NSWC/WOL/TR 75-35 



techniques, or a sufficiently sensitive analytical procedure chosen 

 to eliminate the need to concentrate. 



4.3 PROCEDURE 



4.3.1 Dissolved Gases 



4.3.1.1 Gas Chromatographic Methods 



The gas chromatographic approach has been recognized as one of 

 the best methods for the determination of dissolved gases in water. 

 The method provides rapid and accurate measurement, and data may be 

 collected easily and routinely on shipboard. The method consists of 

 stripping the dissolved gases from the test solution with an inert 

 gas and subsequent separation and detection by gas chromatography. 



Stripping is essentially a gas-liquid extraction procedure in 

 which an inert carrier gas is bubbled through a sample to carry off 

 the dissolved gases for further separation, concentration, or 

 detection. Gas transfer efficiency in such systems is dependent on 

 the gas-liquid interfacial area and on the degree of mixing. 



Gas-exchange separation can be carried out as either a batch or 

 a continuous flow process. In one design, a continuous mixed stream 

 of sample and carrier gas is forced through an aspirator nozzle 

 under 50 pounds of pressure. 14 In another design, the dissolved gases 



are stripped from the test solution by multiple spinning discs 



rotating at high speed. 



The gas stream from the exchange unit is then passed through the 

 gas chromatographic columns. After the chromatographic separation 

 of the different components, the gas stream is passed through the 

 detector cells (thermal conductivity or flame ionization) and the 

 elution curve is recorded by a strip-chart recorder. 



14 Dixon, W. S., "Pollution Control by Co»tinuous Dissolved Oxygen 

 Analysis and Associated Instruments", Proc. Water Quantity 

 Measurement and Instrumentation, Technical Report, Robert A. Taft 

 Sanitary Engineering Center, Cincinnati, Ohio (1960). 



15 Swinnerton, J. W. , Linnenbom, V. J., and Cheek, C. H., "Dissovled 

 Gases in Aqueous Solution by Gas Chromatography", Anal. Chem. , 3A_, 

 483 (1962). 



39 



