PCB Testing - Part 1

PCB is the abbreviation for polychlorinated biphenyl. These are a class of chemical compounds comprised of biphenyl molecules that are chlorinated to varying degrees. They were first commercially produced around the 1930’s and were subsequently produced in large quantities until federal law banned their production in the late 1970’s, due to health concerns. They were originally produced because they had excellent properties for use as a dielectric fluid: they were effective electrical insulators, were very stable, and would not burn. They were produced in formulations called Aroclors, of which the common types were Aroclor 1242, Aroclor 1254, and Aroclor 1260. The numbers represent the chemical formulation: the 12 represents the 12 carbon atoms in a biphenyl molecule and the last two numbers represent the chlorine mass percentage of the PCB. For example, Aroclor 1260 is 60% by mass chlorine.

There are several scenarios where testing a dielectric fluid for PCB content is warranted. For example, PCB testing is appropriate for new dielectric fluid, such as would be used to fill a new transformer. In this case, the result of the PCB test should be None Detected (ND). The common laboratory test method for PCBs in dielectric fluids is ASTM D 4059. By this method, ND means that the PCB concentration is < 2 mg/kg (per Aroclor). The “mg/kg” means milligrams per kilogram, which is commonly known as parts per million (ppm) by weight.

PCB testing is also appropriate for in-service dielectric fluids, for the purposes of risk management and/or compliance with regulations. For example, PCB testing of in-service fluids is appropriate:

• As a check for PCB contamination.
• To test dielectric fluid after a spill or leak.
• For disposal purposes.

How does a laboratory actually perform PCB analysis?

The following is a general description of how a typical laboratory using ASTM method D 4059 might perform the test on a dielectric fluid sample.

First the fluid sample must be prepared for analysis. The sample is first diluted one hundred-fold with a suitable laboratory solvent, such as hexane, heptane, or iso-octane. Next, the diluted sample is cleaned by acid-washing with sulfuric acid, in order to remove impurities that can interfere with the measurement of the PCBs. A water wash is also performed with distilled water to remove any remaining traces of the acid. In some cases, an additional cleaning step may be performed with an adsorbent powder called Florisil.

Next, two microliters of the diluted and cleaned sample is injected into an instrument know as a gas chromatograph (GC). The sample is injected into one end of a long, thin, coiled column which is inside the oven of the GC. Due to the elevated temperature, the special packing inside the column, and a flow of gas through the column, the components of the sample take differing amounts of time to pass through the column. In general, the higher boiling point a component has, the longer it takes to pass through the column. At the other end of the column lies an electron capture detector (ECD), which is extremely sensitive to chlorinated compounds like PCBs. The signal from the detector is recorded electronically and/or on paper in the form of a graph known as a chromatogram. The chromatogram has time on one axis and signal strength on the other axis, and shows the various PCB Aroclors as groups of peaks. Different Aroclors produce different patterns or “fingerprints” on the chromatogram, and this is used to identify the specific Aroclor(s) in the sample.

The area of the PCB peaks is mathematically compared to the area of these same peaks from a previous injection of PCB standard of known concentration. The dilution and specific gravity of the fluid being tested are also taken into account to arrive at the PCB concentration in the original sample [in parts per million (ppm) by weight – milligrams per kilogram (mg/kg)].

Laboratories that perform PCB analysis on dielectric fluids can also usually test solids and surfaces for PCB content as well. When performing PCB analysis on a porous solid (such as soil, gravel, paper, etc.), the sample itself cannot be injected into the GC, as can be done with diluted fluid samples. The PCBs must first be extracted from the solid. This is often done using an apparatus known as a Soxhlet. In a Soxhlet, over the course of several hours, hot solvent is used to draw out the PCBs from a weighed amount of sample. After this extraction phase, the solvent containing the PCBs is cleaned as described earlier, and then a sample of this solvent is injected into the GC. As with fluid samples, the area of the PCB peaks on the chromatogram is mathematically compared to the area of these same peaks from a previous injection of PCB standard of known concentration. The dilution and weight of the solid sample are also taken into account to arrive at the PCB concentration in the original sample [in parts per million (ppm) by weight – milligrams per kilogram (mg/kg)].

Non-porous materials (such as steel or a non-porous floor) can also be tested for PCB content. For these materials, any PCB contamination will be on the surface. Therefore, PCB regulations governing contamination of non-porous materials are written in terms of the weight of PCB per 100 square centimeters of surface area.

To test a surface for PCBs, the PCBs must first be removed from the surface. This is done by wiping a measured amount of the surface (often a 10 cm by 10 cm area) with a gauze pad that has been moistened with solvent. This causes the PCBs to transfer from the surface to the gauze. The gauze is then put in a sample container and sent to a laboratory. In the lab, the gauze is shaken with a measured larger amount of solvent. This extracts the PCBs from the gauze into the solvent. A sample of this solvent is then cleaned and injected into the GC as described earlier. The amount of PCB detected is compared to the size of the wiped area to obtain a final result in micrograms of PCB per 100 cm2 of surface area (μg/100 cm2).