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

Radiochemical Methods and Data Evaluation

Wm. Kirk NemethNew 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 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 (co-precipitation)

EPA 903.0: Radium 226 NJ Method: Radium 228 EPA 00-07: Uranium EPA 913: Radon

Required Detection Limits

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

Gross Alpha

Gross Beta226Ra228Ra

Uranium134Cs89Sr90Sr131I

Tritium

Other Radionuclides and Photon Emitters

Detection LimitContaminant

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 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?