DETERMINATION OF CARBONIC ACID IN STEAM-CONDENSATE CYCLE SAMPLES USING NONSUPPRESSED ION CHROMATOGRAPHY

摘要

The main limitations for the determination of low-level carbonic acid (H2CO3) in the steam-condensate cycles of nuclear and fossil fuel generating plants are the use of techniques with insufficient sensitivity and the risk of sample contamination bq atmospheric CO2. To avoid contamination, a measuring chamber and an analytical protocol, including procedures for container preconditioning, sampling, and sample conservation, have been developed and validated. This system was used to establish the performance of two nonsuppressed ion chromatographic techniques implemented on plastic-free systems for carbonic acid determination. The best results were obtained with a high-capacity anion-exchange resin, an eluent with a high basic ionic strength, and direct conductivity detection of the species. This approach shows good linearity up to 860 mu g/L H2CO3, with a detection limit of 0.4 mu g/L for a preconcentrated volume of 40 mL, which represents an absolute limit of 0.016 mu g of H2CO3. The precision (relative standard deviation) for the lower and upper ranges of the calibration plot, as established with laboratory samples, was 10% and 3% respectively, with an accuracy of +2% and +5%. The precision and accuracy of the technique were further validated using a field sample containing 28 mu g/L H2CO3; in this case, the precision was 6.3% and the accuracy as measured by spiking recovery was +6.8%. Combined with reliable knowledge of the system operating conditions, this new technique can be used to determine the severity of air ingress, makeup water contamination, feedwater conditioning agent contamination, and some condensate polisher operating problems.