Suppressed ion chromatographic determination of lithium, sodium, ammonium and potassium concentrations in sub-surface brines

Suppressed ion chromatographic method for simultaneous determination of lithium, sodium, ammonium and potassium in sub-surface waters of high salinity has been reported. A short column, Dionex CG-2 (50x4.6 mm I.D.), was used as separator column in combination with another CG-2 column as guard column with 0.005 moll^-1 HCl as eluent at 2.0 ml min^-1 flow-rate. High resolution between lithium/sodium, sodium/ammonium and ammonium/potassium peaks allowed baseline separation of these cations even though the molar concentrations of lithium, and potassium and ammonium differ from sodium by about 500 and 50 times, respectively. A single calibrating solution, containing lithium at 0.035 mg l^-1 sodium at 54 mg l^-1, ammonium at 0.7 mg l^-1 and potassium at 2.5 mg l^-1 was used to determine the concentrations of these ions in water samples using a computerized routine. Total average analysis time of approximately 10 min (including column cleaning time) was considerably shorter than that reported in the literature. Due to its good reproducibility (%R.S.D.<2.5%) and accuracy (established by method comparison), the method was adopted for routine analysis of ammonium and alkali metals lithium, sodium and potassium in sub-surface waters, seawater, ground waters of high salinity and aqueous extracts of soil and aerosols.