Low level determination of gallium isotopes by ICP-QQQ

Determination of low concentrations of Ga in environmental or biological samples can benefit from interference free measurement of both Ga isotopes. Unfortunately, both isotopes have potential interferences, i.e doubly charged Ba at m/z 69 and MnO at 71. Analysis using collision and reaction gases by ICP-QQQ as an alternative to HR-ICP-MS is investigated here using conventional nebulization and a desolvating nebulizer. Analysis at m/z 71 is not appreciably affected by MnO at 200 ug/l Mn or in either water reference material; excellent detection limits of < 0.1 ng/l were obtained for He, H₂, or on-mass O₂ and NH₃ gas modes. Analysis of Ga at m/z 69 was severely affected by doubly charged Ba across all gas modes except +17 mass-shift (i.e. 69 - 86) NH₃ gas mode. Despite Ga being only 1-2% reactive at the 69-86 mass shift, the doubly-charged interference was not mass-shifted and detection limits of < 1 ng/l and precise and accurate quantification of two water reference materials and nine natural water samples were achievable for this analysis mode.