11, Number 7
A Gossman Consulting, Inc.
Increasing Speed and Decreasing
of PCB Analysis of Alternative Fuels and Raw Materials
David Gossman, Gossman Consulting, Inc.
Environmental Regulations in many countries control the use of
waste-containing PCBs. It may therefore be necessary to test incoming
alternative raw materials and/or fuels for PCBs based on regulatory
requirements or a desire to limit corporate liabilities. The
concentration for which this control is needed may vary considerably
state to state. In many areas of the world including the US the
critical threshold is 50 ppm but it can be as low as 2 ppm and as high
as 500 ppm depending on the specific circumstances. In any case it is
desirable to have testing methods that can perform this testing in a
minimal amount of time (generally less than 30-60 minutes) and at a
minimal cost. There are three steps to achieve this goal. First,
implement a process that evaluates clearly the data quality objective
(DQO) and thus limits or eliminates unnecessary testing. Second,
develop a sample preparation process that targets the specific sample
matrix, and minimizes sample preparation time. Finally, develop
analytical instrumentation specifications and operating conditions that
meet the DQO while minimizing the analytical time required.
The DQO Process
The DQO process is a seven-step process summarized at
http://gcisolutions.com/AWMADG99.htm. This process needs to be used to
help set clear data quality objectives based on a variety of factors
all outlined in the process. By performing this process first, the
laboratory can be assured that the data that is produced will meet the
end use needs and that more time and cost than is needed will not be
invested. It is often the case that laboratories perform testing blind
to the final use of the data. For example, in most PCB testing of
alternative raw materials and fuels all that is required is a threshold
determination – is the concentration above or below a
Generally this type of determination does not require the multipoint
calibration curves that may be present in standard methods. Instead the
sample preparation, and method calibration needs to focus on meeting
the need to quantitate at the threshold level. Concentrations below the
threshold level are of little concern and concentrations above the
threshold level need only be noted as such.
Sample preparation for PCB analysis consists of three basic steps for
most alternative fuels and raw materials. Sample extraction, the first
step, may not be necessary for some samples such as waste oils or
solvents. Solid samples will require extraction with a solvent
generally the same solvent that is used for sample dilution, the second
step. The precise nature of the sample extraction and the time required
will depend on the specific sample matrix. Spiked samples should
occasionally be used to validate this step in the methodology.
Sample dilution is performed in a suitable nonpolar solvent. The most
common solvent seen in standard methods is n-hexane. I strongly
recommend against using n-hexane – it is both more toxic and
volatile than other suitable solvents. Isooctane is preferred, reducing
error due to solvent volatilization and potential exposure issues for
laboratory personnel. The amount of sample dilution required will
depend largely on the quantitation limit needed. For samples needing a
low quantitation limit, such as 1-2 ppm, a ten-fold dilution is
recommended. Higher dilutions are recommended when higher quantitation
limits will meet the DQOs. It is important to note that the dilution
solvent can be prespiked with internal standards. Said internal
standards are not used to quantify the results but rather to verify
that the third step in sample preparation process, sample cleanup, does
not result in the loss of the analytes of interest. I recommend that
the dilution solvent contain 10-100 ppb of 2,4,5,6-tetrachloro-m-xylene
and decachlorobiphenyl. These internal standards neatly bracket the
chromatographic range over which various PCB Aroclors elute.
Once the sample has been extracted and diluted in the appropriate
solvent, which has been prespiked with internal standards, it is now
necessary to perform a chemical cleanup of the sample. This sample
cleanup can vary considerably depending on the degree of interferences
present in the original sample and the proportion of them that extract
into the solvent used for extraction. In order to minimize sample
preparation time and cost it is generally necessary to investigate a
variety of sample cleanup options to determine the optimal threshold
for cleaning up the sample but not going into overkill. For a typical
waste oil sample there are two recommended sample cleanups that can be
performed fairly quickly. The first is the use of concentrated sulfuric
acid to wash the diluted sample and chemically destroy interfering
compounds such as oxygen containing compounds like esters and
phthalates. Depending on the level of cleanup needed this step can be
repeated a number of times. An additional step that is often performed
is to clean the sample with florosil. Most often this is done by
passing the diluted sample through a preprepared florosil column.
Another faster method that can achieve the same result is to simply add
a small amount of florosil to the diluted sample and agitate it.
Interfering compounds are adsorbed onto the florosil.
Taking this series of steps into account and using waste oil needing a
2 ppm quantitation limit as an example, the following would be a
typical resulting operating procedure:
1. Dispense 4.5 ml of solvent that has
with internal standards into a test tube.
2. Pipet 0.5 ml of waste oil into the
Agitate the sample of oil just prior to removing the sample and then
mix the diluted sample using a vortexer.
3. Add 2 ml of concentrated sulfuric acid
to the test
tube in 0.5 ml increments. With each incremental addition mix with the
vortexer allowing any reaction to diminish prior to adding additional
acid. Make certain that the test tube is pointed toward the back of the
fume hood during this procedure in case of a more violent reaction.
4. Centrifuge the sample to separate. If
(top) layer is reasonably clear go on to step 5, otherwise decant the
organic layer to a new test tube and repeat steps 3 and 4 as necessary.
5. Decant most of the organic layer to a
tube and add ~1 g of florosil. Agitate the sample for at least 15
seconds with the vortexer. Allow the sample to separate and withdraw ~1
ml of solvent to be placed in the gas chromatograph autosampler vial.
This entire procedure can be accomplished by a practiced technician
within a matter of a just a few minutes.
There are numerous columns that can be used to efficiently separate and
quantify PCB Aroclors. Many years ago the standard was a packed glass
column with a mixed phase support. Today I prefer a wide bore capillary
column with a thick nonpolar phase. The exact configuration that will
be chosen by the analyst may depend on available instrumentation and
other potential uses such as chlorinated herbicide analysis. Electron
capture detectors are generally used for PCB determination although
other detectors have been successfully used including mass selective
detectors. Further, to minimize analytical times and maintain
appropriate peak separation the use of aggressive gas flow levels are
sometimes needed. Modern instruments with electronic flow control can
aid significantly in maintaining high gas flow through the column
during the temperature-programmed run. With sample turn-around time of
critical importance and the need to push the quantitation limit down to
<200 ppb in the diluted sample the following parameters would
provide a good starting point for developing a standard operating
· Column – SPB-608,
30 m x 0.53mm ID, 1.0 µm film
· Carrier – helium
· Detector – ECD,
320°C, nitrogen makeup gas
· Injection –
250°C, splitless, 2.0 µl
· Oven –
120°C (2 min) to 300°C (15°C/min) hold
If interferences were minimal a thinner coating of 0.5 µm
speed the analysis and enhance the resolution a small amount. All of
these parameters should be considered a starting point for optimizing
an operating procedure.
Standards of 200 ppb of various Aroclors should be maintained in a
computerized database for quick overlay and comparison with samples.
Aroclors typically used are 1016, 1221, 1232, 1242, 1248, 1254, 1260
and 1262. A mixture of two of these Aroclors, such as 1232 and 1260 can
be used for routine checks on the retention time calibrations.
Separately prepared check standards can be used to verify that the
sensitivity of the ECD has not changed over time.
By using a system of data quality objectives and then developing sample
preparation and instrumentation analysis procedures to optimize the
determination of PCBs in alternative raw materials and/or fuels, a
system can be put into place that allows an individual sample to be
analyzed within 30 minutes of receipt with a high degree of confidence
that the results meet a predetermined threshold determination.
contact David Gossman at 847-683-4188 or
by e-mail at email@example.com
for additional information.