Determination of sodium at low ng/l concentrations in simulated power plant waters by ion chromatography

The determination of low ng/l sodium in the power industry is critical in identifying and preventing corrosive conditions in many power plant components. To address this challenge, we developed an ion chromatographic method to determine sodium at ng/l concentrations in power plant samples. The ion chromatography system used on-line electrolytic eluent generation with a continuously regenerated trap column to minimize system contaminants and therefore allow low detection limits. A 10-ml sample was preconcentrated on a cation-exchange column followed by separation on a high capacity column with 20 mM methanesulfonic acid and detected using suppressed conductivity. Sodium response was linear from 25 to 250 ng/l (r2=0.9990). Method performance was evaluated by analyzing synthetic samples containing ethanolamine as an additive that are typical of samples encountered in the power industry. Retention time precision for sodium was less than 0.4% (n=7) in ultrapure water and simulated sample matrices. The recovery of sodium spiked in synthetic samples at the low ng/l levels was 85–110%. System parameters were optimized to achieve method detection limits in ultrapure water to 3.2 ng/l.