by Greg Rankin, Technical Science Writer
Metals-in-oil testing is routine laboratory work, but the results often guide expensive decisions. In equipment maintenance, rising levels of iron, copper, aluminum or other wear metals can indicate that a component is beginning to degrade. In lubricant production, additive metals help confirm whether an oil contains the chemistry required to perform. In food and product testing, elemental analysis can also be used to check for toxic or unwanted metals in edible oils and other oil-based matrices.
The work is established, but it comes with compromises. Organic-rich oil matrices can contribute to carbon buildup, torch cleaning and wear on sample introduction components, especially in high-volume ICP-OES labs. Selecting calibration standards can also be limiting. Organometallic standards have long been the practical choice for metals-in-oil analysis, but laboratories may still have to manage shorter shelf lives, narrower element options, sulfur-specific calibration steps, supplier limitations and solvent handling concerns.
In many other areas of elemental analysis, aqueous certified reference materials can offer broad element availability, customization options and longer shelf-life advantages. For oil testing, however, they have historically been difficult to use for one simple reason: aqueous standards and oil samples are not naturally compatible.
That is why hybrid aqueous/bio-based organic solvent standards are gaining attention as a new calibration option for metals-in-oil testing. Instead of replacing established metals-in-oil methods, these systems are designed to give laboratories a way to employ aqueous standards in oil analysis while preserving the ICP-OES workflow they already know.
Where the Workflow Gets Complicated
The difficulty of metals-in-oil analysis is not limited to calibration. Used oil samples can vary widely. One may be relatively clean and fluid, while another may be dark, viscous or loaded with particulate matter. Those differences can affect sample introduction, internal standard correction and the ability to maintain accuracy across a long run.
“There is a wide range of viscosities, and for ICP, since you have to introduce the sample into the plasma, that presents a challenge for achieving accuracy,” said Sergei Leikin, managing director of Texas Scientific Products.
The analytical expectations also vary by application. In wear metals testing, laboratories are often watching trends. A gradual increase or sudden spike in iron, copper, aluminum or another metal may indicate abnormal wear in an engine, gearbox, turbine or other lubricated system. For additive metals, the challenge can be different. Elements such as calcium, magnesium, zinc and barium may be present at much higher concentrations, and relatively small percentage errors can affect lubricant formulation and quality control.
Maintenance is another pressure point in high-volume oil analysis.
“Carbon buildup is one of the major things that oil analysis labs are facing,” Leikin said. “People are always asking how to deal with it and what can be improved.”
Bringing Aqueous Standards into Oil Analysis
The idea of using aqueous standards in oil analysis has appealed to analytical chemists for years. The challenge has been finding a solvent chemistry that makes them practical for oil-based samples.
More than two decades ago, Leikin saw an opportunity to address this need. With decades of ICP and ICP-MS application experience, including work with petroleum-related samples, he recognized that labs had limited options for metals-in-oil standards. In conversations with Inorganic Ventures founder Dr. Paul Gaines, the question was not whether another organometallic standard could be produced. It was whether the chemistry could be approached differently.
The technical requirement was specific. The solvent system had to dissolve oil-based samples while allowing aqueous inorganic standards to remain compatible in the calibration workflow. In plain terms, it had to bridge two chemistries that usually separate.
That idea has now moved from long-running technical discussion into an emerging calibration approach. Hybrid aqueous/bio-based organic solvent systems are designed to make aqueous CRMs usable in oil-based analysis while still fitting the expectations of laboratories that already run ICP-OES methods for metals in oils.
One example is Inorganic Ventures’ ASOSolv, a hybrid aqueous/bio-based organic solvent system developed for ICP-OES analysis of wear metals, additive elements, sulfur and contaminants in lubricating and edible oils. The product gives laboratories a way to use aqueous CRM chemistry without discarding existing metals-in-oil practices.
Leikin views the shift as more than an incremental change.
What Changes for the Lab
For a lab manager, the value starts with more choices. Traditional organometallic standard sets are useful, but they can be limited by available element combinations, source chemistry and supplier options. A hybrid aqueous/organic approach can open the door to broader elemental coverage, more custom mixes and access to the longer shelf-life advantages often associated with aqueous CRMs, while allowing labs to keep working within a familiar ICP-OES environment.
Sulfur is another area where hybrid aqueous/organic calibration can reduce complexity. Sulfur analysis by ICP is already possible with organometallic standards, but it often requires extra calibration considerations.
“With organometallic standards, the starting materials are often sulfonated compounds,” Leikin said. “With a hybrid aqueous approach, those issues are eliminated because the solvent does not contain sulfur, so sulfur can be included in the same calibration operation.”
Cleaner operation is a third consideration. Solvent chemistry designed to burn cleaner may help limit carbon residue in the sample introduction system. This does not necessarily mean a lab will run more samples per hour. The more realistic benefit is reduced maintenance pressure: less buildup, fewer cleaning interruptions and potentially less wear on components over time.
Hybrid solvent systems should not be framed as shortcuts around method discipline. They are calibration options for labs that want to reduce known constraints while maintaining analytical control.
Validation Comes Before Adoption
A new calibration approach must do more than work in principle. It has to produce comparable results, remain reproducible and fit the realities of established laboratory methods.
As Leikin explained, a lab manager evaluating a new technology needs confidence that switching methods will produce the same value within an acceptable statistical range, not only once, but consistently.
Inorganic Ventures evaluated its hybrid aqueous/organic calibration approach against traditional organometallic standards and NIST SRM 1085c, a standard reference material for wear metals in lubricating oil. The reported results for the evaluated organometallic standards run as unknown samples were largely within 2% of certified values, and the validation also included NIST SRM 1085c. For an oil testing lab, that type of comparison addresses the first question behind any method change: will the new approach produce numbers that agree with trusted reference materials?
“NIST reference materials are the gold standard internationally,” Leikin adds. “If you hit the number within 2% to 3%, that puts the question to bed in terms of whether the validated method of analysis can provide an accurate number.”
Adoption will still require lab-by-lab evaluation. Laboratories will need to review accuracy, reproducibility, matrix behavior, internal standard performance, method compatibility, cost, logistics, shipping classification and waste handling. Labs that follow ASTM methods closely may also look for clearer recognition within established method frameworks.
Hybrid aqueous/organic calibration does not remove the need for method validation, and it does not make established organometallic workflows obsolete. It gives laboratories another option to consider when carbon-related maintenance, limited elemental flexibility, sulfur calibration or standard stability become persistent constraints.
For labs that have traditionally had to keep aqueous CRM chemistry separate from oil-based analysis, the ability to bring the two together could be one of the most significant advantages.
About the author
Greg Rankin is a Houston-based freelance writer with more than 20 years of experience covering laboratory science, equipment and supplies.