Presented by Sergei Leikin, Ph.D.
The following post is based on a technical poster presented at the 2016 ICP Winter Conference in Tucson, Arizona. Modifications of the original presentation have been made to accommodate the blog layout as well as more detail around the primary application being Wear Metals and Additives in Oil and Ethylene Glycol. The shown analytical capabilities of “OPTI” series Nebulizers will also apply to the analysis of samples with high particulate and high Total Dissolved Solids (TDS) content – which will be addressed in forthcoming TSP BLOG entries.
- Analysis of the certain types of real world samples by ICP-AES still remains a difficult task due to a number of reasons.
- Presence of large particulates (over 300 µm) and high amount of total dissolved solids (TDS) in the sample is quite often combined with the strict performance requirements to reach lowest possible detection limits on a consistent basis.
- In a high production environment, analysis of these types of samples becomes a very challenging task.
- Commonly used concentric type nebulizers are specified to handle just small particulates of < 75 µm . Some of the nonconcentric alternatives are either made from an expensive polymer material, resistant to Hydrofluoric Acid, or (Babington type) do not reach a required level of sensitivity and precision .
- The OptiMist® and OptiSolids XL™ nebulizers were specifically designed to bridge the gap in performance between concentric and Babington V-Groove type nebulizers.
Nebulizer Design Approach
- Made from glass or quartz, both Nebulizers feature simple, non-concentric configuration and a relatively large sample channel internal diameter (ID).
- The ID of the sample channel is in the range from 0.5 mm for an OptiMist® to 1.0 mm for OptiSolids XL™.
- The sample channel ID of OptiSolids XL™ can be custom tuned for up to 2.0 mm depending on the application (Fig.1).
- Both Nebulizers from the “OPTI” series have a standard 6 mm outside diameter (OD) to fit into cyclonic spray chambers.
Fig. 1. TSP’s OptiMist® and OptiSolid XL™ Nebulizers
Instrumentation and Setup
The instrument used for testing purposes was a SPECTRO ARCOS SOP ICP-AE spectrometer with wavelength coverage from 130-770 nm. It features sealed optic filled out with Ar gas that recirculates through the filter to remove oxygen, water vapors and hydrocarbons. This provides excellent optical transmission in VUV spectral region.
The sample introduction components consisted of a nebulizer and cyclonic spray chamber connected to the vertically aligned torch of the ARCOS ICP ( Fig. 2) .
Fig. 2. Sample Introduction Setup
As shown on Fig.2 the OptiMist® and the OptiSolids XL™ selected for testing feature very large sample channel ID relative to traditional commonly used concentric nebulizers. Also, the sample and gas exit orifices are separated. This approach offers radically different sample handling characteristics as compared to nebulizers having concentrically aligned paths, particularly the robustness and good tolerance towards high particulate and high TDS content.
At the same time both the OptiMist® and the OptiSolids XL™ provide the sensitivity and precision level comparable to concentric nebulizers which is shown by a few real sample data examples.
Results – Pb 220nm – Ethylene Glycol (Engine Coolant)
Low level Pb determination in Engine Coolant (Ethylene Glycol) is a critical analytical task. The results comparison between the “OEM” style nebulizer and the OptiMist® for Pb 220 nm analytical line in Ethylene Glycol are shown on Figure 3 and 4. While the spectral scan for 1 ppm Pb is at the background level for “OEM” nebulizer there is a clear peak for OptiMist® nebulizer. The comparison of the Pb 220 nm background corrected intensity for 5 and 10 ppm standard in Ethylene Glycol shows approximately factor of 5-6 gain in sensitivity for OptiMist®.
Analysis of Additives in Lubricating Oil has strict requirements to accuracy and the precision obatined. The performance capabilities of the OptiMist® and the OptiSolids XL™ Nebulizer running such type of application are shown by the spectral scans and calibration data for P 185.95 nm and S 182.0 nm analytical lines (Fig. 5-8) as well as precision results (Fig. 9).
Results – P 185.95 nm – Lubricating Oil
Results – S 182.0 nm in Lubricating Oil
Results – Precision for Additives in Lub Oil (n=3)
Results and Discussion
- The results of applying OptiMist® and OptiSolidsXL™ nebulizers for direct ICP-AES analysis of lubricating oils, engine coolants, and industrial waters are presented on Fig.3-9.
- A typical precision level of less than 0.6 % RSD are shown for analysis of additives in lubricating oils (Fig.9). Cl was analyzed with 1.3% RSD, which is considered a typical and good value for an analytical line located so deeply in vacuum ultraviolet part of the spectrum at 134 nm.
- Trace level analysis of Pb in engine coolant showed a significant (factor 5-6) increase in sensitivity as compared to the OEM nebulizer (Fig.3 and 4).
- The “OPTI” series Nebulizers combine the ability to handle samples containing large particulates from 500 μm to over 1000 μm and high amount of TDS up to 20% with sensitivity comparable to Cross Flow type nebulizers and precision of less than 1% RSD.
- The OptiMist® and OptiSolidsXL™ showed a potential to be successfully applied to direct analysis of slurries, blood, serum and pharmaceuticals with tendency to form coagulated particles.
 José-Luis Todoli, Jean-Michel Mermet, Liquid Sample Introduction in ICP Spectrometry: A Practical Guide, (2011)