by Joseph Stefkovich, Product Manager, Xenosep Technologies
Ozone is a naturally occurring substance found in the stratosphere. For every
10 million air molecules, 3 ozone molecules play a key role in protecting humans
from the harmful effects of the sun's radiation, which include skin cancer and
cataracts. Analogous to the SPF 45 (Sun Protection Factor 45) sun block you would
apply liberally before going to the beach, ozone protects by absorbing the UVB
portion of ultraviolet light. If ozone isn't readily available in the stratosphere,
sun blocks of the future might need to be 10 to 100 times stronger, say SPF 5000.
Radiation from the sun not only affects humans but the entire earth's surface.
It is already known that many crops, plastics and other materials are and would
continue to be negatively impacted from decreasing ozone levels in the atmosphere.
Freon—The Miracle Solvent
In 1931 Freon® was introduced as a miracle solvent. It was stable, nonflammable, had low toxicity and was inexpensive. Unfortunately it was discovered many years later that Freon along with other CFC's (chlorofluorocarbons) could deplete the protective concentration of ozone found naturally in the stratosphere. This is because Freon is so stable and doesn't dissolve in rain water that over time winds drive the CFC's into the stratosphere. There strong UV radiation breaks down ozone molecules and releases atomic chlorine, which can further destroy an additional 100,000 ozone molecules. From here, it's easy to see that the net effect of CFC's in the stratosphere means the depletion of ozone faster than it can be naturally replenished. CFC's form the basis for a new category of compounds designated ODS's (ozone depleting substances).
One of the main laboratory uses for Freon is as an extraction solvent for the determination of oil and grease in wastewater. "Oil and Grease" is a conventional pollutant regulated by the CWA (Clean Water Act) of 1977. The main purpose of the CWA is to restore and protect the quality of the nation's surface waters. Since "Oil and Grease" is a very common pollutant, its potential discharge into the environment needs to be monitored and controlled by many industries to prevent the many undesirable effects downstream at the local wastewater treatment plant. Over 20,000 NPDES (National Pollutant Discharge Elimination System) permits contain requirements for companies to monitor and control their discharges for Oil and Grease on a regular basis.
Freon—The Pollutant
"Green Chemistry" was born with the passage of the Pollution Prevention Act of 1990. The goal of this national policy was to prevent or reduce pollution at its source whenever possible. Concurrently, the harmful effect a new pollutant called Freon was having in the atmosphere was beginning to be well understood. With support from the Pollution Prevention Act of 1990, the Clean Air Act Amendments of 1990 proposed the complete phase out of Freon for all non-essential uses by the end of 1996.
As such, a new extraction solvent for the determination of Oil and Grease was now needed for the greater good of protecting the planet from the harmful effects Freon availability in the atmosphere. Many replacement solvents were evaluated and, after much debate, the EPA decided on n-hexane and EPA Method 1664 became known as the "green" method for the determination of Oil and Grease because of its friendliness to the environment.
Timeline/Background Highlights
1931 Freon introduced as the miracle solvent 1970 Researchers begin investigating various chemicals affecting
the ozone layer 1977 Clean Water Act. Regulation of conventional pollutants,
i.e., Oil and Grease among others 1980 Annual ozone "hole" over Antarctica forms increasing issue
awareness 1985 Vienna Convention, formalizes international cooperation
on issue 1987 Montreal Protocol. Freon now a pollutant. Phase out by 1996
1990 Pollution Prevention Act of 1990. The beginning of "Green
Chemistry" 1990 Clean Air Act Amendments. Phaseout of all CFC's including
Freon 1995 Laboratory exemption granted for EPA Method 413.1 1996 Proposed EPA Method 1664 to replace EPA Method 413.1 1999 Promulgated EPA Method 1664A to replace EPA Method 413.1 2002 No new Freon allowed; recycling permitted until supplies
exhausted 2006 Methods Update Rule signed to withdraw EPA Method 413.1
from use 2007 Methods Update Rule Promulgated?
As can be seen above, the "greening" of Oil and Grease analysis is at least 27 years in the making. Upon promulgation of the pending Methods Update Rule, all Freon based Oil and Grease methods will be withdrawn from use and laboratories that were using Freon for their oil and grease testing requirements will have some serious choices to make in a hurry.
EPA Method 413.1
One reason this Freon-based LLE (Liquid Liquid Extraction) method is still in use today is because many environmental chemists find it very simple, universal and easy to use. The basic procedure is described below:
1. Acidify the 1 L sample to pH<2 2. Add 1 L sample to 2 L separatory funnel 3. Add 30 mL Freon to sample bottle and rinse 4. Transfer Freon extract to funnel and vigorously shake for
2 minutes 5. Allow immiscible layers to stand and separate for 10 minutes 6. Drain lower Freon layer through sodium sulfate into pre-tared
boiling flask 7. Repeat steps 3-5 two more times 8. Distill solvent in boiling flask to dryness and place in dessicator
for 30 minutes 9. Obtain stable weight for dried extract and calculate results
As mentioned earlier, Freon is nonflammable and has low toxicity. If it weren't for protecting the population via the earth's ozone layer, it's unlikely many lab folks would change to the new method willingly—which uses n-hexane as the extraction solvent, both flammable and a neurotoxin.
EPA Method 1664A
After years of research and development, EPA proposed and promulgated EPA Method 1664A as the replacement for EPA Method 413.1. Besides the solvent differences described above, EPA updated the QC requirements to reflect the minimum level necessary to demonstrate that any analytical results generated by the new method would be reliable. In addition, two compounds were selected to represent the "oil" and "grease" analytes in the QC tests. They were:
1) hexadecane the major component of diesel oil and petroleum
based samples and 2) stearic acid the major component of animal fat and non-petroleum
based samples
It would later be learned that the inclusion of stearic acid into the QC standard would prove especially challenging for the extraction options of EPA Method 1664A. When spiked into an acidified water sample, stearic acid reforms back into 2 - 25 μm sized solid particulates that want to stick to everything, especially wet glassware surfaces, making highly efficient and reproducible extractions very difficult, to say the least.
Although similar in procedure, EPA Method 1664A LLE is significantly more cumbersome
and time consuming to perform than EPA Method 413.1 LLE. The main reason is that
the solvent n-hexane is less dense than water. This causes the n-hexane to locate
itself in the upper portion of the separatory funnel upon standing after shaking.
As a result, the 1 L water sample must be drained back into the sample bottle
before the n-hexane extract can be collected, creating additional transfer steps
and glassware surfaces for the stearic acid to stick to, making analyte recoveries
not as easy and forgiving as the old method.
SPE Option
Originally introduced as a technique to prevent the formation of emulsions prevalent with the LLE option above, SPE (Solid Phase Extraction) is a relatively new technique permitted in EPA Method 1664A and now gaining in popularity for several reasons.
First, newer high capacity SPE Filters with built-in prefilters can now completely process QC and real world wastewater samples much faster than the original SPE filters available when EPA Method 1664A was first proposed and promulgated. An example of such a triple layer SPE filter is depicted in Figure 1. Wastewater and/or stearic acid particulates are filtered out at each layer according to their relative size maximizing filtration speed and sample throughput.
As soon as the Methods Update Rule is promulgated, EPA Method 413.1 will be officially
withdrawn from use and replaced with EPA Method 1664A. The elimination of Freon
as the extraction solvent will complete the greening of oil and grease analysis.
Current Freon users who want or need to continue testing for oil and grease will
have to make a choice between hexane LLE or SPE. Many of the issues associated
with the early SPE Filters and glassware have been recently resolved while the
same hexane LLE problems that existed 50 years ago, still exist (hexane was the
oil and grease extraction solvent before Freon). If history is any indicator of
the future, most users will eventually choose SPE as their method of choice for
the analysis of oil and grease.
Joseph Stefkovich, Product Manager, Xenosep Technologies, may be contacted at
joe.stefkovich@xenosep.com
or by phone at 973-239-0247.
AT A GLANCE • Freon depletes the protective concentration of
ozone found naturally in the stratosphere
• Freon is used in the lab as an extraction solvent for the determination of oil and grease in wastewater
• "Green Chemistry" was born with the passage of the Pollution Prevention Act of 1990
• Current Freon users who want or need to continue testing for oil and grease will have to make a choice between hexane LLE or SPE.
