Presentation on theme: "Radiochemical Methods and Data Evaluation Wm. Kirk Nemeth New Jersey Department of Health & Senior Services, Environmental Chemical and Laboratory Services,"— Presentation transcript:
Radiochemical Methods and Data Evaluation Wm. Kirk Nemeth New Jersey Department of Health & Senior Services, Environmental Chemical and Laboratory Services, Radioanalytical Services
WHAT WELL COVER TODAY 4 The analytical process: sample collection to data reporting and uncertainties 4 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 4 The total error for any analytical scheme involves errors in all steps: sampling, preparation and measurement. 4 If sampling uncertainty is 50%, and the analysis only has a 2% error; your total error is still very large
DATA QUALITY OBJECTIVES (DQOs) 4 A statement of the overall level of uncertainty that a decision-maker is willing to accept in results derived from environmental data 4 The level of uncertainty can be defined through defining the uncertainty in each step of the analytical process. 4 QA data are key in defining the level of uncertainty
STEPS TO BE DISCUSSED 4 Sample Collection and Preservation 4 Methods 4 Quality Assurance
SAMPLE COLLECTION & PRESERVATION IN THE FIELD 4 Consult DEP Field Sampling Manual and Laboratory SOP manual 4 Collection of radiological samples 4 - typically 1 gallon plastic for all but Radon-222 and Tritium 4 Preservation (Where and How?) –HNO 3 to pH < 2 is ideal –Filtration before or after H + 4 Holding Times –within 48 hours for gross alpha/beta (includes collection, transport, preparation and counting) –Analyze within 6 months
SAMPLE PREPARATION METHODS CAVEATS 4 NJDEP/OQA only certifies for certain preparation methods 4 You must match the method of preparation to the method of analysis 4 SDWA samples must use Federally approved methods
Analytical Methods Approved by EPA for Radionuclide Monitoring
DETECTION LIMIT DEFINITIONS 4 Instrument Detection Limit (IDL) –Lowest observable value above instrument background in the absence of sample matrix 4 Method Detection Limit (MDL) –Minimum detectable concentration that has 99% confidence of being greater than 0.
CALIBRATION 4 EPA approves the use of particular isotopes to create attenuation curves. Typically 20 or more planchets of varying weight. 4 Attenuation standards are typically laboratory created using NIST traceable materials. 4 They should mimic actual samples. 4 Some methods use internal tracers for calibration. 4 Samples must be within the weight range dictated by the method.
BLANKS 4 Trip Blank: Deionized water carried from laboratory to sampling location and back to the laboratory. 4 Instrument Background: typically clean sample holder or planchet is used. 4 Method Blank: Deionized water containing all reagents carried through sample preparation & measurement procedures
DUPLICATES 4 Field Duplicate: Extra sample taken from same place, analyzed independently to document sampling precision. 4 Matrix Duplicate: Intralaboratory split sample used to document method precision in a given matrix
SPIKES 4 Spike: Known activity/nuclide addition to deionized water. 4 Matrix Spike: Known activity/nuclide addition to sample aliquot prior to preparation to document bias in a given matrix. (Matrix interference) 4 Matrix Spike Duplicate: Intralaboratory split sample with known additions prior to preparation to document precision and bias
OTHER QA/QC COMPONENTS 4 Continuing Calibration Verification –Evaluates instrument drift 4 Second Source Reference Materials –Different source than used for calibration 4 Certified Reference Materials –Evaluate method bias –Various Sources: NIST best
QA/QC SUMMARY 4 You cannot do too much QA 4 Sample data w/o QA data has limited meaning 4 Each type of QA sample evaluates a different part of the analytical process 4 You must match reference materials to media being analyzed 4 Labs. that do and report QA data usually produce reliable data
ISSUES TO CONSIDER 4 Is the lab. certified to perform the specific procedure? 4 Is the lab. using the correct preparation and analysis methods for the DQO? 4 Can the lab. achieve the MDL? 4 Are QA data (blanks, duplicates, spikes, reference materials, …) within defined limits?