How Is PCB Content Tested in Dielectric Fluids and Solids?

This article is Part 1 of a two-part series on PCB testing in electrical equipment. Here we will address what PCBs are, when testing is required, and how laboratories perform PCB analysis on dielectric fluids, porous solids, and non-porous surfaces using ASTM D4059. In Part 2, we will cover regulatory thresholds, compliance requirements, and how to interpret PCB test results.

Polychlorinated biphenyls (PCBs) were widely used as dielectric fluids in electrical equipment for decades before being banned in the late 1970s. Despite the ban on production, PCBs remain present in aging transformers and other in-service equipment — making accurate testing essential for risk management, regulatory compliance, and safe disposal. Understanding how PCB testing is performed helps equipment owners, environmental professionals, and utility engineers interpret results correctly and make informed decisions.

What Are PCBs?

PCBs (polychlorinated biphenyls) are a class of synthetic organic compounds consisting of biphenyl molecules chlorinated to varying degrees. Commercial production began around the 1930s and continued at significant scale until the U.S. federal ban on production in the late 1970s, driven by growing evidence of environmental persistence and health risks.

PCBs were valued in electrical applications for their dielectric properties: they are highly effective electrical insulators, chemically stable, and non-flammable — characteristics that made them well-suited for use as transformer and capacitor fluids.

Commercial PCBs were manufactured under the trade name Aroclor, with common formulations including Aroclor 1242, Aroclor 1254, and Aroclor 1260. The naming convention is chemically informative: the first two digits (12) refer to the 12 carbon atoms in the biphenyl backbone, while the final two digits denote the chlorine content by mass. Aroclor 1260, for example, contains 60% chlorine by mass — the highest chlorine content among the common commercial formulations, and the most environmentally persistent.

When Is PCB Testing Required?

New Dielectric Fluid

New dielectric fluid — such as fluid used to fill a new transformer — should be tested to confirm the absence of PCB contamination prior to service. The expected result for uncontaminated new fluid is None Detected (ND). Under ASTM D4059, ND indicates that PCB concentration is below 2 mg/kg (per Aroclor). Concentrations are expressed in milligrams per kilogram (mg/kg), equivalent to parts per million (ppm) by weight.

In-Service Dielectric Fluid

For fluid already in service, PCB testing is appropriate in several situations:

• Routine contamination screening — to confirm whether PCBs are present in equipment not originally manufactured with PCB fluid, or to monitor known PCB-containing equipment
• Post-spill or post-leak assessment — to characterize the extent of contamination following a fluid release and support regulatory reporting obligations
• Disposal and decommissioning — to classify fluid for proper disposal under applicable PCB regulations, including TSCA (Toxic Substances Control Act) requirements in the U.S.

The ASTM D4059 Test Method

The standard laboratory method for PCB analysis in dielectric fluids is ASTM D4059. This method uses gas chromatography with electron capture detection (GC/ECD) — a technique well-suited to PCB analysis given the extreme sensitivity of the electron capture detector to chlorinated compounds. ASTM D4059 applies specifically to dielectric fluids; PCB analysis of solids and surfaces follows related but distinct procedural steps, described below.

Testing Dielectric Fluids

Sample Preparation

Before analysis, the fluid sample undergoes a multi-step preparation process. The sample is first diluted 100-fold using a suitable nonpolar laboratory solvent — typically hexane, heptane, or iso-octane. The diluted sample is then acid-washed with sulfuric acid to remove co-extractable impurities that could interfere with chromatographic detection. A subsequent distilled water wash removes residual acid. In some cases, additional cleanup is performed using Florisil, an adsorbent powder that selectively retains certain interfering compounds.

GC/ECD Analysis

Following preparation, a 2-microliter aliquot of the cleaned, diluted sample is injected into a gas chromatograph (GC). The sample enters a long, coiled capillary column housed within the instrument’s oven. A carrier gas flow, combined with the column’s stationary phase and elevated temperature, causes the individual components of the sample to migrate through the column at different rates — generally, higher-boiling components elute more slowly.

At the column outlet, an electron capture detector (ECD) registers the signal as components emerge. The ECD is highly sensitive to halogenated compounds, making it particularly effective for PCB detection at trace concentrations. The detector signal is recorded as a chromatogram — a plot of signal intensity versus elution time — on which PCB Aroclors appear as characteristic clusters of peaks. Each Aroclor produces a distinct peak pattern, or “fingerprint,” which allows the analyst to identify which specific Aroclor(s) are present in the sample.

Quantification

PCB concentrations are determined by comparing the integrated peak areas from the sample chromatogram to those from a previously injected calibration standard of known PCB concentration. The sample’s dilution factor and specific gravity are incorporated into the calculation to back-calculate the PCB concentration in the original, undiluted fluid. Results are reported in mg/kg (ppm by weight).

Testing Porous Solids

PCB analysis of porous solid matrices — such as soil, gravel, or paper — requires an additional extraction step prior to GC/ECD analysis, since the solid itself cannot be injected directly into the instrument.

Extraction is commonly performed using a Soxhlet apparatus. In this technique, a weighed quantity of solid sample is loaded into the Soxhlet extractor, and hot solvent is cycled through the sample over several hours. The repeated solvent contact draws PCBs out of the solid matrix and into solution. Once extraction is complete, the resulting solvent is subjected to the same cleanup steps used for fluid samples — acid washing, water washing, and Florisil treatment where required — before a measured aliquot is injected into the GC.

Quantification follows the same peak area comparison approach used for fluid samples, with the solid sample weight and extraction solvent volume incorporated into the final concentration calculation. Results are expressed in mg/kg (ppm by weight), referenced to the dry weight of the original solid sample.

Testing Non-Porous Surfaces

For non-porous materials such as steel, painted concrete, or sealed flooring, PCB contamination is limited to the surface layer. Accordingly, PCB regulations governing non-porous materials define contamination thresholds in terms of surface loading — expressed as micrograms of PCB per 100 square centimeters of surface area (μg/100 cm²).

Surface sampling is performed using a wipe technique. A known area of the surface — typically a 10 cm × 10 cm section — is wiped using a gauze pad pre-moistened with solvent. The solvent facilitates transfer of PCBs from the surface to the gauze. The gauze is then sealed in a sample container and submitted to the laboratory.

In the lab, the gauze is agitated with a measured volume of solvent to extract the collected PCBs into solution. This extract is cleaned and injected into the GC using the same procedures described for fluid samples. Final results are calculated by dividing the total PCB mass detected by the surface area sampled, yielding a result in μg/100 cm².

Summary:

• PCBs are chlorinated biphenyl compounds that were widely used as dielectric fluids due to their electrical insulating properties, chemical stability, and non-flammability; commercial production was banned in the late 1970s under TSCA.
• Aroclor nomenclature encodes formulation chemistry — the trailing two digits indicate chlorine content by mass (e.g., Aroclor 1260 = 60% chlorine), which correlates with environmental persistence and regulatory classification.
• ASTM D4059 is the standard method for PCB analysis in dielectric fluids, with a detection limit of <2 mg/kg per Aroclor; results below this threshold are reported as None Detected (ND).
• PCB testing is warranted for new fluid (pre-service verification), in-service fluid (contamination screening, post-spill assessment), and at end-of-life (disposal classification).
• GC/ECD analysis is the core analytical technique; each Aroclor produces a characteristic chromatographic fingerprint enabling both identification and quantification
• Porous solids require Soxhlet extraction prior to GC analysis; results are reported in mg/kg referenced to dry sample weight.
• Non-porous surface testing uses solvent wipe sampling; results are reported in μg/100 cm², consistent with surface-loading regulatory thresholds.

In This Series:

• Part 1: How Is PCB Content Tested in Dielectric Fluids and Solids?
• Part 2: How Are PCB Regulations Applied to Electrical Equipment Classification?