Jeff Rohrer

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.

Determination of trace anions in organic solvents.

Ion chromatography along with matrix elimination was used to reliably determine trace levels of anionic contaminants in organic solvents. A 5-ml sample volume was injected directly into the instrument without any sample pretreatment. High-purity deionized water was used to deliver the sample to a preconcentration column, where the anions of interest were retained while the organic matrix was rinsed to waste. A sodium carbonate eluent eluted concentrated anions from the preconcentration column and separated them on a 2-mm pellicular anion-exchange column. The separated anions were detected by suppressed conductivity. This method was used to determine the anionic contaminants of isopropanol, acetone and N-methylpyrrolidone. Method detection limits for chloride, nitrate, sulfate and phosphate were all lower than 1 microg/l.

Recent Developments in the Analysis of Perchlorate Using Ion Chromatography

Ammonium perchlorate, a key ingredient in solid rocket propellants, has recently been found in ground waters in regions of the U.S. where aerospace materials, munitions, and fireworks were developed, tested, or manufactured. Perchlorate has been found in ground and surface waters in California, Nevada, Utah, Texas, New York, Maryland, Arkansas, and West Virginia, although the total extent of the contamination problem is not known. Perchlorate poses a human health concern as it interferes with ability of the thyroid gland to utilize iodine to produce thyroid hormones. Current data from the EPA indicate that exposure to a concentration less than 4–18 μg L−1 (ppb) perchlorate provides adequate health protection.2 Recently, the EPA National Center for Environmental Assessment has announced a new provisional oral reference dose (RfD) for perchlorate of 9 μg kg−1 day−1, which would correspond to an action level of 32 μg L−1 in drinking water.3 A final action (e.g., health advisory) level is expected sometime in 2000.

Monitoring trace anion contamination in disk drive components

Ion chromatography was used to determine trace anionic contamination on the surface of hard disk drive components. These contaminants can have a detrimental effect on device reliability and yield. Disk drive components were soaked in deionized water and these extracts were analyzed for anions. The anions fluoride, acetate, formate, acrylate, methacrylate, chloride, nitrite, bromide, nitrate, benzoate, sulfate, oxalate, phthalate and phosphate were separated on a high-performance anion-exchange column and determined at concentrations less than 1 microg/l with suppressed conductivity detection. The extract solutions were analyzed either by injecting 1 ml or by preconcentrating 5 ml. We evaluated the performance of both methods.