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Figure 4. Base load impurity levels throughout water/steam cycle during drum boil er plant test. Na+ (A), C I " ( · ) , β θ Γ ( • )
under our operating conditions, varies as a function of suppressor column resin exhaustion, moving toward ear lier times as the suppressor column exhausts. With a freshly regenerated suppres sor column the water dip interferes with the chloride peak, resulting in an anomalously low apparent peak height. As the column exhausts and the water dip migrates away from the chloride peak, the peak appears to grow. At an exhaustion level of ~50% of the suppressor column, the water dip is sufficiently resolved that it no longer has any effect on the chloride peak. Not only is maximum peak height (and sensitivity) attained after ~50%
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suppressor column exhaustion, but re producibility is better. A comparison of peak heights for 10 runs on an unexhausted anion suppressor column showed a relative standard deviation of 22.0% for chloride, while the rela tive standard deviation was reduced to an acceptable 12.7% following 50% suppressor column exhaustion. The effect of suppressor column ex haustion on sulfate analysis is insig nificant, with data showing a relative standard deviation of 12.0% and 13.0% for 1% and 50% exhaustion, respec tively. The relative standard deviation for seven cation samples showed a re duction to about 13.5% for sodium fol lowing an exhaustion of ~10% of the cation suppressor column. Slight ex-
