J-10 The Chesapeake Bay Institute Tech- 

 nique for the Winkler Method. — A modified 

 technique for the Winkler determination of dis- 

 solved O2 has been developed by Dr. James H. 

 Carpenter of the Chesapeake Bay Institute, 

 The Johns Hopkins University, Baltimore, Md. 

 This technique is described in the January 1965 

 issue of Limnology and Oceanography, vol. 

 10. no. 1. 



This (Micro) Winkler technique, as it will 

 be referred to in the remainder of this chapter, 

 has been adopted by the U.S. Naval Ocean- 

 ographic Office because it is a fast, precise, accu- 

 rate, and convenient method of determining 

 dissolved oxygen content of sea water samples. 

 The chemical reactions involved are the same 

 as those described in paragraph J-2, Modified 

 Winkler (Macro) Method. 



Replicate samples are collected from each 

 Nansen bottle in 125-ml. glass stopj^ered Erlen- 

 meyer flasks that have been calibrated "to con- 

 tain" by weighing. (These flasks vary in volume 

 from 130 to 145 ml.j enough to cause consider- 

 able error if volume is not calculated ; therefore, 

 sample flasks to be used are calibrated by the 

 weighing of distilled water content of each and 

 multiplying the weight of H2O by the 

 specific volume of distilled HoO at weighing 

 temperature.) 



The entire sample is titrated, and the amount 

 of Na2S203-5H20 required is indicated on a 

 burette digital readout to the nearest 0.0001 ml. 

 By titrating the entire sample, the transfer of 

 I2 solution by either pouring or pipetting is 

 avoided; thus, no loss of I2 occurs. 



A higher normality NaaSaOs-SHzO is used, 

 and less than 1 ml. of solution is required for 

 each titration; therefore, 0.2 liters of solution 

 will titrate 240 samples while approximately 

 3 liters of NajSjOa -51120 are required for the 

 (Macro) Winkler method. 



J-11 Chemicals Required. — The chemicals 

 required for the (Micro) Winkler method are 

 the same as those required for the (Macro) 

 method (see para. J-3). 



J-12 Apparatus Required.— In addition to 

 the apparatus previously listed in chapter H, 

 the following apparatus is required to carry 

 out titration by the (Micro) Winkler method : 

 Bottle, amber glass*, S.T. stopper, capacity : 



1,000 ml. 

 Bottle, dropping, capacity: 125 ml. 

 Bottle, polyethylene, screw cap, capacity : 500 



and 1,000 ml. 

 Flask, Erlenmeyer, glass*, S.T. 19/38 solid 

 glass stoppered, capacity: 125 ml. (cali- 

 brated to contain) 

 Micro Burette with glassware. 



•Heat resistant borosillcate glass is preferred. 



Pipette, automatic, A.B.A.-type, capacity : up 



to 2 ml. 

 Pipette, volumetric, transfer type Class 



"A", capacity : 1 and 10 ml. 



J-13 Setting up the Apparatus.— Figure J-4 



shows the (Micro) Winkler apparatus set up 

 in the laboratoiy. Shown are the reagents, the 

 rapid delivery pipettes, a magnetic stirrer, a 

 fluorescent light case, and the microburette with 

 the burette digital readout counter. 



The details of the microburette and the digital 

 counter are shown in figure J-5. To zero the 

 counter and operate the microburette, perform 

 the following steps : 



Step 1. With the three-way stopcock in the 

 FILL position (Arm B toward the reservoir; 

 arm A toward the digital counter) and with 

 glass stopper in the reservoir turned to open the 

 vent, carefully rotate the delivery crank in a 

 counterclockwise direction until the piston is 

 flush with the glass-metal point between the 

 burette and the counter. Do not draw the piston 

 inside the digital counter assembly. Always 

 make certain the three-way stopcock is in the 

 fill position when the delivery gear is being 

 turned in a counterclockwise direction; other- 

 wise, bubbles will form in the burette. 



Step 2. Press the ZERO SET button on the 

 digital counter assembly to clear the counter and 

 set it at zero. 



Step 3. To deliver the solution from the 

 microburette, which is titrating, place the de- 

 livery tip 1/4 inch below the surface of the solu- 

 tion receiving delivery, turn the three-way stop- 

 cock to delivery position (B toward counter; 

 A toward delivery tip) and rotate the delivery 

 gear in a clockwise direction. This will move 

 the piston to the left and the digital counter 

 will record the amount of solution forced from 

 the burette to the nearest 0.0001 ml. In order to 

 avoid damaging the microburette, do not deliver 

 more than 0.8 ml. Do not turn the delivery gear 

 in a counterclockwise direction while delivery 

 tube is in a solution and three-way stopcocK 

 is in DELIVERY position, as this will con- 

 taminate the solution in the burette. 



Wliile the apparatus arrangement shown in 

 figure J^ is usable in the laboratory, the titra- 

 tion box designed by Dr. J. H. Carpenter (fig. 

 J-6) is higlily recommended for shipboard 

 oxygen analysis. 



The titration box is approximately 12 inches 

 wide, 24 inches high and 14 inches deep, and 

 the interior is painted with a high quality white 

 paint. The shielded eight-watt fluorescent lamps 

 attached to the inside of the box provide the 

 brilliant lighting required for best end point 

 titration results. The counter assembly extends 

 through an opening in the right side of the box, 

 and the microburette glass components are con- 

 nected to tlie counter assembly by a standard 



J-7 



223-812 0-68-8 



