Instrumentation & Methods: s & Tritium Richard Sheibley Pennsylvania Dept of Env Protection Principle Beta particle emission Energy transferred to Solute Energy released as UV Pulse Intensity proportional to beta particle initial energy Low energy beta emitters Tritium 3 H Iodine 125 I, 129 I, 131 I Radon 222 Rn Nickel 63 Ni Carbon 14 C 1
Energy Spectrum Isotope specific Beta particle Neutrino Total energy constant Components Vial with Sample + Scintillator Photomultipliers Multichannel Analyzer Timer Data collection & Output Variables Temperature Counting room Vial type glass vs. plastic Cocktail Energy window 2
Other considerations Dark adapt Static Quenching Interferences Chemical Absorbed beta energy Optical Photon absorption Instrument Normalization Photomultiplier response Unquenched 14 C Standard 3
Performance assessment Carbon-14 Efficiency Tritium Efficiency Chi-square Instrument Background Method QC Background Reagent background Efficiency Method Quench correction Tritium 3 H (EPA 906.0 & SM7500-3 H B) Prescribed Procedures for Measurement of Radioactivity in Drinking Water EPA 600 4-80-032 August 1980 Standard Methods 17 th, 18 th, 19 th & 20 th 4
Interferences Non-volatile radioactive material Quenching materials Double distill eliminate radium Static Fluorescent lighting Tritium 3 H Method Summary Alkaline Permanganate Digestion Remove organic material Distillation Collect middle fraction Liquid Scintillation Counting Calibration Method Raw water tritium standard Distilled Recovery standard Background Distilled Deep well water Distilled water tritium standard Distilled water to which 3 H added Not distilled 5
Instrument Calibration Calibrate each day of use Instrument Normalization Performance assessment Carbon-14 Efficiency Tritium Efficiency Instrument Background NIST traceable standards Calculations 3 H(pCi/L) = (C-B)*1000 / 2.22*E*V*F Where: C = sample count rate, cpm B = background count rate, cpm E = counting efficiency F = recovery factor 2.22 = conversion factor, dpm/cpm Calculations Efficiency: E = (D-B)/G Where: D = distilled water standard count rate, cpm B = background count rate, cpm G = activity distilled water standard, dpm 6
Calculations Recovery correction factor F = (L-B) / (E*M) Where: L = raw water standard count rate, cpm B = background count rate, cpm E = counting efficiency M = activity raw water standard (before distillation), dpm Quality Control Batch Precision: Sample duplicate OR Matrix spike duplicate Calculate relative percent difference Calculate control limits Should be < 20% Frequency 1 per 20 Quality Control, continued Accuracy Laboratory fortified blank Matrix spike sample 2 10 Xs detection limit Reagent background < detection limit Instrument drift 7
Quality Control, continued Daily control charts Acceptance limits Corrective action Preventative maintenance Standard Operating Procedure Written Reflect actual practice Standard format EMMC or NELAC Demonstration of Proficiency Initial Method detection limit MDL 40 CFR 136, Appendix B Alternate procedure 4 reagent blanks < Detection limit (DL) 4 laboratory fortified blanks (LFB) DL < LFB < MCL Evaluate Recovery and Standard Deviation against method criteria 8
Demonstration of Proficiency Ongoing Repeat initial demonstration of proficiency Alternate procedure 4 Reagent blanks and laboratory fortified blanks Different batches Non-consecutive days Blank < Detection limit (DL) LFB met method precision and accuracy criteria 9