Ask the Lab Expert: Measuring Benzene and Toluene in Fuels, Staying Audit-Ready

Benzene and toluene boost gasoline performance, but both are hazardous. Regulators in the US and EU cap how much benzene and total aromatics a fuel can contain, leaving little room for analytical error.

We spoke with Asher Levy, subject matter expert in fuel testing at AnalytiChem, about the realities of benzene and toluene testing under ASTM D3606. Asher covers ethanol interference, method selection, auditor red flags, and the challenges that renewable bio-blends may bring. His insights offer practical guidance for lab professionals who need accurate, defensible fuel data.

1. Why is precise measurement of benzene and toluene so critical for petrochemical refineries today?

Benzene and toluene are globally regulated fuel components. While their anti-knocking properties indicate real functional benefits, they’re also hazardous and contribute to air pollution. Over the past several years, regulators have tightened the limits for benzene: The US EPA’s Mobile Source Air Toxics, or MSAT2, rule sets the maximum limit at 0.62 vol%, while the EU’s EN228 standard—also followed in Canada—sets a 1% limit. Toluene is not regulated as a standalone gasoline component, but it counts toward the total allowed aromatic hydrocarbon content, which the EU caps at 35%. The state agencies and fuel programs set their own restrictions on aromatics in the US.

Permitted levels of benzene and toluene are decreasing and vary in each region. Accurate testing is, therefore, critical to prove a fuel’s compliance with an area’s current state and federal regulations.

2. What are the main chromatographic challenges when testing modern fuels containing ethanol?

Today’s fuels have complex matrices and require analysts to select the most appropriate analytical approaches and methods carefully. Ethanol, a common fuel additive, and other oxygenates like sec-butanol, the internal standard suggested for ASTM D3606 Procedure B, elute near benzene. This can cause overlapping or broadened peaks and, therefore, less accurate benzene analysis.

If a laboratory runs Procedure B with the correct packed column, they can theoretically achieve the required resolution between benzene and ethanol, but they must validate the results on their independent system. Ideally, this is done by running certified reference materials (CRMs), which contain all the components at known concentrations. Alternatively, labs analyzing high ethanol-containing fuel for benzene may opt for ASTM D3606 Procedure A. This method employs a different instrument setup, including capillary columns, for better-resolved peaks and efficiency.

Regardless of the procedure selected, validating the instrument’s performance by running CRMs is a necessary best practice.

3. How should a lab choose between ASTM D3606 Procedures A and B?

The main difference in the procedures is the columns. Procedure A utilizes a capillary column setup; Procedure B uses a more traditional packed column. The two setups differ in resolution, precision, sample throughput, and tolerance for “dirty” or blended samples.

Procedure A’s capillary column separates the fuel components more cleanly, but sample overloading and matrix contamination can adversely affect its efficiency. That’s why many labs opt for Procedure B’s packed column instead: Though it uses more carrier gas at a higher flow rate, Procedure B’s packed column is more tolerant of complex matrices and higher sample volumes.

4. What is the most common red flag auditors look for in ASTM D3606 results?

Auditors working through ASTM D3606 results use fairly consistent checklists with questions like: Is the lab using the correct, current version of the standard with a matching internal SOP? Are calibration standards and traceability in order? Were the internal standard and calibration procedures used correctly? They also verify benzene and toluene peak resolution and separation, review GC maintenance and check standards, and assess how out-of-range results are handled.

Auditors will want to trace a sample from receipt through disposal, look for changes to calculations or raw data, and ensure technicians’ training records and sample scope are in order. Above all, what they’d look for are calibration and check standards, peak identification, data integrity, and sample traceability.

5. What key daily QC steps are essential to ensure fuel testing data is completely audit-ready?

Running a quality control (QC) or “check” sample is the most important daily activity. A check sample is a certified reference material run in the same program conditions as regular samples to confirm the accuracy of the results.

Control charts for check samples are as important as actually running them. A control chart with consistent check runs within established limits helps resolve any data reliability questions an auditor may have. Frequent and well-charted check sample runs help an analyst detect any variation in the analysis early, before it becomes a bigger/expensive problem or warrants a re-run.

6. What expected challenges with emerging renewable bio-blends could impact traditional GC fuel testing?

We don’t have direct experience running bio-blended fuels through GC as yet, but one could expect technical challenges from: (a) oxygenates, the common components of renewable fuels, that co-elute with benzene, and (b) matrix variation, caused by fuels the methods aren’t set up to measure.

Detection limits are likely to be pushed lower as renewable fuels without benzene and toluene are blended with traditional fuels. Testing will still be needed for compliance. Some bio-blended feedstocks come from recycled material, so their formulations may carry new and unexpected chromatographic interferences. This will call for higher instrument sensitivity and robust analytical practices to verify and validate the data.

Asher Levy is director of North America Sales and subject matter expert in fuel testing at AnalytiChem—the developers and manufacturers of CONOSTAN® Oil Standards. Asher works directly with petrochemical customers at AnalytiChem, giving him a detailed understanding of the sector’s key regulatory and analytical needs and challenges. With a degree in biochemistry, he combines scientific expertise with practical industry insight to help laboratories achieve accurate, compliant results.