Glyn Russell

Nebulizer selection is challenging because there are many types available: concentric, parallel-path, and cross-flow, to name a few. By far, concentric nebulizers are the most common type on instruments today, as they generally provide the best performance. Even within the narrower category of concentric nebulizers, there is quite a range of designs. Glass Expansion offers the largest range by any manufacturer, each model having a variety of applications for which it is ideally suited (1).


It is important to note that all concentric glass nebulizers are not the same. Glass Expansion’s designs feature a unique VitriCone

 sample capillary (Figure 1a), which is machined from a thick-walled capillary, resulting in a highly reproducible geometry and consistent internal diameter (i.d.). Since the thickness is not compromised, the capillary resists harmonic vibration caused by the high-velocity argon flow, giving the best short-term precision. Non-Glass Expansion designs typically use a hand-drawn sample capillary, resulting in an i.d. that varies over the length, preventing a laminar flow and creating points where particulates can lodge. The designs also are fragile and susceptible to harmonic vibrations.

 Glass Expansion concentric nebulizer design features.

Glass Expansion nebulizers also feature a direct connection (DC) gas line, as seen in Figure 1b, which features a ratchet fitting on one end, and an instrument-specific gas fitting on the other. The ratchet fitting provides a reliable, leak-free gas connection to the nebulizer, maintaining optimal backpressure for consistent performance.


 nebulizer is a glass concentric nebulizer that features a self-washing tip with smooth surfaces to avoid build-up of salt crystals. It provides outstanding nebulization efficiency and excellent tolerance up to 20% of dissolved solids without compromising detection limits.


 glass concentric nebulizer is a high-precision nebulizer for routine analysis of aqueous and organic samples.


 concentric nebulizer (Figure 1c) is manufactured from inert PEEK materials. It offers high sensitivity with excellent short-term precision and the highest tolerance to total dissolved solids (TDS) of any concentric nebulizer. It is a great “all-rounder” and the choice for analysis of diverse sample types.


 glass concentric nebulizer is designed for analysis of slurries, suspensions, and wear metals. It provides the excellent sensitivity and short-term precision of a glass concentric nebulizer, and it is tolerant to particulates up to 150 µm in diameter.


Parallel-path (or v-groove) nebulizers vary greatly in cost and performance. The large-bore capillary is designed to resist blockages, but this results in larger droplets and a wider drop size distribution, affecting both efficiency and precision. Parallel-path designs also typically suffer from poorer reproducibility in performance from one nebulizer to the next.


In this study, we compared the performance of the SeaSpray, Conikal, DuraMist, Slurry, and a non-Glass Expansion parallel-path design. Some of the criteria that need to be considered when selecting a nebulizer for ICP-OES applications are listed below:


sensitivity (signal-to-root background ratio, SRBR).


Short-term analytical precision (%RSD) is one of the most critical figures of merit for ICP-OES applications. With RSDs, the lower the figure, the better, as this represents less variability in the analytical signal. In Figure 2, the SeaSpray nebulizer shows the best short-term precision of 0.26% RSD, whereas the parallel-path nebulizer gives the worst precision at 1.3% RSD. Due to the design of the parallel-path nebulizer, precision can be improved at higher sample flow rates (1.5–2 mL/min). However, higher sample flow rates are not desirable in many ICP applications, due to plasma stability issues, limited sample volumes, or autosampler capacity.

 Comparison of short-term analytical precision of 5 ppm Mn at 0.7 mL/min sample uptake.


With a solid-state detector, the most reliable figure of merit for detection limits is the signal-to-root background ratio (SRBR), because measuring detection limits with multiple solutions and a large number of replicates is both slow and prone to significant statistical variation. With SRBR, the higher the value, the lower the limit of detection. In Figure 3, the SeaSpray offers the highest SRBR value (indicating the lowest detection limits), with the DuraMist giving the next best results. The Slurry and Conikal are similar and followed closely behind, with the parallel-path offering the lowest SRBR values (and worst detection limits) of the nebulizers examined.

 Comparison of SRBR at 0.7 L/min nebulizer gas flow.

In order to maximize the lifetime of these performance benefits, it is important to select accessories that will mitigate the effects of certain sample types. For high-TDS samples, pairing the SeaSpray or DuraMist with the Elegra argon humidifier will help maintain analytical performance (2). Humidifying the nebulizer gas helps to alleviate salt deposits in the nebulizer and torch injector, allowing uninterrupted and maintenance-free operation. In order to prevent any issues with clogs or blockages due to particulates, the Guardian inline particle filter can be installed to eliminate the risk of particulates getting trapped in the nebulizer or capillary tubing (3).


Lastly, to keep your nebulizer in good condition, always follow the manufacturer-recommended maintenance procedure, and do not use wires or sonicating baths. Glass Expansion’s Eluo Nebulizer Cleaning Tool provides a safe and convenient way to remove blockages (3).


If you want the best performance your ICP-OES can provide, it is essential that you choose the proper nebulizer to meet the demands of your sample types, in addition to following recommended maintenance procedures to ensure consistent performance and long life. In this application note, we presented a selection guide based on several performance criteria. However, if you require any further assistance selecting a sample introduction system, please contact us at 

“A Nebulizer Update,” Glass Expansion (Pocasset, Massachusetts, 2013).


“The Elegra Argon Humidifier: Uninterrupted and Maintenance-Free ICP Operation.” Glass Expansion (Pocasset, Massachusetts, 2016).


“Considerations when Analyzing Real-World Samples by ICP Spectrometry.” Glass Expansion (Pocasset, Massachusetts, 2017).


31 Jonathan Bourne Dr., Unit # 7, Pocasset, MA 02559
tel. (508) 563-1800, fax (508) 563-1802
Website: 

Articles

Nebulizer selection is a critical but often overlooked aspect of inductively coupled plasma–optical emission spectroscopy (ICP-OES) analyses. There are many different nebulizers available for ICP-OES, and choosing the optimal one can be confusing and difficult. To achieve peak performance from your ICP, it is essential to choose the proper nebulizer based on your sample types in addition to any necessary accessories to maintain long-term performance. In this study, we compare the performance of Glass Expansion’s most popular concentric nebulizer designs for ICP-OES applications as well as a parallel-path nebulizer from another vendor, providing a complete selection guide based on performance and design.


High Performance ICP-OES Sample Introduction: How to Choose and Use the Best Nebulizer for Your Analysis

The analytical performance of your ICP can often be improved by a careful choice of torch, spray chamber and nebulizer components by taking into account the type of samples that will be analyzed. In this article, we focus on the “hard to measure” ICP-OES elements, As, Se and Pb to determine whether we can improve detection limit performance by selection of appropriate sample introduction components.

A High-Performance Sample Introduction System for the Agilent ICP-OES

A single-piece inductively coupled plasma (ICP) torch can be a costly consumable item requiring regular maintenance and replacement, particularly with aggressive sample matrices, such as hydrofluoric acid (HF), organic solvents, and high total dissolved solids (TDS). Dealing with such samples is a common challenge with ICP spectrometry, and, generally, most “real samples” analyzed by ICP laboratories contain considerable concentrations of TDS, including soils, sludges, wastewater, brines, high acid digests, and fusions. Analyzing these types of samples can pose a number of challenges for the ICP analyst, including increased frequency of torch replacement due to shortened torch life.

The combination of high temperature from the plasma and salt deposits on the torch causes a quartz torch outer tube to devitrify. The disadvantage of a single-piece torch is that it is a relatively high-cost consumable item, and the entire torch must be replaced, when, in most cases, it is just the outer tube that suffers from devitrification. For this reason, many ICP manufacturers have moved away from the single-piece torch, and most now use a semi-demountable torch design.


The D-Torch (Figure 1) is a robust and higher-performing alternative to both a single-piece and a semi-demountable quartz torch. Compared to other demountable torches, the D-Torch is the only torch design that comes standard with a ceramic intermediate tube for greater robustness and a lower cost of ownership. With the D-Torch design, the analyst most often replaces only the outer tube, rather than replacing the entire torch or a quartz torch body. With demountable torch designs offered by other manufacturers, the intermediate tube is made of quartz and fused to the quartz outer tube, which is an additional consumable whose cost can quickly add up and negate the economic benefits of the torch itself. The D-Torch also features fully interchangeable injectors, allowing the analyst to install a specific injector (i.e., material and inner diameter) for each application, whether it be for aqueous, organics, high TDS, or HF.

 Glass Expansion D-Torch for Agilent 5100/5110 and 5800/5900 ICP-OES instrument.

Another exclusivity of the Glass Expansion D-Torch is an optional ceramic outer tube, which is of particular benefit for the analysis of high-TDS sample matrices, as the Sialon material does not devitrify. In addition to providing durability, the ceramic outer tube on an ICP torch produces a hotter, more robust plasma, which reduces matrix effects and improves sensitivities and detection limits. Compared to a quartz outer tube, the ceramic outer tube has a much longer lifetime, greatly reducing maintenance, cleaning, and downtime due to torch failure. In some sample matrices, quartz outer tubes can degrade in hours, while the ceramic outer tube will last years under the same conditions.


monitoring of wear metals in engine oils, as quartz outer tubes often suffer cracking and shortened lifetimes due to thermal shock


analysis of fusion samples where the lithium salts rapidly attack quartz


measuring high-TDS samples that will quickly devitrify the quartz outer tube.


Each Glass Expansion D-Torch design is a direct replacement for the standard torch, including ICP models that incorporate an easy-to-use, self-aligning torch installation. Each D-Torch model is designed with a base that provides the same self-aligning, turn-key installation for ICP models such as the Agilent 5800 and 5900, PerkinElmer Avio, Thermo iCAP, and Spectro Arcos MV. Compared to other demountable torches, the D-Torch also offers easier cleaning and maintenance with the ability to remove the injector and outer tube, with no O-rings to degrade and go brittle.


Glass Expansion manufactures a D-Torch design for many of the most-popular ICP models; this particular study highlighted the performance of the fully ceramic D-Torch model designed for the Agilent 5100 and 5110 systems, and is also fully compatible with Agilent’s recently released 5800 and 5900 ICP-OES instruments.


As mentioned previously, a combination of high temperature and salt deposits causes a quartz torch to devitrify. Higher concentrations of salt in the samples lead to more rapid devitrification. The quartz torch in Figure 2 was run for only 6 h with samples containing 10% NaCl and is already badly degraded. By contrast, the D-Torch ceramic outer tube in Figure 1 shows no degradation at all, and it was run for the same period and with the same samples as the quartz torch.


 A Comparison of resistance to devitrification when exposed to high salt matrix.

To further evaluate the performance of the ceramic outer tube in a high TDS matrix, a 1 ppm multi-element standard was prepared in a 10% NaCl matrix and aspirated at 1 mL/min for 4 h with no rinsing. The combination of the DuraMist DC nebulizer, Twister spray chamber, ceramic D-Torch, and Elegra argon humidifier provided exceptional stability (Figure 3). A measurement was taken approximately every minute over a period of 4 h, while a precision of less than 1% was maintained throughout the experiment.

 Ceramic outer tube long term stability test, 4-hour analysis of 1 ppm standard in 10% NaCl.

In addition to providing ICP laboratories with a more robust torch option, the ceramic outer tube of the D-Torch can provide a higher average signal intensity compared to a standard quartz torch. Table I shows the average signal intensity, based on three separate measurements of 10 replicates using a 100 ppb multi-element standard. The overall average increase in signal intensity with the ceramic outer tube was 21%.


The Glass Expansion D-Torch is the most cost-effective torch over the lifetime of the instrument, compared to both single-piece quartz torches and semi-demountable quartz torches, as well as alternative fully demountable designs. The unique ceramic outer of the D-Torch provides the ICP laboratory with an ICP torch that does not devitrify due to high salts or fracture when exposed to organic solvents. The ceramic outer tube also provides a higher average signal intensity, providing laboratories with an additional boost in performance.


31 Jonathan Bourne Dr., Unit 7, Pocasset, MA 02559
tel. (508) 563-1800, (508) 563-1802 (Fax)
Website: 

Glass Expansion designed and patented the D-Torch, a revolutionary, demountable torch. The D-Torch uses high-precision engineering to provide the benefits of a demountable torch, such as lower running costs, chemical inertness, and configurable injector geometry, without compromising usability, performance, or durability. In this report, we discuss the effects of harsh matrices on torches, as well as the features, benefits, and improvements in analysis achieved with the D-Torch. 


A Robust, High Performance, Revolutionary  Demountable ICP Torch

Glass Expansion’s new HydraMist spray chamber can be simultaneously used to determine As, Se, Sb and Hg via hydride generation, in addition to the determination of non-hydride forming elements using conventional pneumatic nebulization. The performance of the HydraMist was evaluated on an Agilent 5100 SVDV ICP-OES, and, when paired with a SeaSpray nebulizer, the detection limits for the hydride forming elements were improved between 15- and 50-fold without compromising the analytical performance of the non-hydride forming elements.

Glyn Russell

Articles

High Performance ICP-OES Sample Introduction: How to Choose and Use the Best Nebulizer for Your Analysis

A High-Performance Sample Introduction System for the Agilent ICP-OES

A Robust, High Performance, Revolutionary Demountable ICP Torch

HydraMist – Simultaneous Cold Vapor-Pneumatic Nebulization Spray Chamber