% HCl and HNO3 mixtures. The speaker magnet samples were separated into several aliquots and one aliquot from each magnet was spiked in the laboratory to demonstrate spike recoveries. A solution simulating the real samples was prepared in the laboratory for long-term analysis experiments. Table 3 shows a list of instrument parameters. A sample introduction system with quartz glass ICP torch, cyclonic spray chamber, etc., normally used for aqueous sample was used. An RF power of 1300 W was applied. As REEs and other analytes of interest can often be present in small concentrations in the samples (ppb to ppm range), analysis was performed only in axial viewing mode of an iCAP PRO XP ICP-OES Duo system. With a complicated sample matrix, as is the case for electronics, and rich not only in REEs but other elements too, interference-free wavelength selection becomes more challenging. A suitable wavelength will have a clean, interference-free spectrum in the subarrays. It will show a curve with Gaussian distribution of the data points. By choosing such a wavelength

Table 3

Figure 6

(Figure 7 - top), and selecting peak and background integration points correctly, reliable results will be obtained. The example shown in Figure 7 (bottom) is that of an unsuitable or less ideal wavelength. This is common for samples containing a mixture of REEs, because REEs have a large number of wavelengths that overlap each other. However, the Thermo Scientific™ Qtegra™ Intelligent Scientific Data Solution™ software delivered with the iCAP PRO Series ICP-OES instruments, determines interferences easily and corrections can be made. The figure shows terbium interfering with an analyte of interest, gadolinium, on the wavelength 336.223 nm. The Qtegra ISDS software helps predict this interference as seen in the right column of the bottom figure. Upon running a single element solution of terbium, a false positive signal is obtained on the gadolinium wavelength. Interference correction by the

Qtegra ISDS software can be enabled for such a wavelength, providing the interfering analyte, in this case terbium, has at least one wavelength itself that is clean and free of interferences. As far as possible, the choice of interference-free wavelengths is advised, and with the new iCAP PRO Series ICP-OES instrument, this is possible because of the improved wavelength separation offered. Very good sensitivity is obtained in the axial mode. Instrumental detection limits (IDLs), of 0.1-2.0 ppb (µg/L) for most of the REEs were achieved. Metal detection limits will vary depending on sample solution. Linearity ranges selected were between 1-10,000 µg/L for REEs, and 1-100,000 µg/L for other analytes. Standards were prepared accordingly, and were acid matrix matched to the samples. Figure 8 shows the results of the analysis. Different REEs and other precious

Figure 7

Figure 8

and/or poisonous elements were found in the mobile phone components. The absolute results are shown in the table on the right-hand side. The proportions of REEs found in different components of the phones were different, as shown in the pie charts for the PCB and speaker magnets.Thorium was found in large concentrations in the PCB, while cerium and neodymium were the major REEs found in the speaker magnets, as expected. Spike recoveries on the magnet speaker samples are shown in Figure 9. The spike recovery is within a ±15% range for most analytes. The lower plot shows the results of long-term stability tests performed on a laboratory simulated sample. Relative concentrations of most analytes were between 85 and 115% over six hours of analysis. A short exposure time of five seconds was used, resulting in analysis times for a single sample of less than 2 min, including uptake time, wash time, and three repeats of the sample. This application on rare-earth elements and other elements in e-waste demonstrates how complicated matrices can be easily analyzed with the iCAP PRO XP ICP-OES instruments. Easy wavelength selection and interference removal is possible, as is fast analysis and high sample throughput. Robust analysis, good accuracy and reproducibility over six hours is delivered. Trace to ultra-trace amounts in complicated matrices are detected and measured with iCAP PRO Series ICP-OES instruments. e-Waste composition categorization as a resource and/or waste is possible via such applications.

ConclusionsThe iCAP PRO Series ICP-OES is ideal for routine measurements of a variety of samples over long time periods, which is excellent for contract laboratories. High sample throughput resulting from a faster camera, and a Teledyne CETAC ASXPRESS is offered, and lower matrix interferences and matrix effects are observed. Different models are available depending on specific application requirements. The low capital investment models give high robustness and simplicity, carried through to the more productive models. With this type of instrument, better return on investment can be achieved and more flexibility in terms of accessories and speed is provided.Improved speed is especially important in high-throughput laboratories and the examples presented in this article show how efficient the iCAP PRO Series

Figure 9

ICP-OES can be without losing robustness for high matrix samples, while keeping user maintenance to a minimum. With the new instrument design and improved software, even inexperienced users are able to learn to operate the instruments quickly.

About the AuthorsNora Bartsch (Product Specialist, ICP-OES, Thermo Fisher Scientific)After finishing her education as Chemical-technical-assistant, Nora joined Thermo Fisher Scientific in Bremen, Germany in 2010. In 2016 she moved to

the position of Application Specialist for ICP-OES, where she supports the customer with the development and implementation of new methods and regulations in their laboratory routines.

Dr Sukanya Sengupta (Application Specialist, Trace Elemental Analysis, Thermo Fisher Scientific)Sukanya completed her MSc in Applied Geology in Kolkata, India. She moved to Germany in 2012 to pursue her Doctoral studies and Post-Doctoral

research on geochemical and triple oxygen isotope investigations in geological samples. Thereafter, she joined Thermo Fisher Scientific in Bremen, Germany in 2020 as Application Specialist for ICP-OES, where she assists customers in their daily laboratory routines by developing new methods and applications that meet the industry/research requirements.

A collaboration between: