Transcript Radiochemical Methods and Data Evaluation Wm. Kirk Nemeth New Jersey Department of Health & Senior Services, Environmental Chemical and Laboratory Services, Radioanalytical Services.

Radiochemical Methods
and Data Evaluation
Wm. Kirk Nemeth
New Jersey Department of Health & Senior Services,
Environmental Chemical and Laboratory Services,
Radioanalytical Services
WHAT WE’LL COVER TODAY
 The analytical process: sample collection
to data reporting and uncertainties
 Methods for sample preparation for drinking
water samples
 QA data: what to look for
SOURCES OF
DATA VARIABILITY
UNCERTAINTIES
RANDOM: Includes the radioactive decay
process itself, random timing uncertainties, variations
in collection, sample preparation, positioning of the
sample at the detector, etc. The list is nearly endless.
SYSTEMATIC:
can be considered to be
conceivable sources of inaccuracy which are biased
and not subject to random fluctuations and those
which may be due to random cause but cannot be or
are not assessed by statistical methods.
PROPOGATION OF ERRORS
 The total error for any analytical scheme
involves errors in all steps: sampling,
preparation and measurement.
 If sampling uncertainty is  50%, and
the analysis only has a 2% error; your
total error is still very large
DATA QUALITY OBJECTIVES
(DQOs)
 A statement of the overall level of uncertainty
that a decision-maker is willing to accept in
results derived from environmental data
 The level of uncertainty can be defined
through defining the uncertainty in each step
of the analytical process.
 QA data are key in defining the level of
uncertainty
STEPS TO BE DISCUSSED
 Sample Collection and Preservation
 Methods
 Quality Assurance
SAMPLE COLLECTION &
PRESERVATION IN THE FIELD
 Consult DEP Field Sampling Manual and
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Laboratory SOP manual
Collection of radiological samples
- typically 1 gallon plastic for all but Radon-222
and Tritium
Preservation (Where and How?)
– HNO3 to pH < 2 is ideal
– Filtration before or after H+
Holding Times
– within 48 hours for gross alpha/beta (includes
collection, transport, preparation and counting)
– Analyze within 6 months
SAMPLE PREPARATION
METHODS CAVEATS
 NJDEP/OQA only certifies for certain
preparation methods
 You must match the method of preparation
to the method of analysis
 SDWA samples must use Federally approved
methods
Analytical Methods Approved by EPA for Radionuclide Monitoring
NJDHSS PREPARATION
METHODS FOR DRINKING WATER
 EPA 900.0: Gross Alpha/Beta
(evaporation)
 EPA 900.1: Gross Alpha (coprecipitation)
 EPA 903.0: Radium 226
 NJ Method: Radium 228
 EPA 00-07: Uranium
 EPA 913: Radon
Required Detection Limits
Contaminant
Detection Limit
Gross Alpha
Gross Beta
226Ra
228Ra
Uranium
134Cs
89Sr
90Sr
131 I
Tritium
Other Radionuclides and Photon Emitters
3 pCi/L
4 pCi/L
1 pCi/L
1 pCi/L
To be proposed
10 pCi/L
10 pCi/l
2 pCi/L
1 pCi/L
1,000 pCi/L
1/10 of the Rule
DETECTION LIMIT DEFINITIONS
 Instrument Detection Limit (IDL)
– Lowest observable value above
instrument background in the absence
of sample matrix
 Method Detection Limit (MDL)
– Minimum detectable concentration that
has 99% confidence of being greater
than 0.
ISSUES AFFECTING
MEASUREMENT CHOICE
 Regulatory implications/limitations
 Detection limit needs
 Potential analytical interferences
 Cost
 Time
 Experience/skill needed to conduct
analyses
QA/QC COMPONENTS
 Instrument Calibration
 Blanks
 Duplicates
 Spikes
 Calibration Verification
 Reference Materials
CALIBRATION
 EPA approves the use of particular isotopes to create
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attenuation curves. Typically 20 or more planchets of
varying weight.
Attenuation standards are typically laboratory created
using NIST traceable materials.
They should mimic actual samples.
Some methods use internal tracers for calibration.
Samples must be within the weight range dictated by
the method.
BLANKS
 Trip Blank: Deionized water carried from laboratory to
sampling location and back to the laboratory.
 Instrument Background: typically clean sample
holder or planchet is used.
 Method Blank: Deionized water containing all
reagents carried through sample preparation &
measurement procedures
DUPLICATES
 Field Duplicate: Extra sample taken from
same place, analyzed independently to
document sampling precision.
 Matrix Duplicate: Intralaboratory split
sample used to document method
precision in a given matrix
SPIKES
 Spike: Known activity/nuclide addition to
deionized water.
 Matrix Spike: Known activity/nuclide addition
to sample aliquot prior to preparation to
document bias in a given matrix. (Matrix
interference)
 Matrix Spike Duplicate: Intralaboratory
split sample with known additions prior to
preparation to document precision and bias
OTHER QA/QC COMPONENTS
 Continuing Calibration Verification
– Evaluates instrument drift
 Second Source Reference Materials
– Different source than used for calibration
 Certified Reference Materials
– Evaluate method bias
– Various Sources: NIST best
QA/QC SUMMARY
 You cannot do too much QA
 Sample data w/o QA data has limited
meaning
 Each type of QA sample evaluates a
different part of the analytical process
 You must match reference materials to
media being analyzed
 Labs. that do and report QA data
usually produce reliable data
ISSUES TO CONSIDER
 Is the lab. certified to perform the
specific procedure?
 Is the lab. using the correct
preparation and analysis methods
for the DQO?
 Can the lab. achieve the MDL?
 Are QA data (blanks, duplicates,
spikes, reference materials, …)
within defined limits?