7. Flame photometry was used to determine the sodium content in the soda production wastewater. Direct determination is carried out when the sodium content in the sample is from 0.1 to 10 mg/l. More concentrated water is pre-diluted, and less concentrated water is evaporated. The determination was carried out by the calibration curve method. The data for its construction are given in Table. 23. The volume of the initial sample is 500 ml, after evaporation - is indicated in table. 24. Calculate the sodium content (mg/l) in the studied wastewater.

Sodium concentration mg/dm3 1 2 3 4 5 7 10
Relative radiation intensity (Irel) 30.0 36.0 40.0 44.0 48.0 56.0 70.0

Sample volume after evaporation, ml 100
Relative radiation intensity (Irel) 32

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