ISOTOPIC ANALYSIS OF A LI-6 ENRICHED LITHIUM SAMPLE EMPLOYING THE LI2BO2-BEAM METHOD - VERIFICATION OF THE THEORETICAL ACCURACY( ION)

It was predicted recently by us (Int. J. Mass Spectrom. Ion Processes, 116 (1992) 87) that accurate measurements of the Li2BO2+ ion yield ra tio(s) do not always imply accurate determination of the elemental iso topic abundance ratio(s). Further insight into this aspect is provided here by demonstrating that the results of the isotopic analysis of a Li-6 enriched lithium sample using different pairs of isotopic Li2BO2 ions as monitors show considerable variations, irrespective of the ac tual experimental errors. A theoretical explanation of the observation s is presented. The present investigation provides the guidelines for selecting the proper monitor Li2BO2+ ion-pair(s) and discusses the oth er analytical requirements for making possible accurate isotopic analy sis of lithium of any given isotopic composition. Experimental observa tions showing the effect of isotopic fractionation on the formation of the Li2BO2+ ions are also elaborated and discussed.