Presentation on theme: "Radiochemical Methods and Data Evaluation"— Presentation transcript:
1Radiochemical Methods and Data Evaluation Wm. Kirk NemethNew Jersey Department of Health & Senior Services, Environmental Chemical and Laboratory Services,Radioanalytical Services
2WHAT WE’LL COVER TODAYThe analytical process: sample collection to data reporting and uncertaintiesMethods for sample preparation for drinking water samplesQA data: what to look for
3SOURCES OF DATA VARIABILITY This list provides a broad sense to some of the sources of imprecision affecting environmental measurements.Definitions of precision and accuracy.Precision is the extent to which a given set of measurements of the same sample agree with their mean.Accuracy is the extent to which a given measurement agrees with the standard value for that measurement.
4UNCERTAINTIESRANDOM: 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.
5PROPOGATION OF ERRORSThe 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
6DATA QUALITY OBJECTIVES (DQOs) A statement of the overall level of uncertainty that a decision-maker is willing to accept in results derived from environmental dataThe 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 uncertaintyOften many clients will request analyses to be performed on aqueous samples and not comprehend what it is they hope to achieve from the data we provide. We attempt to resolve this situation by discussing the circumstances surrounding the sample and our capabilities.
7STEPS TO BE DISCUSSED Sample Collection and Preservation Methods Quality Assurance
8SAMPLE COLLECTION & PRESERVATION IN THE FIELD Consult DEP Field Sampling Manual and Laboratory SOP manualCollection of radiological samples- typically 1 gallon plastic for all but Radon-222 and TritiumPreservation (Where and How?)HNO3 to pH < 2 is idealFiltration before or after H+Holding Timeswithin 48 hours for gross alpha/beta (includes collection, transport, preparation and counting)Analyze within 6 monthsThese manuals will detail the collection of the proper collection technique, the proper container and preservation (if appropriate).Collection:Normally 1 gallon is sufficient for the analyses of alpha/beta, radium 226, radium 228, and Uranium. This will allow for laboratory duplicates, if necessary. Radon and tritium samples are collected separately.Radon-222 and tritium must be collected in glass containers; radon samples are collected in glass liquid scintillation vials (containing mineral oil) without preservation and tritium samples are collected in 50 ml or 100 ml glass bottles without preservation. We require that radon samples be collected in duplicate to observe sampling technique.The preservation should ideally be performed at collection but can be accomplished upon delivery to the laboratory (if delivered the same day), the 16 hour hold is observed if not preserved at collection) The timing can become a difficult issue if the sample is delivered by mail, when considering the analysis must be performed within 48 hours from collection.
9SAMPLE PREPARATION METHODS CAVEATS NJDEP/OQA only certifies for certain preparation methodsYou must match the method of preparation to the method of analysisSDWA samples must use Federally approved methods
10Analytical Methods Approved by EPA for Radionuclide Monitoring
13DETECTION LIMIT DEFINITIONS Instrument Detection Limit (IDL)Lowest observable value above instrument background in the absence of sample matrixMethod Detection Limit (MDL)Minimum detectable concentration that has 99% confidence of being greater than 0.
15QA/QC COMPONENTS Instrument Calibration Blanks Duplicates Spikes Calibration VerificationReference MaterialsInstruments to be used are indicated in each method listed. As an example, a proportional counter (capable of discriminating an alpha particle from a beta) such a as thin window, gas flow counter should be used for alpha/beta counting. It can be used in the analysis of radium 226, radium 228, strontium 89 & 90, iodine Several instruments can be used for the variety of uranium methods listed.Instrument calibration: Attenuation calibration nuclides for alpha are thorium 230 and natural uranium. Amercium 241 is approved for use with gross alpha co-precipitation methodsAttenuation calibration nuclide for beta is Cs-137 or Sr-90/Y-90.Blanks: In the laboratory, methods blanks are run with every batch. Typically blank samples represent 5 to 10% of the sample workload. Blank samples use the same glassware, reagents, hotplates, heating lamps, etc. as that of actual samples and are created and analyzed with samples. Deionized water (or representative water) is used in the creation of blanks.precipitation
16CALIBRATIONEPA 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.Instruments to be used are indicated in each method listed. As an example, a proportional counter (capable of discriminating an alpha particle from a beta) such a as thin window, gas flow counter should be used for alpha/beta counting. It can be used in the analysis of radium 226, radium 228, strontium 89 & 90, iodine Several instruments can be used for the variety of uranium methods listed. The instrument used for our isotopic uranium method is an alpha spectrometer.Instrument calibration: Attenuation calibration nuclide for alpha is Th-230; prior to 1994, Am-241 and U 238 were used as the calibrating nuclides.Attenuation calibration nuclide for beta is Cs-137 or Sr-90/Y-90.
17BLANKSTrip 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 proceduresTrip blanks are typically not utilized in radiological testing.
18DUPLICATESField 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
19SPIKES 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
20OTHER QA/QC COMPONENTS Continuing Calibration VerificationEvaluates instrument driftSecond Source Reference MaterialsDifferent source than used for calibrationCertified Reference MaterialsEvaluate method biasVarious Sources: NIST best
21QA/QC SUMMARY You cannot do too much QA Sample data w/o QA data has limited meaningEach type of QA sample evaluates a different part of the analytical processYou must match reference materials to media being analyzedLabs. that do and report QA data usually produce reliable data
22ISSUES TO CONSIDERIs 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?