Transcript Sampling for semivolatile organic contaminants in

Sampling for semivolatile
organic contaminants in
environmental compartments
Lisa Rodenburg
The Universe of Non-polar
Chemicals
PBTs
VOCs = Volatile
organic chemicals
POPs
SOCs = semivolatile
organic chemicals
POPs = Persistent
Organic Pollutants
VOCs
SOCs
PBTs = Persistent,
Bioaccumulative, &
Toxic
Many classes of contaminants can
be sampled and measured together:
PCBs = polychlorinated biphenyls = myriad uses,
banned since 1970’s = PBTs
PAHs = polycyclic aromatic hydrocarbons =
combustion by-products = less P, very BT
PBDEs = polybrominated diphenyl ethers = current
use flame retardants = not very P, very B, not sure how
T
OCPs = organochlorine pesticides (DDT, etc) = some
in current use (α- and γ-HCH, α- and β-endosulfan ),
some banned (DDT) = most are PBTs
PCBs
PCBs consist of 209 congeners, which may
have 1 to 10 chlorines.
A group of congeners having the same
number of chlorines is a “homolog group”
PCBs were previously sold as “Aroclors” and used as fluids in electrical
equipment, particularly transformers and capacitors.
PCBs are classified as probable human carcinogens and have been
shown to cause a range of serious non-cancer health effects in
animals.
The manufacture, processing, and distribution in commerce of PCBs
were banned in 1976 due to concerns over their toxicity and
persistence in the environment.
About 1.3 million metric tons of PCBs were produced world-wide.
PAHs
PAHs are Polycyclic Aromatic Hydrocarbons
They contain 2 or more fused aromatic rings
Products of combustion of any type as well as
evaporative emissions from fuels.
A small amount of PAHs are produced naturally
(volcanoes, forest fires, etc.)
Humans are exposed to PAHs by breathing
contaminated air (including tobacco smoke) and
eating grilled foods.
The Department of Health and Human Services
(DHHS) has determined that some PAHs may
reasonably be expected to be carcinogens.
PBDEs
Can have 1-10
bromines,
numbered in
same was as
PCBs
2,2’,4,4’,5-pentabromodiphenyl
ether = BDE 99
OCPs
Many different
structures and
numbers of
chlorines
heptachlor
DDT
Outline
• Sampling
– Air
– Water
– Other
Sampling
• Cleanup
Extraction
QA/QC
Cleanup
Detection
– The easy way
– The hard way
• Detection
– GC/ECD
– GC/MS
• Cautionary Tales
What are semivolatile
contaminants?
• On the basis of vapor pressure, we can
divide the nonpolar or slightly polar
compounds into VOCs and SOCs.
– VOCs = vapor pressure > 10-3 atm
not on atmospheric particles
– SOCs = vapor pressure < 10-6 atm
significant fraction on atmospheric particles
– Some things fall through the cracks, like
naphthalene.
VOCs (TO-15)
Fluorinated, chlorinated,
brominated C1, C2, C3
compounds
Mono- and dichlorobenzenes
Methyl and ethyl
benzenes
1,3-Butadiene
Acetone
Acetonitrile
Acetylene
Acrylonitrile
Benzene
Ethyl Acrylate
Ethyl Tert Butyl Ether
Ethylbenzene
Hexachloro-1,3Butadiene
Methyl Ethyl Ketone
Methyl Isobutyl Ketone
Methyl Methacrylate
Methyl Tert-Butyl Ether
n-Octane
Propylene
Styrene
Tert-Amyl Methyl Ether
SUMA
Canister
sampling
SOCs
PCBs
PAHs
Organochlorine pesticides
PBDEs
Others?
Sampled using a high-volume
air sampler
The Hi-Vol
Filter
Canister
(containing PUF or
XAD-2 sorbent)
Vacuum pump
Timer
Measure pressure drop before and after every sample.
Calibration curve converts pressure drop to flow rate.
Timer gives time, hence volume of air sampled.
Pitfalls
• Breakthrough of more
volatile contaminants
(minimize flow rate)
• Gas/particle
partitioning
(minimize flow rate)
• Detection limits
(maximize flow rate)
• Motor instability
(pre- and post-calibration)
• Contamination from
motor, O-rings, etc.
(keep everything clean, vent
motor)
Measure breakthrough by
occasionally cutting a PUF
in half and analyzing the
top and bottom separately.
Sorbent choice
• PUF allows greater breakthrough of
polar and volatile compounds.
• XAD-2 has a huge PAH background,
especially low MW PAHs.
• PUF can be very clean.
Run lots of blanks!
Breakthrough of PCBs on PUF
PCB congener Percent Breakthrough
8,5
29 %
18
22 %
17+15
27 %
16+32
14 %
31
4%
28
7%
21+33+53
2%
22
5%
45
28 %
46
9%
52+43
0%
49
47+48
44
74
87+81
177
202+171+156
201
203+196
195+208
194
8%
1%
1%
1%
8%
3%
100 %
5%
5%
15 %
3%
PCBs can have 1 – 10
chlorines.
PCBs are numbered
such that higher
numbers have more
chlorines.
Heavier PCBs, less
breakthrough.
Breakthrough significant for
PCBs with 3 or less chlorines
Blank contamination
Water Sampling
• Whole water or grab samples
– Detection limits require very large samples
– Blank contamination a big problem
– Volatilization
• Dissolved vs. Particulate
– Filter for particles, sorbent for dissolved
– Choice of sorbent is tough
• XAD-2 PAH contamination
• Tenax, C18 cleanup problems
– Choice of platforms:
• Infiltrex – expensive, unreliable
• TOPS (Trace Organics
Platform Sampler) –
a better way?
• Pepsi cans – low tech
Colloids
8
c 7/5/98 sample
7
log KOC
• Typically a 0.7 mm
filter is used, which
allows small particles
to pass through to be
quantified with the
apparent dissolved
phase.
• This leads to the
“solids concentration
effect”. The apparent
distribution between
dissolved and particle
phases changes as
the total amount of
solids increases.
With correction:
log KOC = 1.06*log KOW - 0.08
6
Without correction:
log KOC = 0.71*log KOW + 1.86
5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
log KOW
K id 
Cis
Ciw
K ioc
K id

f oc
Other sampling
• When sampling for sediment, biota, etc,
homogenization and collection of a
representative sample are paramount.
• Volatilization still a problem – refrigerate
or freeze immediately
Extraction
• Techniques:
– Soxhlet Extraction
– Accelerated Solvent
Extraction (ASE)
(high T and pressure
minimize amount of
solvent needed)
• Solvents:
– Dichloromethane
(toxicity?)
– Pet Ether
– Hexane
(leave behind lipids or
more polar compounds)
Rotovap
Blowdown
Cleanup
• Use column chromatography to remove
interfering compounds from your sample
• Type of analytical method determines the rigor
of the cleanup
Adsorbent:
Alumina
Sample Matrix:
Cleaner
Silica
Florisil
Air
Sediment
Dirtier
Sludge
Size Exclusion Chromatography Biota
(to remove lipids)
Surrogate
recovery
Our Alumina Cleanup
•
•
•
•
•
•
Bake alumina at 550ºC overnight
Deactivate with 3% wt water
Precondition column
F1 = 13 mL Hexane = PCBs
F2 = 15 mL 2:1 DCM/hexane = PAHs
OCPs, PBDEs split between F1/F2
Detection
• Detection method is determined by
concentration of compound in environmental
matrixes.
– PCBs = Electron Capture Detection or HighResolution GCMS
– PAHs = GCMS EI
– PBDEs = GCMS NCI
– Cl Pesticides = GCMS NCI
– PCDD/Fs = High-Resolution GCMS
GC/ECD
Invented by Lovelock around the late
1950s and early 1960s.
Uses a radioactive Beta emitter
(electrons) to ionize some of the carrier
gas and produce a current between
electrodes.
When organic molecules that contain
electronegative functional groups, such as
halogens, phosphorous, and nitro groups
pass by the detector, they capture some
of the electrons and reduce the current
measured between the electrodes.
The ECD is as sensitive as the FID but
has a limited dynamic range and finds its
greatest application in analysis of
halogenated compounds.
Cost ~ $30,000
GC/MS
Solute molecules are ionized in the ion source
Resulting fragments are separated on the basis of their
mass/charge ratio then detected by an analyzer unit
Ionization by electrons (EI) or gas molecules (CI,
Negative or Positive).
NCI similar to ECD
(little fragmentation, best for halogenated compounds)
Scan mode give entire mass spectrum = good for
identification of unknowns
SIM (selective ion monitoring) mode = much more
sensitive
Cost ~ $100,000
QA/QC
•
•
•
•
Sample contamination
Reproducibility
Tracking of mass
Representativeness of samples?
Avoiding Contamination
• Cleanliness
– Bake glassware at 450°C overnight
– New aluminum foil
– High grade solvents
– New building!
• Cleaning sampling equipment
sometimes difficult
– Blanks, blanks, blanks
Reproducibility
•
•
•
•
Side-by-side samples
Duplicates
Matrix spikes
Surrogates
Mass Tracking
• Surrogates
– Added to track recovery through the various
sample processing steps
– Must have same or similar physical-chemical
properties as analytes
– Deuterated or 13C labeled
– Non-native congeners (PCBs 14, 23, 65, 166)
• Internal standards
– Added to allow quantification of mass even though
volume is not known
– Deuterated or 13C labeled
– Non-native congeners (PCBs 30, 204; BDE 75)
Representativeness of
samples?
• Homogenize sediments (Bass-o-matic)
• Take lots of samples
• 12th day sampling
Special considerations for PBDEs
• Flame retardants – designed to break down
at high temperatures!
• BDE 209 has 10 bromines
– extremely labile
– MW = 960 g/mol!
• Use cold on-column
injection
• Very short GC column
• Avoid light
The Pitfalls of Measuring PCBs by
ECD
Some PCBs co-elute,
and there ain’t nothin’
you can do about it.
Example:
PCB s 110+77
This is a GOOD chromatogram!
EPA
Method
1668A
Uses Highresolution GC/MS
(about $1 million)
13C
labeled
compounds:
3 field stds
28 surrogates
3 cleanup stds
5 recovery stds
= 39 stds
Trade-Offs
Would you rather have 28 surrogates with 60%
recovery, or three surrogates with 95% recovery?
209 congener method can reveal surprises
Contract labs are far from infallible
Contract labs only love your money, not your
samples
PCB 11
3,3’-dichlorobiphenyl is not found in
Aroclors
NYSDEC “found” it accidentally in
effluent from PVSC
It is produced inadvertently during
pigment manufacture
(see Litten et al., 2002)
Most data sets do not look for it.
Co-elution a problem even for
method 1668A
1668A can differentiate between (for example) PCBs
110 and 77, even though they co-elute, because 110
has 5 chlorines and 77 has 4.
BUT PCBs within a homolog group that co-elute are
still quantified together
Contract labs report all co-eluting congeners under
the congener with the lowest IUPAC number.
Example: what is reported as PCB 93 is really
93+95+98+100+102 (and is primarily PCB 95).
Cost
Price per sample ~$1,000
METHOD 1668 CALIBRATION SOLUTIONS from Cambridge Isotope Laboratories.
METHOD 1668 CALIBRATION SOLUTIONS SET5X0.2ML
METHOD 1668 DAILY CALIBRATION CHECK STANDARD 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS0.2 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS1 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS2 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS3 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS4 0.2 ML
METHOD 1668A CALIBRATION SOLUTION CS5 0.2 ML
METHOD 1668A CALIBRATION SOLUTIONS CS1-CS5 SET5X0.2ML
METHOD 1668A CLEAN-UP STANDARD SOLUTION 1.2 ML
METHOD 1668A INJECTION INTERNAL STANDARD SOLUTION 1.2 ML
METHOD 1668A NATIVE TOXICS/LOC SOLUTION 1.2 ML
METHOD 1668A TOXICS/LOC/WINDOW DEFINING SOLUTION 1.2 ML
$2,400.00
$495.00
$625.00
$625.00
$625.00
$575.00
$625.00
$625.00
$2,450.00
$575.00
$1,650.00
$795.00
$2,450.00
The pitfalls of measuring
OCPs by ECD
Old Method (ECD):
New Method (GC/MS NCI):
Similar to EPA Test Method 8080
Based on a method developed by
Shannon Nicole Brown (M.S., U.
of Iowa, 2000)
Uses electron capture detection
(ECD)
Uses mass spectrometry (MS)
with negative chemical ionization
(NCI)
6 Pesticides quantified
24 Pesticides quantified
Identifies pesticides based on
retention time
Identifies pesticides based on
retention time and major
ion/secondary ion ratio
If analytes co-elute they will not be
quantifiable
Co-eluting "interferences" can
be excluded
Comparison of ECD and NCI data
4,4’-DDE
60
NCI method
50
40
Jersey City:
N = 28
P < 0.0001
30
20
Gas- phase
y = 1.1037x + 3.8032
R2 = 0.7977
10
0
0
10
20
30
40
50
45
60
2,4’-DDT
40
ECD method
Because OCPs are abundant
enough to be detected by a regular
GC/MS instrument, the mass spec
method is cost-effective.
NCI method
35
y = 0.7574x + 0.1956
R2 = 0.1725
30
25
20
15
N = 28
P = 0.03
10
5
0
0
5
10
15
20
25
30
ECD method
35
40
45
Conclusions
•
•
•
•
•
•
Dirty matrices
Complex mixtures
Cost/benefit analyses
Cleanliness
Blanks, blanks, blanks
Trust but verify