AUTOMATED SPIKE PREPARATION SYSTEM FOR ISOTOPE DILUTION MASS SPECTROMETRY (U)

Isotope Dilution Mass Spectrometry (IDMS) is a method frequently employed to measure dissolved, irradiated nuclear materials. A known quantity of a unique isotope of the element to be measured (referred to as the \"spike\") is added to the solution containing the analyte. The resulting solution is chemically purified then analyzed by mass spectrometry. By measuring the magnitude of the response for each isotope and the response for the \"unique spike\" then relating this to the known quantity of the \"spike\", the quantity of the nuclear material can be determined. An automated spike preparation system was developed at the Savannah River Site (SRS) to dispense spikes for use in IDMS analytical methods. Prior to this development, technicians weighed each individual spike manually to achieve the accuracy required. This procedure was time-consuming and subjected the master stock solution to evaporation. The new system employs a high precision SMI Model 300 Unipump dispenser interfaced with an electronic balance and a portable Epson HX-20 notebook computer to automate spike preparation. Using the computer to collect duplicate net weights on a predetermined number of spike containers, dispensing accuracy is confirmed by a statistically-based sampling plan. The density of the spike solution, the volume setting on the Unipump dispenser, and the calculated net weights of the spikes, the average weight of the spikes are calculated along with the observed variance estimate. If the observed variance meets control limits, the spikes are released and treated as having equal quantities of the \"spiked\" isotope within the calculated uncertainty estimate. This feature eliminates a whole layer of bookkeeping and the need to track individual spike containers and their individual quantities of the spiked isotope.