J-16 Analysis of Oxygen Samples. — Analy- 

 sis of O2 samples includes the following proc- 

 esses: (1) Blank Kun, (2) Standardization, 

 (3) Titration of the O2 samples, and (4) Cal- 

 culation of dissolved oxygen. These processes 

 are recorded on Oceanographic Log Sheet-CCC 

 (fig. J-7). The vessel, cruise, consec. station 

 number, and serial number are obtained from 

 the A-Sheet. 



(1) Blank Run. — The blank run is made to 

 determine the correction to apply for the 

 amount of la-liberating oxidizing substances 

 or reductants present as impurities in the re- 

 agents. A blank run should be made after the 

 reagents are prepared to determine that they 

 are satisfactory, and that the titration equip- 

 ment is functioning properly. In addition, blank 

 runs are made before each series (maximum of 

 24) of O2 samples is analyzed. To make the 

 blank run, perform the following steps : 



Step 1. Place a 1-inch, teflon-covered mag- 

 netic stirring bar in a clean 125-ml. glass stop- 

 pered Erlenmeyer flask that has been calibrated 

 "to contain" by weighing. 



Step. 2. Pipette 1 ml. or KIO3 or KH(I03)2 

 into the flask; then, fill the flask with distilled 

 water to the ground glass neck. 



Step 3. Add 1.0 ml. of ION H.SO4 and 1.0 

 ml. ofNaOH-Nal. 



Step 4. Mix with the magnetic stirrer for 1 

 minute, and then add 1.0 ml. of manganous re- 

 agent and 1.0 ml. of starch solution. Blue color 

 will appear. Zero the digital counter. 



Step 5. Place the flask under tlie delivery tip 

 of the burette (14 inch below surface of solu- 

 tion), and titrate until the instant the solution 

 becomes colorless. As the end point is ap- 



E reached, turn the delivery crank very slowly, 

 ut never reverse the direction of rotation while 

 the stopcock is in DELIVERY position as this 

 will contaminate the reagent in the burette. 



Step 6. Read the digital counter, and record 

 the value in V^ {1st Run) space on the log sheet. 



Step 7. Pipette 1.0 ml. of KIO3 or KH (103)2 

 into the same sample flask; rezero the digital 

 counter; wait 1 minute and then repeat steps 5 

 and 6. Record the digital counter reading in 

 Fj {2d Run) space. Vb's must agree within 

 ± .0010 ml. 



Step 8. Calculate Vb by subtracting Vb (2d 

 Run) from Vb (1st Run).' If Vb is positive, the 

 blank is oxidizing; if negative, reducing. 



(2) Standardization. — Standardization is the 

 process of detennining the slight changes that 

 occur in the NajSjOa solution during O, analy- 

 sis. Standardization should be jjerfonned before 

 each series (maximum of 24 samples) is 

 analyzed. 



Step 1. Place a 1-inch, teflon-covered magne- 

 tic stirring bar in a clean 125-m]. glass stoppered 

 Erlenmeyer flask that has been calibrated "to 

 contain" by weighing. 



J-10 



Step 2. Pipette 10 ml. of KIO3 or KH(I03) 2 

 into the flask, and fill the flask witli distilled 

 water to the gromid glass neck. 



Step 3. Add 1.0 ml. of the H2SO4 and 1.0 

 ml. of the NaOH-Nal reagent, and mix for 1 

 minute. 



Step 4. Titrate the liberated I2 in the same 

 way as for the sample. Place the flask under 

 the delivery tip of tlie burette (i^ inch below 

 surface of solution), and titrate solution with 

 Na2S203 until the deep yellow color turns to 

 pale straw yellow. 



Step 5. Add 1 ml. of starch solution. This 

 will cause the solution to turn blue. Add 

 NaaSaOs until the blue color disappears and the 

 solution is just colorless. 



Step 6. Read the digital counter and record 

 the value in F2 {Ist Rim) space on the log sheet. 



Step 7. Repeat steps 1 through 6 two times, 

 and record the digital counter reading in F^ 

 {2d run) and F2 {3d Run) spaces on the log 

 sheet. Acceptable values must agree within 

 ± .0005. 



Step 8. Calculate average V2. In Sodium, 

 Thiosulfate Concentration block, indicate con- 

 centration of solution used. 



(3) Titration of the Oxygen Samples. — O2 

 samples should be titrated within 4 hours of the 

 time they are treated. Always follow the same 

 techniques for every sample. 



Step 1. Fill burette, return piston to glass 

 metal point, and zero the counter. 



Step 2. Record the sample flask number in the 

 appropriate space on the log sheet. The sample 

 number is etched on the flask and stopper. Enter 

 the volume of the flask in the F {ml.) Flask 

 Weighed '"''To contain^'' column. Flasks are 

 weighed at a shore facility before the survey 

 operation. 



Step 3. Shake the sample flask vigorously. 



Step 4. Remove the glass stopper from the 

 sample flask and place a 1-inch, teflon-covered, 

 magnetic stirring bar in flask. 



Step 5. Place the sample flask under the bur- 

 ette with the delivery tip i^ inch below the sur- 

 face of the sample solution, and turn on the 

 magnetic stirrer. 



Step 6. Add NasSjOs to the sample by ro- 

 tating the delivery crank in a clockwise direction 

 until the dark yellow color of the sample be- 

 comes a pale straw yellow. 



Step 7. Add 1 ml. of starch solution. This will 

 produce a deep blue color. Continue to add 

 Na2S203 slowly until the instant the solution 

 becomes colorless. As the end point is ap- 

 proached, turn the delivery gear very slowly, 

 but never reverse the direction of rotation of the 

 gear while the stopcock is in DELIVERY po- 

 sition as this will contaminate the reagent in the 

 burette. 



Step 8. The instant the sample becomes color- 

 less, stop tlie delivery crank and read the digital 



