NSWC/WOL/TR 75-3 5 



resolution of the higher or lower molecular weight olefins from 

 normal paraffins is desired. A flame ionization detector is used 

 and calibration is with gas saturated distilled water. The system is 

 shown in Fig. 10. 



The sensitivity of the system is about 5 x lO -10 ml/1 with a 

 precision of + 10%. The procedure can also be used for the deter- 

 mination of very low concentrations of carbon monoxide. The carbon 

 monoxide, stripped from the seawater, is trapped in a column of one 

 quarter activated charcoal and three quarters molecular sieve at 

 -77°C. The gas is back flushed from the cold trap by raising the 

 temperature to 90°C and separated by the silica gel column. Before 

 passing to the flame ionization detector, hydrogen is introduced and 

 the carbon monoxide quantitatively reduced to methane by passing 

 through a heated tube containing nickel catalyst supported on 30-60 

 mesh silocel firebrick. 



The time required for analyzing 1 liter of seawater for CO, 

 methane, and other light hydrocarbons is approximately 45 min. The 

 complete system costs approximately $10K. The cost for analyzing 

 the dissolved gases is estimated to be $100 per sample. 



Precaution must be exercised about doing dissolved gas analysis 

 by shipping water samples from the point of collection to a labora- 

 tory for analysis. 18 Methane is probably the most stable gas, but 

 it can be produced or consumed by various organisms. Carbon monoxide 

 and ethane can be affected by presence of bacteria and by the 

 breakdown of dissovled organic matter in the samples. Samples should 

 be treated with sodium azide (which destroys marine bacteria) and 

 kept in a cool dark place. There will most certainly be an air 

 bubble at the top of the water sample when it finally arrives at the 

 laboratory. This will be the result of degassing due to the changing 

 temperature and agitation of the water sample. To be sure of the 

 gas concentration in the water, this air bubble must be analyzed. 



4.3.1.2 Specific Ion Electrodes 



Two dissolved gases in the explosion products, NH 3 and HCN, 

 can be conveniently measured by specific ion electrodes. Specific 

 ion electrodes are basically potent iometric membrane electrodes 

 systems which operate on a principle similar to that of the glass 

 electrode for the measurement of pH. The experimental procedure in 



18 



Lamontagne, R. A., Naval Research Laboratory, Private Comm. (1974) 



43 



