J-18 Gas Chromatography Oxygen Analy- 

 sis. — Gas chromatography has been used as a 

 means of analyzing gtis mixtures for several 

 years; however, application of the technique to 

 dissolved gases in sea water evolved from pro- 

 cedures developed by Swimieiton, Linnenbom, 

 and Cheek of the U.ls. Naval Reseai'ch Labora- 

 tory, while studing gases formed in irradiated 

 solutions. 



The application of gas clrromatograjihy to 

 determining the O2 (and N,) content of a sea 

 water sample, in effect, is a measurement of the 

 difference between the thermal conductivity of 

 pure He gas and the gas mixture obtained by 

 bubbling He gas through a sea water sample. 



Gas chromatography sea water sample anal- 

 ysis has several advantages. It is less time 

 consuming than titration methods, and the in- 

 strumentation is relatively simple to operate 

 and mamtain, yet no loss is ex_{)erienced in either 

 precision or accuracy. In addition, the dissolved 

 N2 content of the sample is obtained at the same 

 time. 



J-19 Theory of Gas Chromatography. — In 



carrying out the quantitative analysis of a sea 

 water sample for dissolved On (and No) by gas 

 chromatography, an inert gas. He, is used to 

 cany the gas mixture through a chromato- 

 graphic column. This column is filled with finely 

 divided powder of a proper type having rela- 

 tively large surface areas. Molecules of different 

 gases travel through the column at different 

 speeds. Therefore, since each component of a 

 gas mixture remains in the column for a differ- 

 ent period of time, it is possible, by a suitable 

 choice of colimin dimension and tyjje, to sepa- 

 rate these components for measurement. 



The gas partitioner is used to measure the 

 amount of each gas component of the gas mix- 

 ture. It contains temperature sensitive devices 

 that detect slight changes in the thermal con- 

 ductivity and thermal capacity of the gas 

 stream; these changes result in an imbalance of 

 an electrical bridge circuit, and this voltage 

 change is recorded on a strip chart recorder 

 with an integrator. 



J-20 Setting Up the Gas Chromatographic 

 Equipment. — The gas chromatographic sea 

 water analysis equipment used by the U.S. Na- 

 val Oceanographic Office includes three major 

 components : An all glass sample chamber with 

 automatic sampling valves, a gas partitioner 

 (either a modified Fisher Gas Partitioner Mod- 

 el 25 or a Fisher-Hamilton Gas Partitioner 

 Model 29), and a Texas Instriunent, Model 

 PWSN, one millivolt Strip Chart, Recorder 

 with an integrator. In addition, a tank of tech- 

 nical Grade A helium, a tank of air, a flow 

 meter, and spare drying tubes and gas parti- 

 tioner columns are required for gas chromato- 

 graphic sea water sample analysis. Figure J-8 



shows the modified Fisher Gas Partitioner, and 

 figure J-9 shows the Fisher-Hamilton Gas Par- 

 titioner. The main difference between the two 

 systems is the arrangement of the four-way 

 valve and the automatic sampling valve. Tlie 

 Fisher Gas Partitioner has been modified with 

 the four-way valve and the automatic sampling 

 valve installed on the partitioner. The Fisher- 

 Hamilton equipment has these valves mounted 

 on a separate cabinet. 



The equipment should be set up and checked 

 out prior to taking an oceanographic station in 

 order for O2 samples to be analyzed iimnediately 

 after they are draw^n. O2 samples for gas chro- 

 matography analysis must be drawn in special 

 sample bottles (see chs. D and F for a descrip- 

 tion of the sample lx)ttle and drawing the O2 

 sample). 



Two 6-inch adjustable wrenches and a me- 

 dium-size screwdriver are the only tools re- 

 quired. All tube fittings are brass Swagelok 

 coimections except wdiere other fittings are in- 

 dicated. Procedures for setting up the instru- 

 mentation follow : 



1. Gas chromatographic equipment with 

 Fisher Gas Partitioner (Modified) (fig. J-10). 



Step 1. Remove the cover from the parti- 

 tioner, and disconnect the Drierite tube (A) 

 from the left connection (facing panel) of the 

 four-way valve. Bring the free end of the 

 Drierite tube (A) out through the slot in the 

 left side of the partitioner cabinet. 



Step 2. Connect a 2-foot long x i4-iiich O.D. 

 polypropylene tube (B) to the left connection 

 of the four-way valve. Bring the free end of 

 tube (B) out through the hole in the front 

 panel. 



Step 3. Replace the partitioner cover, and 

 moimt the automatic sampling valve assembly 

 on the partitioner cover with %-inch brass 

 round head wood screws. 



Step 4. Connect tube (B) to the automatic 

 sampling valve. 



Step 5. Extend tube (A) with 2-foot long 

 X 14-inch O.D. polypropylene drying tube (C) 

 and connect the end to the top side arm of the 

 sample chamber, using a nylon fitting. 



Step 6. Connect the bottom of the glass 

 chamber to the sampling valve (this fitting 

 must be nylon at the glass chamber, and a Per- 

 kin-Elmer fitting at the valve) . 



2. Gas chromatographic equipment with 

 Fisher- Hamilton Gas Partitioner (fig. J-ll). 



Step 1. Connect a 2-foot long x i/^-inch Dri- 

 erite filled drying tube (A) to the rear connec- 

 tion on the left side (facing panel) of the valve 

 cabinet. The valve cabinet contains the four- 

 way valve, the automatic sampling valve, and a 

 support for the glass sample chamber. 



Step 2. Connect 2-foot long x 14-inch O.D. 

 drying tube (C) to tube ( A) . Connect the other 

 end of tube (C) to the upper side arm of the 

 glass sampling chamber with a nylon fitting. 



J-13 



