Freeze Drying
Increasing Extraction Efficiency of Organic Contaminants from Solid Substrates using Freeze
Drying: A Case Study
By Gregory Salata, Ph.D., Todd Poyfair, Jeff Coronado, Carl Degner, and Lance Jording;
[email protected], [email protected], 360.577.7222
Abstract
The accurate identification of organic contamination in any environmental matrix is dependent on the ability to
efficiently extract contaminants from a particular substrate. In many cases, the most efficient extraction solvents for
organic contaminants are non-polar. The extraction efficiency of
organic contaminants from a variety of environmental matrices,
including soil, sediment, sludge, and tissue, is therefore directly
dependent on the removal of water from the sample matrix prior
to extraction. Traditional drying techniques such as mixing the
substrate with sodium sulfate can generate excess heat, potentially
degrading and/or volatilizing low molecular weight target analytes.
Alternatively, the use of diatomaceous earth (Celite®, Hydromatrix®,
etc.) to bind water in a matrix eliminates problems associated with
heat generation. However, this can significantly increase the volume
of a sample with low solids, limiting the amount of substrate that
can be placed in a single extraction vessel. An alternative to these
methods is water removal by freeze drying which, when properly
used, has been shown to efficiently remove water from frozen sample
matrices by sublimation without significant loss of target analytes.
The study presented here compares the extraction efficiency of freeze drying with that of sodium sulfate drying for
analysis of Chlorinated Pesticides, PCBs, Organotins, Semivolatile Organics, and Polycyclic Aromatic Hydrocarbons. The
study shows that extraction of freeze dried samples consistently yields higher recoveries of analytes when compared
with analytical results for chemically dried sediments. Because freeze drying also allows for larger amounts of a given
substrate to be extracted without increasing the size of the extraction vessel, the higher extraction efficiency may
allow for lower detection limits for these analytes to be achieved using traditional laboratory extraction techniques.
Introduction
Freeze drying, or Lyophilization, is the process of removing water from a product by sublimation and desorption. A
sediment, soil, or tissue sample is frozen thoroughly and placed in a vacuum chamber, where the frozen water sublimes
at low pressure (Figure 1). Analytes with higher vapor pressures, i.e. the environmental contaminants of interest, are
left behind. The sample must be completely frozen to prevent removal of the
contaminants of interest during freeze drying.
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Materials & Methods
Bulk sediment was collected from a contaminated Table 1.
area near Palos Verdes, CA, air dried, and Analysis
Method
Detector
% Solids
homogenized to ensure uniformity. For each Pesticides
EPA 3545/8081
GC/ECD
80%
experiment listed in Table 1, deionized water
Pesticides*
EPA 3545/8081
GC/ECD
50%
was added to 100 g of the dried sediment to
EPA 3540/8082
GC/ECD
80%
produce samples of either 50% or 80% solids by PCB Congeners
weight. Eight replicate samples were prepared PAHs
EPA 3541/8270
GC/MS
80%
for each analytical method. To ensure complete PAHs
EPA 3541/8270
GC/MS
50%
water removal prior to extraction, four aliquots
Butyltins
Krone et al, 1988
GC/FPD
80%
were individually freeze dried per the instrument
manufacturers instructions. Additionally, four
*Pesticide spike was added prior to water removal due to low native
aliquots were mixed thoroughly with Sodium concentrations.
Sulfate until the sample was free flowing, indicating
complete water removal from the sediment. The
samples were then processed as outlined in Table
1.
Results and Discussion
Average recoveries for the freeze dried replicates were plotted against the average recoveries for the chemically dried
replicates (Figures 2-7). A best fit linear regression for each data set yielded slopes <1 for all but one of the analytical
sets, with the sixth yielding a linear slope slightly above 1. Also, the %RSDs for the replicate data in each instance were
consistently below 20%, with few exceptions, indicating that no adverse affect was noted in the freeze dried samples
based on molecular weight or compound class, regardless of the percent solids.
Figure 2
Polynuclear Aromatic Hydrocarbons (PAHs), 80% Solids
NaSO4 Dried Sediment (ug/kg)
1500
y = 1.0427x - 44.941
R2 = 0.9821
1200
Pyrene
Benzo(a)pyrene
Benzo(b)fluoranth
ene
900
Fluoranthene
Chrysene
Benzo(k)fluoranth
ene
600
2methylnaphthalen
e
Naphthalene
Anthracene
300
Fluorene
0
0
300
600
900
1200
1500
Freeze Dried Sediment (ug/kg)
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Figure 3
Organochlorine Pesticides, 50% solids
(Log scale, Spike Standard Added)
NaSO4 Dried Sediment
(ug/kg)
100000
y = 0.9532x + 16.772
R20.9998 =
10000
DDE-'4,4
1000
DDD-'4,4
DDT-'4,4
100
Endrin
Heptachlor
EBHC-
Endrin Ketone
Endrin Aldehyde
Aldrin DChlordane-
10
10
100
1000
10000
100000
Freeze Dried Sediment (ug/kg)
Figure 4
Polynuclear Aromatic Hydrocarbons (PAHs), 50% Solids
NaSO4 Dried Sediment (ug/kg)
700
y = 0.7542x - 1.1516
R2 = 0.9444
600
Pyrene
500
Pentachlorophenol
Benzo(e)pyrene
400
Benzo(a)pyrene
Perylene
300
Chrysene
Benzo(b)fluoranthene
Fluoranthene
Benzo(k)fluoranthene
200
2-Methylnaphthalene
100
Phenanthrene
Anthracene
Naphthalene
1-Methylphenanthrene
Fluorene
0
0
100
200
300
400
500
600
700
Freeze Dried Sediment (ug/kg)
Figure 5
Organochlorine Pesticides, 80% Solids
(Log scale)
NaSO4 Dried Sediment
(ug/kg)
100000
y = 0.8587x + 71.085
R2 = 1
10000
1000
4,4'-DDE
4,4'-DDD
4,4'DDT
100
100
1000
10000
100000
Freeze Dried Sediment (ug/kg)
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•
•
•
•
Higher recoveries of organic analytes regardless of
water content.
Complete removal of water, preventing possible
interference during extraction of water/drying agent
mixture.
No increase in sample volume due to addition of
chemical drying agent, allowing for extraction of
larger sample aliquot.
No heat generation, preventing breakdown/
volatilization of temperature sensitive analytes.
Figure 6
PCB Congeners, 80% solids
NaSO4 Dried Sediment (ug/kg)
Advantages of Freeze Drying:
80
y = 0.7547x + 0.0842
R2 = 0.9908
60
PCB 118
PCB 52
PCB 153
PCB 44
40
PCB 138
PCB 180
20
PCB 187
PCB 187
PCB 170
PCB128
PCB 206
0
0
20
40
60
80
Freeze Dried Sediment (ug/kg)
Freeze Drying Drawbacks:
• Drying of large aliquots or high water content samples
may require 2-3 days.
Figure 7
• Specialized equipment required, but readily
available.
The extraction of a variety of organic analytes can be
enhanced by using freeze drying as an alternative to
chemical drying. The results of this study indicate that
organic analytes can be extracted more efficiently from
sediment that has been freeze dried than from sediment
that has been chemically dried. Freeze drying also allows
for larger amounts of a given substrate to be extracted
without increasing the size of the extraction vessel, the
higher extraction efficiency may allow for lower detection
limits for these analytes to be achieved using traditional
laboratory extraction techniques.
NaSO4 Dried Sediment (ug/kg)
Conclusion
Butyltins, 80% solids
40
y = 0.6552x - 0.2075
R2 = 0.9955
30
MBT
20
10
DBT
TeBT
TBT
0
0
10
20
30
40
Freeze Dried Sediment (ug/kg)
References
1.
Krone C.A.; Brown, D.W.; Burrows, D.G.; Bogar, R.G.; Chan, S.; and Varanasi, U. A Method for Analysis of Butyltin Species and Measurement of Butyltins
in Sediment and English Sole Livers from Puget Sound, Environmental Conservation Division, Northwest and Alaska Fisheries Center, National Marine
Fisheries Service, NOAA, November 1988.
2.
Test Methods for Evaluating Solid Waste, Automated Soxhlet Extraction, EPA SW-846, Third Edition, Update II, September 1994, Method 3541, Revision
1.
3.
4.
Test Methods for Evaluating Solid Waste, Soxhlet Extraction, EPA SW-846, Third Edition, Update II, September 1996, Method 3540C, Revision 2
Test Methods for Evaluating Solid Waste, Pressurized Fluid Extraction (PFE), EPA SW-846, Final Update III, December 1996, Method 3545, Revision 0.
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